U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2015–5178

Prepared in cooperation with Clean Water Services and the Joint Water Commission

Upstream Factors Affecting Tualatin River Algae—

Tracking the 2008 Anabaena Algae Bloom to 

Wapato Lake, Oregon
Cover: Wapato Lake, as seasonally flooded in winter. Photograph by Stewart 

Rounds, U.S. Geological Survey, January 27, 2015.
Upstream Factors Affecting Tualatin River 

Algae—Tracking the 2008 Anabaena Algae 

Bloom to Wapato Lake, Oregon 

By Stewart A. Rounds, Kurt D. Carpenter, Kristel J. Fesler, and Jessica L. Dorsey

Prepared in cooperation with Clean Water Services and the Joint Water Commission

Scientific Investigations Report 2015–5178

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

resources, natural hazards, and the environment—visit http://www.usgs.gov or call 1–888–ASK–USGS.

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod/.

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Rounds, S.A., Carpenter, K.D., Fesler, K.J., and Dorsey, J.L., 2015, Upstream factors affecting Tualatin River algae—

Tracking the 2008 Anabaena algae bloom to Wapato Lake, Oregon: U.S. Geological Survey Scientific Investigations 

Report 2015–5178, 41 p., http://dx.doi.org/10.3133/sir20155178.

ISSN 2328-0328 (online)
iii

Contents

Significant Findings .......................................................................................................................................1

Introduction.....................................................................................................................................................2

Study Area..............................................................................................................................................4

Study Objectives and Report Scope..................................................................................................7

Overview of Reconstructed Sequence of Events............................................................................7

Background and Context.....................................................................................................................9

Data Sources, Methods, and Quality Assurance/Quality Control .......................................................10

Continuous Water-Quality and Streamflow Monitors...................................................................10

Plankton-Sample Collection, Processing, and Identification......................................................10

Microcystin Algal Toxin Analyses....................................................................................................12

Clean Water Services Data...............................................................................................................13

Joint Water Commission Data ..........................................................................................................13

Oregon Department of Environmental Quality Data......................................................................13

Bloom Origination, Discovery, and Tracking to Wapato Lake ..............................................................14

Early Bloom Indications, June 2008.................................................................................................14

Mature Bloom, July 2008 ...................................................................................................................19

Analysis and Confirmation of Bloom Source .................................................................................26

Upstream Factors Affect Downstream Tualatin River Algae................................................................29

Implications for Monitoring and Management.......................................................................................30

Public Health Hazards........................................................................................................................30

Municipal Water Issues.....................................................................................................................30

Wetland Management .......................................................................................................................31

Managing Dissolved Oxygen ............................................................................................................32

Water-Quality and Plankton Monitoring and Models...................................................................32

Summary and Conclusions.........................................................................................................................32

Acknowledgments.......................................................................................................................................33

References Cited..........................................................................................................................................33

Appendixes ...................................................................................................................................................37

Appendix A. Additional Water-Quality Data from Clean Water Services for Selected 

Sites in the Tualatin River, Oregon, May–August 2008 ...................................................37

Appendix B. Biovolume of Algal Taxa in Water Samples Collected from Wapato Lake 

Pump Discharge and Downstream in the Tualatin River at the Spring Hill 

Pumping Plant, Oregon, July 19–21, 2008..........................................................................41
iv

Figures

1. Map showing Tualatin River basin, northwestern Oregon....................................................2

2. Photograph showing a partially drained Wapato Lake, Oregon...........................................3

3. Photograph showing Wapato Lake, Oregon, viewed from the west ...................................3

4. Map showing sampling sites and streamgage locations, Tualatin River 

basin, Oregon ................................................................................................................................5

5. Map showing sampling sites in and near the Wapato Lake agricultural area in

the upper Tualatin River basin, Oregon.....................................................................................6

6. Photograph showing breached dike before repair, west side of 

Wapato Lake, Oregon...................................................................................................................7

7. Photograph showing repaired levee separating Wapato Lake and Wapato Creek

on the west side of Wapato Lake, Oregon ...............................................................................7

8. Photograph showing algal bloom and duckweed in the internal canal leading to

the pump house at Wapato Lake, Oregon ................................................................................8

9. Photographs showing Wapato Improvement District’s pump house discharge

from Wapato Lake, Oregon and dead fish in the discharge pool .........................................8

10. Photographs showing floating mats of blue-green algae in the Tualatin River 

upstream of Stafford Road and microscopic views of a colony and filament of 

Anabaena in the Tualatin River, Oregon....................................................................................9

11. Graph showing estimated discharge from the Wapato Creek drainage, as 

estimated from a mass balance of measured streamflows in Scoggins Creek 

and the Tualatin River, Oregon, June–July 2008....................................................................15

12. Graph showing total organic carbon concentrations in the Tualatin River at the

Spring Hill pumping plant, Oregon, March–July 2008 ..........................................................25

13. Graphs showing longitudinal pattern in Anabaena flos-aquae abundance

and chlorophyll-a concentrations in the Tualatin River along with measurements 

from the Wapato Lake pump discharge, Oregon, July 2008................................................25

14. Graph showing comparison of measured dissolved oxygen percent saturation 

in the Tualatin River near Scholls, Oregon in 2008 with long-term conditions in 

1997–2012 .....................................................................................................................................27

15. Graph showing dissolved-oxygen percent saturation in the Tualatin River at river

miles 24.5, 9.9, and 3.4, showing a substantial increase in dissolved oxygen

associated with the arrival of the Anabaena bloom at each location, Tualatin

River, Oregon, July 2008.............................................................................................................27

16. Boxplots showing comparison of chlorophyll-a and total phosphorus

concentrations in the Tualatin River, Oregon, July 2005–07 and July 2008.......................28
v

Tables

1. Data sources and water-quality constituents analyzed in river water and

finished drinking water at selected sites in the Tualatin River basin, Oregon,

2008 ...............................................................................................................................................11

2. Selected sampling sites and data collection activities in the Tualatin River basin,

Oregon, 2006–08..........................................................................................................................12

3. Reconstructed timeline of events associated with the bloom of Anabaena

flos-aquae in Wapato Lake and downstream in the Tualatin River, Oregon, 2008...........14

4. Water-quality data from the Joint Water Commission for sites in the upper

Tualatin River basin, Oregon, May–August 2008...................................................................16

5. Chlorophyll and total phosphorus data from Clean Water Services for sites in the

Tualatin River, Oregon, May–August 2008..............................................................................20

6. Anabaena flos-aquae cell counts and microcystin algal toxin concentrations for

select sites in the Tualatin River basin, Oregon, June–August 2008 .................................22

7. Results of water-quality tests on samples of Wapato Lake pump discharge

compared with nearby locations, upper Tualatin River basin, July 19 and 21,

2008 ...............................................................................................................................................23

8. Ten most abundant algal taxa in Wapato Lake pump discharge and abundances

downstream in the Tualatin River at the JWC/TVID Spring Hill pumping plant,

Oregon, July 19 and 21, 2008.....................................................................................................24

9. Zooplankton taxa in water samples collected from Wapato Lake pump discharge

and downstream in the Tualatin River at the JWC/TVID Spring Hill pumping

plant, Oregon, July 19 and 21, 2008..........................................................................................24

10. Water-quality data from the Oregon Department of Environmental Quality for

selected sites in the upper Tualatin River basin, Oregon, August 2008.............................29
vi

Conversion Factors

Inch/Pound to International System of Units

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Volume

million gallons (Mgal) 3,785 cubic meter (m3

)

acre-foot (acre-ft) 1,233 cubic meter (m3

)

Flow rate

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

gallon per minute (gal/min) 0.06309 liter per second (L/s)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3

/s)

International System of Units to Inch/Pound

Multiply By To obtain

Length

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Area

square meter (m2

) 0.0002471 acre 

square meter (m2

) 10.76 square foot (ft2) 

Volume

cubic meter (m3

) 0.0002642 million gallons (Mgal) 

cubic meter (m3

) 35.31 cubic foot (ft3)

cubic meter (m3

) 0.0008107 acre-foot (acre-ft) 

Flow rate

cubic meter per second (m3

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

Mass

kilogram (kg) 2.205 pound avoirdupois (lb)

kilogram per day (kg/d) 2.205 pound per day (lb/d)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8×°C) + 32.

Datum

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).
vii

Supplemental Information

Algal cell densities for phytoplankton are given in cells per milliliter of sample (cells/mL), and 

zooplankton densities are given in number of organisms per cubic meter (#/m3). Algal cell 

biovolumes are given in cubic microns per milliliter (μm3/mL).

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25 °C).

Concentrations of chemical constituents in water are given in either milligrams per liter (mg/L), 

micrograms per liter (μg/L), or nanograms per liter (ng/L).

Abbreviations and Acronyms

BOD biochemical oxygen demand

COD chemical oxygen demand

CWS Clean Water Services

DO dissolved oxygen 

ELISA enzyme-linked immunosorbent assay

EPA U.S. Environmental Protection Agency

JWC Joint Water Commission 

MIB methyl isoborneol

ODEQ Oregon Department of Environmental Quality

OWRD Oregon Water Resources Department

QA quality assurance

RM river mile

SPME solid-phase micro-extraction

SRS USGS Standard Reference Sample program

TOC total organic carbon

TVID Tualatin Valley Irrigation District 

USGS U.S. Geological Survey

WTP water treatment plant

WWTF wastewater treatment facility

Significant Findings

• A large bloom that included floating mats of the bluegreen algae Anabaena flos-aquae occurred in the lower 

20 miles of the Tualatin River in northwestern Oregon 

between July 7 and July 17, 2008.

