Cover photograph: 

The Wild and Scenic stretch of the upper Clackamas River has deep pools, swift runs, and swirling rapids. 
U.S. Department of the Interior

U.S. Geological Survey

Water-Quality and Algal Conditions in the 


Clackamas River Basin, Oregon, and their 


Relations to Land and Water Management


By KURT D. CARPENTER 

Water-Resources Investigations Report 02–4189 

Portland, Oregon: 2003 
U. S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary 

U.S. GEOLOGICAL SURVEY

CHARLES G. GROAT, Director 

The use of trade, product, or firm names in this publication 

is for descriptive purposes only and does not imply 

endorsement by the U.S. Government. 

For additional information: Copies of this report may be 

purchased from: 

District Chief 

U.S. Geological Survey U.S. Geological Survey 

10615 S.E. Cherry Blossom Dr. Branch of Information Services 

Portland, OR 97216-3103 Box 25286 

E-mail: info-or@usgs.gov Denver, CO 80225-0286 

Internet: http://or.water.usgs.gov/clackamas Telephone: 1-888-ASK-USGS 

Suggested citation: 

Carpenter, K.D., 2003, Water-quality and algal conditions in the Clackamas River Basin, Oregon, and 

their relations to land and water management: U.S. Geological Survey Water-Resources Investigations 

Report 02–4189, 114 p. 
CONTENTS


Glossary ................................................................................................................................................................................... vii


Acknowledgments.......................................................................................................................................................................x


Executive Summary ....................................................................................................................................................................1


Introduction .................................................................................................................................................................................8


Study Background and Objectives ..................................................................................................................................10


Overview of the Clackamas River Basin ........................................................................................................................11


Methods.....................................................................................................................................................................................13


Sampling Activities........................................................................................................................................................ 13

Data Collection ...............................................................................................................................................................15


Data Quality Control .......................................................................................................................................................19


Data Analysis ..................................................................................................................................................................21


Results .......................................................................................................................................................................................23


Stream Conditions...........................................................................................................................................................23


Reservoir Conditions.......................................................................................................................................................45


Ground-Water Conditions...............................................................................................................................................54 


Relations Between Land Use and Nutrient and Algal Conditions..................................................................................55


Effects of Hydroelectric Projects on Stream Conditions ................................................................................................56


Discussion .................................................................................................................................................................................58


Stream Nutrient Conditions ............................................................................................................................................58


Comparison of Nutrient Concentrations to Suggested Criteria ......................................................................................59


Nutrient Sources in the Clackamas River Basin .............................................................................................................60


Algal Conditions in Streams ...........................................................................................................................................62


Algal Conditions in Reservoirs .......................................................................................................................................64


Effects of Algae Blooms on Water Quality and Drinking Water ...................................................................................66


Land Use and Water Management in the Clackamas River Basin .................................................................................68


Evaluation of Management Strategies to Improve Conditions .......................................................................................75


Information Needs and Potential Future Studies ............................................................................................................79


Conclusion ................................................................................................................................................................................82


References Cited .......................................................................................................................................................................83


PLATE 

1. Map showing sampling site locations in the Clackamas River Basin, Oregon 

FIGURES 

1. Land-cover map of the Clackamas River Basin, Oregon, 1992–93..................................................................................9


2. Schematic diagram of the Clackamas River Basin, Oregon ...........................................................................................12


3–27. Graphs showing: 

3. Daily mean streamflow values for the upper Clackamas River above Three Lynx Creek, USGS


gaging station 14209500, water year 1998 .....................................................................................................................24


4. Comparison of water year 1998 streamflow with long-term values in the upper Clackamas River 


above Three Lynx Creek, U.S. Geological Survey gaging station 14209500 ................................................................24


III 
5. Seasonal variation in streamflow and water-quality variables for main-stem sites in May, July, and


September, and values for tributary sites in July 1998 ...................................................................................................26


6. Streamflow balance for the main-stem Clackamas River, Oregon, July 7–15, 1998 .....................................................27


7. Streamflows in the Clackamas River Basin, Oregon, during sampling in July 1998 .....................................................29


8. Diel fluctuations in water temperature, pH, and dissolved oxygen in the lower Clackamas River, 


June 28–29, 1998, and July 15–16, 1998 ........................................................................................................................32


9. Seasonal variation in nutrient concentrations, nutrient ratios, and algal biomass at main-stem sites 


in May, July, and September, and values for tributary sites in July 1998 ......................................................................35


10.	 Estimated contributions of dissolved inorganic nitrogen loads (A) and yields (B) from the tributaries, 

wastewater treatment plants, and fish hatcheries in the Clackamas River Basin, Oregon, July 1998............................36 

11.	 Seasonal variation in nutrient loads at main-stem sites in May, July, and September, and values for


tributary sites in July 1998 ..............................................................................................................................................37


12.	 Relations between total phosphorus and dissolved silica concentrations (A), total phosphorus 


concentrations and specific conductance (B), and dissolved silica and specific conductance (C) .................................38


13.	 Estimated contributions of total phosphorus loads (A) and yields (B) from the tributaries, wastewater 

treatment plants, and fish hatcheries in the Clackamas River Basin, Oregon, July 1998...............................................39 

14. Soluble reactive phosphorus load balance in the main-stem Clackamas River, Oregon, July 7–15, 1998 ....................40


15.	 Relations between water quality and indicator algal taxa in the Clackamas River Basin, Oregon,


July 1998 .........................................................................................................................................................................44


16. Monthly temperature profiles in North Fork Reservoir, station 1, March–September 1998..........................................45


17.	 Longitudinal profile of water temperature and soluble reactive phosphorus concentration in the upper 


Clackamas River and North Fork Reservoir, August 1997 ............................................................................................46


18.	 Depth profiles of water temperature, pH, and dissolved oxygen concentration in North Fork Reservoir, 


station 1, August 1998 ....................................................................................................................................................46


19.	 Seasonal variations in water-quality and environmental variables at stations 1 and 2 in North Fork 


Reservoir, April–September 1998...................................................................................................................................47


20. Water temperature profiles in Timothy Lake at the log boom, May–September 1998 ..................................................50


21.	 Depth profile of water temperature, pH, and dissolved oxygen in Timothy Lake at the log boom, 


August 1998 ....................................................................................................................................................................51


22. Seasonal variations in water-quality and environmental variables in Timothy Lake, May–September 1998................52


23. Phytoplankton chlorophyll a–total phosphorus relationship in Timothy Lake, May–September 1998 .........................53


24.	 Relations between percentage of nonforest upland and concentrations of nitrate (A) and total 


phosphorus (B) at forested tributary sites in the Clackamas River Basin, Oregon, July 1998 .......................................55


25.	 Seasonal pattern in concentrations of disinfection by-products in treated drinking water from the 


Clackamas River, 1998 ...................................................................................................................................................67


26. Acres of timber harvested or lost to fire in the Clackamas River Basin, Oregon, 1900–98 ...........................................69


27. Fertilizer application in the Mount Hood National Forest in the Clackamas River Basin, Oregon, 


1986–98...........................................................................................................................................................................70


IV 
TABLES 

1. Characteristics of the hydroelectric projects in the Clackamas River Basin, Oregon ....................................................13


2. Data-collection activities in the Clackamas River Basin, Oregon, 1996–99 ..................................................................14


3. Sampling sites and data-collection activities in the Clackamas River Basin, Oregon 1996–99.....................................16


4. Description of land-cover categories used in the 1992–93 Thematic Mapper classification 


system..............................................................................................................................................................................19


5. State of Oregon water-quality criteria for pH, water temperature, and dissolved oxygen for the 


Clackamas River Basin, Oregon .....................................................................................................................................22


6. Periodicity chart outlining timing of spawning, egg incubation, and fry emergence for fish in the 


Clackamas River Basin, Oregon .....................................................................................................................................23


7. Basin characteristics and environmental conditions at sites sampled in the Clackamas River Basin, 


Oregon, July 1998 ...........................................................................................................................................................28


8. Seasonal patterns in streamflow, field parameters, nutrients, and algal conditions at main-stem and


tributary sites in the Clackamas River Basin, Oregon, May–September 1998...............................................................30


9. Average values for environmental conditions for groups of sites sampled in the Clackamas River Basin, 


Oregon, July 1998 ...........................................................................................................................................................34


10. Relative abundance of algal indicator taxa in the Clackamas River Basin, Oregon, May–September 1998 .................43


11. Nutrient and algal conditions in North Fork Reservoir, Oregon, April–September 1998 ..............................................49


12. Nutrient and algal conditions in Timothy Lake, Oregon, May–September 1998...........................................................53


13.	 Conditions in the Oak Grove Fork and upper main-stem Clackamas River before and during the drawdown 


of Timothy Lake, Oregon, September 1998 ...................................................................................................................54


14.	 Chemical characteristics of ground-water wells and springs in the lower Clackamas River Basin, 


Oregon, January 1999 .....................................................................................................................................................54


15.	 Reference conditions suggested by the U.S. Environmental Protection Agency for streams in the 


Willamette Valley and streams and reservoirs in the Cascade Range ............................................................................60


APPENDIXES 

1. Minimum Laboratory Reporting Levels for constituents analyzed in the Clackamas River Basin, Oregon, 1998........93


2. Quality-control sample results for nutrients in water......................................................................................................95


3. Quality-control sample results for algae collected in the Clackamas River Basin, Oregon, 1998 ................................ 97

4. Periphyton taxa occurrence at main-stem Clackamas River sites, Oregon, 1998...........................................................99


5. Periphyton taxa occurrence at tributary sites in the Clackamas River Basin, Oregon, 1998........................................103


6. Phytoplankton taxa occurrence in North Fork Reservoir, Clackamas River Basin, Oregon 1997–98 .........................109


7. Phytoplankton taxa occurrence in Timothy Lake, Clackamas River Basin, Oregon 1997–98.....................................113


V 
CONVERSION FACTORS 

Multiply By To obtain 

Length 

micrometer (μm) 0.00003937 inch (in) 

meter (m) 3.281 foot (ft) 

mile (mi) 1.61 kilometer (km) 

Volume 

milliliter (mL) 0.001057 quart (qt) 

liter (L) 1.057 quart (qt) 

liter (L) 0.2642 gallon (gal) 

liter (L) 28.317 cubic feet per second (ft3/s) 

cubic feet per second (ft3/s) 0.02831 cubic meters per second (m3/s) 

cubic meter per second (m3/s) 35.31 cubic foot per second (ft3/s) 

acre-feet (acre-ft) 1.233 × 103 cubic meters (m3) 

Mass 

microgram (mg) 0.00000003527 ounce (oz) 

milligram (mg) 0.00003527 ounce (oz) 

kilogram (kg) 35.27 ounce (oz) 

Area 

square miles (mi2) 640 acres (ac) 

acres (ac) 0.0015625 square miles (mi2) 

square meters (m2) 10.75 square feet (ft2) 

Temperature 

degrees Celsius (°C) 1.8 (°C) + 32 degrees Fahrenheit (°F) 

Concentration, in water 

micrograms per liter (μg/L) 0.001 milligrams per liter (mg/L) 

parts per million (ppm) 

milligrams per liter (mg/L) 1000 micrograms per liter (μg/L) 

parts per billion (ppb) 

Vertical coordinates in this report are referenced to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)—a 

geodetic datum derived from a general adjustment of the first-order level nets of both the United States and Canada. 

Specific conductance is given in microsiemens per centimeter (μS/cm) at 25°C. 

MAPPING SOURCES: 

Base map modified from various digital data sets from Portland, Oregon, METRO and U.S. Geological Survey (scales vary). 

Projection: State Plane, Zone 5076, North American Datum 1983. 

VI 
GLOSSARY 

SITE CODES 

CLEAR Clear Creek near the mouth 

COLLA Collawash River near Two Rivers Campground 

CR_ABNFK Clackamas River upstream of North Fork Reservoir 

CR_BARTON Clackamas River at Barton Park 

CR_BLNFK Clackamas River below North Fork Reservoir 

CR_CARVER Clackamas River at Carver 

CR_MCIVER Clackamas River at McIver Park (near Estacada) 

CR_UPPER Upper Clackamas River at Two Rivers Campground 

CR_3LYNX Clackamas River upstream of Three Lynx Creek 

CR_99E Clackamas River upstream of Hwy 99E Bridge 

DEEP Deep Creek upstream of Hwy 224 

EAGLE_M Eagle Creek near the mouth 

EAGLE_W Eagle Creek near the wilderness boundary 

FALL Fall Creek near the confluence with the North Fork Clackamas River 

FISH Fish Creek near the mouth 

NFCLACK North Fork Clackamas River at the mouth 

NFK_BUOY1 North Fork Reservoir at buoy 1 (near Promontory Park) 

NFK_BUOY2 North Fork Reservoir at buoy 2 (upstream of Promontory Park) 

NFK_BUOY3 North Fork Reservoir at buoy 3 (upstream of buoy 2) 

NFK_BURN North Fork Reservoir near burn pile on north shore 

NFKRES_1 North Fork Reservoir at log boom (station 1) 

NFKRES_2 North Fork Reservoir at powerlines (station 2) 

NFKRES_B North Fork Reservoir at North Fork Bay 

OAK_BLTLK Oak Grove Fork below Timothy Lake 

OAK_RAIN Oak Grove Fork at Rainbow Picnicground 

RICHARDSON Richardson Creek at Hwy 224 

ROARING Roaring River near mouth 

ROCK Rock Creek near mouth 

SFCLACK South Fork Clackamas River near mouth 

SIEBEN Sieben Creek at Hwy 224 

WINSLOW Winslow Creek near mouth 

VII 
SYMBOLS, ABBREVIATIONS, ACRONYMS, AND TERMS 

Algal guilds Groups of algal taxa that have particular preferences or tolerances for water-quality conditions, or that possess 

some unique physiochemical characteristic such as the ability to fix atmospheric nitrogen. 

As Arsenic. 

AFDM Ash-free dry mass, a measure of the organic content of a biological sample. 

biovolume A volumetric estimation of algal biomass reported in cubic micrometers (microns) per square centimeter. 

°C Degrees Celsius. 

CCA Canonical Correspondence Analysis, a multivariate statistical technique that allows for evaluation and testing 

of significance of relations among sites, environmental variables, and species. 

cells/cm2 Cells per square centimeter, a measure of cell density. 

CaCO3 Calcium carbonate. 

chl a Chlorophyll a. 

Cl- Chloride. 

CO2 Carbon dioxide. 

DIN Dissolved inorganic (bioavailable) nitrogen, the sum of nitrite, nitrate, and ammonium nitrogen. 

DKN Total dissolved Kjeldahl nitrogen, includes organic nitrogen and ammonium nitrogen (filtered, digested). 

DO Dissolved oxygen. 

DOC Dissolved organic carbon. 

epilimnion The parcel of water in a lake or reservoir extending from the surface to the metalimnion (where the thermocline 

occurs). 

EWI Equal-Width Increment: A sampling method whereby a depth- and width-integrated sample is collected, 

composited, and homogenized prior to dispensing subsamples for analysis. 

ft3/s Cubic feet per second: A measure of streamflow. 

GIRAS Geographic Information Retrieval and Analysis System (USGS data base). 

GIS Geographic Information System. 

HAAs Haloacetic acids, toxic disinfection by-products that occur when water containing organic carbon is treated 

with chlorine for drinking. 

hypolimnion	 The parcel of water in a lake or reservoir that extends from just off the bottom to the bottom of the metalimnion, 

where the thermocline occurs. 

kg/d	 kilograms per day. 

MCL	 Maximum Contaminant Level. 

metalimnion	 The parcel of water in a lake or reservoir where the temperature is changing rapidly with depth, located between 

the epilimnion and the hypolimnion. 

MRL	 Minimum laboratory reporting level, smallest measured concentration of a constituent that may be reliably 

reported using a given analytical method. 

mg/L	 Milligrams per liter, or parts-per-million. 

mg/m2	 Milligrams per square meter. 

mL	 Milliliter, or 10-3 liters. 

VIII 
SYMBOLS, ABBREVIATIONS, ACRONYMS, AND TERMS 

μg/L Micrograms per liter, or parts-per-billion. 

μm Micrometer, or 10-6 meters. 

μm3/cm2 Cubic micrometers (microns) per square centimeter: A measure of algal biovolume. 

N Nitrogen. 

N2 Nitrogen gas. 

NADP National Atmospheric Deposition Program. 

NH3 Ammonia. 

NH4 

+ Dissolved ammonium nitrogen. Used in this report to indicate ammonium (NH4 +) or ammonia (NH3), 

regardless of pH. 

NPDES National Pollution Discharge Elimination System. 

NO2 

- Dissolved nitrite nitrogen. 

NO3 

- Dissolved nitrate nitrogen. 

NTU Nephelometric turbidity unit. 

NWIS National Water Information System (USGS data base). 

NWQL USGS National Water-Quality Laboratory in Arvada, Colorado. 

P Phosphorus. 

pH A measure of the acidity of a solution, calculated as −log (concentration of H+ ion). 

PO4 

3- Orthophosphate phosphorus, a form of dissolved phosphorus (filtered). 

QC Quality control. 

RM River mile. 

SC Specific conductance (the electrical conductivity of water at 25°C). 

SiO2 Silicon dioxide, an important nutrient for diatom algae. 

SOC Suspended organic carbon. 

SRP Soluble reactive phosphorus includes PO4 

3-, dissolved polyphosphates, and other forms of dissolved 

P (filtered, not digested). 

TDP Total dissolved phosphorus (filtered, digested). 

Thermocline	 The layer of water in a lake or reservoir between the epilimnion and the hypolimnion, where the rate of decrease 

in water temperature with depth is greatest. 

THMs	 Trihalomethanes, toxic disinfection by-products that occur when water containing organic carbon is treated 

with chlorine. 

TKN	 Total Kjeldahl nitrogen includes organic nitrogen and ammonium nitrogen (unfiltered, digested). 

TN	 Total nitrogen (unfiltered, digested), the sum of TKN and nitrite-plus-nitrate. 

TP	 Total phosphorus (unfiltered, digested). 

USEPA	 U.S. Environmental Protection Agency. 

USGS	 U.S. Geological Survey. 

WWTP	 Wastewater treatment plant. 

IX 
ACKNOWLEDGMENTS 

Many scientists, water managers, and friends 

contributed to this project. Special thanks to the 

Clackamas River Water Providers (Clackamas 

River Water, South Fork Water Board, Sunrise 

Water Authority, North Clackamas County Water 

Commission, City of Estacada, and City of Lake 

Oswego) for contributing funding towards this study. 

The author especially wishes to thank Gordon McGhee 

(Clackamas River Water), whose interest in the 

health of the Clackamas River led to the development 

and funding of this study. Dan Shiveley (U.S. Forest 

Service) helped with the initial project development and site selection, and provided expertise on 

forest management in the Clackamas River Basin. 

Valuable contributions were made by Lolita Carter, 

Doug Cramer, and Tim Shibahara (Portland General 

Electric), John Berry, Tom Horning, Tom Rottman, and 

Ivars Steinblums (U.S. Forest Service), Karen Streeter, 

Andrew Swanson, and Ella Whelan (Clackamas 

County Department of Water Environment Services), 

Gregory Petit and Manette Simpson (Oregon Department of Environmental Quality), Robert Edgar 

(Oregon Department of Transportation), and several 

members of the Clackamas River Basin Council, 

especially Cole Gardiner, Lowell Hannah, Ed Hendrix, 

Lloyd Marbet, and Michael Carlson. 

Thanks also to Ian Waite, Chauncey Anderson, 

and Stephen Porter (U.S. Geological Survey), 

Yangdong Pan (Portland State University), Rick Hafele 

(Oregon Department of Environmental Quality), 

R. Jan Stevenson (Michigan State University), and 

Stan Gregory (Oregon State University), who contributed expertise on various topics, including nutrient 

dynamics, algal ecology, and macroinvertebrates. 

X 
Water-Quality and Algal Conditions in the 


Clackamas River Basin, Oregon, and their 


Relations to Land and Water Management


By Kurt D. Carpenter 

EXECUTIVE SUMMARY 

This report presents findings from a waterquality assessment conducted in the Clackamas 

River Basin, northwestern Oregon, from 1996 to 

1999, focusing on nutrient and algal conditions. 

Concerns about the quality of the Clackamas 

River emerged in 1994, when a bloom of bluegreen algae (Anabaena spp.) occurred in North 

Fork Reservoir, concurrent with taste and odor 

problems in drinking water supplied by the river. 

Providing clean water for drinking and supporting 

a cold-water fishery, including several stocks 

of salmon, steelhead, and trout, are among the 

beneficial uses designated by the State for the 

Clackamas River. Supporting these uses requires 

high-quality cold water that is well-oxygenated 

and low in chemical contaminants. With regard to 

those characteristics, the Clackamas River has 

withstood pressures from human activities in the 

basin relatively well; with the exception of high 

water temperatures and E. coli bacteria during 

summer, which currently do not meet waterquality standards, the river’s water quality is 

rated good to excellent compared with other 

rivers in Oregon. However, recent algal blooms 

are a sign of eutrophication (nutrient enrichment). 

Declines in water quality that can result from 

algal blooms—including taste and odor problems, 

increased concentrations of toxic disinfection 

by-products in drinking water, low levels of 

dissolved oxygen, and high pH—are beginning 

to appear in the Clackamas River. 

The purpose of the study was to determine 

the extent of eutrophication in the Clackamas 

River Basin, including the Clackamas River, 

its major tributaries, and reservoirs, with an 

emphasis on basic water quality (nutrients, 

dissolved oxygen, pH, temperature, and conductance), water quantity (water sources within 

the basin), and algal conditions (biomass and 

species composition). Sampling sites were located 

in streams draining areas with a variety of land 

uses, including forest management, agriculture, 

and urban development, as well as downstream 

from the hydroelectric projects in the basin, to 

examine how these human influences might be 

affecting water-quality and algal conditions. Most 

of the data were collected from May to September 

1998, with monthly sampling of reservoirs and 

sampling of streams every other month. Nutrient 

concentrations in ground water also were examined during a one-time sampling of a few wells 

and springs to evaluate whether ground water is 

transporting nutrients to the Clackamas River. 

Major Findings 

Nuisance algal growths, with accompanying negative effects on water quality, were 

observed at several locations in the basin during 

this study, including certain tributaries, reservoirs, 

and the main-stem Clackamas River. Algal 

assemblages in well-shaded streams (greater 

than 90% canopy closure) produced low biomass 

(11 to 23 mg/m2 [milligrams per square meter] 

1 
chlorophyll a), probably the result of light 

limitation. Streams with greater light availability 

sometimes reached high algal biomass. 

In 1998, biomass in the lower Clackamas 

River reached a maximum of 300 mg/m2 

chlorophyll a, which exceeded the threshold 

range of 100–150 mg/m2 suggested to prevent 

the occurrence of nuisance algal conditions, such 

as fouled stream channels and daily fluctuations 

in concentrations of dissolved oxygen and pH. 

Algal biomass at sites immediately downstream 

from the hydroelectric project’s reservoirs and/or 

powerhouses also exceeded the nuisance threshold, sometimes by a factor of 4 or more, especially in September. Nuisance algal conditions 

also were observed in some of the tributaries, 

including the North Fork of the Clackamas River, 

Clear Creek, Rock Creek, and Sieben Creek. 

High algal biomass in the Clackamas River 

appears to be a recent phenomenon, as biomass 

was low during a previous study that found 

21 mg/m2

 chlorophyll a in the lower Clackamas 

River at river mile 0.4 in late August 1993. 

High biomass was sometimes observed during 

1998 in locations where nutrient concentrations 

appeared relatively low. Although this finding 

appears contradictory, growing algae may deplete 

water column nutrient concentrations, giving the 

deceptive appearance of low nutrient availability. 

Hypotheses explored in this report to explain 

such growths include (1) high water velocities, 

(2) an apparent symbiotic relationship between 

nitrogen-fixing algae and green algae, (3) utilization of nutrients from ground-water infusions 

along stream margins, (4) utilization of dissolved 

organic nitrogen that is typically not considered in 

nutrient assessments, (5) reduced grazing on algae 

by aquatic invertebrates, and (6) highly efficient 

recycling of nutrients. 

Although blue-green algae were consistently 

observed in both of the major reservoirs during 

this study, sometimes forming blooms, the foul 

tastes and odors that occurred in the water supply 

in 1994 did not occur in 1998. Prolific growths 

of filamentous green algae (Cladophora and 

Stigeoclonium) were, however, observed on 

streambed substrates in the lower Clackamas 

River, where the effects of excessive algae on 

dissolved oxygen, pH, and stream habitat were 

pronounced. Further, as the algae began to decay, 

aesthetic and water-quality conditions in the 

lower Clackamas River also deteriorated as 

clumps of drifting algae became entangled on 

docks and fishing lines, clogged drinking water 

intakes, and increased turbidity levels in the river. 

Concentrations of disinfection by-products, toxic 

compounds that form during chlorination, also 

increased in drinking water during this time, 

presumably the result of the increased organic 

matter in the river from the drifting algae. 

These are unambiguous signs of nutrient 

enrichment. Any restoration efforts will require 

management strategies aimed at reducing the 

transport of nutrients to the Clackamas River and 

its tributaries. Nutrient sources can be difficult to 

identify and quantify, especially in watersheds 

such as the Clackamas Basin that contain diverse 

land uses. Evaluating potential nutrient sources in 

the basin and proposing hypotheses to explain the 

observed proliferations of algae, one of the goals 

of this study, was the first step. More detailed 

follow-up studies at smaller scales will be 

required to better quantify nutrient sources and to 

examine cause-and-effect relationships between 

land and water management and water quality. 

Nutrient concentrations in the basin 

showed considerable variation among sites, and 

the sources of phosphorus and nitrogen were different, especially with respect to streams draining 

forested land. There, concentrations of dissolved 

phosphorus (up to 26 μg/L [micrograms per liter]) 

were found in streams draining portions of the 

High Cascades Ecoregion, including the upper 

Clackamas River (at river mile 57) and the lower 

Oak Grove Fork, possibly the result of naturally 

occurring phosphorus from young volcanic 

rocks in this area. Total phosphorus concentrations at all main-stem sites in the upper basin, 

and several upper basin tributaries, exceeded 

9 μg/L, the reference condition suggested by 

the U.S. Environmental Protection Agency 

for streams in the Cascade Range Ecoregion. 

2 
Nitrogen concentrations in these and other 

streams in the upper basin, however, were mostly 

below laboratory reporting levels (<5 μg/L).In 

contrast, streams draining the middle Clackamas 

Basin, including Clear Creek, Eagle Creek, and 

the North Fork of the Clackamas River, showed 

the opposite pattern, with relatively high concentrations of nitrogen and relatively low concentrations of phosphorus. The nitrate concentrations in 

these basins ranged from 43 to 206 μg/L in July, 

significantly exceeding the 5 μg/L reference condition suggested by the U.S. Environmental Protection Agency for streams in the Cascade Range 

Ecoregion. Nitrate concentrations in upper Eagle 

Creek in the Salmon-Huckleberry Wilderness 

Area and Roaring River (two reference streams) 

were 9 and <5 μg/L, respectively, in July, which 

is close to the suggested reference condition. 

Inputs of nitrogen from middle-basin watersheds (and from North Fork Reservoir, which 

appeared to release nitrogen during the spring), 

combined with inputs of phosphorus from the 

upper basin, provide the necessary nutrients to 

support algal growth in the Clackamas River. 

Therefore, due to the abundance of phosphorus 

in the main stem, any inputs of nitrogen from 

tributaries and other sources, including nitrogen 

fixed by blue-green algae in the reservoirs 

and streams, may stimulate algal growth in the 

Clackamas River. 

Inputs of nitrogen and phosphorus also occur 

from the lower basin tributaries, including Deep, 

Richardson, Rock, and Sieben Creeks, which had 

much higher nutrient concentrations compared 

with other sites, likely reflecting anthropogenic 

activities. Inputs from these tributaries likely 

contributed to the observed proliferations of 

algae in the Clackamas River during this study. 

However, due to the relatively low streamflow 

in Richardson, Rock, and Sieben Creeks, they 

contributed smaller loads of nutrients, despite 

their high nutrient concentrations. Deep Creek, 

however, with higher flow, did contribute relatively large loads of both nitrogen and phosphorus 

to the Clackamas River. 

Several potential sources of nutrients were 

identified in the basin, including point-source 

discharges from wastewater treatment plants and 

fish hatcheries. Nonpoint sources, including soil 

erosion, fertilizers, nitrogen-fixing plant species, 

atmospheric deposition, field burning, and livestock, also may contribute to enriching streams 

with nutrients. Another potentially important 

source of nutrients is ground water, which was 

shown to contain high levels of nitrogen and 

phosphorus. Although the quantity of ground 

water entering the Clackamas River was not 

determined, the streamflow data suggest that 

it may be significant, especially in the reach 

between River Mill Dam and Barton. 

Most of the streamflow in the Clackamas 

River originated from the upper basin, where 

large amounts of precipitation and infiltration 

recharge ground-water aquifers, thus supplying 

the river with consistent flows into late summer, 

despite the lack of rain at that time. Water from 

the Oak Grove Fork of the Clackamas River (via 

discharges from the Oak Grove Powerhouse) and 

the Collawash and Roaring Rivers accounted for 

much of the streamflow in the Clackamas River. 

Other tributaries, especially those in the lower 

basin, contributed lesser amounts of summertime 

streamflow. The basin’s largest reservoir, 

Timothy Lake, which stores snowmelt during the 

spring, provided a steady supply of water to the 

Oak Grove Fork and downstream reaches during 

summer and contributed about one-third of the 

streamflow in the upper Clackamas River during 

reservoir drawdown in late September. 

Although temperature, dissolved oxygen, 

and pH data from this study indicate that 

State water-quality standards may have been 

exceeded at times during this study, the temperature and dissolved oxygen criteria are based 

on multiple-day averages, not single point 

“instantaneous” measurements, as were typically 

collected for this study. The water temperature, 

for example, is based on the 7-day average of 

the maximum daily temperature, whereas the 

dissolved oxygen criterion is based on a 30-day 

mean minimum concentration. Nevertheless, 

continuous data (15-minute intervals) collected 

in late June and mid-July in the lower Clackamas 

River at river mile 2.7 showed instantaneous 

3 
exceedances for water temperature, dissolved 

oxygen, and pH, sometimes for much of the day. 

These data suggest that water-quality criteria 

were not being met for a period spanning at least 

2 weeks, however, the data were not sufficient to 

fully characterize compliance with water-quality 

criteria. 

Water-quality criteria for water temperature 

and dissolved oxygen are more stringent during 

fish spawning, egg incubation, and fry emergence 

periods, which, in the Clackamas Basin, occur 

nearly year round (from August 15 through 

July 15). The dissolved oxygen standard, 

however, also depends on the intergravel dissolved oxygen concentration, which, because 

such measurements may disturb fish spawning 

areas, has not been measured in the Clackamas 

River. As a result, it was not possible to determine 

whether dissolved oxygen standards were being 

met. 

Water temperatures were generally 

cold (less than 11°C [degrees Celsius]) in the 

Clackamas River in May, but increased to levels 

that might have exceeded State water-quality 

criteria in July. All main-stem Clackamas River 

sites, from just upstream of the Collawash River 

to the mouth, and most tributaries potentially 

exceeded the 7-day average maximum daily 

temperature criterion of 12.8°C in July. Water 

temperature in some tributaries, including the 

upper Oak Grove Fork (downstream of Timothy 

Lake), Winslow Creek, Fall Creek, and Eagle 

Creek (at the downstream boundary of the 

Salmon Huckleberry Wilderness Area) was less 

than 12.8°C during sampling in July. 

The reservoirs appeared to increase water 

temperatures in downstream reaches, especially in 

September. Water temperatures in the Oak Grove 

Fork increased during the drawdown of Timothy 

Lake by about 2°C in September 1998, whereas a 

larger temperature increase of about 4°C was 

observed in the Clackamas River as it flowed 

through North Fork Reservoir. At this time, water 

temperatures probably exceeded the criterion 

within the reservoir, and at all main-stem sites 

downstream, with the highest value (20.4°C) 

occurring in the Clackamas River at Barton. 

However, the inputs of warm tributaries in the 

lower basin, especially Eagle, Clear, and Deep 

Creeks, also contributed to high water temperatures in the lower Clackamas River. 

Levels of dissolved oxygen and pH varied 

among sites, with substantial fluctuations occurring throughout the day at some sites. Dissolved 

oxygen concentrations appeared to be controlled 

in many places by water temperature and reaeration rather than by biological processes, with the 

highest concentrations coinciding with the coldest 

temperatures. In some cases, however, patterns in 

the dissolved oxygen concentrations and pH were 

consistent with the effects of algal photosynthesis, 

with highest levels occurring during the day and 

lowest levels at night or early morning. Such 

fluctuations resulted in potential exceedances of 

State water-quality criteria in the lower Clackamas River at river mile 2.7 in late June and midJuly, when the respective minimum dissolved 

oxygen concentrations were 8.3 and 7.7 mg/L 

(milligrams per liter [parts-per-million]). In 

September, a spawning period for spring and 

fall Chinook salmon, the 30-day 11 mg/L mean 

minimum dissolved oxygen criterion was 

probably not met at any of the main-stem sites. 

The lowest measured dissolved oxygen concentrations for tributary sites occurred in Clear, 

Eagle, Deep, and Rock Creeks in August, when 

dissolved oxygen concentrations ranged from 

8 to 8.4 mg/L. The Oak Grove Fork downstream 

from Timothy Lake also probably did not meet 

the 11 mg/L or the 95% saturation criterion in 

September, when dissolved oxygen concentrations in Timothy Lake were especially low. 

Fluctuations in pH also were observed in 

the lower Clackamas River (at river mile 2.7) 

in late June and mid-July, with the highest 

values occurring in the late afternoon, slightly 

exceeding the State single-measurement criterion 

of 8.5 pH units. Similar fluctuations in pH also 

were observed in the lower Clackamas River (at 

Carver, river mile 7.9) in August. Exceedances of 

the pH criterion were observed in only one of the 

tributaries (Deep Creek), where the afternoon pH 

was 8.8 units in July. 

4 
Timber production, agriculture, and 

urban development, the major land uses in the 

basin, may each be contributing to declines in 

water quality. These activities all have potential 

to contribute nutrients, either directly through soil 

erosion and inputs of fertilizers, for example, or 

through ecosystem or habitat disturbances that 

can alter nutrient cycling processes. The highest 

concentrations of nitrogen and phosphorus were 

found in tributaries draining land having these 

uses, whereas nutrient concentrations (and algal 

biomass) in streams in undisturbed watersheds, 

including upper Eagle Creek and Roaring River, 

were substantially lower. 

Forest management (timber harvesting, 

roads, and fertilization in some areas) appeared to 

be a source of nutrients to streams. A positive 

correlation was found between the amount of 

nonforest upland (including clear cuts and other 

areas without vegetation) and concentrations of 

total phosphorus among streams in the middle 

and upper Clackamas Basin, where forest management is the dominant land use. This finding, 

combined with the positive correlation between 

concentrations of total phosphorus and silica, an 

important component of most soils, suggests that 

timber harvesting and associated network of 

roads in these watersheds may be transporting 

phosphorus through erosion of phosphate-rich 

soils. A similar relationship was found between 

nitrate concentrations and the amount of nonforest 

upland, although the increase in nitrate was 

observed only at sites in the middle basin, where 

most the timberland is privately owned. Nitrogen 

from these sites may originate from several 

sources, including tree harvesting (which reduces 

uptake of N by vegetation), post-harvest burning 

of slash debris, wildfires, fertilizer applications, 

atmospheric deposition, and proliferations of Nfixing plants such as red alder and scotchbroom 

that often colonize disturbed soils. 

Sites in basins containing the highest 

amounts of agricultural and urban land had the 

highest concentrations of nutrients, and algal 

assemblages included several taxa that are indicative of nutrient enrichment. The highest concentrations of both nitrogen and phosphorus, and the 

highest algal biomass for a lower basin tributary, 

occurred in Sieben Creek, which drains a watershed undergoing rapid urbanization. The excessively high concentration of nitrate in Sieben 

Creek (>7,000 μg/L) may have resulted from 

applications of fertilizer on urban or agricultural 

land in the basin, or from leaky septic systems. 

Other areas in the lower Clackamas Basin, such as 

mobile home parks, also may contribute wastewater high in nutrients to the Clackamas River. 

The hydroelectric projects in the basin 

produce electricity, provide water storage, and 

regulate streamflows in much of the basin. As 

such, water quality in the Oak Grove Fork and 

Clackamas River is closely related to the quality 

of the water within Timothy Lake and North Fork 

Reservoir. Processes within the reservoirs, such as 

heating of the water, the uptake of dissolved nutrients by growing phytoplankton, and the decomposition of organic material and release of nutrients 

from reservoir sediments, may alter thermal 

regimes, nutrient availability, and concentrations 

of dissolved oxygen in downstream reaches. In 

September, for example, water released from the 

reservoirs increased water temperatures in the Oak 

Grove Fork and in the Clackamas River, as previously indicated. Longitudinal temperature measurements collected in August 1997 showed that 

warming in North Fork Reservoir largely occurred 

in the uppermost reaches of the reservoir, where 

streambed material transported from upstream has 

created a shallow reach that is ideal for warming. 

The reservoirs also provide a favorable habitat for planktonic blue-green algae to develop, 

sometimes to bloom proportions that occasionally 

produce taste and odor problems in drinking water 

supplies. The highest surface chlorophyll a concentrations in Timothy Lake and North Fork Reservoir (18 μg/L in July and 24 μg/L in September 

1996, respectively) occurred during blooms of 

blue-green algae (Anabaena spp.). Although these 

instantaneous values indicate a possible exceedance of the State Action Level for nuisance phytoplankton growth (15 μg/L chlorophyll a, based 

on a 3-month average) in 1996, chlorophyll a 

values were much lower in the reservoirs in 1997 

and 1998, typically less than 8 μg/L. 

5 
At times, algal blooms appeared to affect 

levels of nutrients, dissolved oxygen, and pH 

in the reservoirs and in downstream reaches. 

Phytoplankton growth in North Fork Reservoir 

and the settling of algal cells appeared to lower 

phosphorus concentrations downstream from 

the reservoir. Downstream from Timothy Lake, 

however, an increase in the phosphorus concentration was observed in September, possibly due 

to the release of phosphorus from the reservoir’s 

anoxic hypolimnion. 

The nitrogen fixed by blue-green algae, and 

other nutrients from organic materials that collect 

in the reservoirs, may be transported to the 

reservoir sediments. Here, they can be recycled 

into dissolved inorganic nutrients and transported 

downstream, thus providing a source of nutrients 

to algae in downstream reaches. As noted earlier, 

excessive growths of algae were observed immediately downstream from each of the hydroelectric project reservoirs during this study. Other 

factors, including power peaking, which often 

produces daily fluctuations in water levels downstream from the projects, also may stimulate algal 

growth in downstream reaches through mechanisms hypothesized in this report. 

Numerous hypotheses to explain the 

occurrence of blue-green algae blooms in the 

reservoirs were explored in this report. The low 

concentrations of nitrogen that were typically 

found in the reservoirs provide an advantage to 

algae that are capable of fixing nitrogen, such 

as Anabaena. The positive correlation between 

chlorophyll a and total phosphorus suggests that 

phosphorus availability may regulate blue-green 

algal growth in the reservoirs. In August 1997, 

concentrations of chlorophyll a and soluble 

reactive phosphorus were higher in the upstream 

reaches of North Fork Reservoir compared with 

those near the dam, indicating that the blooms 

were forming near the inlet, again suggesting 

the importance of phosphorus in regulating algal 

biomass. 

Meteorological factors, such as rainstorms 

or mixing events caused by wind also may 

contribute to algal blooms. The September 1994 

algae bloom in North Fork Reservoir, which 

coincided with taste and odor problems in drinking water, occurred about 5 days after a 0.85-inch 

rainstorm in the basin. The September 1996 

bloom of Anabaena in North Fork Reservoir 

occurred shortly after fall turnover, when reservoir bottom water mixes to the surface. These 

events may have transported phosphorus to the 

surface, where an existing algal population was 

stimulated into a bloom during subsequent sunny 

weather. 

Potential Management Strategies to Improve Conditions 

Nutrient management strategies aimed at 

reducing the effects of eutrophication often target 

the nutrient that is in shortest supply (relative 

to demand) and thus limits further algal growth. 

Multiple lines of evidence presented in this report 

suggest that algal growth in many of the streams 

in the Clackamas Basin, including the main-stem 

Clackamas River, is regulated by nitrogen. If this 

is the case, reductions in nitrogen through management strategies could ultimately reduce algal 

growth in the river. Phytoplankton growth in the 

reservoirs, however, appears to be regulated by 

phosphorus, both nitrogen and phosphorus, or by 

the amount of time available for growth, which 

is dictated by the flushing rate of the reservoirs 

(particularly North Fork Reservoir). Future 

studies suggested in this report could more 

definitively test which nutrient(s) are regulating 

algal growth in the streams and reservoirs, which 

could help prioritize future nutrient management 

strategies and restoration efforts in the basin. 

Many of the strategies suggested in this 

report to reduce the effects of nutrient enrichment, 

such as restoring riparian vegetation and reducing 

erosion through storm-water management, also 

may help alleviate other water-quality problems 

in the basin, such as high levels of turbidity 

or high water temperatures. Other strategies 

specifically aimed at nutrients include fertilizeruse education and removal of invasive nitrogenfixing plants. Habitat restoration efforts include 

enhancing the natural functions of riparian zones 

and wetlands, as well as increasing stream complexity. 

6 
Management strategies aimed at reducing 

the frequency or severity of blue-green algae 

blooms in the reservoirs include erosion control 

to lower phosphorus concentrations, which were 

positively correlated with algal biomass in the 

reservoirs. The severity and frequency of algal 

blooms in North Fork Reservoir might be reduced 

through dilution by releasing water from Timothy 

Lake, depending on the water quality in Timothy 

Lake at the time. Management strategies aimed 

at reducing concentrations of disinfection byproducts in drinking water could include watershed restoration efforts that reduce algal growth in 

the basin (nutrient reduction strategies and stream 

vegetation enhancements), thereby reducing the 

amount of organic matter in raw water. Additionally, mechanical modifications to drinking water 

treatment plants, including prefiltration of raw 

water to reduce levels of organic material prior 

to chlorination, also may reduce concentrations of 

disinfection by-products. 

Potential Future Studies 

This study documented current baseline 

water-quality and algal conditions in streams and 

reservoirs, generated hypotheses to explain the 

observed patterns in conditions, and evaluated 

management strategies that might improve 

conditions. Additional monitoring could further 

define water-quality and algal conditions in the 

basin, thereby providing a benchmark against 

which future studies may be compared. Also, 

detailed watershed assessments that examine the 

interactions between land use, habitat, and water 

quality could help further our understanding of 

how human activities affect water-quality and 

algal conditions in areas where water-quality 

problems were identified in this study. Focused 

studies could then lead to the development and 

implementation of management strategies aimed 

at improving conditions. 

Routine monitoring could help detect 

changes in water quality and provide information 

on year-to-year variability necessary for identifying trends in water quality over time and for determining compliance with water-quality standards. 

Although the Oregon Department of Environmental Quality collects water-quality data from four 

main-stem Clackamas River sites about six times 

per year, sampling of algal biomass or species 

composition is not included and no data are collected from tributaries. Other agencies, such as 

Clackamas County Water Environment Services, 

have collected some water-quality data from 

some of the lower basin tributaries, but no comprehensive analysis of all data has been conducted. 

Routine monitoring of nutrients, contaminants, 

and streamflow in the lower-basin tributaries is 

needed to identify how these streams affect water 

quality in the main-stem Clackamas River. The 

highest nutrient concentrations were observed in 

the lower-basin tributaries, and future restoration 

efforts or changes in land-use practices in these 

subbasins could be quantified through routine 

monitoring. 

Focused studies aimed at identifying factors 

that contribute to or limit algal growth, and determining to what extent algal growth is affecting 

water quality, habitat conditions, and drinking 

water supplies could lead to the development 

and implementation of management strategies to 

improve conditions. Determining which factors 

(nutrients and/or light availability) are limiting 

algal growth in the Clackamas River, tributaries, 

and reservoirs could be accomplished by nutrientaddition experiments. Once limiting nutrients 

are identified, nutrient-reduction strategies can be 

prioritized. 

Evaluating nutrient sources in the basin, 

including point sources (wastewater treatment 

plants, fish hatcheries, and reservoirs) and nonpoint sources (runoff from land surfaces, phosphate rock deposits, ground water, and atmospheric 

deposition) could help in the development of management strategies. Identifying nitrogen and phosphorus inputs from land-use activities (agriculture, 

urban development, and forest management) could 

benefit from up-to-date, small-scale, and fieldverified information on the amount, condition, 

and distribution of land cover, crop types, and 

vegetation classes, along with other variables such 

as population density, road density, and areas or 

distribution of impervious surfaces. 

7 
Additional studies that identify the sources of 

organic matter, including algae, could help reduce 

concentrations of toxic disinfection by-products 

in treated drinking water. Further, testing for the 

presence of algal toxins, which are sometimes 

produced by blue-green algae including Anabaena 

and Microcystis, which were found in the reservoirs, could identify whether this is an issue in 

the Clackamas Basin. Also, evaluating whether 

the tidal effect in the lower Clackamas River 

causes water from the Willamette River to reach 

drinking-water treatment plant intakes may help 

managers ensure that only high-quality raw water 

is withdrawn from the river. Lastly, evaluating 

the potential effects of fluctuating water levels 

on aquatic biota (algae and macroinvertebrates), 

caused by hydroelectric project operations, 

also may result in opportunities for improving 

conditions. 