• The floating bloom was deemed a hazard to 

recreational users of the river due to the potential 

production of algal toxins (anatoxin-a and 

microcystin), and a public health advisory was posted 

for the lower 10.8 miles of the river by the Oregon 

Department of Human Services for July 12–25, 2008.

• The bloom caused nuisance taste and odor issues and 

required modified drinking-water treatment techniques 

where water was withdrawn for municipal uses in the 

upper reaches of the Tualatin River, some 46 miles 

upstream of the worst algae problems.

• Using water sample data from Clean Water Services 

and the Joint Water Commission, and continuous and 

discrete monitoring data from the U.S. Geological 

Survey, the source of the anomalous water-quality 

conditions and the likely source of the Anabaena

bloom was traced upstream to discharges from the 

Wapato Lake agricultural area near Gaston, Oregon, in 

the upper part of the watershed near river mile 60.

• The Wapato Lake algae bloom occurred as standing 

water remained on the lakebed far longer than 

normal—into early summer. A failure of the levee on 

the edge of Wapato Lake in December 2007 caused 

by heavy rainfall and high water in the canal outside 

the levee inundated the lakebed to a depth of 7–9 feet, 

storing thousands of acre-feet more water than its 

normal winter volume. The water could not be pumped 

out until the levee was repaired or river levels receded, 

thus delaying drainage of the lake until summer and 

facilitating the bloom.

• In normal summers, the lower Tualatin River grows 

a moderate crop of algae that responds strongly 

to streamflow (residence time), light available for 

photosynthesis, and phosphorus concentrations. 

In 2008, however, inoculation of the river with 

phytoplankton and zooplankton discharged from 

Wapato Lake some 30 miles upstream of the lower, 

pooled reach of the river demonstrated the importance 

of upstream factors on plankton communities and 

water-quality conditions in the Tualatin River.

• The Wapato Lake algae bloom of July 2008 provided 

useful information and lessons for agencies managing 

public health, wetlands, agricultural activities, and 

water quality in the Tualatin River basin and similar 

river basins elsewhere.

• The results and insights derived from this study can be 

used to enhance future monitoring and data collection 

strategies designed to improve water quality and 

plankton models and better predict dissolved-oxygen 

concentrations in the lower Tualatin River.

Upstream Factors Affecting Tualatin River Algae—

Tracking the 2008 Anabaena Algae Bloom to 

Wapato Lake, Oregon

By Stewart Rounds1, Kurt Carpenter1, Kristel Fesler2, and Jessica Dorsey2

1

 U.S. Geological Survey.

2

 Joint Water Commission.
RM

60

RM

70 RM

30 RM

20

RM

40

RM

50

RM

10

RM

0

Lake

Oswego

Tualatin

Sherwood

Portland

Tigard

Beaverton

Cornelius Hillsboro

Forest

Grove

Cherry

Grove

Gaston

ROCK

CREEK

DURHAM

WILLAMETTE

TUALATIN

RIVER

RIVER

RIVER

COLUMBIA

Hagg

Lake

Wapato

Lake

Jackson

Bottom

Wetland

Barney

Reservoir

217

26

5

5

5

205

205

84

WASHINGTON

COLUMBIA

TILLAMOOK

YAMHILL

CLACKAMAS

MULTNOMAH

East

Fork

Dairy

Gales

Creek

Scoggins

Creek

McKay

Creek

Rock

Creek

TUALATIN MOUNTAINS

CHEHALEM MOUNTAINS

COAST RANGE

Fanno

Creek

JWC

WTP

Beaverton Creek

Creek Chicken

0 10

10

20 MILES

0 20 KILOMETERS

Base map modified from U.S. Geological Survey and Metro digital data sets (1:24,000)

Projection: Oregon Lambert, North American Datum 1983

123°30’ 123°15' 123° 122°45' 122°30'

45°

45'

45°

37'

30"

45°

30'

45°

22'

30"

OREGON

Study

Area

EXPLANATION

Designated urban growth boundary (2009)

Basin boundary

Wastewater treatment facility

Water treatment plant

RM River mile

60

ROCK

CREEK

JWC

WTP

Figure 1. Tualatin River basin, northwestern Oregon.

2 Upstream Factors Affecting Tualatin River Algae, Oregon

Introduction

In early July 2008, a large blue-green algae bloom was 

discovered in the lower Tualatin River, which is a tributary 

to the Willamette River in northwestern Oregon (fig. 1). 

Although floating algal mats had occurred approximately 

30 years prior, this bloom was the worst in memory for 

many water-quality scientists and managers familiar with 

the Tualatin River. This slow-moving, warm, and nutrientenriched section of river has a long history of water-quality 

problems related to summertime algal blooms through the 

1980s. Upgrades in wastewater treatment in the early 1990s 

greatly diminished the severity of the blooms by capping 

nutrient levels, and flow augmentation from upstream 

reservoirs has added dilution and increased water velocity that 

reduces the time available for blooms to develop. The 2008 

bloom, though, was different in many ways.

In June 2008, the Joint Water Commission (JWC) was 

working to identify the source of anomalous tastes and odors 

in its drinking-water supply, which is drawn from the Tualatin 

River at the Spring Hill pumping plant at river mile (RM) 

56.1. In early July 2008, sampling crews from Clean Water 

Services (CWS) and the U.S. Geological Survey (USGS), 

as well as members of the Tualatin Riverkeepers advocacy 

group, reported seeing a distinct algal bloom in the lower 

river between Elsner (Roy Rogers Road, RM 16.2) and 

Stafford Road (RM 5.5). The bloom included thick surface 

accumulations and shoreline scums. Samples were collected 

and examined microscopically, revealing that the bloom and 

floating mats were composed primarily of Anabaena flosaquae—a colonial blue-green algae that is considered to be a 

nuisance species because (1) it often forms surface scums and 

floating mats, (2) it is capable of producing nerve and liver 

toxins that pose a potential public health hazard to recreational 
Figure 2. A partially drained Wapato Lake, Oregon. (Photograph taken by Stewart Rounds, U.S. Geological 

Survey, July 19, 2008.)

Figure 3. Wapato Lake, Oregon, viewed from the west. (Photograph taken by Matt Nussbaumer, City of Hillsboro, 

June 25, 2008.)

Introduction 3

network of continuous water-quality monitors and streamgages 

in the river and its tributaries and initiated additional sampling. 

Results indicated that the source of the blue-green algae 

bloom was drainage water from Wapato Lake near Gaston, 

Oregon (figs. 1–3). A bloom had developed in the shallow 

lake, and pumps used to drain the lake for farming conveyed 

enough algal biomass and nutrients into Wapato Creek and 

downstream to the Tualatin River to initiate a riverine algae 

population that not only persisted, but thrived in the nutrientenriched water, multiplying into a large bloom resembling a 

thick green chowder in parts of the lower reservoir-like reach 

of the Tualatin River some 50 mi downstream.

water users and drinking water supplies, and (3) it can produce 

nuisance taste and odor compounds that are difficult for 

drinking water treatment plants to remove. Given the presence 

of surface scums and the dominance of a potentially toxigenic 

species in an area of the river where recreational users are 

known to visit, the Public Health Division of the Oregon 

Department of Human Services (now part of the Oregon 

Health Authority) issued a public health advisory for the lower 

Tualatin River from Jurgens Park (RM 10.8) downstream to 

the river mouth on July 12, 2008 (Bonn, 2008). 

To identify the longitudinal extent and source of the 

bloom, JWC along with CWS and USGS relied on data from a 
4 Upstream Factors Affecting Tualatin River Algae, Oregon

The series of events related to the 2008 Wapato Lake 

algal boom demonstrates the importance of upstream 

inoculation, or seeding, as one of the factors controlling 

phytoplankton (free-floating algae) populations in the 

Tualatin River, a concept that was previously described for 

this river by Carpenter and Rounds (2013). Although other 

studies and modeling efforts have shown that phytoplankton 

populations in the Tualatin River are largely controlled by 

streamflow, light, and phosphorus concentrations, the 2008 

bloom demonstrated that periodic inputs of viable algal cells 

from wetland drainage, nursery ponds, reservoirs, or other 

sources can greatly influence the composition and abundance 

of phytoplankton in the Tualatin River. This process is critical 

to understand because although phytoplankton photosynthesis 

is important for maintaining minimum dissolved-oxygen 

(DO) concentrations in the lower river, a population crash of 

a large algal bloom can deplete DO to critical levels that may 

harm fish and other aquatic life in the river during the summer 

low-flow period, often when temperatures are at or near their 

seasonal maximum. Anabaena blooms also can produce 

and release toxins that can affect aquatic life, pose a public 

health hazard for direct contact and consumption, and be a 

drinking-water nuisance.

Study Area

The study area consists of the Tualatin River and 

Wapato Lake in northwestern Oregon (fig. 1). The Tualatin 

River begins in the Coast Range and flows generally 

east, meandering across a fertile valley before joining the 

Willamette River south of Portland. The river reach of 

particular interest in this study extends from the Old Highway 

47 bridge in the city of Gaston (RM 62.3) just upstream of 

the Wapato Lake diversion and continues downstream to the 

Oswego Dam (RM 3.4, fig. 4). Several continuous waterquality monitors and streamgages are located in this 58.9-mi 

river reach. Water-quality data from water samples collected 

by several agencies also are available from a dozen or so 

routine monitoring sites along the Tualatin River from Cherry 

Grove (RM 67.8) upstream of the Wapato Lake area to near 

the river’s mouth.

Land use in the Tualatin River basin consists of forestry 

in the headwater tributaries, agriculture in the valley lowlands, 

and urban areas that are home to 550,000 people (U.S. Census 

Bureau, 2012) on the west side of the Portland, Oregon 

metropolitan area. Northwest Oregon tends to have warm and 

dry summers that result in seasonally low flow during summer 

and early autumn. Coincident with ample sunshine and 

sufficient nutrients in most summers, the low-flow season can 

produce moderate algal blooms in the “reservoir reach” of the 

Tualatin River. Compared to upstream reaches, the reservoir 

reach is defined as a deeper, wider, and slower river reach 

between RMs 30 and 3.4 that has the characteristics of a long, 

narrow lake with a 7–10 day residence time in summer. In the 

absence of much algae in this reach (for example, <5 μg/L 

chlorophyll-a), photosynthetic production of DO is insufficient 

to offset oxygen demands from decomposing organic materials 

in river sediments, resulting in low-DO conditions that may 

persist for weeks or even months in summer and early autumn 

until rainfall, higher flow, or cooler temperatures improve 

conditions.

Flow in the Tualatin River is augmented for multiple 

purposes by water releases from Henry Hagg Lake on 

Scoggins Creek and Barney Reservoir in the adjoining Trask 

River system (made through an interbasin diversion into the 

headwaters of the Tualatin River) (fig. 1). Some of those 

releases are withdrawn at the Spring Hill pumping plant at 

RM 56.1, which serves the Tualatin Valley Irrigation District 

(TVID) and JWC. The JWC is a collective drinking-water 

supply agency formed between the cities of Hillsboro (the 

managing agency), Forest Grove, Beaverton, and the Tualatin 

Valley Water District. JWC and its partners provide wholesale 

water to the cities of North Plains, Cornelius, and Gaston. 

JWC operates the largest conventional water-treatment 

plant in Oregon, relying on processes such as flocculation, 

sedimentation, and filtration to produce as much as 75 Mgal of 

drinking water each day to serve more than 300,000 people.

Clean Water Services is the primary stormwater- and 

wastewater-management utility for the urban areas of 

Washington County and treats wastewater from most of 

the basin’s population. Wastewater treatment occurs at 

two small and two large facilities, but only the two large 

wastewater-treatment facilities (WWTFs), Rock Creek and 

Durham, at RMs 38.1 and 9.3, respectively, discharged 

effluent to the Tualatin River during summer for the period 

of this study. These WWTFs were upgraded in the early 

1990s to meet stringent summertime effluent load limits for 

ammonia and phosphorus. In recent years (2006–08), treated 

effluent from these two WWTFs during summer contained 

comparatively small concentrations of dissolved ammonianitrogen (0.03–0.07 mg/L) and soluble reactive phosphorus 

(0.013–0.018 mg/L) (median concentrations), whereas 

nitrate-nitrogen concentrations in effluent were considerably 

higher (10–15 mg/L; Carpenter and Rounds, 2013, table 4). 

Although nitrogen concentrations are elevated, phosphorus 

concentrations at times are low enough to limit phytoplankton 

growth and may initiate algal population crashes (Carpenter 

and Rounds, 2013).
tac16-1036_fig04

217

26

5

5

205

13

18

20 19 21

14

15

16

17

10

11

12

9

8

6 5

7

4 3

2

1

ROCK

CREEK

Lake

Oswego

Tualatin

Portland

King

City

Tigard

Beaverton

Farmington

Forest Cornelius Hillsboro

Grove

Dilley

DURHAM

WILLAMETTE

RIVER

TUALATIN RIVER

TUALATIN

RIVER

Rock

Beaverton

Creek

Creek

Creek

Fanno

Gales Creek

Summer Creek

Wapato

Lake

Hagg

Lake

Scoggins Creek

TUALATIN RIVER

Oswego

Canal

RM 60

RM 30

RM 20

RM 40

RM 50

RM 0

RM 10

Cherry

Grove

Gaston

JWC

WTP

Creek

Chicken

Base modified from U.S. Geological Survey and Metro digital data sets (1:24,000)

Projection: Oregon Lambert, North American Datum 1983

0 7.5

7.5

15 MILES

0 15 KILOMETERS

123°10' 123° 122°50' 122°40' 122°30'

45°

35'

45°

30'

45°

25'

45°

20'

EXPLANATION

#

1

 1 Tualatin River at Weiss Bridge (RM 0.2)

 2 Tualatin River at Oswego Dam (RM 3.4)

 3 Tualatin River downstream of Stafford Road (RM 5.5)

 4 Tualatin River at Boones Ferry Road (RM 8.7)

 5 Tualatin River downstream of Fanno Creek and Durham WWTF (RM 9.2)

 6 Tualatin River downstream of Cook Park (RM 9.7)

 7 Tualatin River at RM 9.9 near Tualatin (RM 9.9)

 8 Tualatin River at Jurgens Park (RM 10.8)

 9 Tualatin River at Elsner (Roy Rogers Road) (RM 16.2)

10 Tualatin River near Scholls (RM 24.5)

11 Tualatin River at Scholls Bridge (RM 26.9)

12 Tualatin River at Farmington (RM 33.3)

13 Tualatin River at Rood Bridge (RM 38.4)

14 Tualatin River at Highway 219 Bridge (RM 44.4)

15 Tualatin River at Golf Course Road (RM 51.5)

16 Tualatin River at JWC/TVID Spring Hill Pumping Plant Intake (RM 56.1)

17 Tualatin River at Dilley (Spring Hill Road) (RM 58.8)

18 Wapato Creek at Gaston Road (includes Wapato Lake pump discharge)

19 Tualatin River at Wapato Improvement District headgate (RM 61.9)

20 Tualatin River at the Old Highway 47 Bridge (Gaston) (RM 62.3)

21 Tualatin River at Cherry Grove (RM 67.8)

Designated urban growth boundary (2010)

Sampling site and map No.

Wastewater treatment facility

Water treatment plant

RM River mile

60

ROCK

CREEK

JWC

WTP

OREGON

Study

Area

Figure 4. Sampling sites and streamgage locations, Tualatin River basin, Oregon.

Introduction 5
4

5

6

7

11 8

9

10

2 3

1

Gales

Carpenter

Scoggins Creek

Wapato Creek

Hill Creek

Creek

Creek

Ayers

Creek

Wapato

Lake

Hagg

Lake

TUALATIN RIVER

TUALATIN RIVER

Cornelius Forest

Grove

Cherry

Grove

Gaston

JWC

WTP

Base modified from U.S. Geological Survey and Metro digital data sets (1:24,000)

Projection: Oregon Lambert, North American Datum 1983

0 2.5

2.5

5 MILES

0 5 KILOMETERS

123°10' 123°00'

45°

30'

45°

25'

EXPLANATION

#

1

1 Tualatin River at JWC/TVID Spring Hill Pumping Plant Intake (RM 56.1)

2 Gales Creek at Highway 47 Bridge

3 Carpenter Creek at Anderson Road

4 Carpenter Creek at Plum Lee Road

5 Tualatin River at Dilley (RM 58.8)

6 Scoggins Creek at Old Highway 47

7 Scoggins Creek below Hagg Lake

8 Wapato Creek at Gaston Road

9 Hill Creek at Spring Hill Road

10 Ayers Creek at Northeast Flett Road

11 Tualatin River at Old Highway 47 Bridge (RM 62.3)

Designated Urban Growth Boundary (2010)

Sampling site and map No.

Water treatment plant JWC

WTP

OREGON

Study

Area

6 Upstream Factors Affecting Tualatin River Algae, Oregon

The Wapato Lake agricultural area near Gaston (fig. 5) 

includes a 730-acre lake and wetland that historically 

supported a wild crop of wapato, a potato-like bulb considered 

a “First Food” of Native Americans. Winter rains once 

expanded the seasonally inundated area to nearly 1,500 

acres, creating an extensive wetland with scrub-shrub plant 

communities that supported large numbers of resident and 

migrating bird populations and waterfowl (U.S. Fish and 

Wildlife Service, 2007; Clean Water Services, 2010). The soils 

of the lakebed are known as Labish mucky clay, a type of soil 

that is relatively rich in organic matter and nutrients (Green, 

1982). By 1895, efforts to drain Wapato Lake and use the 

lakebed for agriculture had begun through the installation of 

drainage canals (Cass and Miner, 1993). In the 1930s, a levee 

and pump system was constructed around Wapato Lake. The 

system allowed farmers of the Wapato Improvement District 

to divert tributary creeks around the lake and drain the lake 

each spring so that the rich lakebed soils could be farmed for 

Figure 5. Sampling sites in and near the Wapato Lake agricultural area in the upper Tualatin River basin, Oregon.
Figure 6. Breached dike before repair, west side of Wapato 

Lake, Oregon. (Photograph taken by Matt Nussbaumer, City of 

Hillsboro, July 30, 2008.)