Despite the episodes of poor water quality 

that were occasionally observed in the Clackamas 

River, tributaries, and reservoirs during this study, 

the Clackamas River remains one of the highest 

quality streams in Oregon, and runs of wild 

salmon, steelhead, and trout can still be found 

in its waters. However, if the river is to continue to 

support other designated beneficial uses, such as 

providing high-quality drinking water, efforts are 

needed to reduce nutrient enrichment and restore 

natural processes in order to reverse the symptoms 

of eutrophication that are beginning to appear. 

Restoration efforts and future studies proposed 

here should result in improvements over time, 

thus improving habitat and water quality in the 

Clackamas Basin. 

INTRODUCTION 

“I have been on all rivers and tributaries of the 

Columbia from the Cascades to Priest’s Rapids, to 

which the Chinook salmon go...and I do not hesitate 

to say that the Clackamas River, with its clear, cold 

water, its rapids, and its long, shallow gravel beds, 

is the most natural and favorite region for salmon 

spawning (L.T. Barin, 1885 [in Taylor, 1999]).” 

The Clackamas River in northwestern Oregon is 

valued for its scenic beauty, recreational opportunities, 

salmon and steelhead runs, and for providing a highquality source of drinking water. From its headwaters 

in the Cascade Range between Mount Hood and Mount 

Jefferson, the upper Clackamas River descends 

7,200 feet on a northwesterly course, winding through 

steep canyons and gorges and cutting through prominent basalt outcrops and cliffs. The many falls and 

rapids, separated by deep, clear pools and expansive 

cobble bars, make the upper Clackamas River a favorite 

among whitewater enthusiasts, anglers, and hikers. 

Downstream from Estacada, the river emerges into 

gentler terrain, forming a broad floodplain that is 

confined by steep cliffs that form upland terraces in 

places. Here, the lower Clackamas River is wider, 

flowing past volcanic buttes in the lower basin before 

meeting the Willamette River south of Portland. 

From the high mountainous areas to the low 

valleys, the landscape of the Clackamas Basin is 

diverse, featuring five ecoregions, each with its own 

unique combination of climate, geology, soils, and vegetation that shape the various hydrologic and chemical 

factors that influence water quality. Human activities in 

the basin, including timber harvesting, construction of 

roads and urban developments, farming, gravel mining, 

and hydroelectric power generation also may affect 

water quality. The largest inputs of contaminants introduced by human development occur in the lower basin, 

particularly on the north side of the Clackamas River, 

where agricultural and urban land is concentrated 

(fig. 1). Water-quality problems, such as high levels 

of turbidity, also occasionally occur from soil erosion, 

particularly in the upper basin, where steep topography 

and geologic instability, combined with abundant 

winter precipitation, contribute to erosion during 

periods of heavy runoff. 

The Clackamas River Basin encompasses 

940 square miles of public and private forestland, 

agricultural land, rural residential areas, and urban 

developments. Most (69%) of the land in the basin is 

managed by the U.S. Forest Service, mostly within the 

Mount Hood National Forest. Twenty percent of the 

basin is privately owned, with 5% belonging to private 

timber companies. The Confederated Tribes of the 

Warm Springs Indian Reservation, the U.S. Bureau of 

Land Management, and other agencies own the remaining area (Metro, 1997). Extensive timber harvesting of 

Douglas fir, Pacific silver fir, and western red cedar has 

occurred on public and private commercial forestland in 

the basin, although most (51%) of the basin is mature 

forest, 22% is regrowth forest, and 19% is nonforested 

upland (fig. 1). 

8 
Figure 1. Land-cover map of the Clackamas River Basin, Oregon, 1992–93 (Refer to table 4 for land-cover descriptions). 

9

About one-third of the privately owned land 

is used for agricultural crops, including Christmas 

trees, landscaping plants and ornamentals, cane berries, 

hay, hazelnuts, oats, wheat, vegetables, and fruits 

(Hassanein and Peters, 1998). Industries in the basin 

include food processing plants, aggregate gravel mining 

operations, metal foundry companies, and others, 

mostly in the lower portion of the basin. Residential 

developments in the basin range from small rural homes 

to densely populated urban areas. 

Study Background and Objectives 

Water quality in the Clackamas River is considered very good to excellent compared to other rivers in 

the State, based on the Oregon Water Quality Index 

(Greg Petit, Oregon Department of Environmental 

Quality, written commun., 1998), and has withstood 

pressures from human impacts and natural disturbances 

seemingly well. In September 1994, however, foul 

tastes and odors appeared in drinking water supplied by 

the Clackamas River. A survey of the watershed for a 

potential cause of this problem indicated that an algal 

bloom had developed in North Fork Reservoir (Bruce 

Hemenway, South Fork Water Board, oral commun., 

1998). Water samples collected from the reservoir 

contained Anabaena, a blue-green alga that is notorious 

for causing taste and odor problems in drinking-water 

supplies (Terrell and Perfetti, 1989). Chemical analysis 

of the raw and treated drinking water identified geosmin 

(Gordon McGhee, Clackamas River Water, written 

commun., 1999), a taste and odor compound that is 

produced by many blue-green algae (Safferman, 1967; 

Izaguirre and others, 1982) and certain actinomycete 

bacteria (des Eaux, 1987). 

Nuisance blooms of blue-green algae are fueled 

by excess nutrients, and their presence may be an 

indication that eutrophication, the process of nutrient 

enrichment, is occurring. Other signs of eutrophication, 

such as large growths of algae, also have been observed 

in the Clackamas River and some of its tributaries. 

During the spring of 1996, moderate-to-heavy growths 

of green algae were observed in the upper Clackamas 

River and some of its tributaries, including Fish Creek 

and the Oak Grove Fork. 

Although algae can be an important food resource 

for stream invertebrates, contributing to food webs, 

excessive growths of algae can stress fish and other 

aquatic life by causing low levels of dissolved oxygen 

(DO) and high pH and smothering stream channels. 

Further, when large proliferations of algae senesce and 

decay, they often lead to episodes of poor water quality, 

making the water turbid as algae are transported downstream during die-off (sloughing) events. 

In addition to nutrient overenrichment, another 

potential cause of excessive algal growth, particularly in 

the lower Clackamas River, is high water temperatures. 

The lower Clackamas River has experienced high water 

temperatures for at least 15 years, and the Oregon 

Department of Environmental Quality currently lists the 

lower 23 miles of the river (from River Mill Dam to 

the mouth) on the 303 (d) list of water bodies considered water-quality limited because of persistent high 

water temperatures during summer (Oregon Department of Environmental Quality, 2000). Additionally, 

the Oregon Department of Environmental Quality has 

recently listed the lower 15 miles for E. coli bacteria 

(Oregon Department of Environmental Quality, 2002). 

Although some water-quality data have been 

collected in the Clackamas Basin, studies of basic water 

quality relating tributary conditions to those in the 

main stem have been lacking. To fill this data gap, the 

U.S. Geological Survey (USGS), in cooperation with 

the Clackamas River Water Providers, U.S. Forest 

Service, Portland General Electric, Clackamas River 

Basin Council, Clackamas County Department of 

Water Environment Services, and the Oregon Department of Transportation, began a study to examine and 

document the current baseline water-quality and algal 

conditions in the Clackamas Basin. The objectives of 

the study were to: 

1. Characterize spatial and temporal variations in 

streamflow, water quality (nutrients, DO, pH, 

water temperature and conductance), and algal 

conditions (algal biomass and species composition) in the major streams and reservoirs; 

2. Monitor for the occurrence of algal blooms 


in the reservoirs and attempt, if possible, to 


identify potential triggers for such blooms; 


3. Characterize nutrient concentrations in ground 

water and estimate potential ground-water 

discharges to the main-stem Clackamas River; 

4. Examine relations between water-quality and 

algal conditions with respect to land and 

water management (forestry, urbanization, 

agriculture, hydroelectric power generation, 

and the drawdown of Timothy Lake), and 

evaluate possible management scenarios that 

might improve conditions. 

10 
Overview of the Clackamas River Basin 

For purposes of this report, the Clackamas River 

Basin as a whole was partitioned into three regions 

having different basin characteristics: (1) the mostly 

forested upper basin, (2) the middle basin, which generally corresponds to the Western Cascades Lowlands 

and Valleys Ecoregion (Metro, 1997), and (3) the lower 

basin, where most of the human development is located 

(figs. 1 and 2). 

Upper and Middle Clackamas River Basin— 

The upper and middle Clackamas Basin hosts several 

large tributaries, including the Collawash River, Oak 

Grove Fork, Roaring River, and Fish Creek, whose 

watersheds are within the Mount Hood National Forest. 

The U.S. Forest Service manages about two-thirds 

of this area, primarily for timber production (Metro, 

1997), and a dense network of logging roads traverses 

the upper basin (U.S. Forest Service, 1995c). The North 

and South Forks of the Clackamas River and the upper 

portions of Eagle and Clear Creeks are in the middle 

basin, where much of the private timberland is located 

(figs. 1 and 2). Streamflow regulation in this area occurs 

in the main-stem Clackamas River from the Oak Grove 

Powerhouse (at river mile [RM] 47.8) downstream 

to North Fork Reservoir (at RM 33.5) and within the 

11-mile hydroelectric project on the main stem. 

The Clackamas River from Big Springs (near the 

headwaters at Olallie Butte) to Big Cliff (about 1 mile 

upstream of North Fork Reservoir) and about 14 miles 

of the Roaring River were designated Wild and Scenic 

in 1988. State Scenic Waterways in the basin include 

12 miles of the North Fork Clackamas River and 

4 miles of the South Fork Clackamas River. There 

are two federally designated wilderness areas, both 

within the Mount Hood National Forest: The Bull-ofthe-Woods Wilderness Area encompasses 34,900 acres 

in the Collawash River Basin, and the Salmon-Huckleberry Wilderness Area in the headwaters of Eagle Creek 

contains 44,600 acres. The Roaring River watershed, 

another large parcel of land (27,500 acres), also is 

largely unmanaged compared with nearby watersheds 

(U.S. Forest Service, 1996c). 

Oak Grove Fork Basin and Hydroelectric 

Project Area—The Oak Grove Fork of the Clackamas 

River is located in the northeastern, high-elevation 

portion of the Clackamas River Basin (fig. 2). Most 

of the land in the basin is managed by the U.S. Forest 

Service and the Confederated Tribes of the Warm 

Springs Indians (Metro, 1997). Timothy Lake, a popular 

recreation destination in the summer, is located near the 

headwaters of the Oak Grove Fork and is the largest 

reservoir in the Clackamas River Basin, holding 

70,000 acre-feet of water (table 1). Timothy Lake was 

completed in 1956, when Timothy Meadows, a wetland 

area once grazed by sheep (Johnson and others, 1985), 

was flooded to form the reservoir. Grazing allotments 

for cattle still exist in the Timothy Lake basin, with 

about 100 cow-calf pairs grazing the area in 1995 

(U.S. Forest Service, 1996b). 

Water levels in Timothy Lake are typically held 

constant during the summer and lowered in September 

during the annual drawdown, which provides enhanced 

flow for power generation and provides storage capacity for spring snowmelt. Water released from Timothy 

Lake flows down the Oak Grove Fork to the Stone 

Creek diversion, where most of the water is diverted 

out of the channel through a pipe, returning through 

a downstream powerhouse (fig. 2). Downstream, 

the Oak Grove Fork is again diverted at Harriet Lake, 

where, under normal streamflow conditions, all of the 

streamflow is routed to Frog Lake, a small forebay for 

the Oak Grove Powerhouse located 925 vertical feet 

below on the main-stem Clackamas River. The USGS 

operates a streamflow gage in the Clackamas River 

upstream of Three Lynx Creek, about 0.2 miles downstream from the Oak Grove Powerhouse (fig. 2). 

North Fork, Faraday, and River Mill Hydroelectric Project Area—Near the downstream boundary 

of the Mount Hood National Forest, the Clackamas 

River enters North Fork Reservoir (fig. 2), the second 

largest reservoir in the Clackamas Basin (table 1). High 

streamflows in the Clackamas River typically flush 

through North Fork Reservoir quickly, producing a 

relatively short residence time of about 1 week, on 

average (table 1). As will be discussed later, longer 

residence times may result during summer, when solar 

heating produces a warmer surface layer above the 

colder and denser bottom water. The deep-water release 

depth of 130 feet may entrain this colder water, thus 

reinforcing thermal stratification in the reservoir. 

Downstream of North Fork Dam the Clackamas 

River, minus about 100 ft3

/s (cubic feet per second), is 

diverted to Faraday Forebay by the Faraday Diversion 

Dam. After passing through the powerhouses at 

Faraday, water is routed back to the natural channel and 

into Estacada Lake, a small reservoir formed by River 

Mill Dam near the town of Estacada (fig. 2). The USGS 

operates a streamflow gage in the lower Clackamas 

River 0.25 miles downstream from the dam at RM 23.3. 

The Clackamas River is free flowing from River Mill 

Dam to its confluence with the Willamette River. 

11 
Figure 3. Daily mean streamflow values for the upper Clackamas River above Three Lynx Creek, U.S. Geological Survey gaging station 

14209500, water year 1998. 

Figure 4. Comparison of water year 1998 streamflow with long-term values in the upper Clackamas River above Three Lynx Creek, 

U.S. Geological Survey gaging station 14209500. 

24 
Table 1. Characteristics of the hydroelectric projects in the Clackamas River Basin, Oregon 

[Data source: Bob Steele, Portland General Electric, written commun., 1999; nd, no data; <, less than; mi2, square miles; >, more than; e, estimated; 

ft3/s, cubic feet per second; na, not applicable; ~, approximately] 

Hydroelectric Project 

Oak Grove Fork Main-stem Clackamas River 

Stone Creek Frog Lake/ Faraday River Mill 

Diversion Harriet Oak Grove North Fork Diversion Faraday Forebay 

Characteristic Timothy Lake Dam Lake Powerhouse Reservoir Dam Forebay (Estacada Lake) 

Normal pool surface area (acres) 1,430 nd 22 6 375 70 50 150 

Normal pool volume (acre-feet) 69,000 nd 400 228 18,630 550 175 2,600 

Normal pool elevation (feet) 3,229 nd 2,030 1,981 665 526 520 389 

Maximum depth (feet) 100 <10 30 31 140 40 40 80 (25a) 

Water release depth (feet) 70 surface surface 27 130 surface 37 25 

Drainage area (mi2) 54 >70e 131 131 665 665 665 671 

Dam height (feet) 110 10 80 70 206 10 nd 85 

Discharge capacity (ft3/s) 500 250 565 680 5,300 5,500 5,500 4,600 

Instream flows downstream (ft3/s) 10–300 nd 0 na nd 100 nd nd 

Average residence timeb ~8.5 months < 1 hour 0.4 days nd 7.3 days 5 hours 1.6 hours 1 day 

a Average depth.
 b Calculated as normal pool volume/average inflow from USGS (U.S. Geological Survey) flow data (1998).


Lower Clackamas River Basin—Downstream 

of Estacada, the Clackamas River widens and the 

channel gradient eases. The lower basin contains a 

predominantly alluvial valley, where the river flows 

through a broad floodplain of coarse material, much 

of which is mined for rock and gravel (Metro, 1997). 

Steep cliffs constrain the floodplain, and much of the 

Christmas tree and commercial tree plantations, agriculture, and rural residential areas are located on plateaus and terraces well above the floodplain. With few 

exceptions, the land in this area is in private ownership. 

The Clackamas River is designated as a State Scenic 

Waterway from its headwaters to Carver (excluding the 

hydroelectric projects on the main stem). Downstream 

from Carver, the landscape becomes more urban, and 

industrial development is conspicuous, particularly 

on the northern side of the river. Thirteen major and 

35 minor National Pollution Discharge Elimination 

System permits have been issued in the Clackamas 

River Basin, most of which are for direct or indirect 

discharges to the lower river (Oregon Department of 

Environmental Quality Web site, http://www.deq. 

state.or.us/wq/SISData/FacilityHome.asp, accessed 

3/20/2000). Permittees include wastewater treatment 

plants (WWTPs), fish hatcheries, sand and gravel 

operations, mobile home parks, meat processing plants, 

golf courses, and metal foundry companies, and there 

are two permitted toxic release sites in this part of the 

basin (Metro, 1997). Several major drinking-water 

intakes, which supply about 225,000 customers with 

drinking water (Gordon McGhee, Clackamas River 

Water, written commun., 2000) are located along the 

lower Clackamas River. The Clackamas River joins 

the Willamette River near the cities of Gladstone and 

Oregon City, south of Portland. 

The larger tributaries in the northern part 

of the lower Clackamas Basin include Deep, Rock, 

Richardson, and Sieben Creeks, which emerge from 

upland buttes in the geologic formation known as the 

Boring Lava. These watersheds contain steep slopes in 

the headwaters, which give way to more gently graded, 

open valleys, where soils consist of silt loams and 

hydric clays that have poor-to-moderate drainage. 

Wetlands occur in many areas, and early settlers 

drained much of the land for farming with slotted pipes 

or tile drains (Ecotrust, 2000). Permeable deposits of 

cobble and gravel occur under the soil layers in some 

areas (KCM, Inc., 1995), and aquifers are tapped for 

domestic water supply and irrigation, particularly 

in the northern portion of the lower Clackamas Basin 

(Leonard and Collins, 1983). 

METHODS 

Sampling Activities 

Data collection occurred primarily from March 

through September 1998, although some reconnaissance nutrient and/or algal data were collected from 

select streams and reservoirs in 1996 and 1997, and 

ground water was sampled in January 1999 (table 2). 

13 
Table 2. Data-collection activities in the Clackamas River Basin, Oregon, 1996–99 

[Bullets indicate type, location, month, and year of data collection] 

Basic monitoring 

1996 1997 1998 1999 

June July Sep May July Aug Sep Mar April May June July Aug Sep Jan 

North Fork Reservoir sampling • • • • • • • • • • • • 

Timothy Lake sampling • • • • • • • • • 

Stream sampling • • • • • • 

Ground water sampling • • 

Event sampling 

Periphyton sloughing event • 

Diurnal surveys of field parameters • • • 

Timothy Lake drawdown sampling • 

Specific sampling activities are described in the following paragraphs, and sampling site information, along 

with information about samples collected at each site, 

is listed in table 3 and shown on plate 1. 

Stream sampling—The primary stream sampling 

sites included eight main-stem sites located from 

RM 57 to RM 0.3, the Oak Grove Fork below Timothy 

Lake and the Collawash, Roaring, and North Fork 

Clackamas Rivers. Primary stream sites were sampled 

in May, July, and September 1998 (table 2, table 3, 

and plate 1). Thirteen additional sites were sampled in 

July 1998, increasing the total number of stream sites to 

24, expanding the spatial coverage of sites to include 

sites in basins draining wilderness areas, private and 

public forestland, and agricultural and urban land. 

Sites in the hydroelectric projects included stations 

immediately downstream from both powerhouses and 

dams (plate 1 and fig. 2). To obtain a snapshot of conditions in July, the eight main-stem sites were sampled 

synoptically within 1–2 days, and all sites were sampled 

within 9 days of each other. Stream discharge and field 

parameters (water temperature, pH, DO, and specific 

conductance [SC—the electrical conductivity of water 

at 25°C {degrees Celsius}]) were measured at each site, 

and samples were collected for nutrients, algal species 

composition, and algal biomass (table 3). Algal biomass 

was estimated using chlorophyll a (chl a) and ash-free 

dry mass (AFDM—the amount of organic matter, 

commonly used as a measure of standing crop [Welch 

and others, 1988, 1989]). 

Additional samplings were conducted to investigate potential nutrient sources or biological processes, 

such as nutrient uptake. These are described in the 

results section with their associated data. In April 1998, 

one effluent sample was collected from the Eagle Creek 

National Fish Hatchery, and samples were collected 

from Eagle Creek upstream and downstream of the fish 

hatchery for soluble reactive phosphorus (SRP) - and nitrite-plus-nitrate (NO2

- + NO3 ) analyses. In 

September 1998, three nutrient samples were collected 

from the upper Clackamas River at Highway 224 

milepost 37 (RM 38.3) to examine whether higher 

nearshore nutrient concentrations might be stimulating 

algal growth along the stream margins where abundant 

green algae was observed. Samples were collected at 

the water’s edge, 15 feet from shore in deeper water, 

and 30 feet from shore in the main current. 

Periphyton sloughing event—In June 1998, a 

synoptic sampling for drifting algae and nutrients was 

conducted in the lower Clackamas River after decaying 

clumps of filamentous green algae (Cladophora and 

Stigeoclonium) became detached from the riverbed 

downstream of Barton. The drifting algae clogged 

drinking-water intakes (Gordon McGhee, Clackamas 

River Water, oral commun., 1998), made the river 

turbid, and prompted complaints from anglers, 

boaters, and residents that live on the river (Robert 

Baumgartner, Oregon Department of Environmental 

Quality, oral commun., 1998). 

Diurnal field parameters—In July and August 

1998, diel measurements of DO and pH were made 

during the morning (5–8 a.m.) and late afternoon 

(3–6 p.m.) at selected sites to determine whether cycles 

in algal productivity were affecting DO and pH levels. 

Timothy Lake drawdown—To examine potential changes in downstream water quality resulting 

from the annual September drawdown of Timothy 

Lake, water samples were collected before and during 

reservoir drawdown. Samples were collected from 

two sites on the Oak Grove Fork (near Government 

Camp [RM 15.5] and upstream of the powerplant intake 

[RM 6.1]), and one site on the main-stem Clackamas 

River (at the USGS gage above Three Lynx Creek 

[RM 47.8]) and analyzed for nutrients, organic carbon, 

14 
and algal abundance and species composition. Of 

particular interest was determining whether Anabaena 

cells are transported from Timothy Lake to downstream 

reservoirs. 

Reservoir sampling—Reservoir sampling began 

in July 1996 and continued each summer through 1998 

(table 2). Depth profiles of field parameters (water temperature, DO, pH, and SC) and light were measured in 

the water column at discrete intervals from the deepest 

accessible location in each reservoir along the log 

boom. Two additional sites were sampled in North Fork 

Reservoir: approximately 1.8 miles upstream from 

North Fork Dam (station 2) and in North Fork Bay north 

of Highway 224 (table 3 and plate 1). Water samples 

were collected for dissolved and total nutrients, chl a, 

phytoplankton abundance, and phytoplankton species 

composition from the epilimnion (about 1 foot depth), 

the metalimnion (in the thermocline), and the hypolimnion (3 feet off the bottom). An additional sample 

was collected from the log boom from the depth of 

water release. 

Ground-water sampling—Three ground-water 

wells (depths ranging from 80 to 103 feet) and three 

springs located between Estacada and Carver along 

cliffs within 1 mile of the Clackamas River were 

sampled in January 1999 for nutrients, major ions, 

arsenic (only in wells used for drinking water), and 

field parameters. Two springs located in the Eagle 

Creek Basin upstream of the fish hatchery also were 

sampled for nutrients in April 1998. 

Data Collection 

Water 

Stream and reservoir water sample collection 

and processing—Clean techniques described by Horowitz and others (1994) were used for collection and 

processing of nutrients and major ion samples. Water 

samples were collected from stream sites (table 3) using 

the Equal-Width Increment method, where the entire 

cross section is sampled using a depth-integrating 

sampler (Edwards and Glysson, 1999). Grab samples 

were collected in the tailwaters of North Fork Dam, 

where the river was well-mixed. Water samples collected from streams were composited and homogenized 

in a churn splitter before dispensing total phosphorus 

(TP) and total Kjeldahl nitrogen (TKN—the sum of 

ammonia plus digested organic N) samples. Samples 

for dissolved nutrients were pumped from the churn 

using a peristaltic pump and filtered through Gelman 

0.45-μm (micrometer) pore-size filtration capsules. 

Water samples were collected from the reservoirs 

using a 2.5-liter Van Dorn sampler. Unfiltered samples 

were collected directly from the Van Dorn sampler, 

whereas samples for dissolved nutrients were processed 

using the same methods as for stream samples. Water 

samples for dissolved and total nutrients were chilled 

on ice (unpreserved) and shipped within 24 hours to 

the USGS National Water Quality Laboratory (NWQL) 

in Arvada, Colorado, where they were kept at 4°C until 

analysis. 

Samples for suspended organic carbon (SOC) 

and dissolved organic carbon (DOC) were collected 

into 1-quart, baked glass jars using a USGS DH-76 

bronze sampler (Edwards and Glysson, 1999) with a 

1/4-inch-diameter plastic nozzle. SOC samples were 

processed by filtering 50 mL (milliliters) of sample 

through a 0.45-μm pore-size silver filter in a stainlesssteel column pressurized with nitrogen gas (N2). 

DOC samples were collected from the same column 

into 125-mL baked amber glass bottles. 

Ground-water sampling—Samples were 

collected from domestic wells for dissolved and total 

nutrients, major ions, and arsenic following standard 

protocols (Wilde and others, 1998). Water samples 

collected from springs were analyzed for dissolved and 

total nutrients and major ions only. 

Field-parameter measurements—Instantaneous measures of water temperature, DO, pH, and SC 

were made at stream sites using a Hydrolab Datasonde 

3 multiparameter probe adapted for low ionic-strength 

waters. Depth profiles of field parameters were measured in the reservoirs from the surface to the bottom. 

Hydrolab calibrations were performed according 

to the manufacturer's specifications and included 

daily morning calibrations for DO, pH, and SC, plus 

additional DO calibrations at each site. Continuous 

measurements (15-minute intervals) of field parameters 

were made in the Clackamas River at RM 2.7 downstream from Cow Creek for a period of approximately 

24 hours on four occasions. Field parameters in ground 

water were measured using individual DO, pH, and SC 

probes housed in a flow-through chamber. 

Streamflow measurements—The USGS operates five continuous-record gaging stations in the basin 

(plate 1 and fig. 2). Discharge records for these stations 

were compiled according to methods described by 

Buchanan and Somers (1984) and Kennedy (1983) 

and are published in Hubbard and others (1999). 

Streamflow was measured at all ungaged sites using 

standard USGS methods (Rantz and others, 1982). 

15 
--

--

---- --------

-- ---- ----

-- ---- ------ ---- ---- ------ -- 

----

--

Table 3. Sampling sites and data-collection activities in the Clackamas River Basin, Oregon 1996–99 [no., number; RM, river mile; USGS site ID, site identification number permanently assigned by the USGS (U.S. Geological Survey) and recorded in the National W

--, not applicable; X, field parameters or streamflow measured; N, nutrients; na, not analyzed; Hwy, highway; E, east; P, periphyton; G, gaged; S, suspended algae; C

Site data, in upstream order 

Map no. Clackamas Tributary Elevation USGS on plate RM RM (feeta) Site codes Name site ID pa

1 0.1 5 Clackamas River at Clackamette Park 452221122361200 2 0.3 5 CR_99E Clackamas River at Hwy 99E bridge 452223122360100 3 1.2 15 Clackamas River at walking bridge above Hwy 99E bridge 452243122345800 4 2.7 33 CR_COW Clackamas River below Cow Creek 452331122340600 5 5.8 0.5 155 SIEBEN Sieben Creek at Hwy 224 452438122311500 6 6.4 0.2 95 ROCK Rock Creek near mouth 452431122303200 7 7.9 75 CR_CARVER Clackamas River at Carver 452335122294500 8 8.0 0.1 80 CLEAR Clear Creek near Carver 14210750 9 9.1 0.5 125 RICHARDSON Richardson Creek at Hwy 224 452352122281500 

10 12.1 0.7 165 DEEP Deep Creek at Hwy 224 452340122251000 11 13.4 149 CR_BARTON Clackamas River near Barton 452255122244500 12 16.7 0.4 205 EAGLE_M Eagle Creek at Bonnie Lure State Park 452105122223200 13 6.2 505 Eagle Creek at Eagle Fern State Park 451928122171600 14 0.1 505 North Fork Eagle Creek near Eagle Fern State Park 451932122171400 15 17.9 1,500 EAGLE_W Eagle Creek near wilderness boundary 451755122064300 16 18.9 220 Clackamas River at Feldheimer Ferry 451941122224800 17 20.2 255 Clackamas River at lower McIver Park 451844122224400 18 23.1 287 CR_MCIVER Clackamas River at Estacada (upper McIver Park) 14210000 19 26.9 525 Canal above Faraday Lake 451546122182000 20 27.1 525 Canal above Faraday Lake Bridge 451542122180700 21 27.7 485 Fish Ladder below Faraday Diversion Dam 451514122174400 22 29.9 645 CR_BLNFK Clackamas River below North Fork Reservoir 451435122164600 23 31.2 663 NFKRES_1 North Fork Reservoir station 1 at log boom 451438122164000 24 31.7 663 NFKRES_2 North Fork Reservoir station 2 at powerlines 451345122151100 25 31.0 0.1 663 NFKRES_B North Fork Reservoir at North Fork Bay 451329122150400 26 31.5 0.4 660 NFCLACK North Fork Clackamas River at mouth 451414122144900 27 0.2 1,240 FALL Fall Creek near confluence with North Fork Clackamas River 451432122130500 28 0.3 2,100 WINSLOW Winslow Creek at U.S. Forest Service Road 4610 451215122085500 29 32.6 0.0 660 Fry Lake outfall 451318122143300 

16 
-- --

-- --

---- --

-- ---- ---- --

--

--

------ -- 

---- -- -- -- -- -- -- -- -- 

17 

Table 3. Sampling sites and data-collection activities in the Clackamas River Basin, Oregon 1996–99—Continued [no., number; RM, river mile; USGS site ID, site identification number permanently assigned by the USGS (U.S. Geological Survey) and recorded in the National W

--, not applicable; X, field parameters or streamflow measured; N, nutrients; na, not analyzed; Hwy, highway; E, east; P, periphyton; G, gaged; S, suspended algae; C

Site data, in upstream order 

Map no. Clackamas Tributary Elevation USGS on plate RM RM (feeta) Site codes Name site ID pa

30 33.4 663 Clackamas River at North Fork Reservoir inflow 451349122135600 31 34.5 660 Clackamas River at Big Cliff 451159122133000 32 34.6 0.1 660 SFCLACK South Fork Clackamas River near mouth 451156122132500 33 34.7 660 CR_ABNFK Clackamas River above North Fork Reservoir at powerlines 451151122130200 34 35.6 700 Clackamas River at Memaloose Bridge 451133122123900 35 38.3 780 Clackamas River at mile post 37 451128122101300 36 39.4 800 Clackamas River at Big Eddy 451052122100600 37 41.8 860 Clackamas River at Fish Creek Bridge 450931122110000 38 41.7 1.2 940 FISH Fish Creek near Three Lynx 14209700 39 44.0 0.1 980 ROARING Roaring River near Estacada 14209600 40 46.5 0.1 1,340 Dinner Creek at Hwy 224 450455122082000 41 47.8 1,090 CR_3LYNX Clackamas River above Three Lynx Creek 14209500 42 53.0 0.5 1,380 OAK_RAIN Oak Grove Fork at Rainbow Picnicground 450448122023000 43 6.1 2,050 OAK_PP Oak Grove Fork above powerplant intake 14209000 44 15.5 3,040 OAK_BLTLK Oak Grove Fork near Government Camp 14208700 45 15.9 3,227 Timothy Lake at log boom 450653121481000 46 57.0 1,460 CR_UPPER Upper Clackamas River at Two Rivers Campground 450156122033100 47 57.0 1.1 1,500 COLLA Collawash River near Two Rivers Campground 450119122034800 48 9.5 WELL_1 Well number 1—02S/03E-20BAB2 452319122280701 49 10.7 255 SPRING_1 Spring number 1—02S/03E-21BBB 452317122271101 50 17.3 WELL_2 Well number 2—03S/03E-01BAB 452042122230801 51 17.3 265 SPRING_2 Spring number 2—03S/03E-01BAC 452037122231201 52 20.2 WELL_3 Well number 3—03S/03E-13AAC 451850122223601 53 20.2 280 SPRING_3 Spring number 3—03S/04E-18BBB 451859122221501 

a Elevation is in feet above the National Geodetic Vertical Datum of 1929 (NGVD of 1929)—a geodetic datum derived from a general adjustment of the first-o

and Canada, formerly called Sea Level Datum of 1929. 

b Continuous data collected on four occasions. 
Laboratory analysis—All chemical analyses 

were performed at the NWQL, with the exception 

of alkalinity and chl a, which were analyzed at the 

USGS Oregon District Laboratory in Portland, Oregon. 

Nutrient analyses were performed within 7 days of 

delivery to the NWQL. Unfiltered water samples were 

analyzed for TKN and TP using a Jirka modification 

(Patton and Truitt, 1992). Analysis of organic carbon 

was performed by the NWQL using the method of 

Wershaw and others (1987). 

Dissolved inorganic nutrients included nitrite­ - plus-nitrate (NO2

- + NO3 ), ammonia plus ammonium 

(NH3 + NH4

+), soluble reactive phosphorus (SRP), 

and dissolved silica (SiO2). Dissolved organic nutrients 

(filtered, then digested) included total dissolved phosphorus (TDP) and total dissolved Kjeldahl nitrogen 

(DKN). All nutrient concentrations in this report 

are reported on an atomic basis (as nitrogen [N] or - phosphorus [P]). Nitrite-plus-nitrate (NO2

- + NO3 ) 

is referred to simply as NO3

-

 because all or nearly all 

was in the form of nitrate. Ammonia-plus-ammonium 

(NH3 + NH4

+) is referred to as NH4+ because all or 

nearly all was present as ammonium. Chemical data 

were stored in the USGS National Water Information 

System (NWIS) database and can be accessed at 

http://waterdata.usgs.gov/or/nwis/qwdata. The 

minimum laboratory reporting levels (MRL—the 

smallest measured concentration of a substance that 

can be reliably measured using a given analytical 

method) in effect during 1998 are listed in appendix 1. 

Algae 

Periphyton sampling—Algae samples were 

collected at 24 stream sites from rock or cobble substrates in wadeable portions of each stream (table 3). 

For partially wadeable sites, rocks were sampled from 

stream margins. Representative rocks were removed 

and sampled using round plastic pipe ends (scribes) 

with outside diameters of 4, 5.6, 7.9, and 10.4 cm 

(centimeters). Scribes were placed on each rock, and 

the algae located outside the scribe was removed with 

a plastic-bristle brush and/or scraped off with a knife 

and discarded. The circular patch of algae remaining on 

the rock was then scraped into a basin, and the sample 

was rinsed into a sample bottle using stream water. 

Approximately 1–2 L (liters) of algal material was 

composited from 5 to 10 rocks from each site. This 

technique samples a larger area than many published 

methods (for example, Porter and others, 1993) and 

thus reduces the variation associated with sampling 

smaller areas when algal growth is patchy as was often 

the case. The large variation in the size of the substrate 

sampled, however, resulted in a large range of total 

area sampled per site (140 to 2,700 cm2). The algal 

slurry was placed on ice and transported to the laboratory, where it was homogenized in an electric blender 

and transferred to a churn splitter. Subsamples for algal 

biomass (chl a and AFDM) were removed from the 

churn using a large-orifice pipettor and transferred to a 

47-mm (millimeter) glass fiber filter under vacuum 

pressure using a filtration apparatus. Subsamples for 

species identification and enumeration (abundance) 

were dispensed into sample bottles and preserved with 

a relatively high concentration of buffered formalin 

(10% final concentration) to aid in preserving the 

dense collections of periphyton that were sometimes 

encountered. 

Phytoplankton sampling—Phytoplankton 

samples were collected from multiple depths within the 

reservoirs using a 2.5-liter Van Dorn sampler, transferred into sample bottles, and preserved with Lugol's 

solution at a final concentration of 1%. Suspendedalgae samples (from stream sites) were processed the 

same way, but were collected using a USGS DH-76 

bronze sampler with a 1/4-inch-diameter nozzle. 

Algal biomass—Chl a was determined at the 

Oregon District Laboratory. Glass-fiber filters containing algal material were hand ground using an electric 

tissue-grinding apparatus with a Teflon pestle and glass 

mortar containing 10 mL of 90% acetone. This slurry 

was filtered through 25-mm glass fiber filters and the 

extracted pigments were analyzed fluorometrically, 

correcting for the presence of phaeopigments. 

AFDM was analyzed gravimetrically according 

to methods described by the American Public Health 

Association (1989). Filters for AFDM were dried at 

105°C for 24 hours and burned at 500°C for 2 hours. 

The AFDM was calculated as the difference in filter 

weights before and after burning (i.e., the weight of the 

burned [ashless] material). 

Algal identification and enumeration—Algal 

species identifications, numbers, and biovolumes 

were determined at Bowling Green State University 

(BGSU), Ohio. Cell density, in number of cells per 

square centimeter, and cell biovolume, in cubic 

microns per square centimeter, were determined for 

each taxon by measuring the cell dimensions of 10 

randomly selected individuals for each taxon in each 

sample. Five hundred algal units (diatoms or soft algae) 

were counted in a Palmer-Maloney counting chamber 

and identified to the lowest possible taxonomic level. 

18 
A subsample was processed with fuming concentrated 

nitric acid to create a permanent (Naphrax-mounted) 

slide of diatoms. Counting chamber diatom identifications were verified by viewing the permanent slide 

preparations at 1,000× magnification. 

Light/Canopy Closure 

The potential sunlight availability was measured 

at stream sites using a Solar Pathfinder. This device 

measures the panoramic shading at a site, and therefore 

estimates the potential amount of light (as a percentage 

of the average total radiation that will fall on a location 

for a given month and latitude) from the southern sky 

during cloudless conditions (Platts and others, 1987). 

Percent canopy closure was obtained by subtracting the 

percent sunlight available from 100. Light penetration 

into the reservoirs was measured using a spherical 

quantum sensor light meter, and water transparency 

was measured using a 210-mm Secchi disk when water 

column conditions permitted adequate viewing. 

Land Cover 

Basin boundaries for each site were digitized 

from 1:24,000 USGS topographic maps and processed 

using Arc/Info (ESRI, copyright 1982–2002) geographic information system (GIS). Land cover for 

each basin was estimated from 30-meter resolution 

satellite images (Landsat thematic mapper [TM] data) 

collected for the entire Willamette Basin in June and 

August 1992 and 1993. The spectrum signatures were 

interpreted by the USGS EROS Data Center using 

a clustering statistical program and ancillary data, 

including slope and elevation. The major land-cover 

classifications were mature forest, regrowth forest, 

nonforest upland, agriculture, and urban (table 4). 

The nonforest-upland classification (table 4) 

included areas in mid-to-high elevation areas that 

did not produce a green vegetation signature. Because 

most of the watershed is not above timberline, the 

amount of exposed rock is probably limited. Thus, 

nonforest-upland areas were interpreted mostly as 

being previously forested (recently harvested). 

Urban areas were defined by a combination of 

USGS GIRAS (Geographic Information Retrieval and 

Analysis System) data and 1990 census population 

data, defined by areas containing 1,000 or more 

persons per square mile. Based on field observations 

and discussions with Clackamas County personnel, the 

amount of urban land in the Sieben Creek watershed, 

which according to the land-cover data was determined 

to be about 10% in 1990, was probably higher in 1998. 

To determine how much higher, a more detailed urban 

land-cover analysis of the Sieben Creek watershed 

was performed in 2001 using WES Works, Clackamas 

County Department of Water Environment Service’s 

GIS analysis system. Urban developments were identified from aerial photographs taken in 2000, and the 

individual areas were digitized and summed to obtain 

the percentage of urban land. 

Data Quality Control 

Quality control (QC) samples consisted of blank 

water samples to check for nutrient contamination or 

bias during collection, processing, and/or analysis; 

standard reference nutrient samples to check laboratory 

accuracy; replicate nutrient samples to check laboratory precision; triplicate chl a and AFDM samples to 

check laboratory precision; replicate chl a and AFDM 

samples to check field and laboratory variability; 

triplicate chl a samples to check laboratory accuracy by 

Table 4. Description of land-cover categories used in the 1992–93 Thematic Mapper (TM) classification system 

(after Uhrich and Wentz,1999) [see fig. 1] 

[GIRAS, Geographic Information Retrieval and Analysis System] 

Land-cover category Description 

Mature forest Represented by the darkest shades of green in the spectral mosaic. 

Regrowth forest Forested areas with open spaces and trees of smaller size than mature forest. 

Nonforested upland Spectral class without a green vegetation signature. Distinguished from valley areas by elevation and slope 

differences. Includes recent clearcuts, open grassland, nonforested alpine areas, rock outcrops, and barren land. 

Agriculture Fields that were bare ground (nonvegetated) in June and vegetated in August (irrigated agriculture), plus grass 

seed, hay, and small grain fields, and pastures. 

Urban Area of urban development. Defined by a combination of GIRAS and 1990 Census of Population data. 

Represents a population density of 1,000 or more persons per square mile. 

19 
an independent analyst; replicate algal cell counts to 

check for laboratory precision; and replicate algal 

cell counts by an independent analyst to check laboratory variation. Results of the QC data are summarized 

next. Tables of the QC data for nutrients and algae are 

in appendix 2 and appendix 3, respectively. 

Nutrients in water—Eleven nutrient blank 

samples were submitted to the NWQL for analysis. 

Nutrient blank samples were collected and processed 

similar to the environmental samples: blank water 

was used to rinse and fill the sample collection equipment (bottle, cap, and nozzle for stream samples, 

or Van Dorn sampler for reservoir samples), and then 

passed into a churn splitter, pumped through tubing and 

filter capsule, collected in a sample bottle, and shipped 

to the NWQL. 

Phosphorus was detected in blank samples more 

frequently than nitrogen, with four SRP detections 

at the MRL of 1 μg/L (microgram per liter), four 

detections of TDP (ranging from 1 to 14 μg/L), and 

six detections of TP ranging from 1 to 8 μg/L. Blank 

samples contained no detectable NH4

+, TKN, or DKN, 

but one blank contained 8 μg/L of NO3

-

 (appendix 2). 

This sample also contained 14 μg/L TDP, which may 

indicate a common source of contamination for that 

sample. 

Five standard reference nutrient samples contain­ - ing known concentrations of NH4

+, NO3 , SRP, TDP, 

and TP were submitted to the NWQL for analysis at 

concentrations that were low but reflected ambient 

concentrations in the river (appendix 2). Results for 

the TDP and TP samples were all within the method 

variance, and the SRP values were within the method 

variance for all but one sample, for which 26 μg/L was 

reported for a reference sample with an expected concentration of 36 μg/L. Concentrations of dissolved 

inorganic nitrogen (DIN) in standard reference samples 

were lower than expected, with a periodic low bias for - NH4

+ and a consistent low bias for NO3 of 16–66% 

(appendix 2). 

Eight replicate nutrient samples were submitted 

to the NWQL to determine laboratory analytical 

precision. All NO3

-

, DKN, TKN, SRP, TP, and SiO2 

replicate values showed good agreement, and all 

were within the method variance. TDP concentrations, 

however, showed occasionally high variability 

(up to about 100%) in two of the replicate samples 

(appendix 2). In this report TDP data are not 

interpreted so this variability does not affect any 

conclusions. Although most replicate samples had 

similar NH4

+ concentrations, one set of samples collected from North Fork Reservoir had replicate NH4

+ 

concentrations of 5 and <2 μg/L (appendix 2). 

The nutrient quality-assurrance data show that, 

for most constituents, sample processing and analytical 

variations were small, and instances of sample contamination, when indicated, appeared to be isolated cases. 

Further, interpretations or conclusions drawn from 

the nutrient data, with few exceptions, were made 

when overall patterns in spatial or temporal variation 

supported those conclusions or when larger differences 

among sites were found. Exceptions to this are 

addressed in the results section on a case-by-case basis. 

Algal biomass—The mean relative standard 

deviation (MRSD), the average of all the individual 

relative standard deviation (RSD) (the standard deviation [SD] for a set of three measurements, normalized 

by dividing by the mean) for 53 AFDM and 159 chl a 

samples was 4.3% and 3.5%, respectively. Samples 

containing filamentous green algae had higher MRSDs 

for chl a (maximum of 7.8%) and AFDM (maximum 

of 8.9%) compared with samples dominated by other 

algae. The MRSD for phytoplankton chl a samples 

was 8.1% for 49 samples, although the SDs were low, 

averaging 0.1 μg/L. 

To investigate variability in chl a and AFDM 

due to sampling technique, replicate samples were collected in July from two sites dominated by filamentous 

green algae (the Clackamas River upstream and downstream from North Fork Reservoir) and two sites dominated by diatoms (the Clackamas River at Highway 

99E and the South Fork Clackamas River near the 

mouth). Replicate biomass samples were in general 

agreement, with the largest differences occurring at 

sites having greater biomass (appendix 3). The differences may have been caused by the patchy growth 

of algae or from uneven subsampling from the churn 

splitter, particularly for samples dominated by filamentous algae. 

Algal species composition—To evaluate variation in the identification and enumeration of algal 

species, five samples were each split into replicate 

samples with a churn splitter. Replicate algae samples 

were analyzed at the BGSU Laboratory for both diatoms and soft algae. The percent similarity of replicate 

samples ranged from 67 to 86% for all species (using 

relative abundance). Similarities were slightly higher 

when restricted to diatoms, which ranged from 77 

to 85% using relative abundance and 70 to 87% using 

relative biovolume (appendix 3). 