Figure 7. Repaired levee separating Wapato Lake and Wapato 

Creek on the west side of Wapato Lake, Oregon. (Photograph 

taken by Matt Nussbaumer, City of Hillsboro, September 23, 2008.)

Introduction 7

onions and other crops. Irrigation water was delivered through 

a diversion at RM 61.9 on the Tualatin River. Water pumped 

out of the lake flows into Wapato Creek, which flows north 

for about 1 mile until it joins the Tualatin River at RM 60.1. 

The Spring Hill pumping plant that feeds the JWC WTP is 

located at RM 56.1, only 4.0 mi downstream of the confluence 

of Wapato Creek with the Tualatin River. In 2008, the U.S. 

Fish and Wildlife Service began to purchase parcels of the 

lakebed inside the levees and now manages the area as the 

Wapato Lake National Wildlife Refuge. During the period of 

interest in 2007–08, however, the area was still managed by 

the Wapato Improvement District.

Study Objectives and Report Scope

The objectives of this investigation were to: 

(1) characterize and document water-quality conditions 

associated with the 2008 blue-green algae bloom in the 

Tualatin River; (2) identify the cause(s) of the bloom; (3) 

examine how water discharges from Wapato Lake affected 

plankton communities in the Tualatin River; and (4) document 

how the bloom affected municipal water providers and users.

This report documents the sequence of events of the 2008 

blue-green algae bloom in the Tualatin River, including how 

the source was tracked to discharges from Wapato Lake, and 

describes the downstream response using readily available 

data and previously published accounts of the bloom (Bonn, 

2008; Oregon Department of Environmental Quality, 2009). 

The report also includes suggestions and insights for future 

research, management, and monitoring activities aimed 

at a more refined characterization of factors that control 

phytoplankton in the river, including upstream discharges of 

plankton inocula.

The study focused on June through early August 2008, 

with particular emphasis on July when the bloom occurred 

in the lower river. Although the emphasis here is on 2008, 

knowledge gained from data gathered since the early 1990s was 

useful in understanding the 2008 event. This report reiterates 

some relevant findings presented by Carpenter and Rounds 

(2013), and readers are referred to that report for more detailed 

information on the plankton assemblages and factors that 

influence their abundance and composition in the Tualatin River.

Overview of Reconstructed Sequence of Events

On December 2–3, 2007, more than 6 in. of rainfall 

were recorded at several weather stations across the Tualatin 

River basin, causing near-flood levels in the Tualatin River at 

Gaston (RM 62.3) and Dilley (RM 58.8). The peak streamflow 

at Dilley was nearly 10,000 ft3/s—almost identical to the 

peak streamflow recorded during the large flood of February 

1996. During these high-water conditions, a small section 

of the aging levee on the west side of Wapato Lake failed 

(figs. 6–7), causing water to inundate the lakebed to a depth of 

approximately 7–9 ft. The levees normally keep water levels in 

the lake low by diverting tributaries around the outside of the 

lake and restricting inflows to rainfall, groundwater seepage, 

and some leakage through the levees. Without first repairing or 

temporarily patching the levee, Wapato Improvement District 

personnel could not pump flood waters out of the lake because 

discharges would return to the lake through the levee breach. 

The breach could not, however, be repaired because high 

water levels prevented access. Consequently, the lake was not 

drained in early spring as usual, and water remained ponded 

on the lakebed until early summer when river levels finally 

receded enough to render the breach inconsequential. The 

levee may or may not have been temporarily patched in early 

June, but a full levee repair was completed in early September 

2008. 
Figure 9. Wapato Improvement District’s pump house discharge 

from Wapato Lake, Oregon (A–B) and dead fish in the discharge 

pool (B–C). (Photographs A and B taken by Stewart A. Rounds, 

U.S. Geological Survey, August 8, 2008; photograph C courtesy of 

the U.S. Fish and Wildlife Service.)

8 Upstream Factors Affecting Tualatin River Algae, Oregon

As water remained on the lakebed into early summer, 

the water warmed, became nutrient-enriched, and developed 

a bloom of algae (fig. 8). Some water likely left the lake 

through the levee breach as river levels began to recede. Once 

water levels dropped below the levee breach, pumps were 

turned on and the algae-laden and nutrient-rich lake water 

was discharged to Wapato Creek and then downstream to the 

Tualatin River at RM 60.1. During pumping, a number of dead 

fish (carp, catfish, bluegill, and perch) were observed (fig. 9) 

that presumably had entered the lake with the floodwaters. 

These fish may have died as a result of warm temperatures, 

low DO concentrations, or injuries sustained while passing 

through the pumps (Oregon Department of Environmental 

Quality, 2008). 

The Wapato Lake discharge was the likely cause of 

nuisance surface scums of algae many miles downstream 

(fig. 10) and a contributor to low-DO conditions later that 

summer (Carpenter and Rounds, 2013, table 14). Algal growth 

in Wapato Lake was the likely source of geosmin and organic 

carbon that required additional treatment by JWC’s water 

treatment plant. Geosmin has a taste and smell that often is 

described as “earthy” or “musty,” and is resistant to oxidation 

by the conventional drinking water treatment methods 

typically used by the JWC WTP (Izaguirre and others, 1982), 

potentially resulting in drinking water with an objectionable 

taste and smell.

Figure 8. Algal bloom and duckweed in the internal canal 

leading to the pump house at Wapato Lake, Oregon. (Photograph 

taken by Matt Nussbaumer, City of Hillsboro, on June 18, 2008.)
Introduction 9

Background and Context

Although the blue-green algae bloom in the lower 

Tualatin River was a highly unusual occurrence due to the 

presence of a surface scum, it was not unprecedented. The 

Tualatin River has a well-documented history of water-quality 

problems, including warm water temperatures, algal blooms, 

and periodic low-DO concentrations, the causes of which have 

been the subject of much research and water-quality model 

development over the past several decades (Carter and others, 

1976; Oregon Department of Environmental Quality and 

Unified Sewerage Agency, 1982; Berger, 1993; Rounds and 

Doyle, 1997; Rounds and others, 1999; Risley, 2000; Rounds 

and Wood, 2001; Sullivan and Rounds, 2005; Bonn and 

Rounds, 2010).

Research and data have shown that algal populations in 

the Tualatin River are governed primarily by three factors: 

streamflow, sunlight available for photosynthesis, and 

phosphorus concentrations. When streamflow at Farmington 

(RM 33.3) decreases to less than about 300 ft3

/s in the 

low-flow summer season, sufficient time is available for 

phytoplankton to grow into a significant population (Rounds 

and others, 1999). Algae blooms in the lower Tualatin River 

typically occur in the reservoir reach of the river that begins 

at about RM 30, where the river widens and slows, providing 

ample time and light (lack of shading) during the summer lowflow period for algae to grow as they float downstream. In a 

typical summer, small populations of algae enter the reservoir 

reach from upstream, and substantial algal populations are not 

achieved until they have floated downstream as far as Elsner 

(RM 16.2) or farther. Prior to 2003, with sufficient time and 

light, an algal bloom was almost guaranteed in the reservoir 

reach of the lower river between Elsner (RM 16.2) and the 

Oswego Dam (RM 3.4). Phosphorus concentrations in the 

river then determined the maximum size of the resulting algal 

bloom, such that less phosphorus resulted in a smaller bloom. 

The bloom often would terminate when flows increased 

or sunlight levels decreased such that algal growth was no 

longer favored, or when phosphorus concentrations decreased 

enough to further limit phytoplankton growth (Carpenter 

and Rounds, 2013). Since 2003, however, this simple threeparameter model often has failed to explain the absence of 

even a moderate algal population in the Tualatin River, despite 

apparently favorable flow, light, and nutrient conditions. 

Typically, moderate phytoplankton populations in the 

lower river would generate enough DO through photosynthesis 

to offset losses from sediment oxygen demand, resulting in 

DO levels that would be above the minimum DO criteria 

specified by the State of Oregon’s water-quality standards. 

Lacking some minimum amount of photosynthesis from 

algal growth, however, DO concentrations in the river tend to 

decrease to levels below the minimum DO criteria toward the 

end of summer. 

Figure 10. Floating mats of blue-green algae (Anabaena flosaquae) in the Tualatin River upstream of Stafford Road (A) and 

microscopic views of a colony (B) and filament of Anabaena (C) in 

the Tualatin River, Oregon. (Photograph A taken by Brian Wegener, 

Tualatin Riverkeepers, July 17, 2008; photographs B and C taken by 

Kurt Carpenter, U.S. Geological Survey, July 9, 2008.)
10 Upstream Factors Affecting Tualatin River Algae, Oregon

Because the DO concentration in the Tualatin River is 

critical for aquatic life and is an important indicator of the 

river’s health, it was imperative that a deeper understanding of 

the factors affecting phytoplankton populations be developed. 