20 
To evaluate interlaboratory variation in algal 

sample processing, identification, and counting, preserved sample material and permanent slides of diatoms 

were shipped to an independent laboratory (University 

of Louisville, Kentucky [ULK]), where soft algae samples were prepared using the same methods as BGSU. 

Observed differences between the two laboratories 

could have resulted from inconsistencies in sample 

processing, species identifications, and/or enumeration 

(species counts). Analysis of identical diatom slide 

preparations, which eliminates the sample-processing 

step, by both laboratories showed differences in both 

identification and enumeration. The percent similarity 

between laboratories for these samples ranged from 

61 to 71% using relative abundance (appendix 3). 

Some of the differences in species identifications 

were reconciled by consulting the different taxonomic 

keys used by the two taxonomists. The BGSU Laboratory uses the taxonomy adopted by the Philadelphia 

Academy of Natural Sciences (Patrick and Reimer, 

1966, 1975), whereas the ULK Laboratory uses more 

recent European classification that tends toward 

“splitting” genera or species into lower taxonomic 

groups. In the case of Anabaena and Nostoc, which 

may appear similar under a microscope, field data were 

used to correctly classify these algae. This is a relatively 

easy task because Nostoc has an identifiable macroscopic structure (a mucilaginous sheath) that is absent 

in Anabaena. 

Data Analysis 

Environmental data analysis—Correlation and 

principle components analyses (PCA [SAS Institute, 

1989]), correspondence analysis, and canonical 

correspondence analysis (CANOCO [ter Braak, 1986]) 

were performed on land-cover, water-chemistry, 

canopy-density, algal-biomass, and algal-speciescomposition data to test for any site or species associations with the environmental variables and to identify 

possible groupings among sites. Four major groups 

were identified: main-stem sites, upper-basin tributary 

sites, middle-basin tributary sites, and lower-basin 

tributary sites. Additional analyses were performed on 

these site groups, and among sites sampled during each 

time period (May, July, and September). The sampling 

site in Clear Creek, which was technically located in 

the lower basin near the confluence with the Clackamas 

River, was included with the middle-basin tributary 

sites in some of the analyses because water chemistry 

and overall stream conditions were more similar to middle-basin sites than to the other lower-basin tributary 

sites, probably because much of the streamflow originates from the higher elevation areas in the middle basin 

(plate 1 and fig. 2). 

Nutrient loads and streamflow balances—A 

mass balance was constructed for streamflow and 

nutrient loads (in kilograms per day) with the July 1998 

data, to identify nutrient or streamflow sources (gains) 

in the main stem that were not accounted for, such as 

inputs from ground water or unmeasured tributaries. 

If negative changes in nutrient loads (losses) were 

observed, then some unmeasured sink, such as algal 

uptake, might be suspected. Nutrient loads were 

calculated as the product of the instantaneous stream 

discharge and corresponding nutrient concentration. 

Nutrient loads from the fish hatcheries and WWTPs 

were estimated using July 1998 effluent discharge rates 

and estimated nutrient concentrations provided by 

facility managers. The NO3

- and SRP content of the 

Eagle Creek fish hatchery effluent was estimated from 

a one-time sampling by the USGS in April 1998. The 

nutrient content of effluent from the WWTPs (NH3 and 

TP) were highly variable and warranted calculating a 

load range using minimum and maximum concentration 

values. TP and NH3 data were available from the Sandy 

WWTP, whereas only NH3 data were available from the 

Boring WWTP. Minimum and maximum values (considering both treatment plants) were used to estimate 

the loads from the Estacada WWTP. It is important 

to consider, however, that these load estimates do not 

include NO3

-

, which could be significant as at least one 

plant (Estacada WWTP) uses a trickling filter to oxidize 

the NH3 into NO3

-

. 

Nutrient ratios—Nutrient ratios, such as the 

N:P ratio and the SRP:TP ratio, were calculated to 

further characterize the nutrient status of the streams 

and reservoirs. The ratio of dissolved, biologically 

available forms of N and P (DIN:SRP), indicates the relative availability of the two primary nutrients that algae 

require for growth. This is important because management strategies aimed at reducing algal growth often 

target the nutrient that is in shortest supply. During 

growth, approximately 16 atoms of N are used for every 

atom of P (or 7:1 by weight), and this ratio, the Redfield 

Ratio, can be used as a benchmark to evaluate which 

nutrient would become depleted first if algae continue 

to deplete existing nutrient pools (Wetzel, 1983). 

21 
Another ratio, the portion of TP that is composed of 

SRP (SRP:TP), also was used to infer whether P in 

streams was predominantly from a particulate source, 

such as algal material or sediment, or a dissolved 

source, such as soluble fertilizers, septic tank wastewater, or ground-water discharges. 

Indicator algal taxa—Information on the environmental preferences and tolerances for the algal 

taxa was obtained from van Dam and others (1994) 

and Lowe (1974). Because stream algae integrate environmental conditions over time, they can be used as 

indicators of current or changing ecological conditions 

(Carrick and others, 1988; Lowe and Pan, 1996). Some 

algae grow best under a particular set of environmental 

conditions, and their proliferation or absence may be 

used to infer water quality. Diatoms, in particular, are 

especially useful and have been used as indicators of 

water quality for years (Kolkwitz and Marsson, 1908). 

Several indicator algal groups were represented, 

including those indicative of high nutrient concentrations, alkaline pH, and low concentrations of N. Only 

diatoms and N-fixing blue-green algae were included 

in this analysis because of the complexities associated 

with quantifying filamentous algae. The relative biovolume (the biovolume of each indicator group as a 

percentage of the total biovolume) was calculated for 

each sample. The relative biovolume of each group was 

summed instead of cell numbers because of the large 

variations in cell sizes commonly observed among 

different algae. Biovolume values correct for potential 

bias in cell numbers for small-celled taxa, which might 

have high numbers but low volume relative to other 

algae. 

Comparisons to water-quality standards— 

Water-quality standards (numeric criteria) for water 

temperature, pH, and DO for the Clackamas Basin are 

listed in table 5. The timing of fish spawning/egg incubation/fry emergence for resident and anadromous fish 

determines the temperature and DO criteria in effect for 

a particular place at a particular time. Fish spawning, 

egg incubation, and/or fry emergence occurs in the 

Clackamas Basin nearly year-round (table 6), but 

proposed standards are less stringent for a 4-week 

period during summer, from mid-July to mid-August 

(Manette Simpson, Oregon Department of Environmental Quality, oral commun., 2002). 

With few exceptions, the field parameter data 

(water temperature, pH, and DO) collected during this 

study were single-point, instantaneous measurements, 

and the frequency and duration of observations 

required to establish compliance with State standards 

were beyond the scope of this study. The numeric 

criterion for water temperature, for example, is based 

on the 7-day average of the maximum daily temperatures, whereas the DO criterion is based on a 30-day 

average of the minimum daily values. Instantaneous 

exceedances of the numeric criteria, therefore, do not 

constitute violations of State water-quality standards. 

Table 5. State of Oregon water-quality criteria for pH, water temperature, and dissolved oxygen for the Clackamas River Basin, Oregon 

[Source: Oregon Administrative Rules, Attachment A to Chapter 340, Division 41, 1996. °C, degrees Celsius; °F, degrees Fahrenheit; mg/L, milligrams per 

liter; DO, dissolved oxygen; %, percent] 

State of Oregon Water-Quality Criteria 

During fish spawning and egg incubation During nonspawning periods, 

through fry emergence periods when fish are rearing, migrating, or holding 

Field parameter (August 15–July 15) (July 15–August 15) 

pH, in standard units 6.5–8.5a 6.5–8.5a 

Water temperature, °C (°F) 12.8°C (55°F)b 17.8°C (64°F)b 

Dissolved oxygen, in mg/L 11.0c,d, 9.0e 8.0f,g, 6.5h, 6.0i 

a Reservoirs may be exempted by the Oregon Department of Environmental Quality (ODEQ) if it is determined that the exceedance would occur 

even without the impoundment and that all practical measures have been taken to bring the pH in the impounded water into compliance. b Based on the 7-day average of the daily maximum temperatures. c Absolute minimum, if intergravel DO is less than 8.0 mg/L d If conditions of barometric pressure, elevation, and temperature preclude achievement of the indicated concentration, then the 95% saturation 

criteria applies. e If the intergravel DO (spatial median) is greater than or equal to 8.0 mg/L. f Based on a 30-day mean minimum concentration. g If conditions of barometric pressure, elevation, and temperature preclude achievement of the indicated concentration, then the 90% saturation 

criteria applies. h Based on a 7-day minimum mean concentration. i Absolute minimum. 

22 
Table 6. Periodicity chart outlining timing of spawning, egg incubation, and fry emergence for fish in the Clackamas River Basin, Oregon 

[Source: Michael Hogansen, Oregon Department of Fish and Wildlife, written commun., 2002. The peak use for summer steelhead was not determined. 

Source: Oregon Administrative Rules, Attachment A to Chapter 340, Division 41, 1996. GRAY area (G) represents lesser levels of use, based on 

professional opinion. BLACK area (B) represents 90% of the periods of peak use, based on professional opinion. (1) Use defined by Olsen and others 

(1992). (2) Use defined by the Oregon Department of Fish and Wildlife (1990).] 

Life stage/activity/species Jan Feb March April May June July Aug Sep Oct Nov Dec 

Winter Steelhead 1 1 G B B B B B B B G G 2 

Summer Steelhead (hatchery) 2 2 2 2 2 2 

Spring Chinook 2 2 2 1 1 B B B G 1 2 2 2 2 

Fall Chinook 2 B B B B B B B G G 

Coho (early hatchery) B B G G 2 1 1 B B B B B B 

Coho (late wild) B B B B B G G G G B 

Cutthroat Trout G B B B B G G 

Life stage/activity/species Jan Feb March April May June July Aug Sep Oct Nov Dec 

Winter Steelhead G G B B B B B B B B B G 1 2 

Summer Steelhead (hatchery) 2 2 2 2 2 2 2 2 2 

Spring Chinook B B B B B B B B 2 2 2 2 2 B B B B B B B B 

Fall Chinook B B B B G G G 2 2 2 G B B B B B 

Coho (early hatchery) B B B B G G G 2 2 1 G B B B B B 

Coho (late wild) B B B B G G G G G G G B B B B B 

Cutthroat Trout B B B B B B B B G G G 

Adult spawning 

Month 

Egg incubation through fry emergence 

Month 

RESULTS 

Stream Conditions 

Streamflow 

1998 Water year—Streamflows in the Clackamas River were near average during the 1998 water 

year, with several fall and winter storms producing 

high streamflow conditions into May (fig. 3). Winter 

base flows at the Three Lynx gage were about 

2,000 ft3/s from mid-January until May, when streamflows began to decline in response to a decline in the 

frequency and magnitude of rainfall events. Steady 

declines in streamflow started in June and continued 

through the summer, reaching a minimum streamflow 

of 680 ft3/s in mid-September (fig. 3). Compared with 

long-term records, the monthly average streamflow 

values at the Three Lynx gage were between the 25th 

and 75th percentile during most months in the 1998 

water year and close to the median (50th percentile) 

during summer (fig. 4). 

Nonetheless, instantaneous exceedances were occasionally observed, particularly during the late 

afternoon or early morning hours, and point to the 

need for further study to establish compliance with 

standards. 

There were possible exceedances of the State 

water-quality criterion for water temperature and DO 

in North Fork Reservoir, and for water temperature, 

DO, and pH in Timothy Lake. The Oregon Department 

of Environmental Quality is currently in the process of 

reviewing water-quality standards for reservoirs (Greg 

McMurray, Oregon Department of Environmental 

Quality, oral commun., 2002). There is, however, a 

recognized Action Limit of 15 μg/L chl a for reservoirs 

that was exceeded once in both North Fork Reservoir 

and Timothy Lake in 1996. Although these one-time 

measurements do not qualify as exceedances of the 

Action Limit which are based on a minimum of three 

measurements collected over 3 consecutive months, 

they do indicate the need for additional monitoring. 

23 
24

Figure 3. Daily mean streamflow values for the upper Clackamas River above Three Lynx Creek, U.S. Geological Survey gaging station 

14209500, water year 1998. 

Figure 4. Comparison of water year 1998 streamflow with long-term values in the upper Clackamas River above Three Lynx Creek, 

U.S. Geological Survey gaging station 14209500. 
Streamflows during sampling—During the first 

stream sampling in May, about 85% of the water near 

the mouth of the Clackamas River at the Highway 99E 

bridge (CR_99E—see glossary or table 3 for an explanation of site codes) originated from the upper basin 

(fig. 5). By July, flows were lower, and discharge from 

the Oak Grove Powerhouse accounted for much of 

the streamflow in the upper Clackamas River (figs. 3 

and 6). Tributary sites with the highest streamflows in 

July included the Collawash River (COLLA), Roaring 

River (ROARING), the Oak Grove Fork below 

Timothy Lake (OAK_BLTLK), and Eagle Creek 

near the mouth (EAGLE_M) (fig. 5). Streamflows 

from the lower-basin tributaries, including Clear Creek 

(CLEAR), Deep Creek (DEEP), Rock Creek (ROCK), 

Richardson Creek (RICHARDSON), and Sieben 

Creek (SIEBEN), contributed a combined 4.5% of 

the total main-stem streamflow (table 7). 

Streamflow balance—July streamflows 

between CR_UPPER (the upper Clackamas River 

at Two Rivers Campground) and CR_ABNFK 

(the Clackamas River just upstream of North Fork 

Reservoir)—Reach 1 in fig. 6—were nearly balanced, 

meaning they were within the limits of compounded 

streamflow measurement errors, indicating no significant unmeasured inputs (such as ground water). 

In the lower Clackamas River, however, an 

unaccounted-for increase in streamflow was observed 

between McIver Park (CR_MCIVER) and Barton 

Park (CR_BARTON, Reach 2 in fig. 6), possibly from 

ground-water inputs. However, because the discharge 

at CR_MCIVER was not steady on the day of 

sampling, fluctuating from 1,350 to 998 ft3/s in the 

morning to 1,460 ft3/s in the late afternoon due to 

variable power generation at River Mill Dam (fig. 7), 

the amount of ground water is difficult to quantify. The 

streamflow balance in this reach required estimating 

the amount of time it takes for a parcel of water to 

travel from River Mill Dam to Barton Park, because 

that determined the instantaneous discharge rate for 

the comparison. In May 1992, Lee (1995) conducted 

a dye study in this reach when the streamflow was 

1,350 ft3/s, similar to that in July 1998. At that flow, 

the water velocity was estimated to be between 1.3 and 

1.8 miles per hour. This produced a range in discharge 

from the dam of between 1,056 and 1,360 ft3

/s, for 

a net unexplained gain of between 140 and 440 ft3

/s 

(8.5–27%) between CR_MCIVER and CR_BARTON 

(fig. 6) that might be attributable to ground-water 

inputs. 

Tidal influence in the lower Clackamas 

River—The pattern of gradually increasing streamflow 

from CR_BARTON to CR_99E that was apparent in 

May and July did not occur in September (fig. 5). The 

discharge at CR_99E in September was about 700 ft3

/s, 

or about 50% greater than expected, given the discharge 

relationships previously observed among sites in the 

lower Clackamas River (fig. 5). This discrepancy in 

flows might be attributable to the influence of tides. 

Tides cause reverse flows in the Columbia and Willamette Rivers during low flow periods, an effect that 

is observed at the streamflow gage in the Willamette 

River downstream of the Oregon City Falls (Hubbard 

and others, 1999), where a tidal fluctuation of 3 feet 

occurred in September 1998. During certain times, 

backwater conditions may develop in the Clackamas 

River, a result of such tides. Greater streamflow in 

the Clackamas River probably resulted from storage 

and release of water from Clackamette Cove (plate 1) 

adjacent to the lower river upstream from CR_99E 

during this tidal cycle. 

Data on river stage, SC, and TP in the lower 

Clackamas and Willamette Rivers support the assertion 

that backwater conditions cause water from the 

Willamette River to travel at least 0.3 miles up the 

Clackamas River to the Highway 99E bridge. A massbalance analysis indicated that about one-third of the 

volume of water sampled at CR_99E was water from 

the Willamette River. Several riffles, however, occur in 

the lower Clackamas River between CR_99E and the 

most downstream drinking-water intake, which likely 

prevents water from the Willamette River from reaching the intake during low flow periods. During high 

flow periods, however, and particularly following 

large storms, when the Clackamas River is receding 

and the Willamette River is rising (as is often observed), 

backwater conditions may develop far enough upstream 

for the Willamette River to reach drinking water 

intakes. Additional studies of this phenomenon, 

discussed later in this report, are necessary to verify 

or refute this possibility. 

Field Parameters 

Water Temperature—Water temperatures in the 

upper Clackamas River were between 8.3 and 9.2°C in 

early May (fig. 5 and table 8), which is less than the State 

of Oregon water temperature criterion of 12.8°C in effect 

(table 5) due to spawning of winter steelhead and resident 

cutthroat trout (table 6). Water temperatures in the lower 

Clackamas River were higher in June and mid-July, reaching levels well above the water-quality criterion (fig. 8). 

25 
Figure 5. Seasonal variation in streamflow and water-quality variables for main-stem sites in May, July, and September, and values for 

tributary sites in July 1998. (Lines connecting main-stem values indicate trends only, and do not imply that values between sites were 

measured. EAGLE_W is a reference site located upstream of EAGLE_M and is included only for comparison.) 

26 
Figure 6. Streamflow balance for the main-stem Clackamas River, Oregon, July 7–15, 1998. 

As discussed previously, the water-temperature criterion is based on the 7-day average of the maximum 

daily temperature; although the data shown in figure 8 

do not include 7 consecutive days, they do suggest 

that high water temperatures occurred for more than 7 

days. The highest measured water temperature in the 

Clackamas River (21.8°C at RM 2.7) was measured on 

July 16, exceeding the 17.8°C criterion in effect during 

nonspawning periods (fig. 8). 

Water temperatures in the Clackamas River 

generally increased in a downstream direction, from 

warming in the main stem and from the inputs of 

warmer tributaries. Temperatures in the main stem 

and most tributaries probably exceeded the State 7-day 

temperature criterion of 12.8°C in early-to-mid July 

(table 7), when the warmest tributaries included Fish 

Creek in the upper basin and most all of the tributaries 

in the lower basin (fig. 5). Most of the highest temperatures were measured in August, when temperatures 

at FISH (21.1°C), in the fish ladder below Faraday 

Diversion Dam (20.1°C), EAGLE (22.9°C), CLEAR 

(20.7°C), DEEP (18.8°C), and ROCK (18.3°C) 

probably exceeded the 17.8°C criterion in effect during 

nonspawning periods (table 5). Recall, however, that 

instantaneous exceedances of the numeric criteria do 

not necessarily constitute violations in the standard or 

qualify a stream for listing on the 303(d) list as waterquality limited. 

27 
28 

Table 7. Basin characteristics and environmental conditions at sites sampled in the Clackamas River Basin, Oregon, July 1998 [Site codes and nutrient abbreviations are listed in the glossary, and site locations are shown on plate 1; mi2, square miles; mi/mi2, miles per square mile; %, percent; 

°C, degrees Celsius; na, not analyzed; μS/cm, microsiemens per centimeter at 25°C; mg/L, milligrams per liter; <, less than minimum reporting levels (see appendix 1

kg/d, kilograms per day; mg/m2, milligrams per meter squared; g/m2, grams per meter squared] 

Main-stem Clackamas River sites Upper- and middle-basin tributary sites 

CR_UPPER 

CR_3LYNX 

CR_ABNFK 

CR_BLNFK 

CR_MCIVER 

CR_BARTON 

CR_CARVER 

CR_99E 

COLLA

OAK_BLTLK

OAK_RAIN

ROARING

FISH 

SFCLACK 

WINSLOW 

FALL 

NFCLACK

EAGLE_W 

BASIN CHARACTERISTICS 

Basin area (mi2) 157 489 602 668 680 785 920 942 150 55 141 43 45 28 7 3 32 15 9Stream density (mi/mi2) 3.1 3.5 3.8 3.9 3.9 4.0 4.0 3.9 4.4 1.6 2.5 5.1 5.4 4.0 4.8 3.0 4.7 6.6 Road density (mi/mi2) 3.6 3.5 3.4 3.5 3.6 3.6 3.7 3.8 3.1 3.5 3.9 1.4 4.0 4.3 5.3 8.3 4.5 1.4 Urban land (%) 0 0 0 0 1 1 2 3 0 1 1 0 0 0 0 1 0 0 Agricultural land (%) 0 0 0 0 0 1 3 3 0 0 0 0 0 0 0 0 0 0 Mature forest (%) 61 62 63 62 61 59 52 51 67 53 57 77 56 54 80 40 65 91 4Nonforest upland (%) 26 23 21 20 20 19 19 19 15 39 32 14 11 11 3 8 5 2 1Regrowth forest (%) 13 14 16 17 18 19 22 22 17 3 9 8 32 34 16 51 30 7 3

WATER QUALITY 

Streamflow (ft3/s) 342 900 1,230 1,100 1,180 1,620 1,760 1,870 176 100 22 128 48 48 9 7 48 41 12Streamflow yield (ft3/s per mi2) 2.2 1.8 2.0 1.6 1.7 2.1 1.9 2.0 1.2 1.8 0.2 3.0 1.1 1.7 1.3 2.3 1.5 2.7 Water temperature (°C) 12.7 14.2 14.5 14 14.9 15.1 15.3 16.7 14.1 8.4 15.3 13.5 18.3 15.2 11.8 12.8 na 12.4 1Specific conductance (μS/cm) 74 61 57 56 54 52 53 54 47 52 77 37 44 40 31 26 37 35 3Dissolved oxygen (mg/L) 9.5 9.4 9.8 9.7 9.8 10.3 9.8 na 9.6 9.6 9.4 9.9 9.6 9.5 9.8 9.5 na 10.2 Dissolved oxygen (% saturation) 94 96 99 96 98 103 98 na 98 91 98 99 106 97 97 94 na 99 9pH (standard units) 8 7.9 8 7.7 7.7 7.7 7.6 7.4 7.6 7.9 7.8 7.8 7.9 7.8 7 7.3 7.2 7.5 NH4 + (μg/L) <2 <2 2 <2 <2 <2 2 <2 <2 <2 <2 <2 <2 <2 7 <2 4 <2 NO3 - (μg/L) <5 <5 <5 6 <5 8 32 20 <5 <5 5 <5 7 8 43 116 81 9 14SRP (μg/L) 22 11 10 8 7 7 8 7 7 2 24 8 7 7 3 <1 3 <1 TP (μg/L) 21 18 17 13 15 16 20 41 10 13 26 12 12 8 7 6 9 4 1DIN:SRP <0.3 <0.6 <0.7 <1.0 <1.0 1.1 4.3 2.9 <1 3.5 0.3 0.9 1 1 17 >116 28 >9 7SiO2 (mg/L) 25.3 20.0 19.9 19.4 18.8 17.6 18.0 18.7 15.3 na 24.3 17.8 17.6 18.3 18.2 15.2 18.4 14.7 1DIN load (kg/d)a <(6) <(15.4) 6.0 16.2 <(20.2) 31.7 146.4 91.5 <(3.0) <(1.7) 0.3 <(2.2) 0.8 0.9 1.1 1.9 10 0.9 4SRP load (kg/d)a 18.4 24.1 30.1 21.5 20.2 27.7 34.5 32 3 0.5 1.3 2.5 0.8 0.8 0.1 <(.01) 0.4 <(0.1) TP load (kg/d) 17.6 39.6 51.2 35 43.3 63.4 86.1 187.6 4.3 3.2 1.4 3.8 1.4 0.9 0.2 0.1 1.1 0.4 

ALGAL BIOMASS / CANOPY CONDITIONS 

Chlorophyll a (mg/m2) 72 226 24 332 276 60 194 55 54 130 95 20 98 137 14 23 48 11 6AFDM (g/m2) 25 218 7 127 65 38 70 25 11 61 20 10 21 23 3 8 18 4 1Canopy closure (%) 15 10 16 11 10 2 15 2 16 10 71 81 32 62 97 92 44 98 6

a Values in parentheses represent the nutrient load with concentrations set to the minimum laboratory reporting levels, and therefore represent theoretical maxim
Figure 7. Streamflows in the Clackamas River Basin, Oregon, during sampling in July 1998. (Sampling occurred in the main stem on July 7–8; 

all other sites were sampled on or before July 15. Shaded areas denote streamflows used for the flow balance.) 

Water temperatures were lower in the upper 12.8°C criterion, at CR_ UPPER on the same date 

Clackamas River in September compared with July, (table 8). 

despite the lower streamflows, probably due to the Downstream, the temperature in the Clackamas 

increasing contribution that ground water makes River increased nearly 4°C through the main-stem 

to streamflow during low-flow periods. Cold-water hydroelectric project (fig. 5), based on instantaneous 

discharges from the Oak Grove Powerhouse, temperature measurements taken upstream of North 

combined with cooler September nights at higher Fork Reservoir (at CR_ABNFK) and downstream of 

elevations, also contributed to lower water River Mill Dam (at CR_MCIVER) between 9 and 

temperatures in the upper Clackamas River. 10 a.m. Downstream from North Fork Reservoir 

The temperature at CR_3LYNX was 11.2°C during (at CR_BLNFK), the water temperature was 15.1°C 

the September measurement, slightly less than on the September measurement date. Here, and at all 

the 12.8°C criterion in effect due to spawning main-stem sites downstream, the 7-day 12.8°C criterion 

by spring and fall Chinook salmon (table 6). The probably was exceeded, with the highest temperature 

temperature was 13.1°C, slightly higher than the (20.4°C) occurring at CR_BARTON (table 8). 

29 
Table 8. Seasonal patterns in streamflow, field parameters, nutrients, and algal conditions at main-stem and tributary sites 

in the Clackamas River Basin, Oregon, May–September 1998 

[Site codes and nutrient abbreviations are listed in the glossary, and site locations are shown on plate 1; ft3/s, cubic feet per second; °C, degrees Celsius; 

μS/cm, microsiemens per centimeter at 25°C; mg/L, milligrams per liter; %, percent; μg/L, micrograms per liter; kg/d, kilograms per day; 

mg/m2, milligrams per meter squared; g/m2, grams per meter squared; na, not analyzed; <, less than minimum reporting levels (see appendix 1)] 

Main-stem sites 

CR_UPPER CR_3LYNX CR_ABNFK CR_BLNFK 

Parameter May July Sep May July Sep May July Sep May July Sep 

Streamflow (ft3/s) 826 342 318 2,470 900 713 na 1,230 863 2,700 1,100 650 

Water temperature (°C) 9.2 12.7 13.1 8.3 14.2 11.2 9.2 14.5 12.7 10.1 14.0 15.1 

Specific conductance (μS/cm) 46 74 80 41 61 65 40 57 64 40 56 64 

Dissolved oxygen (mg/L) 10.5 9.5 9.7 11.0 9.4 9.9 11.1 9.8 10.5 10.9 9.7 9.2 

Dissolved oxygen (% saturation) 96 94 98 97 96 94 98 99 101 98 96 95 

pH (standard units) 7.6 8.0 7.7 7.9 7.9 7.8 7.7 8.0 7.7 7.8 7.7 7.2 

NH4 

+ (μg/L) <2 <2 <2 <2 <2 4 <2 2 <2 19 <2 <2 

NO3 

- (μg/L) <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 6 <5 

SRP (μg/L) 10 22 23 7 11 17 8 10 15 9 8 9 

TP (μg/L) 17 21 26 16 18 19 9 17 19 12 13 14 

SiO2 (mg/L) na 25.3 25.4 na 20.0 21.3 14.7 19.9 21.0 na 19.4 20.5 

DIN load (kg/d)a <(14) <(6) <(5) <(42) <(15.4) 7.0 na 6.0 <(15) 125.5 16.2 <(11) 

SRP load (kg/d) 20.2 18.4 17.9 42.3 24.1 29.7 na 30.1 31.7 59.5 21.5 14.3 

TP load (kg/d) 34.8 17.6 20.5 96.7 39.6 33.1 na 51.2 40.1 79.3 35.0 22.3 

Chlorophyll a (mg/m2) 51.0 71.6 80.3 51.7 226 690 40.8 24.4 61.4 193 332 138 

AFDM (g/m2) 15 25 23 17 218 126 23 8 16 68 127 73 

Main-stem sites 

CR_MCIVER CR_BARTON CR_CARVER CR_99E 

Parameter May July Sep May July Sep May July Sep May July Sep 

Streamflow (ft3/s) 2,640 1,180 951 2,840 1,620 1,080 na 1,760 1,300 2,940 1,870 2,090 

Water temperature (°C) 10.1 14.9 16.6 10.6 15.1 20.4 na 15.3 19.5 10.9 16.7 17.3 

Specific conductance (μS/cm) 40 54 65 40 52 65 na 53 65 40 54 74 

Dissolved oxygen (mg/L) 10.7 9.8 9.2 11.0 10.3 10.0 na 9.8 10.4 11.5 na 10.4 

Dissolved oxygen (% saturation) 96 98 96 98 103 113 na 98 115 104 na 112 

pH (standard units) 7.5 7.7 7.5 7.4 7.7 8.4 na 7.6 8.2 7.6 7.4 7.9 

NH4 

+ (μg/L) <2 <2 <2 <2 <2 <2 na 2 <2 <2 <2 <2 

NO3 

- (μg/L) <5 <5 <5 81 8 <5 na 32 5 28 20 <5 

SRP (μg/L) 6 7 10 6 7 9 na 8 8 5 7 6 

TP (μg/L) 12 15 16 14 16 15 na 20 16 13 41 27 

SiO2 (mg/L) 14.6 18.8 20.1 na 17.6 19.7 na 18.0 19.8 14.9 18.7 19.5 

DIN load (kg/d)a <(45) <(20.2) <(16) 562.9 31.7 <(18) na 146.4 15.9 201.4 91.5 <(36) 

SRP load (kg/d) 38.8 20.2 23.3 41.7 27.7 23.8 na 34.5 25.4 36.0 32.0 30.7 

TP load (kg/d) 77.5 43.3 37.2 97.3 63.4 39.6 na 86.1 50.9 93.5 187.6 138.1 

Chlorophyll a (mg/m2) 63.4 276 182 64.0 59.7 88.7 na 194 147 301 54.5 161 

AFDM (g/m2) 42 65 48 14 38 27 na 70 44 128 25 51 

30 
Table 8. Seasonal patterns in streamflow, field parameters, nutrients, and algal conditions at main-stem and tributary sites 

in the Clackamas River Basin, Oregon, May–September 1998—Continued 

[Site codes and nutrient abbreviations are listed in the glossary, and site locations are shown on plate 1; ft3/s, cubic feet per second; °C, degrees Celsius; 

μS/cm, microsiemens per centimeter at 25°C; mg/L, milligrams per liter; %, percent; μg/L, micrograms per liter; kg/d, kilograms per day; 

mg/m2, milligrams per meter squared; g/m2, grams per meter squared; na, not analyzed; <, less than minimum reporting levels (see appendix 1)] 

Tributary sites 

COLLA OAK_BLTLK ROARING NFCLACK 

Parameter May July Sep May July Sep May July Sep May July Sep 

Streamflow (ft3/s) 943 176 70 103 100 75 193 128 56 54 48 11 

Water temperature (°C) 8.4 14.1 18.0 6.6 8.4 8.0 8.6 13.5 12.4 10.9 na 17.3 

Specific conductance (μS/cm) 29 47 59 47 52 47 30 37 39 30 37 39 

Dissolved oxygen (mg/L) 10.7 9.6 9.3 10.3 9.6 9.6 10.7 9.9 10.3 10.1 na 9.1 

Dissolved oxygen (% saturation) 97 98 105 94 91 91 95 99 101 93 na 98 

pH (standard units) 7.5 7.6 8.2 7.6 7.9 7.2 7.6 7.8 7.5 7.3 7.2 7.4 

NH4 

+ (μg/L) <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 4 <2 

NO3 

- (μg/L) <5 <5 <5 <5 <5 6 <5 <5 21 44 81 98 

SRP (μg/L) 3 7 9 3 2 8 5 8 12 2 3 6 

TP (μg/L) 16 10 13 10 13 13 10 12 14 10 9 9 

SiO2 (mg/L) na 15.3 15.6 na na 19.0 na 17.8 18.7 15.8 18.4 22.1 

DIN load (kg/d)a <(16) <(3.0) <(1.2) <(1.8) <(1.7) <(1.2) <(3.3) <2.2 2.9 5.8 10 2.6 

SRP load (kg/d) 6.9 3.0 1.5 0.8 0.5 1.5 2.4 2.5 1.6 0.3 0.4 0.2 

TP load (kg/d) 37.4 4.4 2.3 2.6 3.2 2.4 4.8 3.8 1.9 1.3 1.1 0.2 

Chlorophyll a (mg/m2) 24.3 53.5 55.6 183 130 545 33.0 20.4 51.7 53.2 48.1 187 

AFDM (g/m2) 15 11 12 66 61 115 20 10 16 23 18 22 

a Values in parentheses represent the DIN load assuming concentrations were at the reporting level, and therefore represent theoretical maximum 

values. 

Dissolved oxygen—Concentrations of DO in 

the Clackamas River and some of its tributaries were, 

at times, closely associated with water temperature, 

with colder temperatures supporting higher levels of 

DO than warmer temperatures. Biological processes, 

such as algal photosynthesis, also appeared to exert 

some control on DO at sites with high algal biomass, 

especially during summer. 

The DO concentrations in the upper Clackamas 

River were at or slightly above 11 mg/L (milligrams 

per liter [parts-per-million]) on measurement dates in 

May (a spawning period for native winter steelhead 

and resident trout); for reference, the State standard 

requires an average minimum of 11 mg/L for 30 days. 

DO concentrations were boosted due to the cold water 

temperatures in May and relatively low algal biomass 

(table 8). Immediately downstream of both North Fork 

and River Mill Dams, however, the DO concentrations 

were less than 11 mg/L (table 8). 

Measurements taken in the early morning and 

late afternoon showed that DO levels in the upper 

Clackamas River and some tributaries, including 

Fish Creek and Roaring River, were inversely related 

to water temperature, demonstrating the effect of temperature on DO. The general decline in DO concentrations in the upper Clackamas River from May to July, 

following the increase in water temperature (table 8 

and fig. 5), further demonstrates the close association 

between water temperature and DO. Temperature 

control on DO also was indicated by the fairly consistent percent-saturation values in the upper Clackamas 

River, which were within 5% of each other in May and 

July (fig. 5). 

In contrast, DO concentrations at some sites 

(FISH, DEEP, SIEBEN, and several sites in the lower 

Clackamas River, especially those downstream of 

Barton) increased through the day during the summer, 

even as the water temperature increased (fig. 8). 

31 
Figure 8. Diel fluctuations in water temperature, pH, and dissolved oxygen in the lower Clackamas River (at CR_COW, RM 2.7), 

June 28–29, 1998, and July 15–16, 1998. (Spawning periods include spawning and egg incubation through fry emergence. 

Nonspawning periods include periods when fish are holding, rearing, or outmigrating [see tables 5 and 6].) 

32 
The percent saturation values at CR_BARTON, CR_ 

CARVER, and CR_99E, for example, were 113%, 

115%, and 112%, respectively, in September (fig. 5). 

This is an indication that some other process, probably 

algal photosynthesis, was affecting DO concentrations. 

DO concentration in the lower Clackamas River at 

RM 2.7 (at CR_COW) showed a distinct diel pattern 

during summer, indicative of algal metabolism, with 

minimum DO concentrations occurring at night and in 

the early morning, when water temperatures were 

lowest. In late June, for example, the DO fluctuated 

from 10.6 mg/L (105% saturation) in the afternoon to 

8.3 mg/L (83.5% saturation) in the morning (fig. 8). 

At this time, the DO concentration probably did not 

meet the 30-day 11 mg/L criterion in effect to protect 

emerging winter steelhead fry (tables 5 and 6). DO 

concentrations were even lower in mid-July, when the 

daily minimum concentration was 7.9 mg/L (85.7% 

saturation) at 2 a.m. (fig. 8). In September, a spawning 

period for spring and fall Chinook salmon (table 6), a 

concentration of 11 mg/L was not attained at any of 

the main-stem sites on measurement dates (table 8). 

The lowest measured DO concentrations for 

tributary sites occurred in Clear, Eagle, Deep, and Rock 

Creeks in August, when DO concentrations ranged 

from 8 to 8.4 mg/L. The DO in the Oak Grove Fork 

downstream from Timothy Lake was 9.6 mg/L (91% 

saturation in September (table 8), when the DO was 

depleted (about 5 mg/L [50% saturation]) at the water 

release depth in Timothy Lake (data presented later in 

this report). 

pH—All of the pH values in the tributaries were 

greater than 7 and most were between 7 and 8 (fig. 5 

and table 7). The highest tributary pH values (8.4 and 

8.8) occurred at SIEBEN and DEEP, respectively, with 

the latter value exceeding the State pH criterion of 8.5, 

which applies to single measurements (table 5). 

Instantaneous afternoon pH measurements taken 

in the lower Clackamas River at CR_BARTON and 

CR_COW slightly exceeded the State criterion for some 

portion of the late afternoon on several occasions during 

summer. Continuous data collected at CR_COW in late 

June (and again in mid-July) showed that pH fluctuated 

roughly 1.4 units through the day, slightly exceeding 

the 8.5 criterion in the afternoon (fig. 8). Pronounced 

diel fluctuations in pH and DO, indicative of high rates 

of algal metabolism, have been found to occur on a 

daily basis for weeks at a time in other Cascade streams 

(e.g., Tanner and Anderson, 1996; Herrett and others, 

2001). 

Several sites had somewhat elevated pH values 

(equal to or greater than 8.0 units) during the summer, 

including CR_UPPER, COLLA, CR_ABNFK, and in 

the fish ladder near the Faraday Diversion Dam (fig. 2). 

Notably lower pH values, ranging from 7.0 to 7.2 pH 

units, characteristic of more heterotrophic systems, 

occurred at sites in the North Fork Clackamas River 

Basin, including the North Fork Clackamas River at the 

mouth (NFCLACK), Fall Creek (FALL), and Winslow 

Creek (WINSLOW) (table 7). 

Specific conductance—SC values in the Clackamas River were relatively low (table 8). SC generally 

declined in a downstream direction (along with P 

concentrations) between CR_UPPER and CR_ 3LYNX 

in July, as inputs from more dilute tributaries entered 

the main stem (fig. 5). A seasonal increase in SC was 

observed from May to September at most sites (table 8 

and fig. 5), presumably caused by the lower streamflows, which cause less dilution. The highest SC values 

were measured at ROCK and SIEBEN in July, when the 

respective SC values were 164 and 256 μS/cm (table 7). 

The large increase in the SC between CR_CARVER 

and CR_99E in September (fig. 5) was likely an artifact 

of tidal interaction with the Willamette River (refer to 

Tidal influence in the lower Clackamas River, p. 25). 

Nutrients 

Nitrogen and phosphorus values (concentrations 

and loads) and ratios differed among main-stem and 

tributary sites and exhibited spatial and longitudinal 

(downstream) variations that may be attributable to differences in the geology, hydrology, biological processing, and/or land use in the basin. Seasonal increases in 

SC and P levels in the Clackamas River were observed 

that were probably related to the decline in streamflow, 

which resulted in less dilution, and the increasing dominance of ground water. Due to the differing implications of concentrations versus loads, results for each of 

these are presented separately for N and P. 

Nitrogen concentrations—In most streams, + NO3

-

 was the dominant form of N, although NH4 

also was occasionally detected at low concentrations. 

A spatial pattern in stream N concentrations was 

observed, with the lowest concentrations (often 

less than 5 μg/L) occurring at upper-basin sites 

and moderate-to-high values at middle-basin sites. 

Nitrate concentrations at tributary sites in the middle 

basin, including the North Fork Clackamas River, 

Eagle Creek, and Clear Creek, for example, were 

10–20 times higher and NH4

+ concentrations 3 times 

higher than at sites in the upper basin (tables 7 and 9). 

33 
Table 9. Average values for environmental conditions for groups of sites sampled in the Clackamas River Basin, Oregon, July 1998 

[Sites in each group are given in table 7. Site codes and nutrient abbreviations are listed in the glossary, and site locations are shown on plate 1; 

ft3/s, cubic feet per second; %, percent; μS/cm, microsiemens per centimeter at 25°C (degrees Celsius); μg/L, micrograms per liter; 

mg/m2, milligrams per square meter; <, less than minimum laboratory reporting levels (see appendix 1)] 

Parameter 

Hydropower 

sites 

Main-stem sites

Upper-basin 

sites 

Lower-basin 

sites 

Upper-basin 

sites 

Tributary sites 

SFCLACK 

and FISH 

Middle-basin 

sites 

Lower-basin 

sites 

Number of sites 4 3 4 4 2 6 4 

Streamflow (ft3/s) 820 825 1,752 107 48 47 8 

Agricultural and urban land (%) 2 0 4 1 0 3 46 

Mature forest (%) 59 62 56 64 55 58 3 

Nonforest upland (%) 22 23 19 25 11 8 25 

Regrowth forest (%) 16 14 20 9 33 31 17 

Specific conductance (μS/cm) 56 64 53 53 42 37 146 

NH4 

+ (μg/L) <2 2 <2 <2 <2 6 114 

NO3 

- (μg/L) <5 <5 20 5 8 100 2,445 

SRP (μg/L) 7 14 7 10 7 4 70 

DIN:SRP (range) <0.6–3.5 <0.7 <1–4.3 <1–3.5 1 9–116 13–62 

TP (μg/L) 15 19 26 15 10 9 82 

Chlorophyll a (mg/m2) 241 107 103 75 118 66 188 

Canopy closure (%) 10 14 6 45 47 75 66 

The highest N concentrations, however, ranging from 

roughly 800 to 7,500 μg/L, were found at sites in 

the lower basin, where agriculture and urban land is 

concentrated. N concentrations in the Clackamas River 

reflected the pattern observed in the tributaries, with 

the lowest concentrations occurring in the upper basin 

(upstream from North Fork Reservoir) and higher concentrations generally occurring downstream (fig. 9). 

In May 1998, N concentrations in the Clackamas River 

were below detection levels in the upper basin and 

increased downstream from North Fork Reservoir 

(at CR_BLNFK), where 19 μg/L of NH4

+ was detected 

(fig. 9). Downstream (at CR_MCIVER), however, all 

forms of N were below detection, possibly from algal 

uptake of N within the hydroelectric project. 

Declines in N concentrations also were observed 

in the lower Clackamas River between CR_BARTON 

and CR_99E (in May) and between CR_CARVER and 

CR_99E (in July). This also suggests algal uptake, 

because N concentrations in the main stem (especially 

NO3

-

) were anticipated to increase, not decrease, 

in response to inputs from the lower-basin tributaries 

(table 7 and fig. 9) and ground water, as will be discussed later. 

A slight increase in N concentrations, possibly 

due to slowing algal growth (and reduced nutrient 

uptake) was observed at some sites in late September 

(table 8). Whereas N concentrations were low at all 

main-stem sites in early September, NO3

-

 was detected 

later that month at sites in the upper Clackamas River 

(at CR_3LYNX, CR_ABNFK, and CR_BLNFK) 

at concentrations ranging from 7 μg/L to 9 μg/L 

(data not shown). The small increase in streamflow 

that occurred in late September (fig. 3) also may have 

contributed to the observed increase in N as previously 

dry riverbeds were again inundated by the higher 

flows. 

Nitrogen loads and yields—Tributary sites with 

the highest N loads in July included DEEP, which had 

a NO3

-

 concentration exceeding 1,000 μg/L with moderate streamflow, and sites in the middle basin having 

much lower N concentrations but relatively higher 

streamflows (fig. 10 and table 7). Sieben Creek, with 

its exceptionally high NO3

-

 concentration (7,500 μg/L) 

contributed 4 times as much N as Rock Creek, even 

though the Sieben Creek Basin is 4 times smaller 

(table 7). 

34 
Figure 9. Seasonal variation in nutrient concentrations, nutrient ratios, and algal biomass at main-stem sites in May, July, and September, 

and values for tributary sites in July 1998. (Zero values for nitrogen and phosphorus compounds indicate that the concentration was less 

than the minimum laboratory reporting level [appendix 1]. Full site names and locations are listed in table 3 and abbreviations for nutrient 

and algal biomass units of measure are listed in the glossary.) 

35 
Figure 10. Estimated contributions of dissolved inorganic nitrogen 

(DIN; NO3

-

 + NH4

+) loads (A) and yields (B) from the tributaries, 

wastewater treatment plants, and fish hatcheries in the Clackamas 

River Basin, Oregon, July 1998. (Contributions from point sources 

were estimated from available data. Site codes and abbreviations 

for nutrients and algal biomass are listed in the glossary.) 

In July, N loads in the upper Clackamas River 

(upstream from North Fork Reservoir) were low 

(fig. 11). The measured load of N entering the reservoir 

(16 kg/d [kilograms per day]) was accounted for by 

inputs from the main-stem Clackamas River (CR_ 

ABNFK, 6 kg/d) and the North Fork Clackamas River 

(NFCLACK, 10 kg/d). This load was matched at the 

downstream site (CR_BLNFK), despite the slightly 

lower discharge downstream from the reservoir 

(fig. 6). 

The three WWTPs in the basin, which discharged 

an estimated 1.3 ft3

/s in July, contributed between + 9 and 49 kg/d of NH4

+ based on available data (NH4 

concentrations in effluent ranged from 1,700 to 

16,000 μg/L during summer, and NO3

-

 data were not 

available). Eagle Creek National Fish Hatchery, which 

typically discharges about 35 ft3

/s, contributed an 

estimated 9 kg/d of N (fig. 10). No nutrient data were 

available from the State fish hatchery at McIver Park, 

although contributions were likely minor in July 

because most of the fish were released in March. 

The highest DIN yields (loads per unit basin 

area) were observed from lower-basin tributary sites 

(SIEBEN, DEEP, ROCK, and RICHARDSON) and 

from tributary sites in the middle basin (EAGLE_M, 

CLEAR, and NFCLACK) (fig. 10). DIN yields 

from upper Eagle Creek (EAGLE_W, in the SalmonHuckleberry Wilderness Area) and at sites in the 

upper basin were much lower (fig. 10). 

The longitudinal pattern of N loads in the lower 

Clackamas River (fig. 11) suggests that algal uptake 

might be occurring in some reaches. For example, 

the N load in the lower Clackamas River increased 

from <20 kg/d downstream from River Mill Dam (at 

CR_MCIVER) to only 32 kg/d at CR_BARTON in 

July, despite the large input by Eagle Creek (45 kg/d of 

N, table 7). At this time, the N load at CR_BARTON 

was 13 kg/d less than the contribution made by Eagle 

Creek alone, which might be attributable to N utilization by algae in this reach. Downstream of Barton, 

the N load increased to 147 kg/d at CR_CARVER, 

with about 85% of that increase being attributable to 

inputs from measured tributaries, with unmeasured 

sources, including Goose Creek and ground-water 

inputs, making up the difference. Despite inputs of 

N from lower-basin tributaries and other sources, the N 

load decreased to 92 kg/d at CR_99E in July (fig. 11), 

again suggestive of algal uptake. An even more pronounced longitudinal decrease in the main-stem N 

load, from 563 to 200 kg/d, also was observed between 

CR_BARTON and CR_99E in May (fig. 11). 

To summarize, the scarcity of N in the Clackamas 

River, combined with sharp declines in N loads, 

suggests a high demand for N, and that N concentrations may be strongly affected by algal uptake. 

The major sources of measured N included tributaries 

in the middle basin, North Fork Reservoir (which 

appeared to release NH4

+ in May), tributaries in the 

lower basin (where agricultural and urban land use is 

concentrated), and point sources, including WWTPs 

and fish hatcheries. 

Phosphorus concentrations—Concentrations 

of P in the Clackamas River also showed longitudinal 

variations that can be attributed to the inputs of 

tributaries, effects of the reservoirs, and possibly algal 

uptake. A general downstream decline in the concentration of SRP was observed in the main stem (fig. 9). 

Relatively high concentrations of P were found at some 

sites in the upper basin (table 7), especially the highelevation sites (CR_ UPPER and the Oak Grove Fork at 

Rainbow Picnicground [OAK_RAIN]), possibly due to 

naturally occurring phosphate rock in these watersheds. 

36 
Figure 11. Seasonal variation in nutrient loads at main-stem sites in May, July, and September, and values for tributary sites in July 1998. 

(Zero values for nitrogen and phosphorus compounds indicate that the concentration was less than the minimum laboratory reporting level 

[appendix 1]. Site codes and abbreviations for nutrients and algal biomass are listed in the glossary.) 

Concentrations of TP at forested sites were positively 

correlated with both dissolved SiO2 and SC (fig. 12), 

a finding that is consistent with a geological source of 

P in the upper basin. The seasonal increase in P concentrations (and SC values) from July to September 

(figs. 5 and 9) also suggests that phosphorus-rich 

ground water was contributing a larger proportion to 

streamflows during low-flow periods. 

The downstream decline in P (fig. 9) was due to 

the combination of low-phosphorus water inputs from 

tributaries, including Roaring River, Fish Creek, and 

the North and South Forks of the Clackamas River, and 

possibly algal uptake. Concentrations of P downstream 

of North Fork Reservoir (at CR_BLNFK) also were 

slightly less compared with those at the upstream site 

(fig. 9), indicating that the reservoir was a sink for P. 

Concentrations of SRP in the lower Clackamas 

River were steady or declined in downstream direction, 

despite the inputs of phosphorus-rich water from lower 

basin tributaries (DEEP, ROCK, RICHARDSON, and 

SIEBEN) affected by agriculture and urban land uses 

(table 7). The highest concentration of P (144 μg/L 

TP at SIEBEN) exceeded the USEPA’s suggested 

goal of 100 μg/L to prevent nuisance algal growth 

for streams that do not drain into lakes or reservoirs 

(U.S. Environmental Protection Agency, 1986). 

37 
Figure 12. Relations between total phosphorus and dissolved silica 

concentrations (A), total phosphorus concentrations and specific 

conductance (B), and dissolved silica and specific conductance 

(C). (Lower-basin tributary sites and lowermost main-stem sites 

were outliers because of high nutrient concentrations and were 

not plotted.) 

A slight, but steady longitudinal decrease in the 

SRP concentration occurred in the lower Clackamas 

River in September (fig. 9), concurrent with an 

increase in the TP concentrations, possibly caused 

by sloughed algal material. The highest TP concentrations in the Clackamas River were observed 

downstream of Barton, especially in July, when 

the TP increased sharply, reaching about 40 μg/L at 

CR_99E. 

The longitudinal declines in SRP concentrations 

might also have been due to uptake by algae. One 

measure of the relative amount of P available for algal 

growth is the ratio of dissolved P to total P (SRP:TP), 

expressed as a percentage. As algae grow, concentrations of SRP in the water column decline, thereby 

reducing the SRP:TP ratio (in the absence of inputs 

of particulate P). In the Clackamas River, SRP was 

the dominant form of P at most sites in the upper 

basin, making up greater than 90% of the TP (fig. 9). 

The SRP:TP ratio in the main stem declined from 

CR_UPPER to CR_99E in July and September (fig. 9), 

a consequence of uptake and incorporation of SRP into 

algal biomass. At the same time there was an increase 

in TP in the lower Clackamas River, probably due to 

increased amounts of algal material suspended in 

the water column, which also resulted in lower SRP:TP 

ratios. 

Phosphorus loads and yields—The highest 

loads of TP came from the upper Clackamas River (at 

CR_UPPER), Deep and Eagle Creeks, the Collawash 

and Roaring Rivers, and the Oak Grove Fork (fig. 13). 

Other lower-basin tributaries, while having relatively 

high TP concentrations, contributed smaller TP loads 

because of their smaller streamflows (fig. 11). The 

three WWTPs in the basin, which discharged about 

1.3 ft3

/s in July, contributed significant amounts of TP 

(between 9 and 16 kg/d, fig. 13), based on available 

nutrient data: TP concentrations from the WWTPs 

ranged from 2,900 to 5,400 μg/L during summer. 

Relatively high TP yields, the load per unit area, 

were found at sites in the upper basin (at OAK_RAIN 

and CR_UPPER, fig. 13), possibly due to the presence 

of phosphate-containing rock in those watersheds. 

Other basins with relatively high TP yields included 

Sieben Creek (SIEBEN) and Rock Creek (ROCK), 

which likely reflects the influence of agricultural and 

urban land uses on water quality in those basins. 

Phosphorus loads in the Clackamas River were 

higher in May compared with other months, partly 

because of higher streamflows (fig. 11). The SRP load 

in the upper Clackamas River about doubled from 

CR_UPPER to CR_3LYNX due to inputs from tributaries and the Oak Grove Powerhouse. Downstream 

of North Fork Reservoir, the SRP load increased to 

60 kg/d, due to increased streamflow downstream of 

the reservoir. Downstream, at CR_MCIVER, the SRP 

load declined to levels found in the upper Clackamas 

River. In contrast, lower SRP loads were observed 

downstream of North Fork Reservoir in July and September compared with the upstream site (CR_ABNFK, 

fig. 11). 

38 
TP loads increased in the Clackamas River 

from CR_UPPER to CR_99E, particularly in 

July and September, and mirrored the downstream 

increase in streamflow (fig. 11). The TP load in the 

upper Clackamas River in May was about equally 

shared by contributions from the upper Clackamas 

River (CR_ UPPER), the Collawash River (COLLA), 

and the Oak Grove Powerhouse. TP loads in the 

lowermost reaches of the Clackamas River between 

CR_CARVER and CR_99E increased sharply in 

July and September (fig. 11). Relatively low streamflows from the lower-basin tributaries resulted in 

small P loads in July despite their relatively higher 

P concentrations (fig. 9). 

Seasonal declines in TP loads were observed at 

most main-stem sites from May to September (fig. 11), 

reflecting the seasonal declines in streamflow. The 

TP load at CR_99E, however, increased sharply from 

May to July, following an algal sloughing (die-off) 

event in June (refer to Algal Biomass, p. 40.) 

Figure 13. Estimated contributions of total phosphorus loads (A) 

and yields (B) from the tributaries, wastewater treatment plants, 

and fish hatcheries in the Clackamas River Basin, Oregon, July 

1998. (Contributions from point sources were estimated from 

available data.) 

Soluble reactive phosphorus load balance— 

In July, the SRP load in the upper Clackamas River 

increased steadily between CR_UPPER and CR_ 

ABNFK (fig. 14). The SRP loads in the main 

stem were boosted from the inputs of tributaries, 

including the Collawash River, Oak Grove Fork 

(via the Oak Grove Powerhouse), and Roaring River. 

A 28% decline in the SRP load was observed downstream of North Fork Reservoir (at CR_BLNFK), due 

to slightly lower concentrations of SRP and reduced 

streamflow downstream from the reservoir in July 

(fig. 14 and table 8). In July and September, the SRP 

load steadily increased in a downstream direction from 

CR_MCIVER to CR_CARVER, in response to inputs 

from the larger tributaries, particularly Eagle, Clear, 

and Deep Creeks (figs. 11 and 14). 

A 9–32% increase in the SRP load that was not 

accounted for in the SRP balance was observed 

between CR_MCIVER and CR_BARTON, although 

fluctuating discharges from River Mill Dam in July 

(presented in the streamflow results) increased uncertainty in mass-balance calculations. An unaccountedfor increase of 5% in SRP load was observed between 

CR_BARTON and CR_CARVER, whereas a 9% 

loss in SRP load, possibly indicative of algal uptake, 

was observed between CR_CARVER and CR_99E, 

despite inputs from Rock and Sieben Creeks (fig. 14 

and table 7). 

Nitrogen-to-phosphorus ratios—The DIN:SRP 

ratio, the relative availability of dissolved inorganic 

forms of N and P, is often used to indicate which nutrient might be regulating algal growth. A ratio of roughly 

7 indicates balanced nutrient availability, whereas 

higher ratios may indicate P limitation, and lower ratios 

may indicate N limitation. DIN:SRP ratios were less 

than 7 at all main-stem sites in July (table 7), owing to 

the low N concentrations at sites in the upper basin, 

suggesting limitation by N. In contrast, DIN:SRP ratios 

were greater than 7 at all tributary sites in the middle 

and lower Clackamas Basin (table 7), owing to the 

relative abundance of NO3

-

 at both middle- and lowerbasin sites and lack of SRP at middle-basin sites. 

This suggests that P could potentially be limiting algal 

growth at middle-basin tributary sites. The high P 

concentrations at lower-basin tributary sites suggests 

that P is probably not limiting algal growth, despite the 

high DIN:SRP ratios. 

39 
Figure 14. Soluble reactive phosphorus (SRP) load balance in the main-stem Clackamas River, Oregon, July 7–15, 1998. (Discharge values 

for the Oak Grove Powerhouse and CR_BLNFK were estimated from power-generation records. The SRP load from the Oak Grove Powerhouse assumed an SRP concentration of 2 μg/L [the concentration at OAK_BLTLK].) 

Algal Conditions 

Algal Biomass (Chlorophyll a) 

In 1998, accumulations of periphyton (algae 

attached to the streambed) were first observed in the 

lower Clackamas River in April, when streamflows 

were beginning to stabilize and day lengths were 

increasing. The heaviest algal growths were observed 

on cobble bars along stream margins and on large rocks 

in moderate water velocities. By May, thick growths of 

macroalgae, mostly Cladophora sp. (a filamentous 

green alga) and Gomphoneis herculeana (a stalked 

diatom) produced high biomass (~300 mg/m2 

[milligrams per square meter] chl a) in the lower 

Clackamas River at CR_99E (fig. 9), fouling stream 

margins. At this time, algal biomass was 2–3 times 

higher than the range (100–150 mg/m2 chl a) considered indicative of nuisance conditions (Horner and 

others, 1983; Welch and others, 1988, 1989; Biggs, 

1996; Dodds and others, 1997, 1998). The waterquality effects of such high algal biomass (large 

fluctuations in pH and DO levels) were pronounced 

in the lower Clackamas River in June (fig. 8). 

As the summer progressed, algal biomass 

declined precipitously in the lower Clackamas River 

(at CR_99E, fig. 9) following an algal sloughing event 

(losses of algal material from the streambed into the 

water column) in June. Chlorophyll a values declined 

40 
nearly 80% in the Clackamas River at CR_99E, from 

300 to 50 mg/m2

, between May and July (fig. 9). As 

a result of this sloughing event, drifting algae clogged 

drinking water intakes, became entangled on docks 

and fishing lines, and increased turbidity in the lower 

Clackamas River, leading to complaints from the 

public (Robert Baumgartner, Oregon Department of 

Environmental Quality, oral commun., 1998). Declines 

in algal biomass indicative of sloughing losses also 

occurred at OAK_BLTLK, CR_BLNFK, and CR_ 

CARVER, particularly after attaining a biomass 

of greater than 150–200 mg/m2 chl a (fig. 9). In 

contrast, gradual seasonal increases in algal biomass 

were observed from May to September at sites such 

as CR_UPPER, COLLA, and ROARING (table 8 and 

fig. 9), where peak biomass values reached between 

50 and 100 mg/m2

 chl a, and punctuated sloughing 

losses in biomass were not observed. 

High algal biomass also was found at sites immediately downstream from the hydroelectric projects, 

where three of the four highest chl a values occurred 

(fig. 9 and table 8). Algal growth in the upper Clackamas River downstream from the Oak Grove Powerhouse was especially prolific, reaching 690 mg/m2

 chl a 

in September (the highest value measured during this 

study). High biomass also was observed downstream 

from the hydroelectric project reservoirs, especially 

Timothy Lake and North Fork Reservoir (at OAK_ 

BLTLK and CR_BLNFK, respectively; table 8). 

Among tributary sites, algal biomass was generally higher at sites in the lower basin in July compared 

with those in the upper basin, with the highest chl a 

value (371 mg/m2

) occurring at SIEBEN (fig. 9). 

Low-to-moderate algal biomass (50–100 mg/m2 chl a) 

was found at most upper-basin sites, and the lowest 

algal biomass, ranging from 11 to 23 mg/m2

 chl a, 

occurred at well-shaded tributary sites in forested 

basins, including ROARING, WINSLOW, FALL, 

and EAGLE_W, where tree canopy densities ranged 

from 81 to 98% (fig. 9). 

Algal Species Composition 

Major types—Nearly 180 algal taxa, mostly 

diatoms, filamentous green algae, and blue-green algae, 

were identified in the Clackamas River (appendix 4) 

and its tributaries (appendix 5). Most sites contained 

a mixture of algae from the different groups, although 

some sites were strongly dominated by just one group. 

Main-stem sites, in general, had greater numbers of 

algal taxa compared to tributary sites. The greatest 

number of taxa (per site) was observed at sites downstream from reservoirs, including OAK_BLTLK and 

CR_MCIVER, where between 75 and 80 taxa per site 

were recorded. Lower taxon richness (14 to 18 taxa per 

site) was observed at sites in the middle basin, including 

EAGLE_W, EAGLE_M, and FALL (appendix 5). 

Diatoms composed 139 (78%) of the taxa 

identified (appendixes 4 and 5). Diatom growth forms 

were diverse and included filament-forming genera 

(Melosira), mobile genera (Navicula, Nitzschia, 

and many others), tightly adhering and epiphytic 

genera that grow on other aquatic plants (Achnanthes, 

Rhoicosphenia, and Cocconeis), large and stalked 

genera (Cymbella, Gomphonema, Gomphoneis), 

and colonial genera (Tabellaria, Fragilaria). Two 

of the diatom genera encountered (Epithemia and 

Rhopalodia) are known to harbor symbiotic blue-green 

algae that have the ability to fix atmospheric nitrogen 

(Floener and Bothe, 1980; DeYoe and others, 1992), 

making them potentially important in N-limited rivers. 

Filamentous green algae included Ulothrix, Zygnema, 

Cladophora, Stigeoclonium, Spirogyra, Mougeotia, 

and Microspora (appendixes 4 and 5). Two filamentous 

golden algal taxa, Vaucheria and Tribonema were 

also identified. Nine species of blue-green algae, 

including three N-fixing species (Nostoc, Calothrix, 

and Tolypothrix), also were identified. 

Algal assemblages at the lower-basin tributary 

sites were dominated by diatom species indicative 

of nutrient enrichment, including Melosira varians, 

Nitzschia palea, N. frustulum, N. inconspicua, and 

Cyclotella meneghiniana (appendix 5). Relatively 

small, tightly adhering diatoms, including Achnanthes, 

Achnanthidium, and Cocconeis (appendix 5), dominated algal assemblages at well-shaded tributary sites 

in the middle and upper basin, possibly due to selective 

grazing by benthic macroinvertebrates. The filamentous, N-heterotrophic diatom Melosira was frequently 

found at these sites, whereas filamentous green algae 

were either absent or present only in minor abundance. 

Many of the dominant taxa in the Clackamas 

River (by biovolume) were filamentous green algae. 

In the upper main stem, these included Ulothrix, 

Zygnema, and Mougeotia, and the golden alga 

Vaucheria, whereas Cladophora and Stigeoclonium 

were prevalent at sites in the lower Clackamas River 

(appendix 4). Cladophora first appeared downstream of 

North Fork Reservoir in July, when it composed about 

30% of the total algal biovolume. Cladophora was 

also a dominant taxon in the lower Clackamas River 

at CR_CARVER and CR_99E in July (appendix 4). 

41 
Filamentous green algae were often found in association with N-fixing algae (both blue-green and diatoms), 

and large diatoms, including Gomphoneis herculeana, 

Cymbella mexicana, Frustulia rhomboides, Epithemia 

adnata, and E. turgida, especially downstream of 

the reservoirs (appendix 4). This association suggests 

that N-fixing algae may be an important source of 

N for filamentous green or golden algae, which lack 

the ability to fix N. 

Seasonal succession—In May, the algal assemblages in the Clackamas River were dominated by taxa 

that are able to withstand strong current by means 

of specialized holding structures, slippery mucilage 

(Sabater and others, 1998), or their small size. They 

included genera of filamentous algae (Ulothrix, 

Zygnema, Cladophora, Stigeoclonium, Spirogyra, 

Mougeotia, Vaucheria, Tribonema, and Microspora), 

cold-water algae (Prasiola), stalked diatoms (Gomphoneis and Cymbella), and small diatoms (Achnanthes, 

Cocconeis, Diatoma, and Fragilaria). 

Nitrogen-fixing algae became increasingly 

abundant in July and September, when concentrations 

of N were low and concentrations of P were relatively 

high (fig. 9). N-fixing diatoms, including Epithemia 

and Rhopalodia, and the N-fixing blue-green alga 

Nostoc were dominant at main-stem sites downstream 

to CR_BARTON (appendix 4). In September, stalked 

diatoms including large-celled species of Gomphoneis 

and Cymbella dominated algal assemblages at sites in 

the upper and lower Clackamas River (appendix 4). 

Algal Indicator Taxa 

Several groups of algae were found in the 

Clackamas River Basin that may be used as “indicator 

species,” based on preferences or tolerances to particular environmental conditions (van Dam and others, 

1994). They included alkaliphilic taxa (prefer pH >7), 

oligotrophic (indicating low-nutrient availability), 

N-fixing, N-heterotrophic (able to use organic N for 

energy and growth), eutrophic (indicating highnutrient availability), and silt-tolerant taxa (table 10). 

The relative abundance of indicator algal taxa 

varied spatially and seasonally, in step with nutrient 

concentrations, especially for N. Eutrophic and Nheterotrophic diatoms were found where concentrations 

of N and P were generally highest (fig. 15), whereas 

N-fixing taxa were prevalent at several sites in the upper 

basin where concentrations of N were low. The relative 

abundance of N-fixing taxa increased seasonally, as 

N concentrations either declined or remained low. 

Relations between the different algal indicator 

taxa and water-quality conditions were not strongly 

correlated, but did show the appropriate responses in 

most cases (fig. 15). For example, the percentage of 

alkaliphilic taxa increased as the pH increased, and 

N-fixing taxa were primarily confined to sites where the 

DIN concentrations were relatively low. Silt-tolerant 

taxa, however, were difficult to evaluate be cause the 

amount of sediment was not measured in this study 

and other potential indicators of sediment (TP) or sediment inputs (road density), were not correlated with the 

percentage of silt-tolerant taxa. 

Alkaliphilic taxa—Over 60 species of alkaliphilic diatoms were identified, which is consistent 

with the alkaline stream pH values (fig. 5). The relative 

biovolume of alkaliphilic taxa was significantly correlated with pH (fig. 15), excluding two sites with the 

lowest pH (FALL and NFCLACK) and two sites 

with the highest pH (SIEBEN and DEEP), which 

were outliers. Most sites contained a relatively high 

proportion of alkaliphilic taxa, particularly in July 

and September, when pH values were generally higher. 

Alkaliphilic taxa were least abundant (<10% relative 

biovolume) at COLLA and OAK_BLTLK in May, 

although proportions increased at these sites in July to 

58% and 68%, respectively (table 10). 

Nitrogen-fixing taxa—The abundance of Nfixing algae, including the blue-green algae Nostoc, 

Calothrix, and Tolypothrix, and the N-fixing diatoms 

Epithemia and Rhopalodia, generally increased from 

May to September in the upper Clackamas River 

(table 10) following the general decline in N concentrations. The N-fixer Nostoc was particularly abundant at 

sites in the upper main stem, which might be attributed 

to the low N:P ratios (low N and high P) that give them 

an advantage over non-N-fixing algae. Ward (1985) 

suggested that some soil stimulatory factor transported 

through soil erosion also might be responsible for the 

success of Nostoc in the Pacific Northwest as several 

species of Nostoc also thrive in soils (Stewart, 1973). 

The relative biovolume of N-fixers in the Clackamas River was much lower immediately downstream 

from North Fork Reservoir in May (0.02% at CR_ 

BLNFK) compared with the upstream sites (12–44%, 

table 10), possibly due to an increase in N downstream 

from the reservoir. The NH4

+ concentration at CR_ 

BLNFK was 19 μg/L in May, whereas all forms of DIN 

were below detection at all upstream main-stem sites 

(fig. 9). The elevated DIN concentrations (table 7) and 

high DIN:SRP ratios may explain the absence of Nfixing algae at the middle-basin sites in July (table 10). 

42 
Table 10. Relative abundance of algal indicator taxa in the Clackamas River Basin, Oregon, May–September 1998 

[Values in percent of the total biovolume of diatoms and nitrogen-fixing blue-green algal taxa; site codes are listed in the glossary. Some algal taxa are 

ubiquitous and were not assigned to a particular guild, whereas others may be classified into more than one guild; therefore, the sums for each site may 

not be 100.] 

Algal indicator taxa 

Site codes 

and 

sampling month 

Alkaliphilic 

taxa 

Nitrogenfixing 

taxa 

Nitrogenheterotrophic 

taxa 

Eutrophic 

taxa 

Oligotrophic 

taxa 

Silttolerant 

taxa 

CR_UPPER (May) 68.7 23.8 0.5 4.3 0.1 0.5 

CR_UPPER (July) 67.4 26.9 3.8 10.8 0.2 6.6 

CR_UPPER (September) 51.8 80.6 4.4 10.6 0.0 9.0 

CR_3LYNX (May) 22.0 44.1 5.0 15.0 2.0 5.5 

CR_3LYNX (July) 56.8 7.9 16.6 24.2 3.4 9.5 

CR_3LYNX (September) 60.5 25.2 39.3 50.7 0.3 20.5 

CR_ABNFK (May) 52.2 11.7 2.4 9.3 0.3 1.1 

CR_ABNFK (July) 56.8 44.2 14.0 22.2 0.1 15.1 

CR_ABNFK (September) 69.9 59.8 14.6 23.0 1.1 17.8 

CR_BLNFK (May) 40.3 0.2 16.9 28.3 0.4 6.4 

CR_BLNFK (July) 81.1 51.7 16.1 22.1 1.6 2.7 

CR_BLNFK (September) 33.0 29.1 15.8 29.6 1.0 31.5 

CR_MCIVER (May) 13.0 0.0 22.2 61.9 3.8 47.4 

CR_MCIVER (July) 73.1 62.3 12.8 26.0 0.8 7.7 

CR_MCIVER (September) 39.3 6.4 24.9 47.7 0.6 10.8 

CR_BARTON (May) 22.5 0.0 9.9 26.1 0.0 18.8 

CR_BARTON (July) 35.1 14.6 21.1 38.8 0.0 1.8 

CR_BARTON (September) 50.9 48.5 4.8 43.8 1.3 7.7 

CR_CARVER (July) 38.4 4.7 7.4 56.9 1.5 5.5 

CR_CARVER (September) 44.9 31.3 5.7 48.6 3.6 4.8 

CR_99E (May) 33.6 7.7 14.4 26.3 0.0 7.2 

CR_99E (July) 16.0 2.6 7.1 24.4 0.7 2.7 

CR_99E (September) 49.2 41.7 4.4 59.6 2.2 5.4 

COLLA (May) 7.0 0.3 0.0 5.5 0.4 1.1 

COLLA (July) 59.1 55.6 0.7 18.8 1.7 8.7 

COLLA (September) 63.9 52.4 6.5 21.7 4.7 20.2 

OAK_BLTLK (May) 7.4 45.8 3.4 8.3 0.0 5.7 

OAK_BLTLK (July) 68.6 49.8 3.8 10.9 5.7 4.8 

OAK_BLTLK (September) 25.1 57.7 0.8 3.3 1.2 9.1 

OAK_RAIN (July) 45.8 41.4 0.9 8.0 2.7 12.4 

ROARING (May) 48.3 15.9 3.3 18.6 0.0 2.0 

ROARING (July) 62.2 21.4 10.7 22.8 0.4 16.9 

ROARING (September) 50.4 0.0 14.7 30.5 3.9 21.3 

FISH (July) 38.7 0.4 21.8 37.0 0.9 7.5 

SFCLACK (July) 50.7 0.0 18.9 24.6 0.6 2.6 

WINSLOW (July) 52.8 0.0 25.9 55.3 0.4 6.2 

FALL (July) 18.3 1.0 0.0 16.0 21.2 2.8 

NFCLACK (May) 83.2 0.0 4.3 91.9 0.0 4.0 

NFCLACK (July) 52.5 0.0 15.8 27.4 9.5 2.5 

NFCLACK (September) 11.2 0.0 28.9 36.2 2.8 31.6 

EAGLE_W (July) 58.6 2.9 0.0 15.2 0.0 9.7 

EAGLE_M (July) 10.5 0.0 0.5 1.5 0.0 0.0 

CLEAR (July) 14.2 0.0 15.0 16.9 2.5 3.0 

DEEP (July) 63.4 0.0 55.1 71.9 2.3 7.0 

RICHARDSON (July) 77.2 0.0 3.1 71.5 0.0 4.3 

ROCK (July) 56.2 0.0 51.6 72.1 0.3 22.0 

SIEBEN (July) 81.8 0.0 82.8 96.7 1.2 5.0 

43 
Figure 15. Relations between water quality and indicator algal taxa (as percent relative biovolume) in the Clackamas River Basin, Oregon, 

July 1998. 

N-heterotrophic taxa—N-heterotrophic taxa 

were most abundant at three of the lower-basin tributary sites (DEEP, ROCK, and SIEBEN), where they 

composed more than 50% of the relative biovolume 

(table 10). The highest concentrations of dissolved 

organic N (dissolved Kjeldahl nitrogen, DKN) also 

occurred at these sites. N-heterotrophic taxa composed 

up to 30% of the total algal biovolume at sites where 

organic N was not detected (fig. 15), although the 

reporting limits for organic N were relatively high 

(100 μg/L, appendix 1). Moderate proportions 

(15–25% relative biovolume) of these taxa also 

occurred at some middle-basin tributary sites 

(SFCLACK, WINSLOW, NFCLACK) and at some 

lower main-stem sites (CR_BLNFK, CR_MCIVER, 

and CR_BARTON, table 10). 

44 
Eutrophic taxa—The abundance of algal taxa 

that thrive in nutrient-rich water was generally lowest 

in May and increased in July and September. Eutrophic 

taxa dominated algal assemblages at the four lowerbasin tributary sites most affected by agriculture and 

urban development (RICHARDSON, DEEP, ROCK, 

and SIEBEN), where they composed between 72% and 

97% of the total algal biovolume in July (table 10). The 

eutrophic and N-heterotrophic diatom Melosira varians 

was the dominant diatom taxon at the three latter sites. 

Reimer (1962) noted the success of this taxon in streams 

with appreciable NO3

-

 content, which may explain its 

success in these Clackamas Basin streams. Eutrophic 

taxa were also dominant at NFCLACK, CR_MCIVER, 

and CR_99E, making up >50% of the relative algal biovolume in July. 

Oligotrophic taxa—Only six algal taxa were 

found that are considered to be indicative of low 

nutrient concentrations (appendixes 3 and 4), generally 

making up less than 5% of the relative biovolume 

(table 10). The highest relative biovolumes of oligotrophic taxa occurred at tributary sites, including FALL, 

NFCLACK, and OAK_BLTLK (table 10), where the 

SRP concentrations were less than 3 μg/L. The highest 

relative biovolume of oligotrophic taxa occurred at 

FALL (21%), where the soluble nutrient concentrations 

were mixed: the DIN concentration was 116 μg/L, 

whereas the SRP concentration was <1 μg/L (table 7). 

This suggests that oligotrophic taxa might be a better 

indicator of low P conditions, rather than low N. 

Silt-tolerant taxa—From May to September, the 

proportion of silt-tolerant taxa increased at sites in the 

upper basin, reaching about 20% relative biovolume 

at CR_3LYNX and CR_ABNFK. These taxa were 

less abundant at lower-basin main-stem sites (<10% in 

July and September), compared with sites in the upper 

main stem (table 10), possibly due to sediment interception by the reservoirs. The highest percentage of silttolerant taxa for the lower-basin tributary sites occurred 

at ROCK, where they accounted for 22% of the total 

biovolume. 

Reservoir Conditions 

North Fork Reservoir 

Profiles of Field Parameters 

Water temperature—Water temperatures in 

North Fork Reservoir were highest at the surface due, 

in part, to the deep-water release depth (130 feet), 

which entrains cooler water through the reservoir, 

leaving the solar-warmed water near the surface. Water 

temperatures near the North Fork Dam (at NFKRES_1) 

increased seasonally from May to August at all depths, 

reaching a maximum temperature of 18.7°C at the surface (fig. 16). Instantaneous surface water temperatures 

in the reservoir indicated possible exceedances of the 

State water-temperature criterion from June through 

September (table 5), although temperature criteria 

are based on the 7-day average of the maximum daily 

temperature, not single point measurements as were 

collected during this study. Surface-water temperatures 

were generally higher at the mid-reservoir sampling 

site (NFKRES_2) compared with NFKRES_1 during 

all months except September, whereas bottom temperatures were generally lower at NFKRES_2. 

Figure 16. Monthly temperature profiles in North Fork Reservoir, station 1 (NFKRES_1), March–September 1998. 

45 
Longitudinal temperature measurements in North 

Fork Reservoir in August 1997 showed that surface 

water temperature between the inflow and NFKRES_1 

increased 6°C, with most of the warming occurring in 

the uppermost reaches of the reservoir, around RM 32 

(fig. 17). 

Figure 17. Longitudinal profile of water temperature and soluble 

reactive phosphorus concentration in the upper Clackamas River 

and North Fork Reservoir, August 1997. (See glossary for explanation of site codes; measurement times are given in parentheses.) 

Dissolved oxygen—Concentrations of DO at 

NFKRES_1 and NFKRES_2 ranged from 8.6 to 

11.5 mg/L (87 to 105% saturation) and showed 

variation with water depth that was partly related to 

variations in water temperature (fig. 18). The DO at 

NFKRES_1 and NFKRES_2 tended to be higher 

near or at the surface than toward the bottom, except 

in August, when both the DO and pH were slightly 

lower at the surface than at the bottom. 

DO concentrations were high (>11 mg/L) in 

March and April at NFKRES_1, but were lower in 

June, when concentrations were between 9.5 and 

10.2 mg/L, which is less than the State criterion of 

11 mg/L (table 5); however, DO criteria are based on 

the 30-day average of the minimum concentration, not 

single point measurements as were collected during 

this study. The DO concentrations at NFKRES_1 

were less than 11 mg/L throughout the water column 

in July and September 1998. Minimum concentrations 

of DO at NFKRES_1 were between 87% and 90% 

saturation from June to September (figs. 18 and 19). 

Figure 18. Depth profiles of water temperature, pH, and dissolved 

oxygen concentration in North Fork Reservoir, station 1 (NFKRES_1), 

August 1998. (Extremes in dissolved oxygen percent saturation also 

are shown.) 

DO was severely depleted in the hypolimnion of North Fork 

Bay (NFKRES_B), the arm of North Fork Reservoir where the 

North Fork of the Clackamas River enters. In July, August, 

and September, the DO concentrations at NFKRES_B were 

less than 0.5 mg/L. Anoxia at this site coincided with increasing nutrient concentrations in the hypolimnion, presumably 

from decomposition of organic material at the bottom. 

pH—The pH at NFKRES_1 ranged from 6.8 to 8.1 units, 

with the latter, highest value occurring at the surface in March. 

The pH was between 0.2 and 0.4 units higher at the surface 

than at the bottom during all samplings except August, when it 

was lowest at the surface (6.8 units) and increased to 7.2 units 

at the bottom (fig. 18). The lowest pH value in North Fork 

Reservoir (6.3 units) was observed in August in the hypolimnion at NFKRES_B. 

46 
Figure 19. Seasonal variations in water-quality and environmental variables at stations 1 and 2 in North Fork Reservoir, 

April–September 1998. (Nutrient abbreviations are listed in the glossary. Zero values for nitrogen and phosphorus 

compounds indicate that the concentration was less than the minimum reporting levels [appendix 1].) 

47 
Specific conductance—SC increased in North 

Fork Reservoir from March to September from about 

53 to 69 μS/cm, and showed only slight variations 

with depth at both sampling stations. The highest SC 

value measured in the reservoir (175 μS/cm in August) 

occurred at NFKRES_B near the bottom, where nutrient concentrations were highest and DO was depleted. 

Nutrient and Algal Conditions 

Nutrients—Nutrient concentrations in North 

Fork Reservoir were at low-to-moderate levels, and 

varied seasonally, longitudinally between stations, 

and also with depth (table 11 and fig. 19). Most of the 

dissolved, bioavailable N detected was in the form of 

nitrate (NO3

-

), and organic N (with higher detection 

levels) was found in 20% of samples at concentrations 

of 101–220 μg/L. Nitrogen concentrations were 

especially low (mostly nondetectable) until late 

summer, when N-fixing blue-green algae (Anabaena 

circinalis and A. spiroides) became abundant. In 

September, NO3

-

 was detected at all sampling depths 

at both stations (fig. 19). 

Phosphorus was detected more frequently than N, 

occurring in all samples collected from the reservoir, at 

concentrations ranging from 5 to 12 μg/L (table 11). 

From May to June, SRP (and TP) concentrations at 

both stations increased at all depths, as P concentrations in the upper Clackamas River also increased 

(fig. 9). In July, however, SRP concentrations declined, 

despite the continued high (and increasing) concentration in the main stem, probably the result of algal 

uptake of P. The longitudinal decrease in SRP concentration observed in August 1997 (fig. 17), and the 

lower concentrations near the surface, also demonstrate 

the demand for P by algae in the reservoir. Algal 

growth continued into July, when the highest chl a 

concentration for 1998 (3.3 μg/L) occurred at the 

upstream station 2 (fig. 19). These patterns indicated 

that small algal blooms were occurring between June 

and July, reducing dissolved nutrients (from algal 

uptake) while increasing nutrients contained in algal 

cells (TP) and decreasing water transparency. 

In August, concentrations of TP and chl a were 

lower, and the Secchi-disk depths increased slightly, 

reflecting the lower phytoplankton abundance and 

greater water transparency. From August to September, 

NO3

- concentrations increased at all sampling depths 

at NFKRES_1, from below detection to 8–9 μg/L 

(fig. 19). The seasonal maximum concentration 

of DKN at NFKRES_1 (220 μg/L) also occurred in 

September. 

Silica concentrations increased seasonally, ranging from 14.1 to 20.5 mg/L, and did not vary much with 

depth or longitudinally between stations. This suggests 

a low demand for silica by diatom phytoplankton, 

which utilize silica during growth. The relative scarcity 

of DIN, combined with moderate amounts of SRP, 

resulted in low DIN:SRP ratios (0.8 to 1.2; table 11), 

which indicates that N was in short supply relative to 

demand. 

Phytoplankton—Sixty-seven phytoplankton taxa 

were identified in North Fork Reservoir (appendix 6). 

Three distinct phytoplankton assemblages were noted: 

small flagellates (Rhodomonas minuta, Cryptomonas 

erosa reflexa, and Euglena sp.) in May through July; 

Anabaena and flagellates in July through September; 

and Aulacoseria granulata in September. 

Blue-green algae bloomed each year in North Fork 

Reservoir, particularly during mid-to-late summer. The 

highest chl a concentration (24 μg/L) was measured at 

the surface in September 1996 during a bloom of Anabaena circinalis shortly after the onset of fall turnover. 

Although this value is relatively high (the State Action 

Level is 15 μg/L, based on a 3-month average), lower 

chl a values were measured in 1997 (maximum of 

7 μg/L) and 1998 (maximum of 3.3 μg/L). In July 1997, 

another bloom of Anabaena circinalis occurred in 

North Fork Reservoir at a cell density of 749 cells/mL 

(cells per milliliter) at the surface, where the highest 

water temperature (20.4°C), highest pH (7.7 units), and 

highest DO value (114% saturation) was observed. 

In August 1998, another bloom of Anabaena 

(560 cells/mL) occurred in North Fork Reservoir, where 

it composed 20% of the total biovolume and 50% of the 

relative abundance at the surface. This bloom occurred 

as the surface water temperature reached its seasonal 

maximum of 18.6°C (fig. 19). In September, a population of Aulacoseria granulata, a filamentous diatom, 

developed in the reservoir, composing nearly 90% of the 

phytoplankton biovolume. At the same time, however, 

the abundance of Anabaena, remained about the same 

(fig. 19). 

Chlorophyll a values in North Fork Reservoir 

were low in 1998 (0.3–3.3 μg/L) despite these small 

blooms. Concentrations of chl a and TP were highest in 

June and July, when the seasonal minimum Secchi-disk 

depth occurred (fig. 19). Slightly higher chl a concentrations generally occurred at NFKRES_2 compared 

with NFKRES_1 (table 11), indicating that blooms 

may be forming near the inlet, where phosphorus-rich 

water was mixed with warm water in the shallow upper 

reservoir. 

48 
-- -- -- -- --

-- -- -- -- --

-- -- -- -- --

-- -- -- -- --

-- -- -- -- --

-- -- -- -- --

-- -- -- -- --

-- -- -- -- --

-- -- -- -- --

Table 11. Nutrient and algal conditions in North Fork Reservoir, Oregon, April–September 1998 

[Samples were collected from the log boom near North Fork Dam (NFKRES_1), mid-reservoir near the powerlines crossing (NFKRES_2), and from the 

center of North Fork Bay (NFKRES_B); site locations are shown on plate 1; ft, feet; μg/L, micrograms per liter; mg/L, milligrams per liter; mL, milliliter; 

na, not analyzed; --, not applicable; <, less than minimum reporting levels (see appendix 1); E, epilimnion; M, metalimnion; R, water release depth; H, 

hypolimnion] 

North Fork Reservoir Station 1 (NFKRES_1) 

April May June July August September 

Parameter E E M R H E M R H E M R H E M R H E M R H 

Sampling depth (ft) 1 1 25 65 100 1 4 40 100 1 10 60 90 1 15 60 90 10 27 60 90 

NH4 

+ (μg/L) 2 <2 <2 <2 <2 <2 <2 3 <2 <2 <2 <2 <2 <2 5 <2 <2 <2 <2 <2 <2 

NO3 

- (μg/L) 7 <5 <5 <5 <5 <5 <5 9 8 <5 5 5 <5 <5 <5 <5 <5 9 9 9 8 

SRP (μg/L) 12 6 7 7 7 8 9 10 8 7 8 7 6 8 10 10 10 8 8 10 10 

DIN:SRP 0.8 <1.2 <1 <1 <1 <1 <1 1.2 1.0 <1 <1 <1 <1 <1 <1 <1 <1 1.1 1.1 <1 <1 

TP (μg/L) 13 7 9 8 9 21 12 12 13 17 17 15 15 11 13 14 16 14 15 18 18 

SiO2 (mg/L) na 14.1 14.6 14.6 14.6 15.9 15.0 14.5 16.1 18.1 17.9 18.4 18.2 20.1 19.5 20.5 20.0 21.0 21.3 20.4 20.6 

Chlorophyll a (μg/L) 0.2 0.7 0.3 0.3 0.3 1.7 1.2 0.3 1.3 2.0 na 2.8 0.5 0.5 na 0.3 na 1.2 1.5 0.8 0.7 

Anabaena (cells/mL) na 0 0 0 5 0 0 0 35 0 0 0 na 566 0 0 144 356 0 0 40 

North Fork Reservoir Station 2 (NFKRES_2) 

April May June July August September 

Parameter E E M R H E M R H E M R H E M R H E M R H 

Sampling depth (ft) na 1 6.5 30 1 10 30 1 10 25 1 12 25 1 20 25 

NH4 

+ (μg/L) na <2 <2 <2 <2 3 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 

NO3 

- (μg/L) na <5 <5 <5 <5 7 <5 <5 <5 <5 <5 <5 <5 8 9 9 

SRP (μg/L) na 6 5 7 8 9 10 7 6 7 8 8 11 10 11 12 

DIN:SRP na <1.2 <1.4 <1 <1 1.1 <1 <1 <1.2 <1 <1 <1 <1 <1 <1 <1 

TP (μg/L) na 9 8 10 11 13 11 19 19 10 12 13 21 15 20 21 

SiO2 (mg/L) na 14.4 14.4 15.1 15.9 15.9 15.4 18.0 18.0 18.5 19.5 20.1 20.3 19.9 19.9 19.6 

Chlorophyll a (μg/L) na 0.6 0.8 na 2.8 na na 3.2 3.3 1.7 1.0 0.8 0.5 1.1 0.9 0.7 

Anabaena (cells/mL) na 0 14 na 0 0 0 0 0 0 0 0 0 289 1 1 

North Fork Bay (NFKRES_B) 

August September 

Parameter E H E H 

Sampling depth (ft) 1 25 10 25 

NH4 

+ (μg/L) 6 67 38 99 

NO3 

- (μg/L) 24 37 50 47 

SRP (μg/L) 3 1 2 1 

DIN:SRP 10 104 44 146 

TN (μg/L) 306 329 192 237 

TP (μg/L) 13 28 13 24 

SiO2 (mg/L) 20 19.3 20.4 20.4 

Chlorophyll a (μg/L) 7.2 na 2.9 na 

49 
Timothy Lake 

Profiles of Field Parameters 

Water temperature—Timothy Lake had already 

started to stratify with respect to temperature by May, 

when the water temperature was 13.7°C at the surface 

and 5.9°C at the bottom (fig. 20). Warming in the lake 

continued until August, when the maximum water temperature of 20°C occurred. Surface water temperatures 

in Timothy Lake were high enough to have exceeded 

the State temperature criterion in May, August, and 

September (table 5). Fall turnover started after the 

August sampling, and by September, surface water 

temperatures decreased while bottom temperatures 

increased (fig. 20), showing the effects of mixing within 

the reservoir. 

Dissolved oxygen—Concentrations of DO in 

Timothy Lake were more dynamic compared with 

North Fork Reservoir, with higher DO in the metalimnion and lower DO in the hypolimnion. High DO levels 

(up to 121% saturation), indicative of phytoplankton 

photosynthesis, were observed in May, August, and 

September (figs. 21 and 22). Concentrations of 

DO in the hypolimnion of Timothy Lake were lower 

than 11 mg/L and so possibly did not meet the State 

criterion from May to September. DO criteria, however, 

are based on the 30-day mean of the daily minimum 

concentrations, not instantaneous measurements as 

were collected during this study. DO concentration 

near the bottom of Timothy Lake steadily declined 

from 9.8 mg/L (87% saturation) in May to 0.9 mg/L 

(8% saturation) in September (fig. 22), and coincided 

with increasing concentrations of N in the lake. 

pH—The highest pH measured in Timothy Lake 

(8.6 units in July 1996) occurred in the metalimnion 

during an Anabaena bloom, slightly exceeding the 

State criterion (table 5). In 1998, the pH in Timothy 

Lake ranged from 6.8 to 8.2 units, and the maximum pH 

increased 0.5 pH units from May to September (fig. 22). 