To that end, as part of a recent USGS study (Carpenter and 

Rounds, 2013), the plankton community (phytoplankton and 

zooplankton) and water-quality conditions were characterized 

in the middle and lower reaches of the Tualatin River during 

the 2006–08 summer low-flow seasons. As part of that study, 

the various sources of streamflow including natural flow, 

WWTF effluent, and reservoir releases from Hagg Lake 

(primarily) and Barney Reservoir were estimated to assess 

how these might affect (1) the abundance and types of algae 

in the river, and (2) the bloom-crash sequences leading to 

the lowest DO concentrations. Given the greater frequency 

of low-DO events in recent years, data from 1991 to 2009 

on longitudinal phytoplankton biomass (chlorophyll-a) and 

water-quality conditions (nutrients, turbidity, and flow) were 

analyzed. 

One of the key findings of the study of Tualatin River 

algae was that declines in the phytoplankton population in the 

lower river were accompanied by a simultaneous decrease in 

chlorophyll-a levels as far upstream as Rood Bridge at RM 38.4 

(Carpenter and Rounds, 2013, fig. 7). The Rood Bridge site is 

well upstream of the reservoir reach where conditions are more 

favorable for algal growth. Conditions at Rood Bridge are more 

indicative of a “feedstock” of algae being transported into the 

reservoir reach. The analyses by Carpenter and Rounds (2013) 

suggested that an upstream algal inoculum was a key factor 

(in addition to flow, light, and phosphorus) in determining the 

eventual algal population (and DO concentrations) in the lower 

river. Although low levels of upstream inocula may contribute 

to low DO concentrations downstream and higher levels of 

such inocula can help maintain DO levels in the lower river, 

inputs of harmful blue-green algae such as those that occurred 

during June and July 2008 from the Wapato Lake area can 

have profound negative consequences for aquatic life, public 

recreation, and municipal water users.

Data Sources, Methods, and Quality 

Assurance/Quality Control

Water quality, streamflow, and (or) plankton data 

used in this study were collected by USGS, CWS, JWC, 

Jackson Bottom Wetlands Preserve, Bureau of Reclamation 

(Reclamation), Oregon Water Resources Department (OWRD), 

and the Oregon Department of Environmental Quality (ODEQ) 

(table 1). In addition to routine monitoring done by these 

groups, event-based targeted samples were collected during 

the early stages of the bloom by USGS and JWC to identify a 

possible source (inoculum) of the bloom and associated taste 

and odor issues. Sites along the Tualatin River where samples 

were collected or other data-collection activities occurred are 

listed in table 2 and shown in figures 4 and 5.

Continuous Water-Quality and Streamflow 

Monitors

The USGS operates a network of continuous waterquality monitors in the Tualatin River and its tributaries that 

collect hourly data (U.S. Geological Survey 2015a, 2015b). 

Three of the USGS water-quality monitors operating during 

the study period were in the Tualatin River near Scholls 

(RM 24.5), at Cook Park (RM 9.9), and at the Oswego Dam 

(RM 3.4). Several other USGS water-quality monitors were 

located on key tributaries including Scoggins, Gales, Dairy, 

Rock, Chicken, Beaverton, and Fanno Creeks. An additional 

continuous water-quality monitor in the Tualatin River at 

Highway 219 (RM 44.4) was operated by the Jackson Bottom 

Wetlands Preserve. The USGS operates streamgages in 

the Tualatin River at West Linn (RM 1.8) and Dilley (RM 

58.8). OWRD operates streamgages in the Tualatin River at 

Farmington (RM 33.3), Rood Bridge (RM 38.4), and Old Hwy 

47 (RM 62.3) among other locations. Flow data for Scoggins 

Creek downstream of Hagg Lake were obtained from 

Reclamation. Release rates from Barney Reservoir and Hagg 

Lake for flow augmentation were obtained from the Tualatin 

River Flow Management Technical Committee (Bonn, 2008).

Plankton-Sample Collection, Processing, and 

Identification

Phytoplankton and zooplankton assemblages were 

characterized using traditional quantitative methods and 

enumeration of preserved plankton samples. Tow-net samples 

of “net plankton, 80-μm” also were collected at selected sites 

for microscopic observation of the unpreserved plankton 

community, starting May 18, 2008, and continuing through 

the summer season. Phytoplankton grab samples were 

collected from just below the river surface into 250-mL 

polyethylene bottles and preserved with 2.5 mL of Lugol’s 

solution (1 percent final concentration). Samples were 

shipped to Aquatic Analysts (Friday Harbor, Washington) for 

identification and enumeration. Permanent microscope slides 

were prepared for each sample by filtering an appropriate 

aliquot of the sample through a 0.45-μm membrane filter 

(American Public Health Association, 1992). A section of 

filter was cut out and placed on a glass slide with immersion 

oil added to make the filter transparent. A cover slip was 

placed on top, with nail polish applied to the periphery for 

permanency. Most algae were identified by cross-referencing 

several taxonomic sources. A minimum of 100 algal units, 

defined as discrete particles (cells, colonies, or filaments), 

were counted along a measured transect on a microscope slide 

with a Zeiss standard microscope using 1,000× magnification. 

Only algae with intact chloroplasts that were believed to 

be alive at the time of collection were counted. Average 

biovolume estimates of each species were obtained from 

calculations of microscopic measurements of each alga taxon 

in each sample analyzed. The number of cells per colony or 
Data Sources, Methods, and Quality Assurance/Quality Control 11

Table 1. Data sources and water-quality constituents analyzed in river water and finished drinking water at selected sites in the Tualatin River basin, Oregon, 2008.

Agency

Stream and source-water samples

Finished 

drinking-water 

samples

Plankton Nutrients and organic carbon Field parameters Taste and odor compounds

Streamflow

Phytoplankton species

Chlorophyll

Zooplankton

Ammonium-nitrogen

Nitrate-nitrogen

Total phosphorus

Total organic carbon

Water temperature

Specific conductance

Dissolved oxygen

pH

Turbidity

Pesticide screen

Geosmin

Methyl isoborneol

U.S. Geological Survey

X

X

X

X

X

X

X

X

Clean Water Services1 X

X

X

X

X

X

X

X

X

Joint Water Commission

X

X

X

X

X

X

X

X

X

X

X

Jackson Bottom Wetlands Preserve

X

X

X

X

X

Bureau of Reclamation

X

Oregon Water Resources Department

X

Oregon Department of Environmental Quality2 X

X

X

X

X

X

X

X

1Routine weekly monitoring data.2Sampled on August 1, 2008.
12 Upstream Factors Affecting Tualatin River Algae, Oregon

the length of a filament was recorded to compute biovolume 

per algal-unit conversion factors to calculate total biovolume 

per taxon for each sample. The cell density, in number of cells 

per milliliter, was also determined for Anabaena only, when 

present.

Zooplankton samples were collected with a 

12-in.‐diameter, 80-μm mesh plankton net that was hand 

tossed from a canoe or from shore, capturing approximately 

10 ft of towing distance per sample for a total volume of 

approximately 222 L or 0.222 m3 per sample. The sample 

was washed down the net toward the “cod” end with repeated 

rinses into a 20-mL plastic vial and preserved with isopropyl 

alcohol (25 percent final concentration, by volume). Samples 

were shipped to ZP’s Taxonomic Services (Lakewood, 

Washington) for identification and enumeration. Zooplankton 

densities, in number of organisms per cubic meter, were 

determined for each sample by counting a minimum of 400 

organisms or, if fewer organisms were present, the entire 

sample.

Microcystin Algal Toxin Analyses

The USGS Oregon Water Science Center analyzed 

several samples for microcystin, a liver toxin sometimes 

produced by blue-green algae, using an enzyme-linked 

immunosorbent assay (ELISA) test kit from Abraxis (Fischer 

and others, 2001). Whole-water samples underwent three 

freeze-thaw cycles to lyse cells and liberate the toxins prior to 

analysis. Tests were run in duplicate, and averages of the two 

results were reported. Results of paired samples were typically 

within 5 percent (range: 0.1–10 percent). The ELISA test kits 

used in this study have a detection limit of about 0.1 μg/L, 

which is well within the range of usefulness for this study.

Table 2. Selected sampling sites and data collection activities in the Tualatin River basin, Oregon, 2006–08.