The pH decreased slightly with increasing depth, 

especially in August (fig. 21), and a seasonal decline 

of 0.7 pH units was observed in the hypolimnion from 

May to September. 

Specific conductance—SC values in Timothy 

Lake were slightly higher at the surface and declined 

with depth, although SC varied only about 5 μS/cm 

throughout the water column during each sampling. 

The SC exhibited a slight seasonal increase from about 

48 μS/cm in May to 54 μS/cm in September. 

Nutrient and Algal Conditions 

Nutrients—Dissolved N and P concentrations 

in Timothy Lake were mostly low, especially SRP, 

which was always less than or equal to the MRL of 

1 μg/L (table 12 and fig. 22). DIN was detected more 

frequently, at concentrations ranging from 5–18 μg/L, 

with the highest concentrations typically occurring in 

the hypolimnion (fig. 22). DIN:SRP ratios, therefore, 

ranged from 5 to 18, with the higher ratios likewise 

occurring in the hypolimnion (table 12). With SRP 

generally <1 μg/L and DIN typically low too, Timothy 

Lake was apparently P limited most of the time, with 

apparent co-limitation by N and P during some periods. 

Figure 20. Water temperature profiles in Timothy Lake at the log boom, May–September 1998. 

50 
Figure 21. Depth profile of water temperature, pH, and dissolved oxygen in Timothy Lake at the log boom, August 1998. 

TP concentrations ranged from 3–15 μg/L 

and showed a seasonal increase from May to July, 

then declined in August and September (fig. 22). 

Regression analysis showed that TP concentrations in 

the epilimnion and metalimnion were significantly correlated with concentrations of chl a (fig. 23). In other 

words, much of the TP occurred within algal cells. 

Phytoplankton—Forty phytoplankton taxa 

were identified in Timothy Lake (appendix 7), 

including small flagellates (Rhodomonas minuta, 

Cryptomonas erosa reflexa, and Chlamydomonas sp.), 

blue-green algae (Anabaena circinalis, Microcystis, 

and Schizothrix calcicola), and diatoms (Asterionella 

Formosa, Urosolenia sp., and Aulacoseria granulata). 

The abundance of Microcystis in Timothy Lake was 

low (10 cells/mL), but its presence is noteworthy 

because this alga often produces toxins (Carmichael, 

2001; Carmichael and others, 2001). Microcystis 

was not found in North Fork Reservoir during this 

study. 

Blue-green algae blooms were observed each 

year in Timothy Lake, with the largest bloom occurring 

in July 1996, when visible Anabaena colonies clouded 

the surface waters of the lake. The chl a concentration 

was 18 μg/L at the surface, but may have been higher 

at mid-depth (about 20 feet), where the maximum pH 

(8.6 units) and DO (108% saturation) values occurred. 

Although this chl a value is relatively high (the State 

Action Level is 15 μg/L, based on the 3-month mean), 

such high chl a values were not typically observed 

in Timothy Lake. In July 1997, another bloom 

occurred, with Anabaena composing 85% of the 

relative biovolume at the surface with an abundance 

of 3,300 cells/mL. Despite the high cell numbers, the 

chl a concentration was low (0.7 μg/L), which could 

indicate a declining (senescing) population. 

In May 1998, the abundance of Anabaena 

circinalis in Timothy Lake exceeded 3,600 cells/mL 

throughout the water column, composing about 80% 

of the algal biovolume. The highest cell density and 

chl a concentration (7,600 cells/mL and 7 μg/L) 

occurred at mid-depth (22 feet, table 12 and fig. 22). 

Concentrations of Anabaena declined thereafter, and 

higher concentrations were observed towards the bottom of the reservoir, especially in July and August. 

In July 1998, a population of Schizothrix 

calcicola, another blue-green alga, developed in 

Timothy Lake, reaching a density of 3,000 cells/mL at 

a depth of 40 feet (table 12). Concentrations of chl a 

and TP increased during this bloom, and the seasonal 

minimum Secchi-disk value also occurred at this time 

(fig. 22). Smaller quantities of diatoms and small 

flagellates dominated surface and metalimnetic samples in September, when Anabaena circinalis shared 

dominance with small flagellates in the hypolimnion 

(appendix 7). 

51 
Figure 22. Seasonal variations in water-quality and environmental variables 

in Timothy Lake, May–September 1998. (Nutrient abbreviations listed in 

the glossary. Zero values for nitrogen and phosphorus compounds indicate 

that the concentration was less than the minimum laboratory reporting levels 

[appendix 1].) 

52 
Table 12. Nutrient and algal conditions in Timothy Lake, Oregon, May–September 1998 

[Data collected from the log boom at Timothy Lake. Site location is shown on plate 1; E, epilimnion; M, metalimnion; R, water release depth; 

H, hypolimnion; ft, feet; μg/L, micrograms per liter; mg/L, milligrams per liter; mL, milliliter; na, not analyzed; <, less than minimum reporting 

levels (see appendix 1)] 

May June July August September 

E M R H E M R H E M R H E M R H E M R H 

Sampling depth (ft) 1 22 60 85 1 37 60 85 1 40 60 80 1 24 60 85 10 35 60 85 

NH4 

+ (μg/L) <2 <2 <2 <2 2 <2 5 3 <2 <2 4 <2 <2 <2 <2 13 <2 <2 <2 4 

NO3 

- (μg/L) <5 <5 <5 <5 7 6 9 7 <5 <5 <5 5 <5 <5 <5 5 6 5 5 5 

SRP (μg/L) <1 <1 <1 <1 <1 1 <1 <1 <1 <1 1 <1 1 <1 1 1 <1 <1 1 1 

DIN:SRP na na na na >9 6 >14 >10 na na >4 >5 <7 na na 18 >6 >5 5 9 

TP (μg/L) 6 14 4 5 8 5 5 5 15 11 10 16 3 6 9 7 3 5 6 7 

SiO2 (mg/L) na na na na 16.5 15.9 15.9 17.2 17.4 17.5 17.4 17.6 17.6 18.3 17.2 17.7 18.1 18.6 17.6 17.6 

Chlorophyll a (μg/L) 3.4 7.0 1.4 na 3.2 3.2 0.9 0.7 3.5 6.1 2.3 na 0.9 2.4 4.5 na 1.7 3.3 1.2 1.1 

Anabaena (cells/mL) 3,668 7,620 5,789 na 2,033 398 104 8 742 1,850 2,840 na 0 860 2,950 na 37 0 214 3 

Figure 23. Phytoplankton chlorophyll a–total phosphorus 

relationship in Timothy Lake, May–September 1998. 

(Includes epilimnion and metalimnion samples only.) 

Reservoir Drawdown 

The annual fall drawdown of Timothy Lake 

started unusually early in 1998, and releases up to 

220 ft3/s occurred for about a 3-week period in July and 

early August. Steady releases from the reservoir began 

on September 23, when streamflow at the USGS gage 

downstream of Timothy Lake increased 420%, from 

81 to 343 ft3/s (table 13). Streamflow at the USGS 

gage upstream of Harriet Lake (at OAK_PP, about 

10 miles downstream from Timothy Lake) increased 

140%, from 440 to 640 ft3/s during drawdown. 

Reservoir drawdown increased stream water 

temperatures about 2–2.5°C in the Oak Grove Fork, 

while a smaller increase in temperature (0.3°C) 

was observed in the Clackamas River at CR_3LYNX 

(table 13). Drawdown appeared to increase concentrations of DOC at downstream sites in the Oak Grove 

Fork and upper Clackamas River, whereas increases 

in SOC concentrations were observed only at the 

two most downstream sites (table 13). The observed 

declines in concentrations of SRP, SiO2, and SC were 

consistent with chemical conditions in Timothy Lake 

at the water release depth prior to drawdown (table 13) 

indicating dilution by Timothy Lake water. 

The concentrations of Anabaena in the Oak 

Grove Fork downstream of Timothy Lake (at 

OAK_BLTLK) were unaffected by drawdown, 

but the higher streamflow increased the total numbers 

(load) of Anabaena cells being transported to 420% 

of predrawdown levels. Anabaena, which was not 

detected at CR_3LYNX prior to drawdown, was 

found at a low concentration (6 cells/mL) during drawdown. 

In 1997, resting “seeds” of Anabaena, called 

akinetes, were observed in water samples collected 

from two sites in Oak Grove Fork (OAK_BLTLK 

and OAK_PP) during drawdown. These cells are 

capable of germinating into viable cells (Fogg and 

others, 1973) and may be a source of Anabaena for 

downstream reservoirs. It is unknown, however, to 

what extent Anabaena filaments or akinetes survive 

in the river between Timothy Lake and downstream 

reservoirs. 

53 
--

Table 13. Conditions in the Oak Grove Fork and upper main-stem Clackamas River before and during the drawdown of Timothy Lake, 

Oregon, September 1998 

[Water releases began midday on September 23; predrawdown samples were collected on September 23; drawdown samples were collected on 

September 24 (stream sites) and on September 25 (Timothy Lake); site codes and parameter definitions are listed in the glossary; ft3

/s, cubic feet 

per second; °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25°C; mg/L, milligrams per liter; %, percent; μg/L, micrograms per liter; 

#, number; <, less than minimum reporting levels; --, not applicable; na, not analyzed] 

Timothy Lake Oak Grove Fork Oak Grove Fork Clackamas River 

(60 feet) (OAK_BLTLK) (OAK_PP) (CR_3LYNX) 

Parameter During Before During Before During Before During 

Streamflow (ft3/s)


Water temperature (°C)


Specific conductance (μS/cm)


pH (standard units)


DO (mg/L)


DO (% saturation)


NH4

+ (μg/L)


NO3

- (μg/L)


TP (μg/L)


SRP (μg/L)


SiO2 (mg/L) 

SOC (μg/L)


DOC (μg/L)


Chlorophyll a (μg/L)


Anabaena spp. (# cells/mL)


10.5 

50 

7.3 

4.2 

42 

4 

5 

6 

1 

17.6 

na 

na 

1.2 

214 

81 

8.3 

57 

7.8 

10 

95 

<2 

10 

11 

7 

18.4 

300 

600 

1.0 

46 

343 

10.3 

52 

7.6 

10 

99 

<2 

7 

7 

1 

17.4 

300 

900 

1.6 

46 

442 

7.0 

57 

7.6 

11.2 

99 

<2 

10 

15 

13 

18.8 

<200 

300 

0.3 

0 

644 

9.5 

55 

7.8 

10.7 

101 

<2 

7 

15 

10 

18.2 

400 

500 

0.9 

8 

816 

9.9 

66 

7.7 

10.2 

94 

<2 

7 

20 

16 

20.4 

200 

400 

0.4 

0 

947 

10.2 

65 

na 

9.8 

91 

<2 

9 

19 

13 

19.1 

300 

500 

0.7 

6 

Ground-Water Conditions 

Ground-water samples contained high concentrations of nutrients compared with stream samples 

(table 14). Concentrations of NH4

+, SRP, iron, 

SiO2, alkalinity, and SC were higher in the wells, 

where concentrations of DO were notably low 

(≤0.2 mg/L). Springs, however, were well oxygenated 

(9–12 mg/L; table 14), with high NO3

- concentrations 

(up 3,000 μg/L) and relatively higher chloride (Cl-

) 

concentrations, compared with wells (table 14). 

Arsenic was detected in all three well water samples, 

at concentrations between 2 and 6 μg/L (table 14). 

Although springs and seeps occur throughout the 

upper basin, inputs of ground water to the Clackamas 

River were most apparent between Estacada and 

Barton, where an unexplained increase in streamflow 

of between 8.5 and 27% was observed, possibly from 

inputs of ground water (refer to streamflow results, 

fig. 6, p. 27). 

Table 14. Chemical characteristics of ground-water wells and springs in the lower Clackamas River Basin, Oregon, January 1999 

[Sites were located within 1 mile of the Clackamas River (plate 1). Site codes are listed in table 3 and nutrient abbreviations are listed in the glossary; 

μg/L, micrograms per liter; mg/L, milligrams per liter; <, less than minimum reporting levels; na, not analyzed] 

Constituent 

Site 

Depth 

(feet) 

DO 

(mg/L) 

NH4 

+ 

(μg/L) 

NO3 

-

(μg/L) 

SRP 

(μg/L) 

SiO2 

(mg/L) 

Cl-

(mg/L) 

Iron 

(mg/L) 

Arsenic 

(μg/L) 

WELL_1 103 0.2 480 <50 520 45 1.5 140 6 

WELL_2 85 0.1 570 <50 390 42 2.0 140 4 

WELL_3 80 0.1 260 <50 160 39 1.9 170 2 

SPRING_1 surface 11.9 <20 680 40 30 2.6 73 na 

SPRING_2 surface 8.7 20 3,000 30 31 7.8 21 na 

SPRING_3 surface 10.8 20 2,100 40 31 4.5 <10 na 

SPRING_4 surface na na 700 30 na na na na 

SPRING_5 surface na na 160 10 na na na na 

54 
Relations Between Land Use and Nutrient 

and Algal Conditions 

Forest Management 

Nutrients—Nutrient concentrations in streams 

draining forestland showed spatial differences among 

sites, with higher levels of N and lower levels of P 

occurring at sites in the middle basin, and the opposite 

(low N and high P) occurring at upper-basin sites. 

Nitrate levels in middle-basin tributaries increased 

steadily as the percentage of nonforest upland in the 

basins increased (fig. 24), which suggests that higher 

N levels might be related to forest management. As 

described earlier, nonforest upland includes areas in 

Landsat images without a green vegetation signature 

(table 4), which were interpreted as recently harvested 

land. Tree removal reduces uptake of N by vegetation in 

the short term, and post-harvest burning of slash debris 

releases N (Fenn and others, 1998). Moreover, fertilization of forestland with N, which is discussed in more 

detail later in this report, also may contribute to elevating N levels in streams if fertilizer leaches into ground 

water. Other potential sources of N, however, including 

proliferations of N-fixing plants such as red alder and 

scotchbroom, atmospheric deposition, and wildfires, 

also may contribute N to streams. NO3

- concentrations 

at the upper-basin tributary sites, however, were mostly 

low and did not increase with the percentage of nonforest upland in these basins, despite the sometimeshigher levels of nonforest upland. This may be due to 

the higher P availability, which may have induced 

uptake of N by algae in the upper-basin streams. 

A similar positive relationship was found between 

nonforest upland and TP concentration for all forested 

tributary sites (fig. 24). Phosphorus in the upper basin 

probably originates from a geologic source, as TP 

concentrations were positively correlated with silica 

(fig. 12). Silica is an important component of most 

soils and when taken together, these associations 

suggest that forest management activities (timber 

harvesting or associated road system) might be enriching ground water and streams with P through erosion 

or dissolution of naturally occurring phosphorus-rich 

volcanic soils. 

Algal biomass—Algal biomass in streams 

draining forestland also showed spatial differences 

among sites, with the highest chl a values ranging from 

95 to 235 mg/m2, occurring at CLEAR, SFCLACK, 

FISH, and OAK_RAIN (table 7). Algal biomass at 

other sites in forested basins was lower, possibly 

due to reduced availability of light needed for photosynthesis and/or lower nutrient concentrations (DIN 

was not detected, and SRP was ≤3 μg/L; table 7). Algal 

biomass at sites in “reference” basins containing high 

amounts (77–91%) of mature forest was lowest of all, 

ranging from 11 to 20 mg/m2 chl a (ROARING and 

EAGLE_W; table 7). 

Agriculture and Urban Development 

Nutrients—Water quality was most impaired 

at the four lower-basin tributary sites (DEEP, 

RICHARDSON, ROCK, and SIEBEN), located in 

basins containing moderate-to-high proportions 

(28–62%) of agricultural and urban land. The highest 

nutrient concentrations and the highest SC values 

occurred at these sites (table 7). Moreover, concentrations of SRP and SC values generally increased as the 

percentage of agricultural and urban land increased. 

Figure 24. Relations between percentage of nonforest upland and concentrations of nitrate (A) and total phosphorus (B) at forested 

tributary sites in the Clackamas River Basin, Oregon, July 1998. 

55 
Due to the relatively small streamflow values in 

Rock and Richardson Creeks (about 1–2 ft3

/s in July), 

nutrient loads from these streams were less than from 

most other tributaries (fig. 11). Sieben Creek, however, 

with its high concentration of NO3

-

, contributed a disproportionately high load of N given its small drainage 

area (<2 square miles) and low streamflow (1 ft3/s, 

table 7). The higher streamflow at DEEP (26 ft3

/s), 

combined with relatively high nutrient concentrations 

(1,045 μg/L NO3

-

 and 68 μg/L SRP), resulted in the 

highest loads of N and P for the lower-basin tributaries 

(fig. 11). The yield of DIN (load per unit basin area) 

was highest at SIEBEN and DEEP (fig. 10). 

Eagle and Clear Creeks, which drain basins 

containing a relatively low proportion of agricultural 

and urban land (7–12%), had lower nutrient concentrations compared with Deep, Richardson, Rock, 

and Sieben Creeks (table 7). The higher streamflows 

at EAGLE_M and CLEAR, however, resulted in 

relatively high NO3

-

 loads for these sites (fig. 10) 

despite their lower NO3

- concentrations. 

Algal biomass—Algal biomass at 3 of the 4 

sites most affected by agricultural and urban influences 

(DEEP, ROCK, and SIEBEN) was within or well 

above the nuisance level of 100–150 mg/m2

 chl a in 

July (fig. 9 and table 7). The chl a at RICHARDSON, 

however, was much lower (51 mg/m2

), possibly 

due to the higher density of grazing macroinvertebrates 

that were observed during sampling. Algal taxa 

indicative of high nutrient conditions (eutrophic taxa), 

however, composed between 72 and 97% of the algal 

biovolume at all four of the lower basin sites, including 

RICHARDSON (table 10). 

Effects of Hydroelectric Projects 

on Stream Conditions 

Streamflows 

About 70 miles of stream reaches (53 miles of the 

main stem and 15 miles of the Oak Grove Fork) 

are affected by the hydroelectric projects. The lower 

6 miles of the Oak Grove Fork downstream from 

Harriet Lake Dam, for example, is typically dewatered 

and all of the flow (several hundred cubic feet per 

second) is diverted to Frog Lake (the forebay of the Oak 

Grove Powerhouse, fig. 2). As a result, streamflow 

near the mouth of the Oak Grove Fork was only 22 ft3

/s 

in July (at OAK_RAIN, table 7). For comparison, 

streamflow at OAK_PP, upstream from the diversion, 

was 376 ft3

/s, or 17 times higher than at OAK_RAIN 

at this time (Hubbard and others, 1999). 

The effects of the hydroelectric projects on mainstem streamflows were most apparent when discharge 

at the Three Lynx gage was less than about 2,500 ft3

/s 

—the approximate value below which power peaking 

typically occurs. During peaking operations, daily fluctuations in streamflow occurred in the Clackamas River 

downstream from the Oak Grove Powerhouse (fig. 7). 

Water releases from Frog Lake occur during the day 

when power demands are high, producing higher daytime flows, which are followed by smaller releases (and 

lower streamflows) at night when Frog Lake is refilled. 

During the July sampling (see shaded area in 

fig. 7), power peaking increased the streamflow in 

the upper Clackamas River by 51% in one day, from 

890 ft3/s to 1,340 ft3/s. Daily fluctuations in streamflow 

of more than 300 ft3/s were recorded in the upper 

Clackamas River on about 50% of the days in 1998 

(Gomez and Sullivan Engineers, P.C., 2000). A 

300 ft3/s change in streamflow equates to an approximate 0.6-foot fluctuation in river stage at a discharge 

of 1,500 ft3/s. Typical summertime fluctuations were 

between 400 and 500 ft3/s (the largest daily fluctuation 

of about 700 ft3/s occurred in July). To accommodate 

the streamflow fluctuations, water was alternately 

stored and released in downstream hydroelectric 

impoundments, causing fluctuating streamflows 

downstream from River Mill Dam, where discharge 

increased 55% in one day, from 998 to 1,550 ft3/s, 

during the July sampling (fig. 7). 

Water Quality 

Water temperature—The effects of the hydroelectric projects on water temperatures in the main-stem 

Clackamas River were most apparent during low-flow 

in September, when streamflows were lowest. At this 

time, discharges from the Oak Grove Powerhouse, fed 

by the cold ground waters in the Oak Grove Fork Basin, 

reduced temperature in the main stem by about 2°C. In 

late September, however, during the drawdown 

of Timothy Lake, water temperatures in the Oak Grove 

Fork were increased by roughly 2°C. 

The effects of lower streamflow on water temperature in the Oak Grove Fork caused by the upstream 

hydropower diversion (described in the preceding 

section) were apparent at OAK_RAIN in July, when the 

water temperature was 15.3°C at 2:20 p.m. For 

comparison, Roaring River, which had about 5 times 

the flow, was 13.5°C at 6:25 p.m. the same day. 

Water temperature in the Clackamas River 

increased nearly 4°C from upstream of North Fork 

56 
Reservoir to downstream of River Mill Dam in September (fig. 5), based on instantaneous temperature 

measurements between 9 and 10 a.m. Continuous data 

(not collected), however, would be more appropriate 

to evaluate warming in the projects due to variable 

project operations, which affect travel times through 

the project. Nevertheless, in August 1997, a 6°C 

longitudinal increase in surface water temperature was 

observed between the inflow to North Fork Reservoir 

and the log boom, with most of the warming occurring 

within about a mile of the reservoir inflow (fig. 17), 

resulting in water temperatures that probably did not 

meet the State water-quality criterion. 

Dissolved oxygen—Concentrations of DO in 

the Clackamas River downstream from the Oak Grove 

Powerhouse resembled those at upstream sites, and 

were close to saturation (94–97%, table 8). Immediately 

below the project reservoirs, however, concentrations 

of DO were sometimes depressed. This was particularly 

true downstream from Timothy Lake in July and 

September, when the DO saturation was 91% at OAK_ 

BLTLK (table 8), reflecting the release of hypolimnetic 

(deep) water that was nearly anoxic at the time (fig. 22). 

DO concentrations also were slightly lower in the 

Clackamas River downstream from North Fork Reservoir (at CR_BLNFK) compared with the upstream 

site (CR_ABNFK). This was most pronounced in 

September (table 8), concurrent with seasonal minimum DO values in the reservoir (fig. 19). 

pH—The pH levels in the Clackamas River 

immediately downstream from North Fork Reservoir 

were 0.3 and 0.5 pH units lower in July and September, 

respectively, compared with those at the upstream site. 

Declines in pH also were observed in the reservoir near 

the water release depth during this time (fig. 19). The 

pH values downstream from Timothy Lake (at OAK_ 

BLTLK) mirrored those at the water release depth in 

the lake, with the lowest value occurring in September 

(table 8). 

Nutrients—Nitrogen concentrations immediately 

downstream from the reservoirs were typically below 

detection. One sample collected in May immediately 

downstream from North Fork Reservoir (at CR_ 

BLNFK), however, contained 19 μg/L NH4

+. Although 

not exceptionally high, the concentration was nearly 

10 times higher than the concentration at the upstream 

site (table 8). No other NH4

+ detections were observed 

immediately downstream from either North Fork 

Reservoir or Estacada Lake. A low-level concentration 

of NO3

- was detected downstream of Timothy Lake 

(at OAK_BLTLK) during reservoir drawdown in late 

September (table 13), consistent with NO3

-

 concentrations in the lake at that time (fig. 22). 

Concentrations of P were lower immediately 

downstream from the main-stem reservoirs (North Fork 

Reservoir and Estacada Lake), compared with those 

at sites upstream from the reservoirs, especially in July 

and September (table 8 and fig. 9), indicating that the 

main-stem reservoirs were sinks for P. The SRP concentration downstream from Timothy Lake (at OAK_ 

BLTLK), however, was higher in September (8 μg/L) 

than in July (2 μg/L, table 8), possibly due to the release 

of P from reservoir sediments. The DO in Timothy Lake 

decreased with depth and was 0.9 mg/L at the bottom in 

September (fig. 22), and probably lower in the bottom 

sediments. The SRP concentration in Timothy Lake 

bottom water, however, was only 1 μg/L in September, 

which suggests that the source of the P was seepage 

water originating from within the anoxic reservoir sediments. 

Algal Conditions 

One apparent effect of the hydroelectric projects 

was to stimulate the growth of algae, particularly 

filamentous green algae below dams and/or powerhouses. Abundant growths of filamentous green algae 

(Ulothrix in May and Cladophora in July, appendix 4) 

developed downstream from North Fork Reservoir and 

Estacada Lake. The chl a was 332 and 276 mg/m2, 

respectively, at CR_BLNFK and OAK_BLTLK in 

July (fig. 9). Cladophora (a common high-biomass 

nuisance alga) composed about 30% of the total algal 

biovolume immediately downstream from North Fork 

Reservoir (at CR_BLNFK in July). This alga was not 

found at any main-stem sites upstream of North Fork 

Reservoir, but was found at other sites downstream of 

the reservoir (appendix 4). 

The highest chl a values occurred in September, at 

sites directly affected by the hydroelectric projects, with 

the highest values occurring downstream from the 

Oak Grove Powerhouse (690 mg/m2 at CR_3LYNX, 

fig. 9 and table 8) and downstream from Timothy Lake 

(545 mg/m2

 at OAK_BLTLK, table 8). The proportions 

of eutrophic algal taxa (high-nutrient indicators) also 

were typically higher immediately downstream from 

the hydroelectric projects compared with upstream 

sites (table 10). The relative proportions of eutrophic 

diatoms, for example, increased two- to threefold at 

CR_3LYNX compared with the next upstream site 

(CR_UPPER) in May, July, and September. In 

May, eutrophic taxa composed 28% and 62% of the 

biovolume downstream from North Fork Reservoir 

57 
(CR_BLNFK) and Estacada Lake (CR_MCIVER), 

respectively, whereas these taxa comprised only 9% 

of the biovolume at the upstream site (CR_ABNFK, 

table 10). Interestingly, N-fixers were nearly absent 

(0.02% of the biovolume) immediately downstream 

from North Fork Reservoir (at CR_ BLNFK) in May, 

presumably due to the higher N concentration (19 μg/L 

NH4

+), which may have eliminated the advantage that 

these taxa have over non-N-fixing algae. 

Aquatic macrophytes (rooted plants) and associated filamentous green algae also were observed at 

some locations in the hydroelectric projects, including 

the fish ladder between North Fork Reservoir and Faraday Diversion Dam, in Faraday Lake, and in the northeastern end of Timothy Lake (fig. 2), particularly in 

July and August. Fouling of canal racks and screens by 

dislodged macrophytes and algae occasionally occurs in 

the main-stem hydroelectric projects, especially in the 

fall (Doug Cramer, Portland General Electric, written 

commun., 2001). 

DISCUSSION 

Stream Nutrient Conditions 

Nutrient concentrations in the main-stem Clackamas River were dynamic and appeared to respond to 

seasonal declines in streamflow, inputs of tributaries 

with differing nutrient levels, biological processes 

such as cycles in algal nutrient uptake (growth) 

and senescence (death and decay), and in-reservoir 

processes (uptake, senescence, and sedimentation). 

Higher spring streamflows resulted in lower concentrations of P at most sites in May, for example, compared 

with July and September, when lower streamflows 

produced less dilution and hence higher concentrations 

of dissolved constituents, including P. 

The spatial distribution of nutrient concentrations 

in streams appeared related to land use and basin 

location (elevation), with the highest concentrations 

of N and P occurring at tributary sites in the lower basin, 

where most of the agriculture and urban development 

is located. Among the tributary sites at higher elevations 

in forested basins, three groups of sites were recognized: (1) the upper-basin sites, characterized by relatively high concentrations of P and low concentrations 

of N, (2) Fish Creek and the South Fork Clackamas 

River, which had intermediate concentrations of N and 

P, and (3) middle-basin sites, where concentrations of 

P were low, but N concentrations (especially NO3

-

) 

were high (tables 7 and 9). This spatial pattern generally 

corresponds to the U.S. Environmental Protection 

Agency (USEPA) Level IV Ecoregions, which are 

delineated for the Clackamas River Basin in Metro 

(1997): lower-basin sites in the Willamette Valley Foothills and Prairie Terraces Ecoregions, middle-basin 

sites in the transition area from the Western Cascades 

Lowlands Ecoregion to the Western Cascades Montane 

Highlands Ecoregion, and upper-basin sites in the 

Cascade Crest Montane Forest Ecoregion (sometimes referred to as the High Cascades Ecoregion). 

Differences in the geology, soils, vegetation, fire 

history, and land use among the different ecoregions 

are reflected in the observed pattern in N and P concentrations among the sites. 

Low DIN concentrations, low DIN:SRP ratios, 

and high abundances of N-fixing taxa in the Clackamas 

River all indicate low N availability, and likely N limitation, an assertion that is consistent with other studies 

on western Cascade streams (Triska and others, 1983; 

Leland, 1995; Bakke and Pyles, 1997; Anderson and 

Carpenter, 1998). Seasonal and longitudinal declines in 

DIN concentrations and loads were observed that demonstrate the high demand for N by algae in the Clackamas River. In contrast to other dissolved substances, 

such as SiO2 and SRP, which increased from May to 

September, DIN concentrations generally decreased 

(fig. 9 and table 8). DIN loads in the Clackamas River 

in July increased substantially between CR_MCIVER 

and CR_BARTON due to the inputs from Eagle Creek 

(figs. 10 and 11) and other unmeasured sources, such as 

ground-water discharges. The DIN load at CR_ 

BARTON, however, was about 30% less than that from 

Eagle Creek alone, suggesting that periphytic algae 

used a significant amount of the DIN in the 3.2 miles 

between the mouth of Eagle Creek and Barton. 

Loads and concentrations of DIN in the lower 

reaches of the Clackamas River also declined, especially downstream from Barton in May, and downstream from Carver in July. This pattern of declining 

N in the lower Clackamas River was somewhat 

unexpected, given the relatively high N inputs from the 

lower-basin tributaries, ground-water discharges, and 

other sources. High rates of N uptake by algae in the 

lower Clackamas River, as confirmed by the high algal 

biomass, may explain the observed decrease in DIN 

in this reach. Efficient uptake of inorganic nitrogen - (NH4

+ and NO3 ) by algae has been shown in other 

Cascade streams (Munn and Meyer, 1990; Peterson 

and others, 2001), and low concentrations of DIN 

often coincide with high algal biomass (Anderson 

and Carpenter, 1998) owing to the efficient use of 

N in these presumed N-limited streams. 

58 
Comparison of Nutrient Concentrations 

to Suggested Criteria 

The effects of nutrient enrichment on aquatic 

ecosystems have been well-documented (Vitousek 

and others, 1997; Correll, 1998; Litke, 1999; Fuhrer 

and others, 1999). Although the U.S. Environmental 

Protection Agency has established upper-limit goals 

for TP to prevent nuisance plant growth in aquatic 

ecosystems (U.S. Environmental Protection Agency, 

1986), it is generally accepted that the criteria for 

N (ammonia and nitrate), which were developed to 

address toxic effects, do not protect aquatic ecosystems 

from excessive plant growth (U.S. Environmental 

Protection Agency, 2000b). In recognition of the 

pervasive problem of nutrient enrichment, the USEPA 

has recently published suggested nutrient criteria on a 

regional scale to protect water bodies from the negative 

effects of nutrient overenrichment, including excessive 

algal growth (U.S. Environmental Protection Agency, 

2000b). The recommended criteria are not water-quality 

standards; they are intended to be starting points for 

States and Tribes to use in setting their own regional 

nutrient criteria. If the States or Tribes do not develop 

their own criteria by the end of 2004, the U.S. Environmental Protection Agency will decide whether to 

promulgate the suggested criteria (Grubbs, 2001). 

The suggested nutrient criteria for streams in the 

Willamette Valley and Cascade Range Ecoregions 

(U.S. Environmental Protection Agency Level III 

Ecoregions) were based on a reference condition that 

represents the natural or least impacted condition, or 

what is considered to be the most attainable condition 

(U.S. Environmental Protection Agency, 2000a). 

The recommended criteria proposed by USEPA were 

derived from the 75th percentile of the distribution 

of reference condition values (averaged for all four 

seasons) within a given nutrient ecoregion, a target 

that would theoretically provide protection against 

the effects of nutrient overenrichment while removing 

the effects of outliers (Grubbs, 2001). 

Suggested reference conditions for Clackamas 

Basin streams located in the Willamette Valley and 

Cascade Range Ecoregions are given in table 15. 

Comparing the values in these tables to data collected in 

the Clackamas Basin (tables 7 and 8) shows that many 

of the streams exceeded the recommended criteria. This 

was especially true of most of the lower-basin streams, 

which typically exceeded the total nitrogen (TN) and 

TP criteria, often by several-fold, with most of the TN 

exceedances due to excessive amounts of NO3

-

. 

Stream sites in the Cascade Range Ecoregion 

occasionally exceeded the suggested TN or TP criteria, 

depending on the location and season. Most of the 

nutrient concentrations in the high-elevation streams 

of the Cascade Range Ecoregion were near or below 

the suggested TN criterion (55 μg/L) and were close to - the suggested reference condition for NO2

- + NO3 of 

5 μg/L. Some of the middle-basin tributary sites, however, significantly exceeded the suggested reference - condition for NO2

- + NO3 (tables 7 and 8). Although - the suggested reference value for NO2

- + NO3 may 

appear low, it may not be unreasonable for streams 

in the Clackamas Basin given that it was often met, 

particularly at sites in the upper basin. Exceedingly low 

concentrations of N are often observed in other Cascade 

streams, leading numerous researchers to conclude 

that N limits algal growth in these streams (Triska and 

others, 1983; Gregory and others 1987; Bothwell, 1992; 

Borchardt, 1996). Low N concentrations, however, also 

may result from efficient uptake of N by algae, which 

suggests that other measures of nutrient enrichment, 

such as algal biomass, might be more informative than 

nutrient concentrations. 

Although middle-basin tributaries were often 

enriched with N, possibly due to the effects of forest 

management (timber harvesting, forest fertilization, and 

prescribed burning), streams in this area also may be 

enriched with NO3

-

 from other sources including 

N-fixing plants, atmospheric deposition, and wildfires. 

However, the NO3

- concentration at the reference 

site (EAGLE_W, located in the Salmon-Huckleberry 

Wilderness Area) was 9 μg/L, which suggests that concentrations of N in the western portion of the Cascades 

Ecoregion are quite low. Such a low reference condition 

for NO3

-

 underscores the importance of obtaining low 

laboratory detection levels for N in future studies in the 

Clackamas River Basin. 

The suggested TP criterion (9 μg/L, table 15) 

was often exceeded by a factor of two or more at 

some sites in the upper basin (tables 7 and 8). There is 

some indication that the TP criterion may be too low to 

represent reference conditions in the Clackamas Basin 

streams located in the Cascade Range Ecoregion, 

as TP concentrations in Roaring River, an unmanaged 

“reference” basin, exceeded this value with TP 

concentrations ranging from 10 to 14 μg/L. Higher 

concentrations of P were observed in some streams 

draining the eastern portion of the Cascades Ecoregion 

(CR_UPPER and OAK_RAIN, tables 7 and 8). 

59 
Table 15. Reference conditions suggested by the U.S. Environmental Protection Agency for streams in the Willamette Valley 

(Nutrient Ecoregion I, Subecoregion 3) and streams and reservoirs in the Cascade Range (Nutrient Ecoregion II, Subecoregion 4) 

[Nutrient abbreviations are listed in the glossary; μg/L, micrograms per liter; NTU, Nephelometric turbidity units; chl a, chlorophyll a; mg/m2, milligrams 

per meter squared; <, less than; MRL, minimum laboratory reporting level; nd, no data] 

Reported values 

Reference condition 

Parameter Number of sites Minimum Maximum (seasonal average) 

WILLAMETTE VALLEY STREAMS 

NO2 

- + NO3 - (μg/L) 85 20 8,640 150 

TKN (μg/L) 96 50 2,750 210 

TN (μg/L) 13 0.00 2,990 320 

TP (μg/L) 138 2 816 40 

Turbidity (NTU) 31 0.78 34.5 4.66 

Phytoplankton chl a (μg/L)a 57 0.4 31.1 1.8 

Periphyton chl a (mg/m2)

a 7 63.7 153.8 63.7 

CASCADE RANGE STREAMS 

NO2 

- + NO3 - (μg/L) 75 < MRL 1,910 5 

TKN (μg/L) 65 < MRL 950 50 

TN (μg/L) 27 < MRL 2,860 55 

TP (μg/L) 95 < MRL 242.5 9.06 

Turbidity (NTU) 32 0.1 13.1 0.25 

Phytoplankton chl a (μg/L)a 19 0.58 12.75 1.01 

Periphyton chl a (mg/m2)

a 11 24.3 209.7 33 

CASCADE RANGE LAKES AND RESERVOIRS 

NO2 

- + NO3 - (μg/L) 85 < MRL 70 1 

TKN (μg/L) 8 120 280 120 

TN (μg/L) nd 120 350 120 

TP (μg/L) 74 1.5 98 6.25 

Turbidity (NTU) 97 0.0 34.4 18.4 

Phytoplankton chl a (μg/L)a 78 0.3 41.4 0.9 

a Chlorophyll a determined by fluorometric method with acid correction. 

However, because P concentrations in the Clackamas 

Basin streams tended to increase seasonally as streamflows declined, the seasonal averages were probably 

lower than these instantaneous measurements. This 

suggests that the 9 μg/L criterion might be suitable for 

the Clackamas Basin, although more data are needed to 

verify this. 

Nutrient Sources in the Clackamas River Basin 

Nutrients in the Clackamas Basin have both 

point and nonpoint sources. Point sources in the 

basin include individual tributary inputs and industrial 

discharges, such as wastewater treatment plants 

(WWTPs), fish hatcheries, and food processing plants. 

Studies show that approximately 90% of the N and 

75% of the P that contributes to nutrient pollution in 

streams comes from nonpoint sources such as runoff 

from farms and urban areas, ground water, and atmospheric deposition (Fuhrer and others, 1999). 

Point Sources 

Wastewater treatment plants—WWTPs discharge effluent into surface water in the Clackamas 

Basin from several locations, including the Job Corps 

Center (into the Clackamas River near Ripplebrook 

60 
Ranger Station), the City of Estacada (into Estacada 

Lake), the town of Boring (into Tickle Creek, a tributary of Deep Creek), and the City of Sandy (into North 

Fork Deep Creek). The total discharge from these 

plants is less than 2 ft3/s, but the nutrient concentrations are sometimes high, up to about 7,000 μg/L 

TP and 16,000 μg/L NH4

+ during summer months. 

Nutrient loads from the WWTPs were significant 

during this study, discharging nearly as much as the 

highest-contributing tributaries (figs. 10 and 13). 

Other potential sources of sewage in the basin 

include overused and leaky pit toilets along the Clackamas River, dispersed camping (U.S. Forest Service, 

1995c), septic tank effluent from unsewered residential 

areas, and some RV parks that sometimes use land 

application for disposal of sewage wastewater. 

Relatively high concentrations of NO3

- and Clwere observed in shallow ground water, which 

could indicate a septic origin. The highest NO3

­

concentration measured in this study (7,000 μg/L) 

occurred in July in Sieben Creek; septic systems 

are prevalent in a residential area a short distance 

upstream of the sampling location (Andrew Swanson, 

Clackamas County Department of Water Environment 

Services, oral commun., 2000). The dominant alga in 

Sieben Creek was Melosira varians, a diatom that is 

known to respond to high levels of organic N (Reimer, 

1962). Its abundance may indicate a septic source for 

the NO3

-

, although additional information is needed to 

verify this. 

Fish hatcheries—Eagle Creek fish hatchery 

effluent contained about 100 μg/L NO3

-

 and 20 μg/L 

SRP in April, when the respective concentrations 

upstream of the hatchery were 90 μg/L and <1 μg/L. 

Discharges from the two hatcheries total approximately 

70 ft3/s during peak operations. In July, the load of N 

from the Eagle Creek hatchery was about the same as 

that from the North Fork Clackamas River (fig. 10), 

and the P load was about the same as that for Clear 

Creek (fig. 13). A one-time sampling of nutrients from 

the fish hatcheries may not be representative, however, 

because of variations in the numbers and types of fish, 

methods for raising and feeding them, and release 

times. 

Nonpoint Sources 

Nonpoint sources of nutrients are potentially 

important in the Clackamas River Basin. Data on most 

nonpoint sources in the basin are limited, and determining the relative contributions and importance of these 

sources was beyond the scope of this study. However, 

this knowledge would be a valuable contribution to 

understanding the potential effects of different land 

uses or management scenarios on stream conditions. 

Nonpoint sources that would bear investigation include 

(1) fertilizer use in agricultural, urban, and forested 

settings, (2) soil erosion, which is discussed separately 

below (3) field burning in agricultural and forested 

areas, which converts organic matter into NO3

- (Fenn 

and others, 1998) that can subsequently leach into 

ground water and streams, (4) livestock, which contribute nutrients and bacteria to streams, (5) atmospheric 

deposition of N from being located in Portland’s 

airshed, also discussed below, and (6) ground water, 

which has already been shown to contain nutrients, 

often at high levels (discussed below). 

Soil erosion—Erosion of soils in the Clackamas 

River Basin is widespread. Unstable geology and steep 

slopes in many upper-basin drainages contributes 

to mass wasting and erosion, particularly in the Fish 

Creek and Collawash River Basins and along portions 

of the upper Clackamas River, where the surface 

erosion potential is relatively high (Metro, 1997). 

An ancient landslide currently being eroded by 

the Collawash River, for example, contributes fine 

sediment that often causes high turbidity during winter 

storms (U.S. Forest Service, 1995b). The suspended 

sediment may contribute to occasionally high concentrations of TP, resulting in depressed water-quality 

scores in the upper Clackamas River at the Oregon 

Department of Environmental Quality’s Memaloose 

Road sampling site (Greg Petit, Oregon Department 

of Environmental Quality, written commun., 1998). 

Turbidity levels in some of the lower-basin tributaries, including Rock, Richardson, Deep, and Sieben 

Creeks, have been especially high (150–1,200 NTU 

[nephelometric turbidity units]) after rainfall events 

(U.S. Geological Survey, unpub. data, 2000). Other 

studies have found streambank erosion in the lower 

reaches of Sieben Creek (KCM, Inc., 1995) and 

Ecotrust (2000) reported excessive streambed sedimentation and marginal visibility in the lower reaches 

of Rock Creek. High levels of turbidity in the Clackamas River also sometimes results from gravel mining 

operations in the lower Clackamas Basin (Andrew 

Swanson, Clackamas County Department of Water 

Environment Services, oral commun., 2001). In 

addition to the habitat problems associated with such 

erosion, sediment-bound contaminants and nutrients, 

especially P, also may be transported to the river 

through erosion. 

61 
Naturally occurring phosphorus—One of the 

likely sources of P in the upper basin is naturally occurring phosphate rock, which may enrich ground water 

with soluble P upon weathering and dissolution. The 

highest P concentrations for the forested sites (about 

25 μg/L TP, most of which was soluble) occurred in the 

upper Clackamas River and Oak Grove Fork Basins, 

where ground water contributes significantly to streamflows. 

The positive correlation (fig. 12) between concentrations of TP and silica (an important component 

of most soils) suggests a naturally occurring mineral 

source of P in the upper basin, which has been reported 

in other Oregon watersheds (Abrams and Jarrell, 1995; 

Wilson and others, 1999). However, TP concentrations 

also were positively correlated with the percentage of 

nonforest upland (includes clear cuts and other nonvegetated areas) in the forested basins (fig. 24). This 

suggests that timber harvesting and the associated network of roads in these watersheds may be transporting 

P through erosion of phosphate-rich soils. Mapping the 

geographic distribution of naturally occurring P may 

help guide future erosion/phosphorus management 

strategies. The positive correlation between SC and 

concentrations of P suggests that monitoring conductance may be an inexpensive screening tool for determining which streams to test for P. 

Atmospheric deposition—Nitrogen enters the 

air through the combustion of fossil fuels from automobiles, powerplants, and other industries. In the 

United States, more than 3.2 million tons of N are 

deposited annually through atmospheric deposition, 

which is about 54% of the total amount released to the 

air (Puckett, 1994). Atmospheric deposition is generally less in Oregon compared with other States 

(Puckett, 1994). Nevertheless, atmospheric deposition 

may deliver appreciable quantities of N to the Clackamas Basin, especially considering that this area is 

contained in the airshed for Portland. Although the 

amount of N in precipitation was not measured during 

this study, the National Atmospheric Deposition Program (NADP) collects precipitation and dry deposition 

data from a nearby station, located at Bull Run in the 

Sandy River Basin. At an elevation of 875 feet, this 

station best approximates atmospheric deposition in 

the foothills and valleys of the Clackamas Basin. The - average DIN concentration (NH4

+ + NO3 ) in precipitation from May to September 1996–2000 was about 

900 μg/L, and concentrations exceeding 1,000 μg/L 

occurred in nearly 15% of samples (NADP website 

http://nadp.sws.uiuc.edu/, accessed 5/28/2001). 

Ground water—Infusions of nutrient-rich 

ground water are another potential nonpoint source. 

Ground-water samples collected from springs and 

wells located near the lower Clackamas River between 

Estacada and Carver contained high concentrations 

of N and P. Springs that are probably fed by shallow 

ground water contained high levels of NO3

-

 (up to 

3,000 μg/L, table 14), a finding that Hinkle (1997) 

also reported for ground water in the Willamette Basin. 

Nitrate originating from nearby recharge areas may 

leach into ground water from a wide variety of sources 

because of its high solubility in water. The deeper 

ground water, represented by the well samples, contained high concentrations of NH4

+ and SRP similar 

to those reported by Leonard and Collins (1983). 

The amount of ground water entering the Clackamas River, although not measured in this study, is 

likely significant in selected reaches, given that there 

are no glaciers or permanent snowfields in its headwaters, yet late summer base flows of about 1,000 ft3

/s 

in the upper basin are common (fig. 4). Numerous 

springs were observed flowing out of hillslopes and 

eroded gravel deposits near or adjacent to the Clackamas River during this study. Piper (1942) suggested 

that streams in the Willamette Basin, including the 

Clackamas River, act as drains for ground water. High 

amounts of precipitation, combined with abundant 

porous rock, support ground-water discharges to the 

Clackamas River and some of its tributaries, especially 

the Oak Grove Fork, which has a high base flow for 

its drainage area (Sherrod and others, 1996). This study 

found that significant inputs of ground water were 

most probable in the lower Clackamas River between 

Estacada and Barton. The mass loading of nutrients 

from ground-water sources, however, was not quantified during this study. 

Algal Conditions in Streams 

Differences in habitat (streamflow, riparian condition, light penetration, and water chemistry) among 

the sites produced a range of algal conditions. Algal 

assemblages at well-shaded tributary sites in forested 

basins (FALL, WINSLOW, and EAGLE_W) were 

sparse, with low biomass and low numbers of different 

taxa (species richness). Greater species richness and 

greater biomass was generally observed at sites located 

near the mouths of the major tributaries, where additional light and/or nutrients were typically available. 

Algal assemblages at main-stem sites had the highest 

62 
species richness and exhibited a pronounced seasonal 

progression of growth (increased biomass), reflecting 

the more favorable conditions in the main stem (greater 

availability of light for photosynthesis, higher streamflow, and possibly greater nutrient availability), which 

sometimes led to conspicuous episodes of algal sloughing (decay and loss of biomass from the streambed to 

the water column). 

Algal biomass was low-to-moderate (50– 

100 mg/m2 chl a) at upper-basin sites not affected 

by the hydroelectric projects. Prolific algal growths 

exceeding 100–150 mg/m2

 chl a, the biomass threshold considered to represent nuisance conditions 

(Horner and others, 1983; Welch and others, 1988, 

1989; Biggs, 1996; Dodds and others, 1997, 1998), 

were found at some sites, especially those immediately 

downstream from dams and powerhouses, and at 

some of the lowermost main-stem sites (fig. 9). Such 

high algal biomass was not observed in 1993, when 

21 mg/m2 chl a as measured in the lower Clackamas 

River at RM 0.4 (Gregory, 1993). At this time, algal 

biomass was less than the half the amount (50 mg/m2 

chl a) proposed by Nordin (1985, cited in Biggs [1996]) 

to protect recreational usage of streams in British 

Columbia, Canada, from nuisance algal growths. 

Interestingly, high algal biomass was often 

observed in conjunction with low-to-moderate nutrient 

concentrations, especially where filamentous algae 

were prevalent. Efficient uptake of inorganic nitrogen - (NH4

+ and NO3 ) by algae probably accounts for the 

observed inverse nutrient-biomass relationship. Highbiomass growths of filamentous green algae have been 

documented in other similar-sized Western Cascade 

streams, including the North and South Umpqua Rivers 

(Tanner and Anderson, 1996; Anderson and Carpenter, 

1998) and the North Santiam, Sandy, and McKenzie 

Rivers (personal obs., 1996–99). Stevenson (1997) 

suggested that increases in filamentous green algae 

might overtake diatom assemblages in rivers when they 

become enriched with nutrients. 

Hypotheses to explain high biomass growths 

of green algae in Cascade Rivers, including the 

Clackamas River, include: 

1. High water velocities that occur in much of 

the Clackamas River may stimulate algal metabolism and growth by delivering nutrients to 

cells at higher rates (Horner and others, 1983; 

Stevenson, 1996), giving the effect of higher 

nutrient concentrations. Many of the filamentous 

algae found in the Clackamas River, such as 

Cladophora, have specialized structures that 

enable them to remain attached to rocks in 

moderately fast water. High water velocities, 

however, also result in increased drag on cells, 

which may result in reduced algal biomass 

(Stevenson, 1996). This may explain the pattern 

of highest biomass along stream margins, where 

the drag from currents would be less than in the 

main current. 

2. Nitrogen fixed by blue-green algae may fuel 

growths of filamentous green algae (Wetzel, 

1983; Dodds and Mollenhaur, 1995). N-fixing 

diatoms and blue-green algae occurred at all 

main-stem sites and showed a general increase in 

abundance as summer progressed. These algae 

may release up to 40% of the N they fix (Fogg 

and others, 1973) and can be a significant source 

of N for other algae. Cladophora, for example, 

has been found to occur in association with Nfixing algae in other N-deficient waters (Dudley 

and D’Antonio, 1991; Dodds and Gudder, 1992), 

which suggests that Cladophora may obtain 

some of its N from N-fixing algae. Indeed, it was 

commonly observed in this study, particularly 

in the upper basin, that Nostoc, a N-fixer, and 

Cladophora occurred on the same rock. This 

suggests that N-fixing algae supply N for other 

algae in streams, similar to the role that terrestrial 

N-fixers, such as alder, plays in providing N 

for other biota in N-limited terrestrial systems 

(Binkley and others, 1992). 

3. Infusions of nutrient-rich ground water may 

stimulate algal growth along stream margins, 

where ground water and surface water interface. 

If algal growth was nutrient limited, then nutrients entrained in ground water might be rapidly 

assimilated by algae growing on the streambed. 

Such nutrients would go undetected in a depthwidth-integrated water sample collected from 

the entire cross section. One set of nutrient samples collected in the upper Clackamas River at 

Highway 224 milepost 37 (RM 38.3), where 

algal growth was prolific, showed that the nearshore NH4

+ concentration was 6 times higher 

than the concentration in the main current, 

possibly the result of ground-water inputs that 

had not fully mixed into the stream. 

4. Organic N might be stimulating periphytic algal 

proliferations. Although DIN is the preferred 

63 
form of N for algae, N-heterotrophic algae may 

utilize dissolved organic N for energy production 

and growth (Hellebust and Lewin, 1977; Rogers 

and Gallon, 1988; Bourdier and others, 1989). 

Organic N was detected sporadically downstream 

from the reservoirs at concentrations ranging 

from 264 to 500 μg/L, although detections of 

organic N were hampered by their higher MRLs 

(100 μg/L for both DKN and TKN), compared 

with inorganic N forms (2–5 μg/L, appendix 1). 

N-heterotrophic algae were found at most 

sites, including downstream from North Fork 

Reservoir and Estacada Lake, where they composed between about 13 and 25% of the algal 

biovolume (table 10). N-heterotrophic algae 

were also observed, in similar proportions, 

downstream from hydroelectric reservoirs in 

the North Umpqua Basin in southwestern Oregon 

(Anderson and Carpenter, 1998). 

5. High algal biomass may have resulted indirectly 

through reduced numbers of herbivorous macroinvertebrates or through reduced grazing rates, 

although additional studies are needed to 

verify this. Power peaking by the hydroelectric 

projects, for example, causes fluctuations in 

river stage and can be detrimental to macroinvertebrates. Also, a large, 50-to-100-year flood 

occurred in the Clackamas Basin in 1996, which 

resulted in numerous landslides, road failures, 

and channel shifts, and caused severe bank 

erosion and high turbidity. The effects of the 

flood on benthic macroinvertebrates were not 

documented, but such an extreme disturbance 

usually causes short-term declines in benthic 

assemblages through scouring of stream 

channels. How stream organisms subsequently 

respond to events such as power peaking or 

floods depends on the various taxonomic 

and physiologic properties of the community 

(Peterson, 1996), and on local hydrology. 

Algal Conditions in Reservoirs 

Both reservoirs supported moderate-to-dense 

populations of phytoplankton, as indicated by the 

relatively high chl a concentrations (18 μg/L chl a 

at the surface of Timothy Lake in July 1996 and 

24 μg/L chl a at the surface of North Fork Reservoir in 

September 1996), both during blooms of Anabaena. 

For the following 2 years, several smaller blooms of 

blue-green algae were observed, along with other types 

of phytoplankton. Blue-green algae strongly dominated some samples, particularly during summer. 

Numerous hypotheses have been put forth to 

explain the success of blue-green algae in freshwaters 

(Sommer and others, 1986; Shapiro, 1990). River 

impoundment creates a lake environment that slows the 

flow of water and increases the residence time, which 

may play a role in determining whether blue-green 

algae become dominant (Rickert and others, 1977). 

Timothy Lake, with a relatively long residence time 

(8.5 months on average, table 1) and strong thermal 

stratification, provides phytoplankton with enough 

growing time to become abundant. The shorter residence time for North Fork Reservoir (about 7 days on 

average, table 1) may have been responsible for the 

smaller phytoplankton blooms that were observed 

compared with those in Timothy Lake. Thermal stratification and creation of a stable warm surface layer, 

however, may increase the residence time of the 

epilimnion, which gives phytoplankton additional time 

to develop. This is especially true for run-of-the-river 

reservoirs with deep-water releases and cold-water 

inflows, such as North Fork Reservoir. Here, cold 

water from the Clackamas River probably flows 

preferentially near the bottom, effectively reducing 

interaction between the surface and bottom water, 

thus slowing the exchange of water between the inflow 

and the epilimnion. This may increase the amount of 

time available for phytoplankton to develop near the 

surface, where blue-green algae often form surface 

scums (Oliver and Ganf, 2000). 

High water temperatures and/or high pH in 

reservoirs and lakes have also been used to explain the 

success of blue-green algae (Shapiro, 1990). However, 

blue-green algae blooms were observed in water as 

cool as 12°C (in North Fork Reservoir). Another possibility, elevated pH, which was observed during blooms 

and is likely related to algal metabolism, did not appear 

to act as a stimulus for bloom formation. Many bluegreen algae have special adaptations that may enable 

them to proliferate in certain lakes and reservoirs 

(Shapiro, 1990, and references contained therein), 

including (1) the ability to fix N2 gas into useable N, 

(2) the ability to regulate their position in the water 

column with gas vesicles (Fogg and others, 1973), 

(3) blue-green photosynthetic pigments that allow 

them to capture light effectively, (4) wide tolerances 

for water temperature, pH, and concentrations of 

carbon dioxide (CO2), and (5) the ability to produce 

mucilage and toxins (Carmichael, 2001) that may discourage grazing by zooplankton. 

64 
In North Fork Reservoir, relatively high concentrations of P and low concentrations of N resulted 

in low DIN:SRP ratios (0.8–1.1), which may have 

contributed to the development of N-fixing blue-green 

algae. TP concentrations in the reservoir (5 to 12 μg/L) 

exceeded the reference condition value (6.25 μ/L) 

suggested by USEPA for reservoirs in the Cascade 

Range Ecoregion (table 15), possibly due to naturally 

occurring sources of P from the upper basin. 

Potential factors that may have contributed to the low 

concentrations of N in the reservoir include the growth 

of periphyton in the Clackamas River upstream, particularly in the reach immediately downstream of the Oak 

Grove Powerhouse. If algal biomass in the upper main 

stem were lower, then nutrient uptake by periphyton 

would be less, and higher loads of soluble nutrients 

(N and P) would likely be transported to the reservoir, 

resulting in higher concentrations in North Fork 

Reservoir. Although higher concentrations of N and P 

might stimulate more phytoplankton growth overall, it 

might result in a lower incidence of blue-green algae 

blooms, because the advantage to N-fixers (low N) 

would be gone, and other algae such as diatoms might 

compete better. Blue-green algae blooms have not 

occurred in the Bull Run River reservoirs, the drinkingwater source for the City of Portland. Concentrations 

of NO3

- in those reservoirs (typically about 40 μg/L) 

are much higher than in the Clackamas Basin reservoirs, which might allow other types of algae (diatoms 

and small flagellates) to outcompete the N-fixing bluegreen algae. 

Schindler (1977) demonstrated that P may 

control phytoplankton growth in lakes dominated by 

N-fixers because their ability to fix N from the atmosphere frees them from limitation by N. Nonetheless, 

the largest abundances of Anabaena observed in this 

study were in Timothy Lake, where, although concentrations of N were low, the SRP concentrations also 

were low (about 1 μg/L). Although the uptake of 

nutrients by phytoplankton likely contributes to the 

low-nutrient concentrations in Timothy Lake, more 

focused studies are needed to determine what factors 

limit phytoplankton growth in the reservoir. 

Meteorological factors such as wind, light, 

and precipitation also may stimulate algae blooms 

(Soranno, 1997). Late summer storms, for example, 

may deliver nutrients directly to the reservoir through 

surface runoff, and winds associated with storms 

may mix nutrient-rich bottom water to the surface, 

where phytoplankton growth may be stimulated. The 

September 1994 algae bloom in North Fork Reservoir, 

which coincided with a taste and odor event, occurred 

about 5 days after a 0.85-inch rain storm in the basin 

(Gordon McGhee, Clackamas River Water, written 

commun., 1996). Cool air temperatures and wind 

also may destabilize the thermocline and stimulate 

phytoplankton. In late September 1996, a bloom of 

Anabaena appeared in North Fork Reservoir, when 

water temperatures at NFKRES_1 were isothermal 

(11.6–12°C), indicating the onset of fall turnover 

(mixing of the lake). During turnover, mixing in the 

reservoir causes colder bottom water, which is rich in 

P relative to water at the surface, to upwell. This event 

may have transported P to the surface, where an existing algal population was stimulated into a bloom. 

In August 1998, the distribution of Anabaena in 

North Fork Reservoir was uneven through the water 

column. Two populations of Anabaena were found: 

a surface population (about 500 cells/mL) and a 

bottom population (about 140 cells/mL), whereas no 

Anabaena was found at depths of 15 and 60 feet. Like 

many other blue-green algae, Anabaena cells contain 

gas vacuoles that cause cells to float toward the surface, 

thereby maintaining their position in the photic zone, 

where light is available for photosynthesis (Fogg and 

others, 1973). This explains the surface population. 

The bottom population may be explained by at least 

two hypotheses: (1) Because gas vacuoles can expand 

and contract, allowing for variable water column 

position, cells migrate to the bottom to obtain nutrients 

from the bottom water, and (2) cells may have originated from within the sediments. Blue-green algae, 

including Anabaena, develop from akinetes (resting 

seeds) that have germinated within the sediments, 

apparently stimulated by an increase in light availability (Reynolds, 1972). 

The shift in dominance from Anabaena circinalis 

to Aulacoseria granulata in North Fork Reservoir may 

have been related to the cooler surface water temperatures in September (14.9°C) compared to August 

(18.6°C) or to a destabilization of the water column 

caused by wind and resulting entrainment of nutrientrich bottom water. Aulacoseria granulata is regarded 

as a eutrophic species and has been shown to compete 

with Anabaena in other rivers and reservoirs, the outcome being dependent on factors including light, water 

temperature, and flushing rate of the reservoir (Wehr 

and Descy, 1998). Anabaena circinalis has been shown 

to prefer slower current and greater temperature stratification than Aulacoseria granulata (Wehr and Descy, 

1998). 

65 
Effects of Algae Blooms on Water Quality 

and Drinking Water 

Stream Algae Blooms 

Proliferations of periphyton, mostly filamentous 

green algae and stalked diatoms, in the lower Clackamas River produced fluctuations in pH and DO concentration, smothered riffle habitats, particularly along 

stream margins, and contributed to problems with the 

drinking water supply. These effects are summarized 

below. 

Effects on dissolved oxygen and pH—Thick 

growths of the green alga Cladophora in the lower 

Clackamas River produced diel fluctuations in pH and 

DO concentrations in June and July 1998. Concentrations of DO in the lower Clackamas River decreased 

from 10.5 mg/L in the afternoon to 7.9 mg/L in the 

morning (fig. 8). Such fluctuations in DO can be stressful for aquatic life (Welch and others, 1989). The pH 

also fluctuated about 1.4 units through the day in June 

and July (fig. 8). 

The Clackamas River, and possibly some 

tributaries, is susceptible to pH fluctuations from algal 

metabolism because of its low alkalinity (<30 mg/L as 

calcium carbonate [CaCO3] which provides only minimal buffering to changes in pH. Variation in pH occurs 

because the algae utilize CO2 during photosynthesis and 

release it during respiration, and the CO2 concentration 

drives pH. In productive streams, the highest pH values 

occur in the afternoon, when much of the available CO2 

has been taken up for photosynthesis, and the lowest 

pH values occur in the early morning, after the algae 

have been respiring all night. The pH in the lower 

Clackamas River slightly exceeded the State criterion 

of 8.5 pH units in late June, and again in mid-July. 

Past research has shown that brook trout gill lamellae 

become injured at a pH of 9.0 units (Daye and Garside, 

1976). The effects at pH values between 6.8 and 9.0 

were not, however, evaluated during their study. 

Effects of algae on streambed habitats—The 

spring bloom of Cladophora in the lower Clackamas 

River also smothered stream substrates (river cobbles), 

enough to make them notably green and slippery. 

Excessive algal growths may clog the top layer of 

channel sediments, which interferes with the downward 

movement of stream water into the streambed (Brunke 

and Gonser, 1997). This has several potential effects, 

including (1) the loss of pollution-sensitive invertebrates (Quinn and Hickey, 1990), (2) reduced delivery 

of oxygenated water to developing fish eggs or early life 

stages of aquatic invertebrates, and (3) a reduction 

in the respiration rates of the hyporheic interstitial 

community (Brunke and Gonser 1997), which could 

result in higher stream pH (Powell, 1997) because 

respiration produces CO2, thereby lowering pH. 

Further, periphyton mats that smother streambeds 

can interfere with upwelling of ground or hyporheic 

water into streams, thereby increasing the transient 

storage of such water (Brunke and Gonser 1997). 

If enriched in nutrients, as was suggested by data 

collected in the present study, then ground water may 

stimulate further algal growth in a positive feedback 

loop. Periphyton mats, while providing beneficial 

habitat for some organisms, particularly chironomid 

midges (Dodds and Gudder, 1992), also may modify 

existing habitats by reducing water velocity in streams 

(Dodds and Biggs, 2002), which may increase the 

water temperature. These habitat effects were not 

evaluated during this study, however. 

Effects on water supplies—In May 1998, the 

algal biomass near the mouth of the Clackamas River 

was high (300 mg/m2 chl a at CR_99E), about two 

to three times higher than the nuisance level. In 

June, clumps of filamentous green algae and stalked 

diatoms began sloughing from the streambed, increasing turbidity and entangling docks and fishing lines 

downstream. Drinking-water intakes became clogged 

(Gordon McGhee, Clackamas River Water, oral 

commun., 1998) and organic carbon from the algae 

may have contributed to the observed increase in the 

concentration of disinfection by-products in chlorinated 

drinking water in June (fig. 25). 

Drinking-water treatment plants using Clackamas 

River water all use chlorine as a disinfecting agent. 

When raw water containing organic matter is treated 

with chlorine, a number of toxic compounds, collectively referred to as disinfection by-products, can form 

(des Eaux, 1987). Two classes of these compounds, 

trihalomethanes (THM compounds, including 

chloroform) and haloacetic acids (HAA compounds), 

are frequently detected in treated drinking-water 

samples collected from the distribution systems served 

by the Clackamas River (Gordon McGhee, Clackamas 

River Water, written commun., 1998). The current 

maximum contaminant level (MCL) for THM in 

drinking water is 80 μg/L and 60 μg/L for HAA (U.S. 

Environmental Protection Agency, 2001). The highest 

concentrations of THM and HAA in treated drinking 

water from the Clackamas River have been as high 

as 60 and 56 μg/L, respectively (Gordon McGhee, 

Clackamas River Water, written commun., 1996). 

66 
Figure 25. Seasonal pattern in concentrations of disinfection by-products (total trihalomethanes [THMs]) in treated drinking water from 

the Clackamas River, 1998. (Chlorophyll a and total phosphorus data were collected in the Clackamas River at CR_99E, and THM sites 

were as follows: 1-8533 SE Luther Street, 2-7000 SE Thiessen Street, 3-152nd/Morning Way, 4-9100 SE Mangan Drive, 5-treated water from 

the Lake Oswego drinking-water treatment plant [THM data provided by Gordon McGhee, Clackamas River Water, and Glen MacDonell, 

Lake Oswego drinking-water treatment plant]. Sloughing of periphytic algae in June 1998 is also noted). 

Although these concentrations do not currently exceed 

the MCL for these compounds, they do indicate a 

potential problem, and one that could worsen if algal 

problems worsen. The quarterly peak in THM concentration observed in treated drinking water obtained 

from the Clackamas River occurred in June, following 

the algal sloughing event described above (fig. 25). 

Future monitoring for disinfection by-products is discussed later in this report. 

Blue-Green Algae Blooms in Reservoirs 

Blue-green algae are notorious for causing 

water-quality problems in lakes and reservoirs. Large 

blooms of certain types of blue-green algae, including 

Anabaena, also may form surface scums that are 

aesthetically displeasing, may produce toxins that 

are harmful to aquatic life (Carmichael, 2001), and 

may lead to taste-and-odor problems in drinking water 

supplies. 

With few exceptions, Anabaena was the dominant blue-green alga observed in Timothy Lake and 

North Fork Reservoir during this study, forming nearmonocultural populations in the reservoirs at times. DO 

and pH were often found elevated at the same depth 

as the chl a maxima, reflecting the bloom conditions. 

Although not extreme, surface scums of blue-green 

algae were sometimes observed in both reservoirs. 

Taste and odor events—No episodes of poor 

tastes or odors were reported during 1996–98, despite 

the relatively high abundances of Anabaena in both 

Timothy Lake and North Fork Reservoir. For example, 

a surface sample from North Fork Reservoir collected 

in August 1997 was strongly dominated by Anabaena, 

containing 14,500 cells/mL, 33 times higher than 

that observed during the taste and odor event in 

September 1994, when 430 cells/mL were found 

(Gordon McGhee, Clackamas River Water, written 

commun., 1996). Why no taste and odor event occurred 

in 1997 is not clear, given the high cell density at the 

surface, although thermal stratification (the surface 

temperature was 18.5°C or 4°C warmer than the rest 

of the water column) may have restricted the bloom to 

the epilimnion, away from the water-release depth. 

During the September 1994 taste and odor event, 

cell densities were much lower, but a summer storm 

delivered 0.85 inches of rain to the basin just 5 days 

prior to the onset of taste and odor problems, which 

may have resulted in partial turnover of the reservoir. 

67 
This might explain the lower cell densities, as turnover 

would mix the cells down into the bottom portions of 

the reservoir, where cells or their taste and odor producing compounds could be transported downstream to 

drinking water intakes. Other factors, such as sustained 

periods of calm, sunny weather after the storm may 

have been important because algal cells at the surface 

are subject to photo-oxidation and are prone to rapid 

decay more than when under the surface (Dae-Young 

and G-Yull, 1997). If rapid decay occurs, intracellular 

compounds, including geosmin and methylisoborneol 

(Hayes and Burch, 1989), may cause taste-and-odor 

problems in drinking water supplies (des Eaux, 1987). 

Algal toxins—While toxins were not addressed 

in this study, two types of blue-green algae known to 

produce toxins (Anabaena and Microcystis) were 

found in the reservoirs. Anabaena spiroides, which 

occurred in North Fork Reservoir at an abundance of 

128 cells/mL in September 1998, has been shown to 

produce toxins that can impact public drinking-water 

supplies (Beasley and others, 1983; Carmichael, 1986, 

1994), and Microcystis, another blue-green alga that 

often produces harmful toxins (Carmichael, 1986, 

1994, 2001), was found in Timothy Lake at low abundance (20 cells/mL) in May 1998. 

Algal toxins have been detected in other western 

Oregon Lakes, such as Diamond Lake, near the headwaters of the North Umpqua River, and Ten Mile Lake, 

near the Oregon coast. In August 2001, a toxic bloom 

of Anabaena occurred in Diamond Lake that closed the 

lake to fishing and contact recreation for about 2 weeks 

(Mikeal Jones, U.S. Forest Service, written commun., 

2001). Future monitoring for algal toxins is discussed 

later in this report. 

Land Use and Water Management 

in the Clackamas River Basin 

Land-use activities such as forestry, agriculture, 

and urban development have occurred extensively 

throughout much of the Clackamas River Basin, 

potentially causing impacts on habitat and waterquality conditions. In addition, the magnitude and 

timing of streamflows, which exert strong controls on 

aquatic life, are affected by the hydroelectric projects. 

Moreover, the two large reservoirs created by these 

projects provide suitable habitats for blooms of bluegreen algae that have the potential to degrade water 

quality, affecting drinking-water supplies and aquatic 

ecosystems. 

Forest Management 

Timber harvesting in the Clackamas River Basin 

dates back to the late 1800s, when roads were few 

and harvesting occurred in riparian areas by felling logs 

into streams and routing them downstream (Taylor, 

1999). In small tributaries, splash dams, log-and-cable 

structures that would store logs in temporary holding 

pools, aided the downstream transport of logs. When 

the cables were released, the water would carry the logs 

downstream to the mills. This practice scoured stream 

channels, damaged riparian vegetation, caused bank 

erosion, and degraded water quality. 

The construction of logging roads and advancements in timber harvesting methods led to the expansion of logging to nearly all parts of the basin; between 

1950 and 1994, timber harvest occurred in about 65% 

of the upper Clackamas Basin (U.S. Forest Service, 

1995c). Today, timber harvest on public lands is much 

reduced compared with 10 years ago, when harvest 

levels peaked at over 5,000 acres per year (fig. 26). 

Nitrogen—The highest concentrations of NH4

+ 

and NO3

- on forestland were found at sites in the 

middle basin, where average concentrations were 3 and 

10–20 times higher, respectively, compared with sites 

in the upper basin (tables 7 and 9). Lower DIN concentrations at the upper-basin sites might be attributable to 

N uptake by algae, especially at sites where P and light 

were more available. The relatively high concentrations of DIN at middle-basin sites might be attributable 

to a combination of forest management activities 

(harvest, prescribed burning, and fertilization), the 

abundance of N-fixing plants, atmospheric deposition, 

and fire history. Also, the lower concentrations of 

P and reduced light availability at middle-basin sites 

probably limited algal growth, thus reducing uptake of 

N by algae. 

The positive and significant relationship between 

the percentage of nonforest upland (primarily clear cuts 

and other nonvegetated areas) and DIN concentrations 

at middle-basin tributary sites (fig. 24) suggests that 

timber harvesting may be accelerating the transport of 

N to these streams. Disturbance from timber harvesting 

and road building has been shown to increase N in 

other streams (Murphy and Meehan, 1991; Greene 

1996; Adams and Stack, 1989; Fredricksen, 1971) 

and prescribed burning after harvest also may increase 

NO3

-

 levels in soils (Fenn and others, 1998), which can 

be transported to streams. 

68 
Figure 26. Acres of timber harvested or lost to fire in the Clackamas River Basin, Oregon, 1900–98 (after Gomez and Sullivan Engineers, P.C., 

2000). 

Forest fertilization, particularly on private forestland, also may contribute to enriching streams with N. 

Urea-N fertilizer is applied to 15- to 25-year-old 

(regrowth) forest stands, often in combination with tree 

thinning, to increase productivity. The highest proportions of regrowth forest, ranging from 30 to 45% were 

in watersheds located in the middle Clackamas Basin, 

where the highest DIN concentrations (for the forested 

sites) were observed (table 7). 

Forest management practices aimed at accelerating tree growth were initiated in the Clackamas 

River Basin during the 1970s, when thinning and 

herbicide treatments began (U.S. Forest Service, 

1995c). The use of urea fertilizers on private and 

public timber land increased in the mid-to-late 1980s 

(Edward Hendrix, Longview Fibre Co., oral commun., 

1999; Tom Rottman, U.S. Forest Service, written 

commun., 1999). Application rates on public lands, for 

example, exceeded 1 million pounds of N at this time 

(fig. 27), and in 1995–96, over 300,000 pounds of N 

were applied in the North Fork Clackamas River Basin 

alone (Tom Rottman, U.S. Forest Service, written 

commun., 1999). Although fertilizer use has declined 

on public forests in recent years, fertilization on private 

land, is expected to increase nationally in the future 

(NCASI, 1999). 

A recent literature review on the effects of forest 

fertilization found that runoff of N to streams from 

forest fertilization in the Pacific Northwest has ranged 

from less than 0.5% to 14.5% of the applied N 

(Anderson, 2002). Most studies, however, only examined N concentrations in streams (not ground water), 

were relatively short in duration, and did not address 

the long-term or cumulative effects of fertilizer applications on stream ecosystems. Potential factors affecting 

retention or loss of N to ground or surface waters 

following fertilization include the extent of timber 

harvesting in the basin, forest composition and age, 

number and frequency of previous fertilizations, soil 

characteristics, fire history, atmospheric deposition, 

and other factors. 

69 
Figure 27. Fertilizer application in the Mount Hood National Forest 

in the Clackamas River Basin, Oregon, 1986–98. (Tom Rottman, 

U.S. Forest Service, written commun., 1999.) 

The highest N concentrations in streams were 

typically found immediately after fertilizer application. 

Brief peaks in TKN concentrations up to 40,000 μg/L, 

from unintended direct application of fertilizer to 

streams and riparian areas, have been observed shortly 

after treatment (Binkley and others, 1999; Anderson, 

2002). Elevated concentrations of NO3

-

 have been 

observed as much as 2 years following fertilizer application, particularly during storm runoff (Fredricksen 

and others, 1975). 

Anderson (2002) presents a conceptual model 

on the potential effects of forest fertilization on N 

concentrations in streams and algal growth. This model 

suggests that headwater streams may become enriched 

with N following fertilization, but that algal growth 

is not stimulated because of light limitation in these 

small streams (Lyford and Gregory, 1995), so excess 

nutrients are transported downstream. Greater light 

availability in downstream reaches, with additional 

nutrients from fertilizers, may stimulate algal growth 

in these reaches (Vannote and others, 1980). Large 

fluctuations in DO and pH levels and high algal 

biomass, such as those observed in the lower Clackamas River, could be one symptom of such nutrient 

enrichment. 

Although forest management may play a role in 

increasing N concentrations in some Clackamas Basin 

streams, fire may also have had an effect (fig. 26). 

Wildfires have the potential to increase N in streams 

either directly by reducing the uptake of N by growing 

trees, or indirectly by allowing colonization of Nfixing species, including scotchbroom, snowbrush 

(Ceanothus), and red alder (Alnus rubra), which may 

colonize disturbed soils and increase nitrate concentrations in streams (Pojar and MacKinnon, 1994; van 

Miegroet and Cole, 1988). Vast stands of red alder 

occur throughout these basins, their abundance being 

due to a combination of factors, including anthropogenic disturbances (road construction and timber 

harvesting) and natural events (wildfires and floods). 

Fire histories in the North Fork Clackamas River 

and Eagle Creek Basins (U.S. Forest Service, 1995a; 

1996a) include large stand-replacement fires (in the 

upper portions of the Eagle Creek Basin in the late 

1800s) and several fires in the North Fork Clackamas 

Basin in the early 1900s. Afterwards, the North Fork 

Basin was salvage logged and grazed by sheep 

(Tom Horning, U.S. Forest Service, oral commun., 

2001). The Clear Creek Basin also has experienced 

significant wildfires, such as the Hillockburn Fire in 

1902, which burned the northern one-third of the basin 

(U.S. Bureau of Land Management, 1995). 

Phosphorus—The positive relationship between 

the percentage of nonforest upland and TP concentrations in streams draining forested basins suggests that 

forest management, including timber harvesting and/or 

roads, may be transporting P to streams. However, 

because nonforest upland also includes areas of 

exposed rock (table 4), and considering that volcanic 

rocks may contain natural sources of P (Abrams and 

Jarrell, 1995; Wilson and others, 1999), dissolution of 

P from rocky outcrops in these watersheds also may 

contribute to this relationship. This possibility is 

supported by the positive relationship between silica 

and P (fig. 12), which suggests that much of the 

P is from a geologic source. However, the erosion of 

phosphorus-rich soils from harvest units and roads also 

could explain these associations. 

The extensive network of roads and roadside 

ditches provides an efficient sediment delivery system 

(U.S. Forest Service, 1995c) by which soil bound P 

may be transported to streams. With the exception 

of the Roaring River watershed, which has 1.4 roadstream crossings per square mile of land (table 7), the 

remaining watersheds in the Mount Hood National 

Forest have between 9 and 16 road-stream crossings 

per square mile of land (Metro, 1997). About 490 miles 

of paved and dirt roads, used mostly for logging, 

dissect the upper basin (upstream of the confluence 

with the Collawash River), resulting in 377 stream 

crossings (U.S. Forest Service, 1995c), and road densities range from about 3 to 4 miles of roads per square 

mile of land (table 7). 

70 
From 1990 to 1995, most of the timber harvesting 

in the upper Clackamas and Oak Grove Fork Basins 

was on land classified as having a moderate to severe 

erosion potential (U.S. Forest Service, 1995c; 

1996b). Debris flows from clear-cut units in the Upper 

Clackamas Basin have delivered sediment to streams 

(U.S. Forest Service, 1995c). Fish Creek, which drains 

a steep basin that has been extensively harvested 

(43% nonforest upland and regrowth forest), also 

experiences erosion problems such as high turbidity 

during winter storms. Fish Creek Basin has the highest 

road density (4 miles of road per square mile of land) 

and the highest number of road-stream crossings 

(16 per square mile of land) of any of the upperbasin watersheds (Metro, 1997). In February 1996, a 

25-to-50-year flood (rain-on-snow event) occurred 

in Fish Creek, resulting in severe damage to the watershed. Post-flood surveys identified 236 landslides in 

the basin, with about three-quarters of the slides being 

associated with roads and harvest units (DeRoo and 

others, 1998). 

Algal biomass—Algal biomass was generally 

low to moderate at tributary sites in forested basins, 

owing to the relative scarcity of light, N, P, or some 

combination. Low concentrations of N probably contributed to the low algal biomass at sites in the upper 

basin, despite the relatively high concentrations of P. 

Algal biomass was even lower at middle-basin tributary sites, where N concentrations were elevated, but 

P and light availability were lower than at the upperbasin sites (table 7). Whether the low nutrient concentrations resulted in low algal biomass at these sites, or 

alternatively, low nutrient concentrations were due to 

algal uptake of nutrients upstream from the sampling 

sites, is unknown. Other studies have shown that 

nutrient uptake by algae may significantly reduce 

nutrient concentrations in small streams (Mulholland 

and Rosemond, 1992; Peterson and others, 2001) and 

larger rivers (Tanner and Anderson, 1996). 

Two sites with detectable levels of N and P, and 

moderate light availability (FISH and SFCLACK), had 

algal biomass values that were 1.5 and 2 times higher, 

respectively, than other sites in forested basins (tables 

7 and 9). This suggests that N limits algal growth at 

upper basin sites, P and/or light limits algal growth at 

middle basin sites, and N and P, or some other factor 

(insect grazing or light), limits algal growth in Fish 

Creek and the South Fork Clackamas River. Nutrient 

addition experiments, such as those described later in 

this report, could be used to determine which nutrients 

limit algal growth in these forested streams. 

Agriculture and Urban Development 

A history of land conversion and development 

in the Clackamas River Basin is presented in Taylor 

(1999), detailing how the current landscape emerged 

from a once largely forested area. Euro-American settlement of the lower basin dates back to the early 1800s 

(Taylor, 1999). During the late 1800s and early 1900s, 

land was logged or burned, cleared, and drained for 

farming (Ecotrust, 2000). Dairy and subsistence farms 

were prevalent in the area until after World War II, 

when much of the land was subdivided for urban housing developments. Later in the 1970’s, urban growth 

boundaries were established to curtail urban sprawl. 

Nutrients—The highest concentrations of N and 

P occurred in streams draining a mixture of agricultural 

and urban land. One common source of nutrients 

from these land uses is chemical fertilizers, which 

are applied to field and nursery crops and landscaping, 

and to promote vegetation cover for erosion prevention. N fertilizer applications have steadily increased in 

the Willamette Basin, from about 2 million kg/year 

in 1945 to about 50 million kg/year in 1980 (Hinkle, 

1997). Rinella and Janet (1998) found a significant 

positive correlation between NO3

-

 concentrations 

in Willamette Basin streams and the percentage of 

agricultural land in each basin, a finding that has been 

reported nationally for streams and ground waters 

(Miller and Hamilton, 2001). Although the Clackamas 

Basin has, on average, less agricultural land than much 

of the Willamette Basin, the use of fertilizers for agriculture in the basin has likely increased. In the lower 

Clackamas Basin, nutrient enrichment in streams may 

be exacerbated by tile drains, which were originally 

installed by farmers to help drain excess water from 

the land (Ecotrust, 2000). These pipes efficiently 

deliver shallow ground water to streams, carrying 

soluble nutrients and minerals that have leached from 

the agricultural fields. 

The highest nutrient concentrations (N and P) 

were found in Sieben Creek, which drains an area 

on the southeastern edge of Portland’s urban growth 

boundary, where development has been rapid in the 

past 10 years. From 1990 to 2000, the population 

of Clackamas County increased 21% (U.S. Census 

Bureau, 2000); during this time, the area of urban 

development in the Sieben Creek Basin quadrupled 

from about 10% to 40%, with densities of up to 

24,000 people per square mile in some residential 

developments. 

71 
Other studies have also found degraded conditions in Sieben Creek, including high concentrations 

of nutrients, sediment, and bacteria (KCM, Inc., 

1995), and an impaired macroinvertebrate assemblage 

(Adams, 2001). The large area of impervious surface in 

the basin (36%, Dewberry and others, 1999) produces 

rapid increases in streamflow following storm runoff, 

and likely contributes to the degraded water quality in 

Sieben Creek. 

In addition to the nutrient inputs that may occur 

from initial construction or fertilizer use from already 

developed areas, a large tract in the central portion of 

the Sieben Creek Basin contains a residential area that 

is not currently connected to sewers (Andrew Swanson, 

Clackamas County Department of Water Environment 

Services, oral commun., 1999), and contamination 

from septic wastewater may have contributed to the 

high nutrient concentrations measured in Sieben Creek. 

Some agriculture also occurs in the basin, however, 

including a few large nurseries, which also may contribute nutrients to streams. 

Algae—Relatively high nutrient levels in the 

lower-basin tributaries fueled high algal biomass, 

reaching nuisance levels (>100–150 mg/m2 chl a) in 

Rock, Sieben, and Deep Creeks. Algal biomass in 

Richardson Creek was lower, possibly due to the high 

abundance of grazers (primarily glossosomid caddis 

flies) that were observed at the time of sampling. Such 

high grazer densities were not observed, however, in 

Rock Creek, where a thick biofilm of high-nutrientindicating diatoms (eutrophic taxa) were found. Many 

of the taxa found in Rock Creek are considered silt 

tolerant, and have adaptations for surviving in silty 

environments, such as the ability to move through 

sediments, thus preventing burial. Dewberry and others 

(1999) found macroinvertebrate assemblages to be 

“healthier” in Richardson Creek compared with Rock 

Creek, and concluded that the low diversity of aquatic 

insects in Rock Creek was due, in part, to habitat 

quality, which was judged to be marginal and moderately impaired by streambed sedimentation. 

Algal assemblages at lower-basin tributary 

sites were largely dominated by Melosira varians, 

a eutrophic and N-heterotrophic diatom that can 

assimilate dissolved forms of organic nitrogen 

(van Dam and others, 1994). This alga was predictably 

abundant at sites where N concentrations also were 

high. In a study of small streams in agricultural and 

urban basins in the Willamette Basin, Carpenter and 

Waite (2000) found similarly high abundances of both 

eutrophic and N-heterotrophic diatoms, including 

Melosira varians, in association with N enrichment. 

Despite the high nutrient concentrations, filamentous green algae, which also require large amounts 

of light (Biggs and others, 1998), were not prolific at 

the lower-basin tributary sites in 1998. This might be 

attributable to the sometimes-low light availability at 

these sites (canopy closure ranged from 43 to 85%). 

Therefore, the undesirable effects that filamentous 

green algae sometimes cause in streams, such as 

excessive algal biomass, low levels of DO, and high 

pH, might be avoided by promoting riparian vegetation 

and shading. 

The impacts on water quality from urbanization 

will likely increase in the Clackamas Basin streams, 

particularly as more farmland is converted to urban 

development to accommodate an expanding urban 

growth boundary. Given current plans for future development, sediment and P loads in Rock and Richardson 

Creeks, for example, are predicted to increase sixand threefold, respectively (URS, 2000). Although not 

assessed in this study, urban runoff from these watersheds during storms likely contributes additional 

pollutants to the Clackamas River, including trace 

elements, volatile organic compounds, and pesticides. 

Hydroelectric Projects 

The hydroelectric projects in the basin (or their 

operation) have the potential to affect several fundamental controlling variables in downstream reaches, 

including streamflow, water temperature, and sediment 

transport. In addition to these effects, the projects also 

appeared to influence levels of DO, nutrient concentrations, and algal conditions during this study. 

Water temperature—The hydroelectric 

projects affect water temperatures through water 

releases from the various impoundments, which, 

depending on the time of the year, may warm or cool 

downstream reaches. Cold water coming down the Oak 

Grove Fork that enters the upper Clackamas River via 

discharges through the Oak Grove Powerhouse (fig. 2) 

cooled the upper Clackamas River, especially during 

low-flow conditions in September, when powerhouse 

discharges accounted for nearly three-quarters of the 

flow in the upper Clackamas River. In late September, 

however, during the drawdown of Timothy Lake, 

water temperatures in the Oak Grove Fork increased 

by roughly 2°C. 

72 
A cumulative temperature increase of 4°C was 

observed in the Clackamas River through the mainstem hydroelectric projects in September. Longitudinal 

water temperature measurements collected in North 

Fork Reservoir in August 1997 indicated a 6°C 

increase in surface water temperature between the 

inflow to the reservoir and the log boom, with most of 

the warming occurring in the uppermost reaches of the 

reservoir (fig. 17). In the past 40 years, sediment deposition has reduced the volume of North Fork Reservoir 

by 30–40% (Robert Steele, Portland General Electric, 

written commun., 1998) and has created a long shallow 

reach near the inflow, producing ideal conditions 

for warming. Temperature increases in the main-stem 

projects in September (fig. 5) were about equally 

attributable to warming in North Fork Reservoir and 

the remaining impoundments (Faraday Forebay and 

Estacada Lake, fig. 2). 

The longitudinal profile of water temperatures in 

the Clackamas River (fig. 5) shows that, while water 

temperatures upstream of the main-stem hydroelectric 

project decreased from July to September, water 

temperatures continued to increase downstream from 

the reservoirs. The warm surface layer that develops in 

North Fork Reservoir eventually becomes entrained 

in water releases from the reservoir as fall turnover, the 

process by which the reservoir is mixed due to the combined action of the wind and the cooling (and sinking) 

of surface waters during cold fall nights, begins. Such 

mixing of warm surface water, which in late September 

was about 4.5°C warmer than the inflowing water, 

ultimately results in warmer releases, thus altering the 

natural thermal regime in downstream reaches. The 

effects of these warmer water discharges may be 

significant on aquatic life in the river, especially if fall 

rains are delayed and high water temperatures persist. 

Changes in the thermal regime below dams, for 

example, are believed to affect macroinvertebrate 

assemblage species composition and diversity through 

eliminating important environmental cues required 

for egg development, hatching, and emergence 

(Lehmkuhl, 1972; Vannote and Sweeney, 1980; Munn 

and Brusven, 1991). These effects, however, were not 

evaluated during this study. 

Dissolved oxygen—Timothy Lake often has low 

concentrations of DO in the bottom water during summer (Shulters, 1976; Portland General Electric, 1988). 

Low DO levels in the hypolimnion of Timothy Lake 

are likely a consequence of decomposing organic matter in the reservoir sediments, a process that consumes 

DO. The strong thermal stratification in the reservoir 

also acts to isolate bottom water from the surface, 

where aeration may increase DO levels. Additionally, 

the relatively long residence time of the reservoir 

(about 8 months) results in a slow exchange rate, which 

also likely contributes to the low DO. Because Timothy 

Lake is in a basin that was once a productive wetland 

(Timothy Meadows), the organic content of the sediments is probably high, especially given the history 

of sheep grazing in the meadow (Johnson and others, 

1985), and the decomposition of this material would 

be expected to deplete DO in the overlying water. 

To increase concentrations of DO in water released 

from Timothy Lake, a special device called a HowellBunger valve has been fitted onto the powerhouse 

release pipe to aerate water exiting the reservoir. 

Although this did increase levels of DO downstream of 

Timothy Lake, concentrations of DO were still somewhat depressed (91% saturation) at OAK_BLTLK 

in July and September. Nonetheless, DO levels were 

much lower (50–60% saturation) at the water-release 

depth in the lake. 