[For a more complete listing of river mile indexes, refer to Carpenter and Rounds (2013). –, no data]

Location Mainstem 

river mile

Plankton 

sampling

Waterquality 

sampling

Continuous 

water-quality 

monitor

Streamgage

Outflow

Tualatin River at Weiss Bridge 0.2 – X – – –

Tualatin River at Oswego Dam 3.4 X X X – –

Tualatin River downstream of Stafford Road 1

5.4/5.5 X X – – –

Tualatin River at Boones Ferry Road 8.7 – X – – –

Tualatin River downstream of Fanno Creek and Durham WWTF 9.2 X X – – –

Tualatin River downstream of Cook Park 9.7 X X – – –

Tualatin River at RM 9.9 near Tualatin 9.9 – – X – –

Tualatin River at Jurgens Park 10.8 X X – – –

Tualatin River at Elsner (Roy Rogers Road) 16.2 – X – – –

Tualatin River near Scholls 24.5 X X X – –

Tualatin River at Scholls Bridge 26.9 – X – – –

Tualatin River at Farmington 33.3 – X – X –

Tualatin River at Rood Bridge 38.4 X X – X –

Tualatin River at Highway 219 Bridge 44.4 – X X – –

Tualatin River at Golf Course Road 51.5 – X – – –

Tualatin River at the JWC/TVID Spring Hill Pumping Plant 56.1 – X – – X

Carpenter Creek at Anderson Road – – X – – –

Carpenter Creek at Plum Lee Road – – X – – –

Tualatin River at Dilley (Spring Hill Road) 58.8 – X – X –

Scoggins Creek at Old Highway 47 – – X – – –

Scoggins Creek below Hagg Lake – – X – X –

Wapato Creek at Gaston Road (includes Wapato Lake pump discharge) – – X – – –

Hill Creek at Spring Hill Road – – X – – –

Ayers Creek at Northeast Flett Road – – X – – –

Tualatin River at Wapato Improvement District headgate 61.9 – – – – X

Tualatin River at the Old Highway 47 Bridge (Gaston) 62.3 – X – X –

Tualatin River at Cherry Grove 67.8 – X – – –

1

U.S. Geological Survey plankton site is located 0.1 mile downstream of the bridge where Clean Water Services collects water samples.
Data Sources, Methods, and Quality Assurance/Quality Control 13

Clean Water Services Data

Clean Water Services conducts routine water-quality 

monitoring at many locations within the Tualatin River 

basin, with weekly sample collection during summer at 

13 or more sites in the Tualatin River between Cherry Grove 

(RM 67.8) and Weiss Bridge (RM 0.2). Grab-integratedcomposite samples were collected at five points across the 

river width, with each sample integrated over the depth of 

the river or as much as the top 10 ft, whichever was less. The 

five subsamples then were composited in a churn splitter. 

Water samples were processed and analyzed by the CWS 

Water-Quality Laboratory (Hillsboro, Oregon) using methods 

published in their watershed monitoring plan (Clean Water 

Services, 2006). Water samples for dissolved constituents were 

passed through 0.45-micron syringe filters prior to analysis, 

and subsamples for chlorophyll-a were collected onto glass 

fiber filters and analyzed fluorometrically (Clean Water 

Services, 2006). 

All CWS data used in this study, including nutrients, 

chlorophyll-a, turbidity, and field parameters (water 

temperature, pH, DO, and specific conductance) were 

subjected to a comprehensive and rigorous quality assurance 

(QA) procedure by the CWS Water-Quality Laboratory. 

CWS Water-Quality Laboratory methods and protocols have 

been reviewed by the USGS Branch of Quality Systems and 

were determined to be suitable for use in this study. Field 

methods in use by CWS, including the collection of samples 

using depth- and width-integrating techniques and the use of 

churn splitters for subsampling, are consistent with USGS 

procedures and appropriate for the sites sampled. The CWS 

laboratory has been certified by the National Environmental 

Laboratory Accreditation Conference (NELAC), participates 

in a monthly-to-quarterly QA program with the USGS Oregon 

Water Science Center for nutrients and chlorophyll-a, and 

participates in many laboratory performance tests such as 

the twice-a-year USGS Standard Reference Sample (SRS) 

program, a national inter-laboratory comparison study (U.S. 

Geological Survey, 2013). SRS results from many years 

of participation in the program have shown that the CWS 

laboratory consistently produces high quality data that are 

sufficiently accurate for all the parameters used in this study.

Joint Water Commission Data

Prior to the water-quality problems of 2008, JWC staff 

monitored sites in the Tualatin River basin upstream of the 

JWC drinking-water treatment plant intake (RM 56.1) as 

part of a project designed to study disinfection by-product 

precursors. Staff collected total organic carbon (TOC) grab 

samples at several sites (fig. 5). Samples for TOC analysis 

were collected weekly beginning in October 2007 and were 

analyzed by Alexin Analytical Laboratory (Tigard, Oregon) 

using standard method 5310-C. Field measurements of water 

temperature, specific conductance, pH, DO, total chlorophyll, 

and turbidity were taken weekly using a Yellow Springs 

Instrument (YSI) 6920 multi-parameter sonde. Although 

the response of the chlorophyll sensor on that sonde was 

blank-checked against deionized water, those sensor data 

are not as definitive as laboratory results derived from water 

samples; regardless, the chlorophyll sensor data agreed well 

with available laboratory results from water samples. This 

monitoring continued until June 2008 when the cities of 

Hillsboro and Beaverton began receiving complaints of taste 

and odors in the treated water from JWC.

In response to changes in water quality at the drinkingwater treatment plant, JWC staff began collecting samples 

for taste and odor indicators (geosmin and methyl isoborneol 

[MIB]) in an attempt to identify the source of the issue. 

Samples also were collected periodically at points within the 

treatment plant and at locations in the distribution system 

to quantify the extent of the issue. Seven new stream sites 

were added to the monitoring program, with weekly or more 

frequent collection of field parameters. Sampling for taste 

and odor indicators continued every 2–12 days until early 

September 2008. Geosmin and MIB samples collected prior to 

July 2008 were analyzed by MWH Laboratories (Monrovia, 

California) by solid-phase micro-extraction (SPME). Geosmin 

and MIB samples collected after July 1, 2008 were analyzed 

by CH2M-Hill (Corvallis, Oregon) using SPME according to 

standard method 6040D (American Public Health Association, 

1992).

Oregon Department of Environmental Quality 

Data

Oregon Department of Environmental Quality staff 

conducted an investigation in response to a report of a fish kill 

near the Wapato Lake pump house during the latter part of the 

bloom period in 2008. Water-quality samples were collected 

and field measurements were taken on August 1, 2008. The 

specific parameters and constituents analyzed are listed 

in table 1. The ODEQ Water-Quality Laboratory also has 

rigorous internal QA procedures and participates in the USGS 

SRS inter-laboratory comparison program; results have shown 

that the data produced by the ODEQ laboratory are sufficiently 

accurate for the parameters used in this study.
14 Upstream Factors Affecting Tualatin River Algae, Oregon

Bloom Origination, Discovery, and 

Tracking to Wapato Lake

Early Bloom Indications, June 2008

The first indications of unusual water quality in the 

Tualatin River during summer 2008 were provided by 

JWC customers in Hillsboro and Beaverton who reported 

complaints of “earthy” and “musty” tasting drinking water 

on June 3. A reconstructed timeline of events is shown in 

table 3. Over the next week, hundreds of customer complaint 

calls were received by JWC, and the local media published 

several stories on the drinking-water issue. JWC attempted 

to remedy the issue with various operational and distribution 

methods, but without success. Suspecting certain taste-andodor compounds in the raw source water, JWC staff began 

to look for potential sources during their routine streammonitoring activities. On June 11, JWC staff were alerted that 

Wapato Lake was still full of water; normally it would have 

been pumped out and growing crops by June. Also on June 11, 

floating algal mats were observed in the internal Wapato Lake 

canal that routes lake water to the pump house (fig. 8).

Table 3. Reconstructed timeline of events associated with the bloom of Anabaena flos-aquae in Wapato Lake and downstream in the 

Tualatin River, Oregon, 2008.

[Abbreviations: RM, river mile; JWC, Joint Water Commission; WTP, Water Treatment Plant; USGS, U.S. Geological Survey; CWS, Clean Water Services; 

TRK, Tualatin Riverkeepers]

Date Description

December 2–3, 2007 Winter storm causes levee to fail

Late May/early June River levels recede enough to allow pumping without repairing the levee; unclear whether levee was patched 

temporarily

June 1 Wapato Lake pump discharge or lake drainage begins intermittently

June 3 First reports of taste-and-odor issues by drinking water customers

June 9 Wapato Lake pump discharge stops or lake drainage decreases temporarily; downstream water quality improves slightly

June 11 Floating algal mats first observed at the Wapato Lake canal by JWC staff; 

Anabaena first discovered in the Tualatin River at Rood Bridge (RM 38.4) and other downstream sites

June 12 Treatment with powdered activated carbon begins at JWC WTP

June 13 Taste-and-odor indicators confirmed present at JWC WTP

June 19 JWC staff observes that Wapato Lake pumps are operating

June 30 Wapato Lake pumping increases; abundant sunshine prevails; Anabaena found at all sites sampled from Rood Bridge 

(RM 38.4) to Oswego Dam (RM 3.4)

July 4–5 Anabaena bloom arrives at RM 24.5 monitor (USGS data)

July 7 Floating algal mats observed at Elsner (RM 16.2) by CWS staff

July 8 Bloom arrives at Cook Park (RM 9.9) monitor (USGS data)

July 9 Surface scums discovered at Jurgens Park (RM 10.8) and Cook Park (RM 9.9) by TRK and USGS; algae in surface 

scums confirmed as Anabaena

July 10 Bloom arrives at Oswego Dam (RM 3.4) according to USGS dissolved oxygen data; CWS increases reservoir releases 

to alleviate water-quality issues

July 12 Oregon Department of Human Services issues public health advisory

July 16 Anabaena streaks still present, Elsner (RM 16.2) to Cook Park (RM 9.9) (USGS observations)

July 17 Some algal mats still present, Cook Park (RM 9.9) to Oswego Dam (RM 3.4) (TRK observations)

July 19 Confirmation of high levels of chlorophyll, plankton, phosphorus, organic nitrogen, and oxygen demands in Wapato 

Lake discharges

July 23 Wapato Lake pumping still at full capacity in effort to pump the lake dry by August 1

July 25 Oregon Department of Human Services lifts public health advisory

July 30 Wapato pumping decreases based on flow balance estimates

August 4 A return to normal water-quality conditions at RM 24.5 monitor (USGS data)

Early September Levee repaired
-25 

0 

25 

50 

75 

100 

125 

150 

175 

200 

225 

250 

275 

300 

 6-01 6-05 6-09 6-13 6-17 6-21 6-25 6-29 7-03 7-07 7-11 7-15 7-19 7-23 7-27 7-31 8-04 

Streamflow, in cubic feet per second 

Month and day in 2008 

Scoggins Creek (river mile [RM] 60)

Tualatin River at Dilley (RM 58.8)

Tualatin River at Gaston (RM 63.9)

Wapato Lake pump discharge estimate 

EXPLANATION

Figure 11. Estimated discharge from the Wapato Creek drainage (and Wapato Lake), as estimated from a mass balance 

of measured streamflows in Scoggins Creek and the Tualatin River, Oregon, June–July 2008.