Nutrients—Over time, reservoirs collect organic 

material in the sediments from tributary inputs and 

from phytoplankton growth in the reservoir. At least 

some of the N that is fixed by blue-green algae in the 

Clackamas Basin reservoirs probably ends up in 

the bottom sediments. Upon decay, inorganic nutrients - such as NH4

+, NO3 , and SRP, which are available for 

algal growth, are released. In this sense, reservoirs 

with organic-rich sediments may effectively become 

“aquatic compost heaps” (Coats and Powell, 2000) 

generating nutrients to downstream communities, 

especially if water is released from the bottom of the 

reservoir (Marcus, 1980; Ward and Stanford, 1983; 

Anderson and Carpenter, 1998). 

Lower DO and pH values and higher nutrient 

concentrations were sometimes observed near the bottom of both North Fork Reservoir and Timothy Lake, 

all indications that such processing of organic material 

was occurring in the reservoir sediments. During 

aerobic decomposition, DO is used and CO2 is 

produced by bacteria, which lowers pH. The NH4

+ 

released during decomposition may be converted into 

NO3

-

 by nitrifying bacteria, a process that also consumes DO and lowers pH. The relatively high NH4

+ 

concentration downstream from North Fork Reservoir 

in May (19 μg/L), in an otherwise severely N-limited 

system, suggests that appreciable decomposition was 

occurring in the reservoir. Although this was the only 

such detection of NH4

+ downstream from North Fork 

Reservoir, NH4

+ is the preferred form of N for algae 

73 
(Wetzel, 1983), and the high algal biomass downstream from the reservoir probably assimilated any 

NH4

+ released by the reservoir in July and September. 

Additional studies, however, are needed to characterize 

important unknown factors such as the organic matter 

content of the sediments and decomposition rates, 

and perhaps more importantly, the relative effects of 

these processes on aquatic ecosystems within and 

downstream from the reservoirs. 

Although concentrations of DIN were occasionally elevated downstream from the reservoirs (relative 

to upstream sites), DIN concentrations in the reservoirs 

were mostly low, and DIN concentrations downstream 

from the reservoirs were often below reporting limits. 

One possible explanation for this apparent contradiction is that nutrients released from decomposition in 

the reservoir sediments may migrate past the dams in 

seepage water and percolate up through the streambed 

downstream from the dams, where algae growing on 

the streambed can intercept nutrients before they 

enter the water column. Such a flow path for nutrientenriched water might escape detection in water 

sampling. Additionally, low concentrations of N may 

result from nutrient uptake by algae growing on the 

streambed. Excessive growths of algae have been 

found in conjunction with low N concentrations downstream from other hydroelectric reservoirs in western 

Oregon, such as Toketee Lake and Soda Springs 

Reservoir in the North Umpqua Basin in southwestern 

Oregon (Anderson and Carpenter, 1998). 

Phosphorus dynamics differed between North 

Fork Reservoir and Timothy Lake. North Fork 

Reservoir, which received a steady supply of SRP 

from the Clackamas River through the summer, 

supported phytoplankton growth that likely contributed 

to the observed decline in P concentrations and loads 

downstream of the main-stem reservoirs compared 

with upstream sites (figs. 9 and 11). Uptake of SRP by 

algae, suggested by the longitudinal decline in SRP 

concentrations in North Fork Reservoir (fig. 17), and 

subsequent settling of algal cells to the reservoir sediments may explain the declines in SRP and TP downstream from North Fork Reservoir. This decline is 

consistent with the observation that reservoirs generally act as sinks for P (Ward and Stanford, 1983). 

In contrast, the SRP concentration downstream 

from Timothy Lake (at OAK_BLTLK) increased from 

2 μg/L in July to 8 μg/L in September (table 8). 

Although the SRP concentration in Timothy Lake was 

only 1 μg/L, the reservoir sediments might be releasing 

phosphorus that is transported through seepage water. 

The P increase observed in September coincided with 

a decline in hypolimnetic DO from about 6 mg/L to 

0.9 mg/L (fig. 22). Further, because the DO declined 

with depth, concentrations in the bottom sediments 

were probably even lower. Release of P from sediments occurs when the DO in overlying water is less 

than about 1 mg/L; above about 3 mg/L DO, P tends to 

sorb to sediment (Gachter, 1976). Movement of water 

from the reservoir through the bottom sediments and 

past the earthen dam is plausible given the relatively 

porous volcanic soils in the area and the hydraulic head 

generated by the reservoir depth (about 100 feet). The 

large number of seeps immediately downstream from 

the reservoir also supports this assertion. 

Algae—Excessive growths of filamentous green 

algae were consistently observed immediately downstream from Timothy Lake, North Fork Reservoir, and 

Estacada Lake, particularly during July and September. 

The highest algal biomass value, 690 mg/m2 chl a— 

more than 4 times higher than what is considered a 

nuisance—occurred in the upper Clackamas River 

downstream from the Oak Grove Powerhouse in 

September. 

One alga that is notorious for reaching high biomass and producing nuisance conditions in streams is 

Cladophora (Dodds and Gudder, 1992; Biggs, 1996). 

This alga, although not found at upstream sites, was 

the dominant filamentous alga downstream from North 

Fork Reservoir in July (appendix 4). Much study has 

focused on the factors affecting the abundance and distribution of this widely occurring alga. In a review of 

the ecology of Cladophora, Dodds and Gudder (1992) 

stated that nuisance growths of Cladophora often result 

from nutrient enrichment, but that the alga may also 

reach high biomass in slightly eutrophic aquatic systems. The absence of Cladophora at all sites upstream 

from North Fork Reservoir suggests that some factor 

related to the reservoir or its operation might stimulate 

its growth, such as streamflow fluctuations (refer to 

Streamflows, p. 75) or lack of scouring high flows 

(Wootton and Power, 1993), which may allow algae 

to accumulate from one year to the next (Dudley and 

D’Antonio, 1991). Excessive growths of Cladophora 

have been reported downstream from other hydroelectric projects, such as those in the North Umpqua 

Basin in southwestern Oregon (Pacificorp, 1995; 

Anderson and Carpenter, 1998), where several reaches 

are currently listed on Oregon Department of Environmental Quality’s 303(d) list of water-quality limited 

water bodies for high pH or low DO (Oregon Department of Environmental Quality, 2000). Cladophora 

74 
has been observed in other streams draining the western Cascade Range, including the North Santiam, 

Sandy, and McKenzie Rivers (personal obs., 1996–99). 

Despite its reputation for causing water-quality 

problems in streams, Cladophora often hosts epiphytic 

diatoms that can be an important food resource for 

herbivorous macroinvertebrates living in the algal mats 

(Dodds and Gudder, 1992). 

Streamflows—The high abundance of algae 

downstream from hydroelectric projects in Cascade 

Range streams, including the Clackamas, might be 

partly attributable to flow fluctuations from power 

peaking operations. Large proliferations of blue-green 

and filamentous green algae that were observed in 

the upper Clackamas River downstream from the 

Oak Grove Powerhouse might be explained by several 

hypotheses: 

1. Fluctuating water levels provide an ideal habitat 

for macroalgae that can attain higher biomass, 

such as filamentous green and blue-green algae, 

because they may tolerate desiccation better than 

other types of algae. Cladophora, for example, 

tolerates repeated drying and often colonizes 

intertidal or splash zones around lakes (Dodds 

and Gudder, 1992; Blum, 1982) and certain 

blue-green algae, including Nostoc, produce a 

mucilaginous sheath that also resists desiccation. 

Nostoc occurred in the variable zone (where the 

stage fluctuated almost daily) in high densities 

along stream margins, primarily downstream 

of the Oak Grove Powerhouse. In July 1998, 

the cell biovolume of Nostoc was nearly twice 

as high below the Oak Grove Powerhouse 

at CR_3LYNX (3.0 × 107 μm3/cm2 [cell biovolume, in cubic microns per square centimeter]) 

compared with the upstream site (CR_UPPER), 

where the biovolume was 1.6 × 107 μm3/cm2. 

2. Fluctuating discharge may stimulate algal growth 

downstream from the projects by providing alternating high and low water velocities. High water 

velocities deliver nutrients at faster rates than low 

water velocities, but lower velocities might result 

in less turbulence and greater light availability for 

algae growing on the streambed. Repeated discharge fluctuations would simulate small flood 

events, which might favor certain filamentous 

green algae that have holding structures that keep 

them attached to the stream bottom, while other 

algae may be washed downstream. 

3. Fluctuating water levels might accelerate the 

death and decomposition of algal cells within 

already established algal populations because 

of increased exposure to air and direct sunlight 

during the day, or lower air temperatures during 

the night. Such accelerated decay might enrich 

stream margin areas (within the streambed or 

existing algal mats) with inorganic nutrients that 

may stimulate additional algal production in a 

positive feedback loop. 

4. Insect grazing can be an important factor regulating filamentous green algae (Dudley and 

D’Antonio, 1991), and power peaking in the 

projects might negatively affect grazers that 

normally keep algal biomass low. During the July 

sampling, numerous dead caddis fly larvae were 

found stranded along the banks of the upper 

Clackamas River about 5 miles downstream from 

the Oak Grove Powerhouse, presumably from a 

recent sharp decline in streamflow. Changes in 

river stage may leave aquatic organisms stranded 

during periods of reduced streamflow, and abrupt 

increases in flow may flush organisms downstream. The decreased flows that often occur at 

night can adversely affect benthic invertebrate 

populations by reducing mayfly species abundance and richness (Malmqvist and Englund, 

1996) or by shifting the invertebrate community 

toward a less diverse assemblage that may 

include large populations of tolerant species, 

such as chironomid midges (Munn and Brusven, 

1991) and scuds, which were observed downstream of River Mill Dam. Although these 

hypotheses may help explain proliferations of 

algae in the Clackamas River, additional studies 

are needed to verify them. 

Evaluation of Management Strategies 

to Improve Conditions 

Despite the episodes of poor water quality that 

were occasionally observed in the Clackamas River 

and some of its tributaries, the river continues to 

support runs of wild salmon, steelhead, and trout, and 

provides reliable drinking water for a large population. 

Public education, management strategies, and restoration efforts could, however, help reduce contamination, 

restore natural processes, and return the high quality 

habitat that was once plentiful. Particular strategies 

aimed at reaching these goals are discussed next. 

75 
Nutrient Reduction Strategies 

Nutrient enrichment can be a difficult process to 

reverse when high levels of nutrients also are present in 

ground water, as is the case in the Clackamas Basin. 

Precipitation events, common in the basin, help flush 

aquifers with large volumes of water upon infiltration. 

However, this is the same mechanism by which nutrients enter the ground water. Following are strategies 

aimed at reducing the transport of nutrients to streams 

and ground water such as fertilizer-use education, 

storm-water-runoff management, erosion control, and 

management of N-fixing plants. 

Fertilizer use education—Raising public 

awareness about the effects of nutrient enrichment and 

the ways to reduce the runoff or leaching of fertilizers 

could help to reduce inputs from residential areas. One 

way to reduce nutrient transport to streams is to avoid 

overfertilization or fertilizer applications immediately 

prior to heavy rainfall and to employ buffer zones that 

may slow the runoff of excess fertilizer. Also, testing 

nutrient levels in soils to determine whether fertilization is necessary, and planting N-fixing cover crops 

(clover, for example) in lieu of using chemical fertilizer, could help reduce nutrient concentrations in 

streams and ground water. 

Stormwater runoff and erosion management 

—Nutrients from fertilizers are often transported 

from the land surface to streams and ground water 

during storms. In the Clackamas Basin, some of the 

runoff to streams, especially those in the lower basin, is 

from impervious surfaces in urban and industrial areas. 

Innovative solutions to dealing with stormwater runoff, 

including constructed wetlands, sediment retention 

basins, and use of pervious paving materials might help 

reduce the runoff of nutrients and sediment to streams. 

Controlling erosion should also decrease the 

transport of nutrients, particularly P, which often 

occurs bound to sediment (Fredricksen, 1971). 

Erosion control, however, is a challenging problem 

in the Clackamas Basin, given the large amounts 

of precipitation and heavy runoff (Uhrich and 

Wentz, 1999). There are numerous sources of soil 

erosion in the Clackamas Basin (presented in Nutrient 

Sources section); determining the relative contributions from each of these sources and implementing 

Best Management Practices, such as preserving the 

existing vegetative cover during construction of urban 

developments (Gerig, 1985), installing (and maintaining) erosion barriers where soils are exposed, and using 

conservation tillage techniques on farms, for example, 

could help reduce erosion. The positive correlation 

between P and SC in Clackamas Basin streams 

suggests that SC might be an inexpensive method to 

identify potential sources of P. 

Removing invasive nitrogen-fixing plants— 

Many species of N-fixing plants are invasive and form 

extensive patches of growth in certain areas, and may 

be an important source of N in the basin. The removal 

of scotchbroom (Cytisus scoparius), an officially 

designated noxious plant, is ongoing (Robert Edgar, 

Oregon Department of Transportation, oral commun., 

1997), but chemical methods, such as the use of 

herbicides, may cause other problems for aquatic life. 

Scotchbroom, red alder (Alnus rubra), and other Nfixing plants colonize open areas along roads, timberharvest units, in riparian areas, and in locations where 

soils have been disturbed. Red alder is an active N-fixer 

and can be a significant source of N to Cascade Range 

streams (van Miegroet and Cole, 1988). Removal or 

thinning of red alder in riparian habitats and planting 

western red cedar (U.S. Forest Service, 1996c) might 

result in lowering concentrations of N in streams (Fenn 

and others, 1998). However, because alder provides 

shade and bank stability along streambanks, such 

manipulations should be evaluated along with the 

potential for increasing water temperature or accelerating erosion. 

Habitat Restoration 

Habitat restoration efforts, such as enhancing the 

natural functions of riparian zones and wetlands, and 

increasing stream complexity with the addition of large 

woody debris or boulders, could improve stream 

habitat and water quality. Fostering healthy riparian 

communities could improve stream habitat and water 

quality by intercepting sediment and soluble nutrients 

bound for streams (Gregory and others, 1991), providing stream cover, helping to reduce water temperatures, 

providing fish habitat, and possibly limiting algal 

photosynthesis through light limitation (Lyford and 

Gregory, 1995). 

Wetland and backwater habitats have been 

reduced or lost in the Clackamas Basin, starting with 

the early settlers, who installed tile drains for farming 

(Ecotrust, 2000). Later, eradication of beavers, removal 

of large woody debris, and road construction activities 

contributed to the loss of wetland habitat and stream 

complexity. In 1956, an extensively braided segment of 

the upper Clackamas River was realigned and channel76 
ized during the construction of Forest Service Road 46 

(U.S. Forest Service, 1995c), separating off-channel 

backwater areas from the primary channel. In recent 

years, the Forest Service has added logs, boulders, 

and culverts in this area to reconnect these backwater 

habitats and to increase stream complexity. Complex 

habitats contain abundant pools as well as riffles, 

benefiting fish and other aquatic organisms. Such restoration efforts would especially benefit fingerling 

coho salmon, which take refuge in backwater 

habitats during periods of high streamflow (Groot and 

Marcolis, 1991). 

In addition to providing fish habitat (Fausch and 

Northcote, 1992), increasing channel structure helps to 

reduce water velocity. This allows for sediments and 

organic matter to settle in backwater areas. Here, 

nutrients from these materials can be processed, and 

denitrification, the process whereby bacteria convert 

NO3

-

 to gaseous forms of N (which are lost to the atmosphere), can occur. Habitat complexity also increases 

the surface area to volume ratio in streams, which is 

important because biological films colonize surfaces 

and add significantly to nutrient retention (Tank and 

Winterbourn, 1995; Tank and Webster, 1998; Peterson 

and others, 2001). A lack of stream complexity may 

reduce interaction of surface water with subsurface 

(hyporheic) water and may contribute to other waterquality problems such as high (or fluctuating) pH 

and low DO levels (Powell, 1997) through decreased 

heterotrophic metabolism (Brunke and Gonser, 1997; 

Naegeli and Uehlinger, 1997; Fellows and others, 

2001). 

During watershed analysis, the U.S. Forest 

Service and Bureau of Land Management found a 

lack of large woody debris in portions of several watersheds, including the North and South Fork Clackamas 

Rivers, Eagle and Clear Creeks, and others, from a lack 

of wood recruitment due to timber harvesting, stream 

cleaning, road construction, and fires (U.S. Bureau 

of Land Management, 1995; U.S. Forest Service, 

1995a, 1995b, 1996a, 1996b, 1997). Continued 

efforts to enhance stream complexity through large 

wood/boulder additions, and planting trees in riparian 

areas could have several benefits. Riparian vegetation 

intercepts sediment and nutrients bound for streams 

and helps maintain bank stability (Gregory and others, 

1991). Undercut banks and overhanging vegetation 

from healthy riparian habitats provide cover for fish 

and also contribute to stream shading. Also, future 

recruitment of wood to streams, an important element 

of channel complexity (Gurnell and others, 2002) 

would be increased with riparian improvements. 

Much of the wood that accumulates in North Fork 

Reservoir during the winter is burned at a site adjacent 

to the reservoir during springtime. Burning the wood 

creates soluble nutrients, which may stimulate algal 

growth in the reservoir. Proliferations of filamentous 

green algae were observed along the reservoir shoreline directly adjacent to the large burn pile during 

summer in 1997 and 1998, which might be attributable 

to leaching of nutrients from the ash piles. An alternative management option, transporting the large wood 

around the dam complexes and keeping the large wood 

in the Clackamas River to increase habitat and stream 

complexity, is under consideration during hydroelectric relicensing (John Elser, Portland General Electric, 

oral commun., 1999). Using the wood for habitat restoration, in lieu of burning, could have the added benefit 

of reducing nutrient inputs to North Fork Reservoir. 

Water Temperature Reduction 

The lower 23-mile reach of the Clackamas River, 

from River Mill Dam to the mouth, is currently considered water-quality limited (Clean Water Act, section 

303(d) listed) because of high water temperatures 

during summer. High temperatures may be related 

to a variety of factors, including reduced stream shading, runoff from impervious surfaces, warm-water 

discharges from the reservoirs, and reduced inputs of 

cold ground water. Other factors, including reduced 

subsurface (hyporheic) flow due to channel scouring, 

reduced cover from loss of channel or bed structure, 

or increased solar warming from increases in stream 

width, also may be important in some areas. 

Enhancing stream shading through riparian restoration and tree planting in areas affected by road building, logging, agriculture, urban development, and the 

construction of farm ponds, could help reduce water 

temperatures in the tributaries locally and downstream 

in the Clackamas River. Also, managing storm runoff 

from impervious surfaces in urban and industrial 

areas with constructed wetlands or other innovative 

methods may help reduce temperatures. Large areas 

of impervious surfaces exist in Richardson, Rock, and 

Sieben Creek Basins, ranging from 22 to 36% of the 

total land area (Dewberry and others, 1999), which 

sometimes produce pavement-warmed runoff instead 

of allowing rainfall to infiltrate into the ground where 

it can recharge aquifers. 

77 
Extensive development of ground-water 

resources, especially in the northern part of the basin, 

also may reduce ground-water discharges to the lower 

Clackamas River, a potential cooling mechanism, by 

lowering the water table. One indication that this is 

occurring is that reports of dry wells by area residents 

have increased in recent years (Bill Ferber, Oregon 

Department of Water Resources, oral commun., 1998). 

A decline in the water table could indirectly increase 

water temperatures in the Clackamas River simply by 

reducing the volume of cold ground-water seepage. 

However, more data on the importance of ground water 

in regulating water temperature in the Clackamas Basin 

are needed to verify this hypothesis. 

Water releases from the hydroelectric project reservoirs also may contribute to high water temperatures 

in the Clackamas River, especially in the fall. From 

July to September, water temperatures in the upper 

Clackamas River decreased, but temperatures downstream from River Mill Dam increased, presumably in 

part from the release of water warmed in the reservoirs. 

Although two of the reservoirs (North Fork 

Reservoir and Timothy Lake) have deep-water 

releases, water from the Faraday Diversion Dam and 

Forebay is taken closer to the surface, where the water 

may be warmed. One strategy to reduce warm-water 

releases from River Mill Dam, and possibly lower 

water temperatures in the lower Clackamas River, 

would be to bypass the Faraday Lake portion of the 

hydroelectric project during warm periods, although 

this could interfere with energy production goals. 

Salmon Carcass Additions 

The Clackamas River and its tributaries were 

once teeming with native anadromous fish, including 

spring Chinook salmon, fall Chinook salmon, coho 

salmon, and winter steelhead trout. These fish were 

important sources of marine-derived nutrients for food 

webs in streams (Bilby and others, 1996). Today, 

anadromous fish populations in Clackamas and other 

western rivers are declining (Nehlsen and others, 

1991), spring Chinook and winter steelhead are listed 

as threatened by the National Marine Fisheries Service, 

and late-run Clackamas River coho salmon, the last 

remaining wild coho salmon stock in the Columbia 

River Basin, was listed as a candidate species in 1995 

(Taylor, 1999). 

For streams that are lacking in nutrients due to a 

reduction in the numbers of returning anadromous 

fish, the addition of salmon carcasses may enhance fish 

production (Wipfli and others, 1998). If nutrient 

amendments are made to streams, carcass additions are 

preferred over inorganic fertilizer because carcasses 

release organic nutrients slowly as they decompose 

over time. Inorganic chemical fertilizers are soluble 

and are immediately available for uptake by algae. 

Although carcass amendments may stimulate 

stream productivity through direct ingestion by insects 

and juvenile fish, or indirectly via increases in primary 

production, caution should be exercised. As discussed 

previously, low nutrient concentrations in streams, 

which might be perceived as limiting stream productivity, also may be due to efficient uptake by algae. 

A moderate-biomass algal assemblage may become 

exacerbated to nuisance levels if additional nutrients 

from carcass additions are provided, especially in 

downstream reaches where additional light may be 

available for photosynthesis. Also, caution should 

be used to avoid spreading disease among native fish 

populations from carcass additions. 

Controlling Phytoplankton Blooms 

Phytoplankton require light, nutrients, and time 

in order to grow and multiply to produce bloom conditions. Positive correlation between TP and chl a suggests that P may be regulating the N-fixing blue-green 

algae in the reservoirs. Reducing the P availability 

through erosion control measures may therefore reduce 

the severity of algae blooms in the reservoirs. Another 

potential limiting factor for blue-green algae is time. 

The hydraulic retention time, or residence time, is one 

indication of how much time is available for phytoplankton to grow. The residence time for a reservoir 

is a function of the rate of inflowing water and the 

volume. Small-volume reservoirs with large inflows 

are not as conducive to growing algae because they 

flush more quickly and have shorter residence times 

compared with large-volume reservoirs with smaller 

inflows. Residence time has been used to explain the 

dominance of diatoms in rivers that move fast and why 

blue-green algae prefer slower rivers and reservoirs 

with longer residence times (Rickert and others, 1977). 

One potential strategy to reduce the occurrence 

or severity of blue-green algae blooms in North Fork 

Reservoir, when they occur, is to use water from 

Timothy Lake to flush North Fork Reservoir. Higher 

flows through the reservoir would decrease the 

residence time and possibly reduce the severity of 

algae blooms. However, management goals, such 

as providing recreation or water supply needs, might 

78 
be affected by early releases from Timothy Lake. 

Additionally, Timothy Lake is prone to algal blooms 

and periods of poor water quality (low levels of DO 

near the bottom or high pH at the surface), making 

routine monitoring in the reservoirs an important tool 

for managing the system as a whole. 

Disinfection By-Products 

As noted previously, toxic disinfection byproducts are routinely detected in chlorinated drinking 

water from the Clackamas River drinking water 

treatment plants. The formation of disinfection 

by-products is related to the occurrence of organic 

matter in raw water supplies. Sources of organic matter 

include decaying leaves, woody debris, septic and 

animal manure waste, and other organic materials, 

including algae. In 1998, the quarterly maximum 

THM concentrations in finished drinking water (fig. 25) 

coincided with an algal sloughing event that increased 

the amount of organic matter in raw drinking-water 

supplies. This suggests that algae or its decomposition 

products may have been responsible for the observed 

increase in disinfection by-products. 

Management strategies aimed at reducing 

disinfection by-product concentrations could include 

watershed enhancements, including previously presented nutrient reduction strategies aimed at reducing 

algal biomass, and mechanical modifications to drinking water treatment plants. Prior to filtration, most of 

the plants in the basin chlorinate raw water, which 

may contain relatively high levels of organic matter, 

especially during algal sloughing events. Other studies 

(Fram and others, 2001) have demonstrated that disinfection by-product concentrations may be reduced by 

as much as 50% by prefiltering raw water before chlorination. Reducing the concentration of organic matter 

by other means, such as settling basins or screens, also 

may help reduce by-product concentrations, depending 

on the specific characteristics of the material. 

Information Needs and Potential Future Studies 

This study documented current baseline waterquality and algal conditions in streams and reservoirs, 

generated hypotheses to explain the observed patterns 

in conditions, and evaluated management strategies that 

might improve conditions. Additional water-quality 

monitoring and focused follow-up studies could address 

specific factors that influence water quality and/or algal 

growth, so that management options can be developed 

and implemented. 

Routine Monitoring 

Sampling a network of sites on a routine basis or 

using continuous monitors could help detect changes in 

water quality and provide information on year-to-year 

variability necessary for identifying trends in water 

quality over time. Data collected at three main-stem 

sites by the Oregon Department of Environmental 

Quality’s Ambient Monitoring Program, for example, 

have been used to detect for trends in water temperature, 

pH, DO, and nutrient concentrations in the Clackamas 

River; however, the spatial and temporal coverage 

of the Department’s monitoring is insufficient to 

address many of the questions generated by this study, 

especially in the tributaries. Routine monitoring could 

quantify potential benefits of restoration activities and 

test or refine hypotheses presented in this report. 

Determine compliance with water-quality 

standards—Instantaneous exceedances of waterquality criteria for temperature, pH, and DO were 

occasionally observed during this study, especially 

during the early morning and late afternoon, when 

extremes in these values occurred. As previously noted, 

however, determining compliance with water-quality 

criteria for temperature and DO require multiple-day 

observations: 7 days for temperature and 30 days for 

DO (table 5). Single point, instantaneous measurements, as were typically made for this study, cannot be 

used to indicate a violation of the standard or qualify a 

water body for listing on the 303(d) list of water-quality 

limited water bodies. Furthermore, the DO criteria also 

depend on the intergravel DO concentration measured 

in fish redds. Nevertheless, the pronounced fluctuations 

in water temperature, DO, and pH that were observed 

during this study may stress aquatic life. The USGS currently operates two continuous water-quality monitors 

in the lower Clackamas River, 0.25 miles downstream 

from River Mill Dam (RM 23.1) and near Oregon City 

(about RM 1.5), which will help determine the extent 

of such conditions. Definitive information on which 

reaches support fish spawning (or rearing), and when, 

is necessary for determining whether water-quality 

standards are being met. 

Watershed Assessments and Focused Studies 

Focused studies aimed at addressing particular 

issues could be used to further evaluate conditions, 

identify sources of nutrients, sediment, and contaminants, or test hypotheses regarding water or habitat 

quality. Some potential studies are evaluated next. 

79 
Watershed assessments—Watershed assessments aimed at characterizing and documenting baseline land-use, habitat, and water-quality conditions 

could provide a benchmark against which future 

studies may be compared. Such information could 

further understanding of how anthropogenic and 

natural influences affect watershed conditions. 

Watershed assessments of public lands administered by the U.S. Forest Service and the U.S. Bureau 

of Land Management provide historical and current 

information on forest stand age and community 

structure, geology, soils and sediment, vegetation, 

and fire history at the watershed level, and relate these 

conditions to land management. Most of these reports, 

however, contain little information on water chemistry 

(although see U.S. Forest Service, 1995c; 1996b). 

Focused studies in the upper basin could, for example, 

address how dispersed camping and other forms of 

recreation, timber harvesting, fertilizer application, 

road construction, erosion, and other activities affect 

nutrient levels in forested streams. 

The Clackamas River Basin Council recently 

sponsored a watershed assessment for Rock and 

Richardson Creeks and for Clear and Foster Creeks 

(Ecotrust, 2000). Future assessments of other tributaries, including Deep and Goose Creeks, and the lower 

main-stem Clackamas River, could help direct and 

focus restoration and other management efforts in the 

basin. Such assessments might include measures of 

streamflow variability, habitat complexity, and waterquality/algal conditions in smaller tributaries that 

would provide data at a more detailed scale. 

Although satellites may provide land-cover data 

useful for examining landscape-level effects on water 

quality, land-cover data used for this study were 5–10 

years old, and changes in land cover, especially in the 

lower basin, are occurring rapidly. Future watershed 

studies would benefit from up-to-date, small-scale, and 

field-verified information on the amount, condition, 

and distribution of urban/agricultural/forest land-cover 

and vegetation classes, along with other variables 

such as population density, road density, and areas or 

distribution of impervious surfaces. Such data might 

help identify particular sources of contaminants and 

strengthen conclusions regarding the effects of a 

particular land use on water quality or habitat conditions. Periodic updates in land-cover data could track 

changes in land use over time and might help explain 

future changes in water quality or habitat from restoration efforts. 

Agricultural and urban land-use studies— 

Some water-quality issues related to land use, such as 

nutrient enrichment and contaminant occurrence in 

streams, may be addressed by “gradient” studies. By 

selecting sites that taken together represent a gradient 

or range of a particular condition, one can isolate the 

effects of one type of land use versus another. A study 

having sampling sites that represent the full gradient 

of the condition from 0 to 100% (for example, urban 

gradient studies [McMahon and Cuffney, 2000]) might 

identify thresholds for some response variable. For 

example, Dewberry and others (1999) found a decrease 

in the number of aquatic macroinvertebrate taxa in 

Clackamas Basin streams when the impervious surface 

area was greater than 15–25% of the basin area. 

Disinfection by-products—The levels of disinfection by-products in finished drinking water supplied 

by the Clackamas River currently approach drinkingwater standards at times. These compounds are formed 

during chlorination of water containing certain types of 

organic matter. Organic matter originates from human 

discharges (WWTPs), leaky septic tanks, and fish 

hatcheries), terrestrial inputs (leaves and wood, and 

their decomposition products), and aquatic sources 

(algae from reservoirs and streams). Monitoring the 

Clackamas River for organic carbon concentrations 

(SOC and DOC), suspended chl a concentration, 

ultraviolet absorbance, and the isotopic makeup of 

the carbon (in raw water and potential terrestrial and 

aquatic sources), could identify the relative contributions from each of these sources. This may help 

water managers predict when raw water supplies are 

most vulnerable to by-product formation. Additionally, 

identifying where in the treatment process such 

by-products are formed (during chlorination of raw 

water, for example), and modifying plant design or 

operations accordingly, may help reduce disinfection 

by-product concentrations in the future. 

Algal toxin surveys—Although testing for algal 

toxins was not performed during this study, the types 

of algae known to produce them were found in both 

reservoirs. Future monitoring of water-quality and 

algal conditions in the reservoirs could include an 

evaluation of algal toxins, especially during blooms. 

Effects of tides on the drinking-water 

supply—Water from the Willamette River can travel 

as much as 0.3 miles up the Clackamas River to the 

lowermost sampling site, where about one-third of 

the water sampled during low flow in September had 

characteristics of water from the Willamette River. 

This backwater condition, presumably caused by an 

80 
unusual, but not uncommon, combination of flow conditions in the Clackamas, Willamette, and Columbia 

Rivers, could possibly reach the lowermost drinkingwater intakes in the lower Clackamas River. Although 

it is unlikely that Willamette River water could regularly travel upstream to the intakes during low-flow 

conditions (because of riffles in the lower river), an 

abnormally high streamflow in the Willamette River, 

combined with receding streamflow in the Clackamas 

River, might produce a backwater condition that could 

occasionally reach drinking-water intakes. Continuous 

monitoring of SC at the lowermost intake, for example, 

could identify potential changes in SC that might 

correspond with tidal cycles or be used to indicate the 

presence of Willamette River water. 

Effects of fluctuating water levels on aquatic 

biota—This study examined algal conditions in the 

upper Clackamas River and proposed hypotheses to 

explain the occurrence of excessive algae downstream 

from the hydroelectric projects, where power peaking 

results in fluctuating water levels. Future studies 

related to the operation of the hydroelectric projects 

could test hypotheses presented in this report and 

evaluate potential changes in project operations. A 

recent study of benthic macroinvertebrates in the 

project-affected reaches of the Clackamas River by 

Wisseman (2001) included multiple samples collected 

at various depths (distances from the stream margin) 

that may be useful for determining the effects of fluctuating water levels. The effects on algae, however, 

were not included in the study, nor were changes in 

nutrient cycling along stream margins. 

Nutrient addition experiments—Although the 

data collected here suggest N limitation for some of 

the streams in the upper basin and P limitation in some 

of the middle-basin streams, uptake and recycling of 

nutrients, N fixation, and infusions of nutrient-rich 

ground water make conclusions about nutrient limitation based on nutrient concentrations alone dubious. To 

better define which nutrients, if any, are limiting algal 

growth in the Clackamas River, its tributaries, and the 

reservoirs, nutrient addition experiments could be 

conducted. Clay pots filled with agar containing N, 

P, or both are placed in streams (Fairchild and Lowe, 

1984) and nutrients added to large plastic containers 

containing reservoir water (Carpenter, 1995) to test for 

algal growth over time. If a limiting nutrient is identified, reduction strategies to prevent its transport to 

surface waters can be developed and implemented. 

Nutrients from point sources—This study 

found that point sources, including fish hatcheries and 

WWTPs, might be a significant source of N and P 

in the Clackamas Basin. Nutrient data was generally 

sparse for both of these sources, however, and 

additional data are needed to understand how plant 

operations, such as hatchery maintenance or methods 

of wastewater treatment, affect discharges. Treatment 

plant upgrades might be used to reduce nutrient inputs 

from these point sources, especially if eutrophication 

in the Clackamas Basin accelerates or if disinfection 

by-product levels begin to exceed drinking-water 

standards. 

Nutrients from reservoirs—Nutrient concentrations were sometimes higher downstream from the 

reservoirs or in reservoir bottom water, suggesting that 

processing within the reservoirs, namely the decomposition and recycling of organic matter into soluble 

nutrients, was occurring. This probably contributed 

to the high algal biomass immediately downstream of 

the impoundments. Nutrient concentrations in water 

samples collected downstream of the reservoirs, however, sometimes did not match those in the reservoir. 

Additional studies that determine the source(s) of nutrients that are stimulating algal growth downstream of 

the reservoirs, such as evaluating the nutrient content 

of the sediments, decomposition rates, and flow paths 

through the sediments or past the dams, might help to 

explain the high algal biomass downstream from the 

dams. 

Nutrients from forested basins—Concentrations of DIN at some forested sites in the middle basin 

were much higher than what the USEPA considers to 

be representative of minimally impacted, “reference” 

conditions. Further, DIN concentrations at these sites 

appeared related to the percentage of nonforest upland 

(clear-cuts and other areas without vegetation) in these 

basins. Other factors, however, besides timber harvesting may affect N concentrations in these streams. Postharvest prescribed burning, fertilization, fire history, 

and N-fixing plants and trees also may be sources of 

N. Smaller-scale studies, including both streams and 

ground water, could help identify what sources are 

most important. 

Concentrations of P at some high-elevation 

sites draining forested basins also exceeded the level 

USEPA suggests being representative of reference 

conditions. Again, P concentrations appeared to be 

related to the percentage of nonforest upland (mostly 

clear-cuts and other areas without vegetation) in these 

basins. The highest concentrations were found in 

the upper Clackamas River and in the Oak Grove 

Fork, both located in the Cascade Crest Montane Forest 

81 
Ecoregion, where young volcanic rock, and possibly 

naturally occurring P, might be found. Better information on the distribution of P concentrations in 

streams and ground water in these areas, along with 

information on geology and soils, might identify naturally occurring P deposits, which could help determine 

or refine reference conditions for the Clackamas Basin. 

Also, targeted erosion control may be used to reduce 

the transport of P to streams in certain areas. The 

significant correlation between TP concentrations 

and SC suggests that SC may be an inexpensive way 

to screen potential sites for nutrient sampling. 

Nutrients in ground water—Ground water was 

found to contain relatively high concentrations of N 

and P, with shallow ground water yielding the higher 

concentrations of NO3

-

 and deeper ground water containing the higher concentrations of P. The distribution 

of nutrient-rich ground water in the basin and the 

relative impacts that anthropogenic activities have on 

nutrient concentrations in ground water is not known, 

nor is the amount of ground water discharging to the 

lower Clackamas River, although data collected as part 

of the current study suggest that it might be significant. 

Additional seepage studies conducted during constant 

discharge from River Mill Dam are needed to verify 

actual inputs of ground water. Once gaining reaches 

are identified, naturally occurring isotopes of C or N 

may be used to identify particular sources of nutrients. 

Isotopes (in tissues or water) can sometimes help 

distinguish between natural and anthropogenic 

nutrient sources, such as sewage or chemical fertilizers, 

if the source produces a unique isotopic signature 

(McClelland and others, 1997). 

Nitrogen from atmospheric deposition—The 

degree to which atmospheric deposition of N affects 

water quality and forest health in the Clackamas Basin 

is not known. Wet deposition data in the Bull Run 

Basin, about 20 miles north of the Clackamas Basin, 

show some high N concentrations: the average - concentration of NH4

+ + NO3 in precipitation from 

May to September 1996–2000 was about 900 μg/L, 

and concentrations exceeding 1,000 μg/L occurred 

in nearly 15% of samples (National Atmospheric Deposition Program [NADP] web site, http://nadp.sws. 

uiuc.edu/nadpdata, accessed 5/28/2001). Monitoring 

for atmospheric deposition of N in the Clackamas 

Basin, particularly at mid-elevation sites, might 

help explain the relatively higher N concentrations 

in streams draining this area. 

CONCLUSION 

Despite the episodes of poor water quality that 

were occasionally observed during this study in the 

Clackamas River and its tributaries and reservoirs, 

the Clackamas River remains one of the highest quality 

waters in the State of Oregon, still supporting runs of 

wild salmon, steelhead, and trout. However, if the river 

is to continue to support other designated beneficial 

uses, such as providing high-quality drinking water, 

efforts are needed to reduce contamination and restore 

natural processes in order to reverse the symptoms 

of nutrient enrichment that are beginning to appear. 

Restoration efforts and future studies described 

here could improve habitat and water quality in the 

Clackamas Basin over time. 

82 
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Ward, J.V., and Stanford, J.A., 1983, The serial discontinuity concept of lotic ecosystems, in Fontaine, T.D., 

and Bartell, S.M., eds., Dynamics of lotic ecosystems: 

Ann Arbor Science Publishers, p. 29–42. 

Wehr, J.D., and Descy, J.P., 1998, Use of phytoplankton 

in large river management: Journal of Phycology, v. 34, 

p. 741–749. 

Welch, E.B., Horner, R.R., and Patmont, C.R., 1989, 

Prediction of nuisance periphytic biomass—A 

management approach: Water Resources, v. 23, no. 4, 

p. 401–405. 

89 
Welch, E.B., Jacoby, J.M., Horner, R.R., and Seeley, M.R., 

1988, Nuisance biomass levels of periphytic algae in 

streams: Hydrobiologia, v. 157, p. 161–168. 

Wershaw, R.L., Fishman, M.J., Grabge, R.R., and Lowe, 

L.E., 1987, Methods for the determination of organic 

substances in water and fluvial sediments: Techniques 

of Water-Resources Investigations of the U.S. Geological Survey, book 5, chap. A3, 80 p. 

Wetzel, R.G., 1983, Limnology, 2d ed.: Philadelphia, 

Saunders College Publishing, 858 p. 

Wilde, F.D., Radtke, D.B., Gibs, J., and Iwatsubo, R.T., 

1998, National field manual for the collection of waterquality data: U.S. Geological Survey Techniques 

of Water-Resources Investigations, book 9 [variously 

paged]. 

Wilson, D.C., Burns, B., Jarrell, W., Lester, A., and 

Larson, E., 1999, Natural ground-water discharge 

of orthophosphate in the Tualatin Basin, northwest 

Oregon: Environmental and Engineering Geoscience, 

v. 5, no. 2, p. 189–197. 

Wipfli, M.S., Hudson, J., and Caouette, J., 1998, Influence 

of salmon carcass on stream productivity—Response of 

biofilm and benthic macroinvertebrates in southeastern 

Alaska: Canadian Journal of Fisheries and Aquatic 

Sciences, v. 55, p. 1503–1511. 

Wisseman, B., 2001, Sensitive or rare aquatic invertebrates 

in the Clackamas River Drainage—June and October 

2000 Sampling Report (Part of WQ3 Study): Prepared 

for the Water Quality Subgroup of the Clackamas 

Fish and Aquatics Workgroup, 6 p. [Available from 

Mary May, Portland General Electric Hydroliscensing 

Department, 121 SW Salmon Street, Portland, Oregon, 

97204.] 

Wootton, J.T., and Power, M.E., 1993, Productivity, 

consumers, and the structure of a river food chain: 

Proceedings of the National Academy of Science, v. 90, 

p. 1384–1387. 

90 
APPENDIXES


APPENDIX 1. MINIMUM LABORATORY REPORTING LEVELS (MRLs) 

FOR CONSTITUENTS ANALYZED IN THE CLACKAMAS RIVER BASIN, 

OREGON, 1998 

[μg/L, micrograms per liter; mg/m2, milligrams per square meter, nutrient 

abbreviations are listed in glossary] 

Chemical Minimum laboratory 

Nutrients symbol reporting levels a 

Soluble reactive phosphorus SRP 1 μg/L 

Total dissolved phosphorus TDP 1 μg/L 

Total phosphorus TP 1 μg/L 

Ammonium - nitrogen NH4 

+ 2 μg/L 

Nitrate + nitrite - nitrogen NO3 

- + NO2 - 5 μg/L 

Dissolved Kjeldahl nitrogen DKN 100 μg/L 

Total Kjeldahl nitrogen TKN 100 μg/L 

Silicon dioxide (silica) SiO2 100 μg/L 

Major ions 

Iron 

Chloride 

Fe+2 

Cl3 μg/L 100 μg/L 

Organic matter 

Chlorophyll a (phytoplankton) Chl a 1 μg/L 

Chlorophyll a (periphyton) Chl a 1 mg/m2 

Ash-free dry mass AFDM 1 mg/m2 

Dissolved organic carbon DOC 100 μg/L 

Suspended organic carbon SOC 200 μg/L 

a Nutrient and major ion MRLs reported on an atom-basis 

(as Phosphorus, for example). 

93 

APPENDIX 2. QUALITY-CONTROL SAMPLE RESULTS FOR NUTRIENTS IN WATER 

[Site codes and nutrient abbreviations listed in glossary; chemical symbols as in appendix 1; μg/L, micrograms per liter; 

mg/L, milligrams per liter; <, less than minimum reporting levels (see appendix 1); nd, no data] 

Blank samples 

NH4 

+ NO3 - DKN TKN SRP TDP TP SiO2 

Site Date Time (μg/L) (μg/L) (μg/L) (μg/L) (μg/L) (μg/L) (μg/L) (mg/L) 

USGS_LAB a 5/13/98 12:00 < < < < < 1 < < 

USGS_LAB b 6/4/98 11:30 < < < < 1 < 1 < 

USGS_LAB a 9/1/98 14:10 < < < < < < < 0.18 

USGS_LAB a 9/22/98 6:08 < 8 < < 1 14 < 0.13 

ROARING b 5/6/98 15:38 < < < < < < < nd 

ROARING b 7/7/98 15:08 < < < < < 6 < nd 

ROARING c 7/7/98 15:09 < < < < < 8 1 nd 

NFKRES_1 d 6/3/98 12:38 < < < < 1 < 1 < 

TIM_LK d 7/1/98 17:08 < < < < < < 4 nd 

TIM_LK d 8/18/98 13:48 < < < < 1 < 1 nd 

TIM_LK c 8/18/98 13:49 < < < < < < < nd 

Standard reference samples 

NO3

- NH4+ SRP TDP 

Sample Date Result (μg/L) (μg/L) (μg/L) (μg/L) 

1 05/13/98 expected 21 42 36 36 

reported 20 22 26 35 

2 07/14/98 10 21 9 9 

3 7 6 6 

expected 

reported 

3 09/01/98 expected 10 25 3 3 

reported 7 19 3 3 

4 09/01/98 10 25 3 3 

6 18 2 3 

expected 

reported 

5 09/22/98 expected 10 25 3 3 

reported 11 21 3 < 1 

Replicate samples e 

NO3

- NH4+ DKN TKN SRP TDP TP SiO2 

Site Date Time (μg/L) (μg/L) (μg/L) (μg/L) (μg/L) (μg/L) (μg/L) (mg/L) 

CR_3LYNX-A 05/06/98 10:50 < < < < 7 10 16 nd 

CR_3LYNX-B 10:52 < < < < 7 19 14 nd 

NFKRES_1-A 06/03/98 < < < 8 12 21 15.9 

NFKRES_1-B < 7 < < 9 11 21 15.9 

12:30 109 

12:32 

NKFKRES_1-A 07/02/98 11:00 < < 106 < 7 11 17 18.1 

NFKRES_1-B 11:02 < < < < 8 11 17 nd 

FISH-A 07/07/98 < 7 < < 7 14 12 17.6 

FISH-B < 7 < < 7 24 12 17.0 

16:40 

16:42 

DEEP-A 07/10/98 11:40 3 1,045 167 161 68 78 78 18.7 

DEEP-B 11:42 2 1,034 122 175 67 78 84 18.9 

NFKRES_1-A 08/20/98 5 < < < 10 10 13 19.5 

NFKRES_1-B < < < < 9 10 13 nd 

11:50 

11:52 

CR_ABNFK-A 09/01/98 9:00 < < < < 15 16 19 21.0 

CR_ABNFK-B 9:02 < < < < 15 17 18 nd 

NFKRES_1-A 09/22/98 < 9 < < 8 9 14 21.0 

NFKRES_1-B < 9 < < 8 9 14 20.8 

11:10 

11:12 

a Lab serial equipment blank (collection bottle, churn splitter, tubing, and filter). 
 b Field serial equipment blank (collection bottle, churn splitter, tubing, and filter). 
 c Certified inorganic blank water (non-equipment blank).
 d Field Van Dorn sampler blank.
 e A and B denote replicate samples.


95 

APPENDIX 3. QUALITY-CONTROL SAMPLE RESULTS FOR ALGAE COLLECTED IN THE CLACKAMAS RIVER BASIN, 

OREGON, 1998 

Appendix 3A. Measures of algal abundance from true replicate samples 

[Site codes are listed in the glossary; A and B denote independent samples collected and composited separately; g/m2, grams per square meter; 

mg/m2, milligrams per square meter; # cells/cm2, number of cells per square centimeter; μm3/cm2

, cubic micrometers per square centimeter] 

Site Month 

AFDM a 

(g/m2) 

Chlorophyll a a 

(mg/m2) 

Abundance 

(# cells /cm2

) 

Biovolume 

(μm3

/cm2) 

CR_BLNFK - A May 83.7 213.7 2.57 × 106 5.00 × 109 

CR_BLNFK - B May 76.1 173.0 2.55 × 106 5.23 × 109 

SFCLACK - A July 25.5 149.1 5.50 × 106 1.33 × 109 

SFCLACK - B July 20.4 125.0 6.68 × 106 7.16 × 108 

CR_99E - A July 24.4 52.8 1.73 × 106 9.26 × 108 

CR_99E - B July 24.9 56.3 1.57 × 106 2.28 × 109 

CR_ABNFK - A September 15.4 60.8 7.45 × 105 7.07 × 108 

CR_ABNFK - B September 17.5 62.0 7.14 × 105 1.25 × 109 

a Average of three replicates. 

Appendix 3B. Percent similarity between true replicate samples analyzed by Bowling Green State University Laboratory 

[Site codes are listed in the glossary] 

Soft algae + Diatoms Diatoms Diatoms 

Site Month (relative abundance) (relative abundance) (relative biovolume) 

CR_BLNFK May 86.1 76.7 74.1 

CR_99E July 79.5 85.1 87.0 

CR_BLNFK July 69.8 76.9 70.5 

CR_99E September 77.6 76.7 74.1 

CR_ABNFK September 67.4 79.6 82.5 

Appendix 3C. Percent similarity for diatom slide preparations analyzed by both algal contractors 

[Site acronyms are listed in the glossary; A and B denote true replicate (i.e., separate samples, not split samples)] 

Site Month Percent similarity 

CR_MCIVER May 60.7 

CR_BARTON May 66.7 

CR_99E May 65.2 

SFCLACK - A July 70.8 

SFCLACK - B July 62.1 

97 

APPENDIX 4. PERIPHYTON TAXA OCCURRENCE AT MAIN-STEM CLACKAMAS RIVER SITES, OREGON, 1998 

[Algal taxa are ordered by major algal Division; site codes are listed in the glossary; *, indicates taxon presence at a site; **, indicates 5 most abundant taxa 

at each site (based on % relative biovolume); some taxa are assigned to autecological guilds as follows: NF, nitrogen fixers; NH, facultative nitrogen 

heterotrophs; E, eutrophic taxa; O, oligotrophic taxa; A, alkaliphilic taxa; HP, halophilic taxa; HB, halophobic taxa; S, silt-tolerant taxa. Sources for 

autecological classification are from Patrick and Reimer, 1966, 1975; Schoeman, 1973; Lowe, 1974; van Dam and others, 1994; Tuchman, 1996; 

Lowe and Pan, 1996; Porter and others, 1993.] 

Main stem sites, in downstream order 

CR_ CR_ CR_ CR_ CR_ CR_ CR_ CR_ 

UPPER 3LYNX ABNFK BLNFK MCIVER BARTON CARVER 99E 

Sampling month (M) May, (J) July, and (S) September 

Algal taxon Guild M J S M J S M J S M J S M J S M J S M J S M J S 

RHODOPHYTA (Red Algae) 

Audouinella sp. * * * 

CHLOROPHYTA (Green algae) 

Ankistrodesmus sp. * * * * * * 

Cladophora sp. **   **  ** ** 

Crucigenia tetrapedia sp. # 1 * 

Microspora sp. ** ** * 

Mougeotia sp. # 2 ** ** ** * * 

Scenedesmus dimorphus * 

Scenedesmus quadricauda * 

Scenedesmus sp. # 2 * * 

Spirogyra sp. ** ** 

Staurastrum sp. * 

Stigeoclonium sp. # 1 * * * 

Ulothrix sp. # 2 * 

Ulothrix zonata **   **  * 

Zygnema sp. ** ** ** 

CHRYSOPHYTA (Golden algae) 

Tribonema sp. * 

Unidentified Chrysophyte filament ** 

Vaucheria sp. ** ** 

CYANOPHYTA (Blue-green algae) 

Calothrix sp. NF * * * * * * * 

Calothrix heterocysts NF * * 

Chamaesiphon sp. * * 

Lyngbya sp. * * * * * * * * * 

Nostoc sp. NF * ** ** ** * * * * * * ** * * * * * * 

Nostoc sp. heterocysts * * * * * * * * * * * 

Nostoc akinete * 

Oscillatoria sp. # 1 * * * * * * * * * * * * * * * * * * 

Schizothrix calcicola * * * * * * * * * * * * * * * * * * 

Tolypothrix sp. NF ** ** * 

Tolypothrix heterocysts NF * * 

BACILLARIOPHYTA (Diatoms) 

Achnanthes deflexa * * * * * * * * ** * * * * * * 

Achnanthes hauckiana O * * 

Achnanthes lapidosa * * 

Achnanthes sp. # 2 * 

99 
APPENDIX 4. PERIPHYTON TAXA OCCURRENCE AT MAIN-STEM CLACKAMAS RIVER SITES, OREGON, 1998—Continued 

[Algal taxa are ordered by major algal Division; site codes are listed in the glossary; *, indicates taxon presence at a site; **, indicates 5 most abundant taxa 

at each site (based on % relative biovolume); some taxa are assigned to autecological guilds as follows: NF, nitrogen fixers; NH, facultative nitrogen 

heterotrophs; E, eutrophic taxa; O, oligotrophic taxa; A, alkaliphilic taxa; HP, halophilic taxa; HB, halophobic taxa; S, silt-tolerant taxa. Sources for 

autecological classification are from Patrick and Reimer, 1966, 1975; Schoeman, 1973; Lowe, 1974; van Dam and others, 1994; Tuchman, 1996; 

Lowe and Pan, 1996; Porter and others, 1993.] 

Main stem sites, in downstream order 

CR_ CR_ CR_ CR_ CR_ CR_ CR_ CR_ 

UPPER 3LYNX ABNFK BLNFK MCIVER BARTON CARVER 99E 

Sampling month (M) May, (J) July, and (S) September 

Algal taxon Guild M J S M JS M J S M JS M J S M JS M J S M JS 

BACILLARIOPHYTA (Diatoms) – Continued 

Achnanthes suchlandtii O, HB * * * * * * * * * * * * * * 

Achnanthidium minutissimum * * * * * * * * * * * * * * * * * * * * * * * 

Amphipleura pellucida E, A * * * 

Amphora ovalis E, A * * 

Amphora perpusilla NH * * * * 

Aulacoseira granulata E, A * * * * * * 

Aulacoseira sp. # 1 * * * * * * * * * 

Caloneis bacillum A * * * * * * * * * * * * 

Cocconeis klamathensis * ** * * * 

Cocconeis pediculus E, A * * * * * * * * * * 

Cocconeis placentula E, A * * * * * * * * * * * * * * * 

Cyclotella meneghiniana E, NH, A * * 

Cyclotella sp. * 

Cyclotella stelligera * 

Cymbella cistula E, A * * 

Cymbella mexicana ** 

Cymbella mexicana v. janischii   **  ** * * * ** * 

Cymbella minuta sp. # 2 * * * * * * * * * * * * * * * * * * ** * * 

Cymbella minuta - like * ** * ** * * * * * * * * * * * * * * * * * 

Cymbella sp. # 2 * 

Cymbella tumida A * 

Cymbella turgidula A * * * * * * * * * * * * * * 

Diadesmis confervacea E, NH, HP * * 

Diadesmus perpusilla * * 

Diatoma hiemale A, HB * * * * * * 

Diatoma hiemale v. mesodon HB * * * * * * * * * 

Diatoma tenue v. elongatum HP * 

Diatoma vulgare E, A * * * * * * * * ** ** * ** ** * ** ** 

Diploneis elliptica A * 

Diploneis oblongella A * * 

Epithemia adnata NF, A * ** ** * **   **  ** ** * **   **  * * 

Epithemia sorex sp. # 1 NF, E, A * * * * * ** * * ** * ** * ** 

Epithemia turgida NF, A * 

Eunotia pectinalis v. minor HB * 

Eunotia perpusilla * * * * * * 

Fragilaria construens v. pumila * * * * * * * * * * 

Fragilaria crotonensis sp. # 2 A * 

Fragilaria vaucheriae E, A * * * * * * * * * * * * * * 

Frustulia rhomboides v. amphipleuroides O, HB * * * * * * * 

100 
APPENDIX 4. PERIPHYTON TAXA OCCURRENCE AT MAIN-STEM CLACKAMAS RIVER SITES, OREGON, 1998—Continued 

[Algal taxa are ordered by major algal Division; site codes are listed in the glossary; *, indicates taxon presence at a site; **, indicates 5 most abundant taxa 

at each site (based on % relative biovolume); some taxa are assigned to autecological guilds as follows: NF, nitrogen fixers; NH, facultative nitrogen 

heterotrophs; E, eutrophic taxa; O, oligotrophic taxa; A, alkaliphilic taxa; HP, halophilic taxa; HB, halophobic taxa; S, silt-tolerant taxa. Sources for 

autecological classification are from Patrick and Reimer, 1966, 1975; Schoeman, 1973; Lowe, 1974; van Dam and others, 1994; Tuchman, 1996; 

Lowe and Pan, 1996; Porter and others, 1993.] 

Main stem sites, in downstream order 

CR_ CR_ CR_ CR_ CR_ CR_ CR_ CR_ 

UPPER 3LYNX ABNFK BLNFK MCIVER BARTON CARVER 99E 

Sampling month (M) May, (J) July, and (S) September 

Algal taxon Guild M J S M JS M J S M JS M J S M JS M J S M JS 

BACILLARIOPHYTA (Diatoms) – Continued 

Gomphoneis eriense v. rostrata * * * * * ** * * * 

Gomphoneis eriense v. variabilis * ** * * * ** * * * * * * * * * * ** * * * * 

Gomphoneis herculeana * ** ** * * * ** ** * **   **  **   **  ** ** 

Gomphonema angustatum E, A * * 

Gomphonema intricatum E, A ** 

Gomphonema parvulum E, NH * * * 

Gomphonema pumilum * * * * * * * * * * * * * * * * * 

Gomphonema quadripunctatum * 

Gomphonema sp. # 1 * * * * 

Gomphonema sp. # 2 * * * * * * * * * * * * * * * 

Gomphonema sp. # 3 * * * * 

Gomphonema sp. # 4 * * * * 

Gomphonema subclavatum O * * * * * 

Hannaea arcus A, HB * * * * ** * * * 

Hantzschia amphioxys A * * 

Luticola mutica E, HP, S ** 

Luticola sp. # 1 S * 

Melosira varians E, NH, A * * ** ** * * * **   **  ** ** ** * * ** ** * 

Meridion circulare E, A * * * * * * * 

Meridion lineare * * * 

Navicula capitata A, S * 

Navicula capitata v. hungarica A, S * 

Navicula cincta E, A, S * * 

Navicula confervacea E, NH, HP, S * * * 

Navicula cryptocephala E, A, S * 

Navicula decussis A, S * * * 

Navicula gregaria E, A, S * 

Navicula menisculus E, A, S * * * * 

Navicula minima Grun. E, NH, A, S * * 

Navicula mutica v. undulata NH, S ** 

Navicula radiosa S * * * * * * * 

Navicula radiosa v. tenella S * * * * * * * ** * * * * * * * * * * * * * 

Navicula salinarum v. intermedia S * * 

Navicula seminulum E, NH, S * * 

Navicula sp. # 1 S * * * * * * 

Navicula sp. # 2 S * 

Navicula tripunctata E, NH, A, S * 

Navicula ventralis v. chilensis S * 

101 
APPENDIX 4. PERIPHYTON TAXA OCCURRENCE AT MAIN-STEM CLACKAMAS RIVER SITES, OREGON, 1998—Continued 

[Algal taxa are ordered by major algal Division; site codes are listed in the glossary; *, indicates taxon presence at a site; **, indicates 5 most abundant taxa 

at each site (based on % relative biovolume); some taxa are assigned to autecological guilds as follows: NF, nitrogen fixers; NH, facultative nitrogen 

heterotrophs; E, eutrophic taxa; O, oligotrophic taxa; A, alkaliphilic taxa; HP, halophilic taxa; HB, halophobic taxa; S, silt-tolerant taxa. Sources for 

autecological classification are from Patrick and Reimer, 1966, 1975; Schoeman, 1973; Lowe, 1974; van Dam and others, 1994; Tuchman, 1996; 

Lowe and Pan, 1996; Porter and others, 1993.] 

Main stem sites, in downstream order 

CR_ CR_ CR_ CR_ CR_ CR_ CR_ CR_ 

UPPER 3LYNX ABNFK BLNFK MCIVER BARTON CARVER 99E 

Sampling month (M) May, (J) July, and (S) September 

Algal taxon Guild M J S M JS M J S M JS M J S M JS M J S M JS 

BACILLARIOPHYTA (Diatoms) – Continued 

Nitzschia sp. # 1 S * * * * 

Nitzschia sp. # 2 S * * * 

Nitzschia sp. # 3 S * * * * 

Nitzschia amphibia E, NH, A, S * 

Nitzschia angustata S * * 

Nitzschia dissipata E, A, S * * * * * * * * * * * * * * * * * * 

Nitzschia frustulum E, NH, A, HP, S * ** * * * ** ** * * * ** ** * ** * * * * * * * 

Nitzschia gracilis HB, S * * * * * 

Nitzschia inconspicua E, NH, A, HP, S * * * * * * * * * * * * * * 

Nitzschia linearis E, A, S * * * * * * 

Nitzschia palea E, NH, S * * * * * * * 

Nitzschia recta A, S * * * 

Pinnularia brebissonii * * 

Planothidium lanceolatum E, A * * * * * * * * * * * * * * * * * * * * 

Planothidium lanceolatum v. dubium * * * 

Pseudostaurosira brevistriata E, A * * * * * * * * * * * * * * 

Reimeria sinuata * * * * * * * 

Rhoicosphenia curvata E, A * * * * * * * * * * * * ** * ** * * * * 

Rhopalodia gibba sp. # 2 NF, E, A * * * * * * * * * ** * * * * 

Sellaphora pupula E * * 

Staurosira construens E, A * 

Staurosira construens v. binodis A * * * 

Staurosira construens v. venter A * * 

Staurosirella leptostauron A * * * * 

Surirella angustata E, A * * 

Surirella sp. # 1 * 

Synedra mazamaensis * * * * * * * * * * * * * * * * * * * 

Synedra parasitica A * 

Synedra rumpens v. fragilariodes * * * * * * 

Synedra rumpens v. rumpens O * * * * * * 

Synedra sp. # 1 * * * * * 

Synedra ulna A * * * ** * * ** * * ** ** * ** * * * ** * ** * * ** ** 

Synedra ulna v. contracta * * * 

102 
APPENDIX 5. PERIPHYTON TAXA OCCURRENCE AT TRIBUTARY SITES IN THE CLACKAMAS RIVER BASIN, OREGON, 1998 

[Algal taxa are ordered by major algal Division; site codes are listed in the glossary; *, indicates taxon presence at a site; **, indicates 5 most abundant taxa 

at each site (based on % relative biovolume); some taxa are assigned to autecological guilds as follows: NF, nitrogen fixers; NH, facultative nitrogen 

heterotrophs; E, eutrophic taxa; O, oligotrophic taxa; A, alkaliphilic taxa; HP, halophilic taxa; HB, halophobic taxa; S, silt-tolerant taxa. Sources for 

autecological classification are from Patrick and Reimer, 1966, 1975; Schoeman, 1973; Lowe, 1974; van Dam and others, 1994; Tuchman, 1996; 

Lowe and Pan, 1996; Porter and others, 1993.] 

Algal taxon Guild 

Audouinella sp. * * * ** 

Tributary sites, in downstream order 

Sampling month (M) May, (J) July, and (S) September 

M J S M J S J M J S J J J J M J S J J J J J J J 

RHODOPHYTA (Red algae) COLLA COLLA COLLA OAK_BLTLK OAK_BLTLK OAK_BLTLK OAK_RAIN ROARING 

ROARING ROARING FISHSFCLACK WINSLOW FALLNFCLACKNFCLACKNFCLACKEAGLE_M EAGLE_W DEEPRICHARDSON CLEARROCKSIEBEN 

CHLOROPHYTA (Green algae) 

Ulothrix zonata   **  ** ** 

Cladophora sp. ** 

Stigeoclonium sp. # 1 ** * * * 

Zygnema sp. **   **  

Spirogyra sp. ** 

Mougeotia sp. # 2 ** ** 

Oedogonium sp. * * * 

Ankistrodesmus sp. * * 

Cosmarium sp. * * 

Crucigenia tetrapedia sp. # 1 * 

Draparnaldia (large cells) ** 

Draparnaldia (small cells) * * 

Microspora sp. * ** ** 

Scenedesmus dimorphus * 

CYANOPHYTA (Blue-green algae) 

Nostoc sp. NF * ** * * * * * 

Nostoc akinete * 

Calothrix sp. NF * * * 

Chamaesiphon sp. ** ** * 

Eucapsis alpina ** 

Lyngbya sp. * * * * * * * * * 

Merismopedia sp. * 

Oscillatoria sp. # 1 * * ** * * * * * ** ** * ** * * ** * ** * * * 

Schizothrix calcicola * * * * * * * * * * * * * * * ** ** * * * * 

Tolypothrix sp. NF ** ** * 

Tolypothrix heterocysts NF * * * 

BACILLARIOPHYTA (Diatoms) 

Achnanthes biasolettiana A * 

Achnanthes deflexa * * * * ** ** ** * ** ** ** * ** * ** * 

Achnanthes hauckiana O * 

Achnanthes lapidosa * 

103 
APPENDIX 5. PERIPHYTON TAXA OCCURRENCE AT TRIBUTARY SITES IN THE CLACKAMAS RIVER BASIN, OREGON, 1998—Continued 

[Algal taxa are ordered by major algal Division; site codes are listed in the glossary; *, indicates taxon presence at a site; **, indicates 5 most abundant taxa 

at each site (based on % relative biovolume); some taxa are assigned to autecological guilds as follows: NF, nitrogen fixers; NH, facultative nitrogen 

heterotrophs; E, eutrophic taxa; O, oligotrophic taxa; A, alkaliphilic taxa; HP, halophilic taxa; HB, halophobic taxa; S, silt-tolerant taxa. Sources for 

autecological classification are from Patrick and Reimer, 1966, 1975; Schoeman, 1973; Lowe, 1974; van Dam and others, 1994; Tuchman, 1996; 

Lowe and Pan, 1996; Porter and others, 1993.] 

Algal taxon Guild M J S M J S J M J S JJJJ M J S JJJJJJJ 

Tributary sites, in downstream order 

Sampling month (M) May, (J) July, and (S) September 

COLLA COLLA COLLA OAK_BLTLK OAK_BLTLK OAK_BLTLK OAK_RAINROARING ROARING ROARING FISHSFCLACK WINSLOW FALLNFCLACKNFCLACKNFCLACKEAGLE_M EAGLE_W DEEPRICHARDSON CLEARROCKSIEBEN 

BACILLARIOPHYTA (Diatoms) – Continued 

Achnanthes sp. # 1 * * 

Achnanthes sp. # 2 * 

Achnanthes sp. # 4 * 

Achnanthes suchlandtii O, HB * * * * * * * * * 

Achnanthidium minutissimum * * * * * ** ** * ** ** * ** ** * * ** * * ** * ** * * * 

Amphipleura pellucida E, A * * * 

Amphora perpusilla NH * * * * * * * * * 

Asterionella formosa E, A * 

Aulacoseira distans O, HB * 

Aulacoseira granulata E, A * * 

Aulacoseira sp. # 1 * * 

Bacillaria paradoxa E, A * 

Brachysira vitrea A, O * * 

Caloneis bacillum A * * * * * * 

Cocconeis pediculus E, A ** * * 

Cocconeis placentula E, A * * * * * * * * * * ** * * * ** ** * * * 

Cyclotella meneghiniana E, NH, A * 

Cyclotella stelligera * 

Cymbella cistula E, A * 

Cymbella mexicana ** * * **   **  

Cymbella mexicana v. janischii ** 

Cymbella microcephala sp. # 2 A * 

Cymbella minuta sp. # 2 * * * * * * * * * * * * * * * 

Cymbella minuta-like ** * * * 

Cymbella prostrata E, A ** 

Cymbella sp. # 2 * 

Cymbella tumida A * ** * 

Cymbella turgidula A * * * * * * * * 

Diadesmis confervacea E, NH, HP * 

Diadesmus contenta A * 

Diadesmus perpusilla * 

Diatoma hiemale A, HB * 

Diatoma hiemale v. mesodon HB * * * * ** ** * * 

Diatomella balfouriana * 

104 
APPENDIX 5. PERIPHYTON TAXA OCCURRENCE AT TRIBUTARY SITES IN THE CLACKAMAS RIVER BASIN, OREGON, 1998—Continued 

[Algal taxa are ordered by major algal Division; site codes are listed in the glossary; *, indicates taxon presence at a site; **, indicates 5 most abundant taxa 

at each site (based on % relative biovolume); some taxa are assigned to autecological guilds as follows: NF, nitrogen fixers; NH, facultative nitrogen 

heterotrophs; E, eutrophic taxa; O, oligotrophic taxa; A, alkaliphilic taxa; HP, halophilic taxa; HB, halophobic taxa; S, silt-tolerant taxa. Sources for 

autecological classification are from Patrick and Reimer, 1966, 1975; Schoeman, 1973; Lowe, 1974; van Dam and others, 1994; Tuchman, 1996; 

Lowe and Pan, 1996; Porter and others, 1993.] 

Algal taxon Guild M J S M J S J M J S JJJJ M J S JJJJJJJ 

Tributary sites, in downstream order 

Sampling month (M) May, (J) July, and (S) September 

COLLA COLLA COLLA OAK_BLTLK OAK_BLTLK OAK_BLTLK OAK_RAINROARING ROARING ROARING FISHSFCLACK WINSLOW FALLNFCLACKNFCLACKNFCLACKEAGLE_M EAGLE_W DEEPRICHARDSON CLEARROCKSIEBEN 

BACILLARIOPHYTA (Diatoms) – Continued 

Diploneis elliptica A * 

Entomoneis ornata HB * 

Epithemia adnata NF, A **   **  * ** 

Epithemia sorex sp. # 1 NF, E, A * * 

Epithemia turgida NF, A ** ** 

Eunotia pectinalis v. minor HB * 

Eunotia perpusilla * * * * 

Fragilaria construens v. pumila * * * 

Fragilaria vaucheriae E, A * * * * * * * * * * * * * * * 

Frustulia rhomboides v. amphipleuroides O, HB * * ** ** * * 

Gomphoneis eriense v. rostrata * 

Gomphoneis eriense v. variabilis ** * * * 

Gomphoneis herculeana **   **  * * * 

Gomphoneis herculeana v. septiceps ** 

Gomphonema angustatum E, A * * * * * * * 

Gomphonema gracile * 

Gomphonema parvulum E, NH * * ** * * * * * 

Gomphonema pumilum * * * * * * ** * * * * * * ** * * ** ** * 

Gomphonema sp. # 1 * * * 

Gomphonema sp. # 2 * ** * * * * * * * * * ** * * 

Gomphonema sp. # 3 * 

Gomphonema sp. # 4 * * 

Gomphonema subclavatum O * * * 

Gomphonema truncatum v. capitatum * * 

Hannaea arcus A, HB * * * * ** ** * * * * ** * 

Melosira varians E, NH, A ** * * * * **   **  **   **  

Meridion circulare E, A * * 

Meridion lineare * 

Navicula accomoda E, NH, A, S * 

Navicula capitata A, S * 

Navicula cincta E, A, S * 

Navicula cryptocephala E, A, S * * 

Navicula cryptocephala v. veneta E, A, S * 

Navicula gregaria E, A, S * * * 

105 
APPENDIX 5. PERIPHYTON TAXA OCCURRENCE AT TRIBUTARY SITES IN THE CLACKAMAS RIVER BASIN, OREGON, 1998—Continued 

[Algal taxa are ordered by major algal Division; site codes are listed in the glossary; *, indicates taxon presence at a site; **, indicates 5 most abundant taxa 

at each site (based on % relative biovolume); some taxa are assigned to autecological guilds as follows: NF, nitrogen fixers; NH, facultative nitrogen 

heterotrophs; E, eutrophic taxa; O, oligotrophic taxa; A, alkaliphilic taxa; HP, halophilic taxa; HB, halophobic taxa; S, silt-tolerant taxa. Sources for 

autecological classification are from Patrick and Reimer, 1966, 1975; Schoeman, 1973; Lowe, 1974; van Dam and others, 1994; Tuchman, 1996; 

Lowe and Pan, 1996; Porter and others, 1993.] 

Algal taxon Guild M J S M J S J M J S JJJJ M J S JJJJJJJ 

Tributary sites, in downstream order 

Sampling month (M) May, (J) July, and (S) September 

COLLA COLLA COLLA OAK_BLTLK OAK_BLTLK OAK_BLTLK OAK_RAINROARING ROARING ROARING FISHSFCLACK WINSLOW FALLNFCLACKNFCLACKNFCLACKEAGLE_M EAGLE_W DEEPRICHARDSON CLEARROCKSIEBEN 

BACILLARIOPHYTA (Diatoms) – Continued 

Navicula lanceolata E, HP, A, S * 

Navicula minima Grun. E, NH, A, S * * * 

Navicula radiosa S * * * ** * * 

Navicula radiosa v. tenella S * ** * * * * * * * * * * * * * 

Navicula salinarum v. intermedia S * 

Navicula seminulum E, NH, S * * 

Navicula sp. # 1 S * * * * * * * 

Navicula symmetrica S * 

Navicula tripunctata E, NH, A, S * 

Navicula viridula E, A, S * ** 

Nitzschia sp. # 1 S * * * * 

Nitzschia sp. # 2 S * * * * * 

Nitzschia sp. # 3 S * * * 

Nitzschia amphibia E, NH, A, S * * * * 

Nitzschia angustata S * 

Nitzschia dissipata E, A, S * * * * * * * * * * * ** * * * * * * 

Nitzschia fonticola E, A, S * * 

Nitzschia frustulum E, NH, HP, A, S * * * * * * ** * * * ** * * * ** ** 

Nitzschia gracilis HB, S * * * * 

Nitzschia inconspicua E, NH, A, HP, S * * * * * * * * * * 

Nitzschia linearis E, A, S * * * * 

Nitzschia palea E, NH, S * * * 

Nitzschia recta A, S * * * * 

Pinnularia acuminata v. bielawskii * 

Pinnularia brebissonii * 

Planothidium lanceolatum E, A * * * * * * * * * * * ** * ** * * * ** * * ** 

Planothidium lanceolatum v. dubium * * 

Pseudostaurosira brevistriata E, A * * * * * 

Reimeria sinuata * * * * * * * * * * * * 

Rhoicosphenia curvata E, A * * * * * * * * * * * * * * * * ** * ** * 

Rhopalodia gibba sp. # 2 NF, E, A * * 

Sellaphora pupula E * * 

Staurosira construens E, A * 

Staurosira construens v. binodis A * 

106 
APPENDIX 5. PERIPHYTON TAXA OCCURRENCE AT TRIBUTARY SITES IN THE CLACKAMAS RIVER BASIN, OREGON, 1998—Continued 

[Algal taxa are ordered by major algal Division; site codes are listed in the glossary; *, indicates taxon presence at a site; **, indicates 5 most abundant taxa 

at each site (based on % relative biovolume); some taxa are assigned to autecological guilds as follows: NF, nitrogen fixers; NH, facultative nitrogen 

heterotrophs; E, eutrophic taxa; O, oligotrophic taxa; A, alkaliphilic taxa; HP, halophilic taxa; HB, halophobic taxa; S, silt-tolerant taxa. Sources for 

autecological classification are from Patrick and Reimer, 1966, 1975; Schoeman, 1973; Lowe, 1974; van Dam and others, 1994; Tuchman, 1996; 

Lowe and Pan, 1996; Porter and others, 1993.] 

Algal taxon Guild M J S M J S J M J S JJJJ M J S JJJJJJJ 

Tributary sites, in downstream order 

Sampling month (M) May, (J) July, and (S) September 

COLLA COLLA COLLA OAK_BLTLK OAK_BLTLK OAK_BLTLK OAK_RAINROARING ROARING ROARING FISHSFCLACK WINSLOW FALLNFCLACKNFCLACKNFCLACKEAGLE_M EAGLE_W DEEPRICHARDSON CLEARROCKSIEBEN 

BACILLARIOPHYTA (Diatoms) – Continued 

Staurosira construens v. venter A * 

Staurosirella leptostauron A * 

Surirella angustata E, A * 

Synedra delicatissima * 

Synedra mazamaensis * * * * * 

Synedra rumpens v. fragilariodes * * * * * 

Synedra rumpens v. rumpens O * * * * * * * * * 

Synedra sp. # 1 * 

Synedra ulna A * * * * * ** * ** * * ** ** * * 

Synedra ulna v. contracta * * ** 

Tabellaria fenestrata HB * * 

Tabellaria flocculosa HB * * 

107 

APPENDIX 6. PHYTOPLANKTON TAXA OCCURRENCE IN NORTH FORK RESERVOIR, CLACKAMAS RIVER BASIN, OREGON 1997–98 

[Algal taxa are ordered by major algal Divisions; *, indicates taxon presence at a site; **, indicates 5 most abundant taxa at each site (based on % relative 

biovolume); B, NFKRES_B (site codes are listed in the glossary); sampling depths are given as follows: (1) surface, (2) thermocline, (3) depth of water release, 

and (4) 1 meter off the bottom; some taxa are assigned to autecological guilds as follows: (NF) nitrogen fixers, (NH) facultative nitrogen heterotrophs, 

(E) eutrophic taxa, (O) oligotrophic taxa, (A) alkaliphilic taxa, (HB) halophobic taxa, and (S) silt-tolerant taxa. Sources for autecological classification are from 

Patrick and Reimer, 1966, 1975; Schoeman, 1973; Lowe, 1974; van Dam and others, 1994; Tuchman, 1996; Lowe and Pan, 1996; Porter and others, 1993] 

Reservoir station, year, month, and sampling depth 

NFKRES_1 NFKRES_2 B 

1997 1998 

Sampling month and depth 

Algal taxa Guild

 July (1) 

Aug (1)

 Sep (1) April (1) 

May (1) May (2) May (3) May (4)

 June (1) June (2) June (3) June (4)

July (1)

 July (2) July (3) 

Aug (1) Aug (2) Aug (3) Aug (4)

 Sep (1) Sep (2) Sep (3) Sep (4) 

May (1) May (2)

 June (1) June (2) June (3)

July (1)

 July (2) July (3) 

Aug (1) Aug (2) Aug (3)

 Sep (1) Sep (2) Sep (3) 

Sep (1) 

CRYPTOPHYTA (Cryptophyte algae) 

Cryptomonas erosa v. reflexa ** * **** ********** * * * * ** * **** ********** * **** * * 

Rhodomonas minuta ** ** * * * * * ****** * ************ * **** * * * ****** ********** * ** * * * 

DINOPHYTA (Dinophyte algae) 

Glenodinium sp. * * **** * ** * * * ** * ****** * ** * 

EUGLENOPHYTA (Euglenophyte algae) 

Euglena sp. ** * * **** 

Trachelomonas sp. * * 

CYANOPHYTA (Blue-green algae) 

Anabaena circinalis NF * **** * * ** **** * * ** 

Anabaen circinalis heterocyst NF **** * * * * 

Anabaena spiroides NF * 

Anabaena spiroides heterocyst NF * 

Anabaena akinete NF ** * * 

Aphanothece sp. * * 

Oscillatoria sp. # 2 ** * ** ** 

Schizothrix calcicola * * * ** * * * * * * * * * * 

CHLOROPHYTA (Green algae) 

Ankistrodesmus sp. * * * * * * * * 

Chlamydomonas sp. * * ** * * * * 

Closterium sp. * * 

Dactylococcus infusionum * 

Dictyosphaerium sp. ** 

Elakatothrix sp. **** * **** 

Eudorina sp. * 

Mougeotia sp. # 1 * ** 

Scenedesmus sp. # 1 ** * 

Stigeoclonium sp. # 2 * 

BACILLARIOPHYTA (Diatoms) 

Achnanthes deflexa * 

Achnanthes hauckiana O * 

Achnanthes lapidosa * 

Achnanthes sp. # 2 * 

Achnanthes sp. # 4 ** 

109 
APPENDIX 6. PHYTOPLANKTON TAXA OCCURRENCE IN NORTH FORK RESERVOIR, CLACKAMAS RIVER BASIN, OREGON 1997–98—Continued 

[Algal taxa are ordered by major algal Divisions; *, indicates taxon presence at a site; **, indicates 5 most abundant taxa at each site (based on % relative 

biovolume); B, NFKRES_B (site codes are listed in the glossary); sampling depths are given as follows: (1) surface, (2) thermocline, (3) depth of water release, 

and (4) 1 meter off the bottom; some taxa are assigned to autecological guilds as follows: (NF) nitrogen fixers, (NH) facultative nitrogen heterotrophs, 

(E) eutrophic taxa, (O) oligotrophic taxa, (A) alkaliphilic taxa, (HB) halophobic taxa, and (S) silt-tolerant taxa. Sources for autecological classification are from 

Patrick and Reimer, 1966, 1975; Schoeman, 1973; Lowe, 1974; van Dam and others, 1994; Tuchman, 1996; Lowe and Pan, 1996; Porter and others, 1993] 

Reservoir station, year, month, and sampling depth 

NFKRES_1 NFKRES_2 B 

1997 1998 

Sampling month and depth 

Algal taxa Guild

 July (1) 

Aug (1)

 Sep (1) April (1) 

May (1) May (2) May (3) May (4)

 June (1) June (2) June (3) June (4)

July (1)

 July (2) July (3) 

Aug (1) Aug (2) Aug (3) Aug (4)

 Sep (1) Sep (2) Sep (3) Sep (4) 

May (1) May (2)

 June (1) June (2) June (3)

July (1)

 July (2) July (3) 

Aug (1) Aug (2) Aug (3)

 Sep (1) Sep (2) Sep (3) 

Sep (1) 

BACILLARIOPHYTA (Diatoms) – Continued 

Achnanthidium minutissimum * * * * * * * * * ** * * * * * * * * * 

Amphora sp. * * * 

Asterionella formosa E, A ** * * ** ** * * * * ** 

Aulacoseira granulata E, A ******** ******** 

Aulacoseira sp. ** * ****** ** * 

Caloneis ventricosa * 

Cocconeis klamathensis * 

Cocconeis placentula A, HB * * * * * * * * * * * * * * * * 

Cyclotella sp. * * * * * 

Cymbella microcephala sp. # 1 A * 

Cymbella minuta sp. # 1 * * * * * * **** * * * * * * * * * 

Cymbella sp. # 1 * 

Diatoma hiemale A, HB ** * 

Diatoma hiemale v. mesodon HB ** ** * * * ** * 

Epithemia sorex sp. # 1 NF, E, A ** ** ** 

Epithemia sp. NF * 

Eunotia sp. * * 

Fragilaria crotonensis sp. # 2 A * ** 

Fragilaria sp. # 3 ** 

Frustulia rhomboides * 

Gomphoneis sp. ** ******** ** * ******   **  

Gomphonema sp. ** * **** * ** ** * **** * * * * * ** * * * 

Hannaea arcus A, HB ** ** * **** **** * 

Melosira varians E, NH, A** ** * * * ** * ** 

Meridion circulare E, A * ** * * * 

Navicula aurora S ** 

Navicula salinarum v. intermedia S ** * 

Navicula sp. S **** * ****** * **** * ** * **** * ****** * * * * * ** ********** 

Nitzschia acicularis S * * * * * * 

Nitzschia dissipata E, A, S * * * 

Nitzschia sp. S * ** * * * * * * **** ** * **** * * * **** * * * * ** * **** * 

Pinnularia sp. * * * ** ** 

Planothidium dubium * * * 

Planothidium lanceolatum E, A * * * ** * * * * * ** * 

Rhoicosphenia curvata E, A * * * ** ** * * 

110 
APPENDIX 6. PHYTOPLANKTON TAXA OCCURRENCE IN NORTH FORK RESERVOIR, CLACKAMAS RIVER BASIN, OREGON 1997–98—Continued 

[Algal taxa are ordered by major algal Divisions; *, indicates taxon presence at a site; **, indicates 5 most abundant taxa at each site (based on % relative 

biovolume); B, NFKRES_B (site codes are listed in the glossary); sampling depths are given as follows: (1) surface, (2) thermocline, (3) depth of water release, 

and (4) 1 meter off the bottom; some taxa are assigned to autecological guilds as follows: (NF) nitrogen fixers, (NH) facultative nitrogen heterotrophs, 

(E) eutrophic taxa, (O) oligotrophic taxa, (A) alkaliphilic taxa, (HB) halophobic taxa, and (S) silt-tolerant taxa. Sources for autecological classification are from 

Patrick and Reimer, 1966, 1975; Schoeman, 1973; Lowe, 1974; van Dam and others, 1994; Tuchman, 1996; Lowe and Pan, 1996; Porter and others, 1993] 

Reservoir station, year, month, and sampling depth 

NFKRES_1 NFKRES_2 B 

1997 1998 

Sampling month and depth 

Algal taxa Guild

 July (1) 

Aug (1)

 Sep (1) April (1) 

May (1) May (2) May (3) May (4)

 June (1) June (2) June (3) June (4)

July (1)

 July (2) July (3) 

Aug (1) Aug (2) Aug (3) Aug (4)

 Sep (1) Sep (2) Sep (3) Sep (4) 

May (1) May (2)

 June (1) June (2) June (3)

July (1)

 July (2) July (3) 

Aug (1) Aug (2) Aug (3)

 Sep (1) Sep (2) Sep (3) 

Sep (1) 

BACILLARIOPHYTA (Diatoms) – Continued 

Rhopalodia gibba sp. # 1 NF, E, A ** 

Sellaphora pupula E * * * * 

Synedra delicatissima * * * ** * 

Synedra mazamaensis * * * * * * * * * 

Synedra ulna A ** * ** ********** ** ** * * ** * **** * ** * * **** 

111 

APPENDIX 7. PHYTOPLANKTON TAXA OCCURRENCE IN TIMOTHY LAKE, CLACKAMAS RIVER BASIN, OREGON 1997–98 

[Algal taxa are ordered by major algal Divisions; *, indicates taxon presence at a site; **, indicates 5 most abundant taxa at each site (based on % relative 

biovolume); site codes are listed in the glossary); sampling depths are given as follows: (1) surface, (2) thermocline, (3) depth of water release, and 

(4) 1 meter off the bottom; some taxa are assigned to autecological guilds as follows: (NF) nitrogen fixers, (NH) facultative nitrogen heterotrophs, 

(E) eutrophic taxa, (O) oligotrophic taxa, (A) alkaliphilic taxa, (HB) halophobic taxa, and (S) silt-tolerant taxa. Sources for autecological classification 


are from Patrick and Reimer, 1966, 1975; Schoeman, 1973; Lowe, 1974; van Dam and others, 1994; Tuchman, 1996; Lowe and Pan, 1996; Porter and 


others, 1993.]


Algal taxon Guild 

TIM_LK 

1997 1998 

Month and sampling depth

 May (1) June (1)

July (1) 

 May (1) May (2) May (3) June (1) June (2) June (3)

 June (4)

July (1)

 July (2) July (3)

 Aug (1) Aug (2) Aug (3) Sep (1) Sep (2) Sep (3) Sep (4) 

CRYPTOPHYTA (Cryptophyte algae) 

Cryptomonas erosa v. reflexa sp. # 1 * * * * * * * 

Cryptomonas erosa v. reflexa sp. # 2 **   **  

Rhodomonas minuta * * * **   **  * * * * ** ** ** * ** ** 

DINOPHYTA (Dinophyte algae) 

Glenodinium sp. * * * * * 

Peridinium sp. # 1 * 

Peridinium sp. # 2 ** ** ** * * * * ** ** 

EUGLENOPHYTA (Euglenophyte algae) 

Euglena sp. * * 

Phacus sp. ** * * * ** 

Trachelomonas sp. * * 

CYANOPHYTA (Blue-green algae) 

Anabaena circinalis NF **   **  ** ** * * **   **  ** * ** * 

Anabaena circinalis heterocyst NF ** * ** * * * * * ** * * ** * 

Anabaena akinete NF ** * 

Microcystis aerugenosa * 

Schizothrix calcicola **   **  **   **  ** ** * ** * * ** * * 

CHLOROPHYTA (Green algae) 

Carteria sp. * * 

Chlamydomonas sp. ** * * * * * * * ** ** * ** 

Crucigenia tetrapedia sp. # 1 * * * 

Crucigenia tetrapedia sp. # 2 ** * 

Dactylococcus infusionum * 

Mougeotia sp. # 1 ** 

Oocystis sp. * 

Unidentified thick-walled oval cell * 

Unidentified thick-walled 4 unit * * * * 

BACILLARIOPHYTA (Diatoms) 

Achnanthidium minutissimum * * 

Amphora sp. * * 

Asterionella formosa E, A **   **  **   **  ** ** * ** ** ** * 

Aulacoseira granulata E, A ** ** 

Aulacoseira sp.   **  ** * ** 

113 
APPENDIX 7. PHYTOPLANKTON TAXA OCCURRENCE IN TIMOTHY LAKE, CLACKAMAS RIVER BASIN, OREGON 1997–98—Continued 

[Algal taxa are ordered by major algal Divisions; *, indicates taxon presence at a site; **, indicates 5 most abundant taxa at each site (based on % relative 

biovolume); site codes are listed in the glossary); sampling depths are given as follows: (1) surface, (2) thermocline, (3) depth of water release, and 

(4) 1 meter off the bottom; some taxa are assigned to autecological guilds as follows: (NF) nitrogen fixers, (NH) facultative nitrogen heterotrophs, 

(E) eutrophic taxa, (O) oligotrophic taxa, (A) alkaliphilic taxa, (HB) halophobic taxa, and (S) silt-tolerant taxa. Sources for autecological classification 


are from Patrick and Reimer, 1966, 1975; Schoeman, 1973; Lowe, 1974; van Dam and others, 1994; Tuchman, 1996; Lowe and Pan, 1996; Porter and 


others, 1993.]


Algal taxon Guild 

TIM_LK 

1997 1998 

Month and sampling depth

 May (1)

 June (1)

July (1) 

 May (1) May (2) May (3)

 June (1) June (2) June (3) June (4)

July (1)

 July (2) July (3)

 Aug (1) Aug (2) Aug (3)

 Sep (1) Sep (2) Sep (3) Sep (4) 

BACILLARIOPHYTA (Diatoms) – Continued 

Cyclotella sp. * * * 

Fragilaria crotonensis sp. # 1 A ** ** 

Fragilaria crotonensis sp. # 2 A * 

Fragilaria sp. #1 ** 

Fragilaria sp. #2 ** 

Gomphoneis sp. ** 

Navicula sp. S ** * * * * 

Nitzschia dissipata E, A, S * * 

Nitzschia sp. S ** * * * * ** * * * * * 

Sellaphora pupula E * 

Staurosira construens E, A * * * * 

Synedra delicatissima **   **  **   **  ** ** 

Urosolenia sp. ** * * **   **  ** * 

114 
Back cover photographs, clockwise from lower left: 

Growths of filamentous green algae often concentrate along the margins of some Clackamas Basin streams, as in this reach of the


Collawash River.


Water exiting Timothy Lake is aerated at the powerhouse to boost oxygen levels in the Oak Grove Fork.


Blooms of the blue-green alga Anabaena in Clackamas Basin reservoirs can degrade water quality and contribute to taste and odor 


problems in the drinking water supply.


Another example of excessive algal growth, this one in the Clackamas River main stem upstream of Eagle Creek.