Bloom Origination, Discovery, and Tracking to Wapato Lake 15

No definitive records exist to document when the Wapato 

pumps were operating in summer 2008, but nearby streamgage 

data were used to estimate the timing and magnitude of the 

Wapato Lake discharges. Wapato Creek joins the Tualatin 

River between the Old Highway 47 (Gaston, RM 62.3) and 

Dilley (RM 58.8) streamgages. By subtracting the sum of 

measured streamflows in Scoggins Creek below Henry Hagg 

Lake (Reclamation station 14202980) and in the Tualatin 

River at Old Highway 47 (OWRD station 14202510) from the 

measured streamflow in the Tualatin River at Dilley (USGS 

station 14203500), a rough estimate of the discharge from the 

Wapato Creek drainage was obtained. TVID did not make any 

diversions from the Tualatin River into the Wapato canals in 

2008. Some diversions from Scoggins Creek or the Tualatin 

River would tend to bias these flow estimates for Wapato 

Creek, but such diversions were likely to be small, on the 

order of less than 2 ft3/s. The estimated discharge from Wapato 

Creek in early June was about 13 ft3/s (fig. 11). The Wapato 

pump house has two pumps, one “large” and one “small,” 

with a combined nominal pumping rate of 13,000 gal/min 

(about 29 ft3/s). It is not clear whether pumping was occurring 

in early June, or whether lake water was draining out of the 

unrepaired levee breach. The date of any initial repair work 

on the levee was not documented, but a partial repair may 

have occurred prior to June 19 when at least one of the pumps 

was observed to be operating by JWC staff. Any pumping 

or drainage was likely intermittent at the beginning of June, 

given the variation in the Wapato Creek discharge estimates, 

but these calculations confirm that water was being discharged 

from Wapato Lake in early June when the first taste-and-odor 

issues were reported.

JWC staff identified odor issues at the WTP on June 12, 

and treatment additions of powdered activated carbon were 

initiated. Water samples collected by JWC staff on June 13 

confirmed the presence of geosmin at concentrations of 

16 and 13 nanograms per liter (ng/L), or parts-per-trillion, 

in samples of raw and finished (treated) drinking water, 

respectively (table 4). Geosmin can be detected by humans at 

concentrations as low as 5–10 ng/L (Gottler and others, 2007). 
16 Upstream Factors Affecting Tualatin River Algae, Oregon Table 4.

Water-quality data from the Joint Water Commission for sites in the upper Tualatin River basin, Oregon, May–August 2008.

[Sites listed in downstream order. Total chlorophyll: From a Yellow Springs Intsrument (YSI) probe. Abbreviations: m, meter; °C, degrees Celsius; μS, microsiemens; cm, centimeter; mg/L, milligram per liter; μg/L, microgram per liter; ng/L, nanogram per liter; NTU, nephelometric turbidity unit; JWC, Joint Water Commission; TVID, Tualatin Valley Irrigation District; WTP, water treatment plant; Hwy, Highway; ND, not detected; –, no data]

Site Date

Water 

temperature

(°C)

Specific 

conductance

(μS/cm)

Dissolved 

oxygen 

(mg/L) 

Dissolved 

oxygen

(percent 

saturation)

pH 

(standard 

units)

Turbidity 

(NTU)

Total

chlorophyll

(μg/L)

Total 

organic 

carbon 

(mg/L) 

Geosmin 

(ng/L)

Methyl 

isoborneol 

(ng/L) 

Raw water at the JWC/TVID Spring Hill Pumping Plant 5-15-2008 13.6 85 10.0 – 7.3 7.1 1.5 2.3 – –

5-22-2008 13.8 89 10.3 – 7.5 – 1.4 2.2 – –

5-29-2008 13.7 84 11.0 – 7.3 15 2.3 2.2 – –

Carpenter Creek at Anderson Road (lower) 6-12-2008 11.0 196 10.6 96 8.1 11 0.7 2.4 3.9 ND

Raw water at the JWC/TVID Spring Hill Pumping Plant 13.8 76 10.1 97 7.6 5.7 0.5 1.8 – –

Scoggins Creek at Old Highway 47 6-13-2008 – – – – – – – – ND ND

Carpenter Creek at Anderson Road (lower) – – – – – – – – 3.9 NDRaw water at the JWC/TVID Spring Hill Pumping Plant – – – – – – – – 16 NDTreated drinking water from JWC WTP – – – – – – – – 13 NDTualatin River at Old Hwy 47 Bridge 6-19-2008 11.3 93 10.4 95 7.7 2.5 0.7 1.1 – –

Ayers Creek at NE Flett Road 14.8 140 8.6 85 7.5 11 0.4 2.5 ND ND

Hill Creek at Spring Hill Road 13.8 107 8.1 78 7.4 23 2.3 3.2 – –

Wapato Creek at Gaston Road (includes Wapato Lake 

pump discharge)

17.8 102 8.2 86 7.1 40 11 16.9 7.2 ND

Tualatin River at Dilley 12.3 74 8.4 79 7.5 8.6 2.2 3.7 14 ND

Carpenter Creek at Anderson Road (lower) 12.0 207 9.7 90 7.1 6.0 1.4 2.8 – –

Gales Creek at Hwy 47 Bridge 14.1 105 9.9 96 7.4 4.8 0.4 1.8 – –

Raw water at the JWC/TVID Spring Hill Pumping Plant 14.6 85 8.1 80 7.4 10 0.4 2.1 – –

Carpenter Creek at Anderson Road (lower) 6-26-2008 13.4 211 9.1 88 7.2 6.5 1.2 3.6 – –

Raw water at the JWC/TVID Spring Hill Pumping Plant 12.3 71 11.1 103 7.5 – 1.6 1.9 – –

Tualatin River at Old Hwy 47 Bridge 7-17 to 7-21-2008 15.3 74 10.1 101 8.0 2.7 0.4 1.3 – –

Ayers Creek at NE Flett Road 10.7 66 11.0 100 7.5 9.4 9.6 1.8 ND 1.1

Hill Creek at Spring Hill Road 15.8 138 8.1 82 7.6 13 2.2 4.2 – –

Wapato Creek at Gaston Road (includes Wapato Lake 

pump discharge)

22.0 131 2.0 23 6.8 81 133 38.3 8.6 2.2

Scoggins Creek at Old Highway 47 – – – – – – – – ND ND

Tualatin River at Dilley 15.3 141 9.0 90 7.6 8.1 2.0 7.0 ND ND

Carpenter Creek at Anderson Road (lower) 14.6 165 5.2 51 7.1 3.3 5.2 – – –

Gales Creek at Hwy 47 Bridge 19.0 127 8.6 93 7.4 3.2 1.4 2.0 3.1 ND

Raw Water at the JWC/TVID Spring Hill Pumping Plant – – – – – – – – 7.2 1.1

Treated drinking water from JWC WTP 13.8 122 10.9 106 7.5 0.1 0.2 – 3.2 ND
Bloom Origination, Discovery, and Tracking to Wapato Lake 17

Site Date

Water 

temperature

(°C)

Specific 

conductance

(μS/cm)

Dissolved 

oxygen 

(mg/L) 

Dissolved 

oxygen

(percent 

saturation)

pH 

(standard 

units)

Turbidity 

(NTU)

Total

chlorophyll

(μg/L)

Total 

organic 

carbon 

(mg/L) 

Geosmin 

(ng/L)

Methyl 

isoborneol 

(ng/L) 

Tualatin River at Old Hwy 47 Bridge 7-23 to 7-24-2008 14.1 71 11.1 108 7.4 3.8 0.7 1.5 – –

Ayers Creek at NE Flett Road – – – – – – – – ND ND

Wapato Creek at Gaston Road (includes Wapato Lake 

pump discharge)

20.1 129 3.1 34 7.0 117 200 52.3 ND ND

Tualatin River at Dilley 10.1 65 13.9 124 7.5 – 13 – 2.1 1.9

Carpenter Creek at Anderson Road (lower) 14.2 209 8.7 85 7.1 9.8 3.3 3.9 – –

Gales Creek at Hwy 47 Bridge 17.4 128 9.3 97 7.3 4.1 1.7 2.7 – –

Raw water at the JWC/TVID Spring Hill Pumping Plant 11.1 71 11.6 105 7.0 11 13 4.5 – –

Tualatin River at Old Hwy 47 Bridge 7-28-2008 14.2 72 10.9 107 7.3 2.2 1.8 1.6 5.2 ND

Wapato Creek at Gaston Road (includes Wapato Lake 

pump discharge)

17.6 126 3.2 34 6.4 126 675 51.9 6.1 ND

Tualatin River at Dilley 10.4 70 11.7 105 6.8 21 37 11.3 7.3 ND

Raw water at the JWC/TVID Spring Hill Pumping Plant 12.2 76 11.4 106 7.0 18 37 10.2 2.1 ND

Treated drinking water from JWC WTP 13.5 128 11.8 114 7.4 0.1 0.5 2.1 4.7 ND

Wapato Creek at Gaston Road (includes Wapato Lake 

pump discharge)

7-31-2008 19.3 255 2.6 28 6.3 174 190 56.9 – –

Tualatin River at Dilley 9.4 65 12.0 105 7.5 8.5 3.1 2.1 – –

Carpenter Creek at Anderson Road (lower) 14.1 246 7.7 75 7.0 11 2.8 5.6 – –

Tualatin River at Old Hwy 47 Bridge 8-07-2008 16.5 73 9.7 99 7.6 3.8 1.2 1.5 1.9 ND

Wapato Creek at Gaston Road (includes Wapato Lake 

pump discharge)

18.0 65 4.2 45 6.8 44 10 8.3 2.1 ND

Scoggins Creek at Old Highway 47 8.6 59 13.3 114 7.5 5.1 1.9 1.5 – –

Tualatin River at Dilley 9.7 65 12.4 110 8.4 15 3.5 2.3 ND ND

Carpenter Creek at Plum Lee Road (upper) 14.8 389 9.9 98 7.4 2.7 1.6 3.3 – –

Carpenter Creek at Anderson Road (lower) 16.4 212 6.4 65 6.9 10 4.1 5.4 – –

Gales Creek at Hwy 47 Bridge 20.5 139 7.6 85 7.3 3.6 1.3 2.7 – –

Raw water at the JWC/TVID Spring Hill Pumping Plant 11.9 69 10.8 100 6.9 8.7 4.1 2.2 ND ND

Treated drinking water from JWC WTP 12.8 102 11.9 113 8.6 0.1 1.3 0.8 ND ND

Table 4. Water-quality data from the Joint Water Commission for sites in the upper Tualatin River basin, Oregon, May–August 2008.—Continued[Sites listed in downstream order. Total chlorophyll: From a Yellow Springs Intsrument (YSI) probe. Abbreviations: m, meter; °C, degrees Celsius; μS, microsiemens; cm, centimeter; mg/L, milligram per liter; μg/L, microgram per liter; ng/L, nanogram per liter; NTU, nephelometric turbidity unit; JWC, Joint Water Commission; TVID, Tualatin Valley Irrigation District; WTP, water treatment plant; Hwy, Highway; ND, not detected; –, no data]
18 Upstream Factors Affecting Tualatin River Algae, Oregon Site Date Water temper- ature (°C) Specific conduc- tance (μS/cm) Dissolved oxygen (mg/L) Dissolved oxygen (percent saturation) pH (standard units) Turbidity (NTU) Total chlorophyll

(μg/L)

Total 

organic 

carbon 

(mg/L) 

Geosmin 

(ng/L)

Methyl 

isoborneol 

(ng/L) 

Tualatin River at Old Hwy 47 Bridge 8-14-2008 16.5 69 10.0 102 7.4 2.4 0.0 1.5 1.6 ND

Wapato Creek at Gaston Road (includes Wapato Lake 

pump discharge)

20.3 82 5.2 59 7.1 39 14 1.8 1.8 ND

Scoggins Creek at Old Highway 47 9.6 59 14.6 130 7.4 6.8 3.9 1.5 ND ND

Tualatin River at Dilley 10.9 60 12.2 40 7.2 7.4 0.8 1.7 1.3 ND

Carpenter Creek at Plum Lee Road (upper) 15.7 396 10.0 100 7.4 7.5 0.4 3.2 – –

Carpenter Creek at Anderson Road (lower) 17.0 221 4.9 50 6.8 8.7 2.0 4.9 4.2 ND

Gales Creek at Hwy 47 Bridge 21.7 139 7.8 89 7.3 4.4 0.7 2.9 2.8 ND

Raw water at the JWC/TVID Spring Hill Pumping Plant 11.7 65 11.8 109 7.0 9.3 1.5 1.6 ND ND

Treated drinking water from JWC WTP – – – – – – – 0.6 ND ND

Tualatin River at Dilley 8-26-2008 – – – – – – – 1.7 2.1 1.0

Tualatin River at Old Hwy 47 Bridge – – – – – – – – 1.8 NDWapato Creek at Gaston Road (includes Wapato Lake 

pump discharge)

– – – – – – – – 2.5 ND

Scoggins Creek at Old Highway 47 – – – – – – – – 2.1 NDCarpenter Creek at Anderson Road (lower) – – – – – – – – 4.9 3.5

Gales Creek at Hwy 47 Bridge – – – – – – – – 2.4 NDRaw water at the JWC/TVID Spring Hill Pumping Plant – – – – – – – – 2.3 NDTreated drinking water from JWC WTP – – – – – – – – 1.6 ND

Tualatin River at Old Hwy 47 Bridge 8-21-2008 14.2 69 10.6 103 7.4 3.8 0.4 1.9 – –Carpenter Creek at Plum Lee Road (upper) 14.8 400 9.8 97 7.5 4.4 0.7 3.8 – –

Carpenter Creek at Anderson Road (lower) 16.0 291 6.9 69 7.1 11 1.9 4.7 – –

Gales Creek at Hwy 47 Bridge 17.4 133 8.6 90 7.5 6.9 1.3 3.4 – –

Scoggins Creek at Old Highway 47 9.1 60 14.5 126 7.7 6.5 0.5 1.4 – –

Raw water at the JWC/TVID Spring Hill Pumping Plant 14.2 79 10.6 104 7.7 6.5 1.9 1.9 – –

Tualatin River at Old Hwy 47 Bridge 8-28-2008 13.5 67 9.5 91 7.7 2.4 0.0 1.5 – –

Scoggins Creek at Old Highway 47 10.2 60 11.6 103 7.1 5.1 0.4 1.6 – –

Carpenter Creek at Plum Lee Road (upper) 13.1 396 9.6 91 7.5 6.8 0.6 3.3 – –

Carpenter Creek at Anderson Road (lower) 15.7 320 6.6 66 7.2 14 1.3 6.3 – –

Gales Creek at Hwy 47 Bridge 16.9 131 9.6 100 7.4 3.6 0.6 2.7 – –

Raw water at the JWC/TVID Spring Hill Pumping Plant 14.3 73 9.8 95 7.4 7.6 1.5 1.9 – –

Treated drinking water from JWC WTP – – – – – – – 0.7 – –

Table 4. Water-quality data from the Joint Water Commission for sites in the upper Tualatin River basin, Oregon, May–August 2008.—Continued[Sites listed in downstream order. Total chlorophyll: From a Yellow Springs Intsrument (YSI) probe. Abbreviations: m, meter; °C, degrees Celsius; μS, microsiemens; cm, centimeter; mg/L, milligram per liter; μg/L, microgram per liter; ng/L, nanogram per liter; NTU, nephelometric turbidity unit; JWC, Joint Water Commission; TVID, Tualatin Valley Irrigation District; WTP, water treatment plant; Hwy, Highway; ND, not detected; –, no data]
Bloom Origination, Discovery, and Tracking to Wapato Lake 19

Samples collected June 19 from Wapato Creek at Gaston 

Road, directly downstream of the Wapato pump house 

(fig. 5), revealed elevated concentrations of geosmin, total 

chlorophyll, turbidity, and TOC compared to other samples 

collected that day. Downstream in the Tualatin River at Dilley 

(RM 58.8), the concentration of geosmin was two times 

higher (14 ng/L) than at the Wapato pump house (table 4). 

Concentrations of geosmin in Wapato Creek may have varied 

substantially as a function of pumping rate and river level, 

and concentrations at the Dilley site also could have been 

affected by other sources, including some tributary ponds 

that were not sampled. Although the highest overall geosmin 

concentrations tended to occur in the Wapato Lake discharge 

and sites downstream affected by that discharge, geosmin also 

was detected in Carpenter and Gales Creeks, although at lower 

concentrations. Another taste-and-odor compound, MIB, was 

detected only a few times and at concentrations less than the 

human detection threshold level of 29 ng/L (Izaguirre and 

others, 1982) (table 4).

The source of the Anabaena cells that produced the 

bloom in Wapato Lake is unclear. Anabaena produces copious 

quantities of resting spores (akinetes) during blooms, which 

deposit in sediments. The bloom could have originated from 

akinetes previously deposited in the lakebed sediments or the 

adjacent hydrologic system. Although most of the lakebed 

dries out and is farmed in summer, the internal canals of 

the lake stay wet and would remain as viable habitat for the 

akinetes. Another possibility is that viable cells could have 

been transferred to the lake from the Tualatin River through 

the levee breach or from upstream ponds in the Wapato Lake 

drainage basin (fig. 5).

Chlorophyll-a samples for laboratory analysis were not 

routinely collected from sites upstream of the Highway 219 

bridge (RM 44.4) in 2008 (table 5), and JWC monitoring of 

total chlorophyll with a field probe was not performed at sites 

in and around the Wapato Lake area until June 19 when total 

chlorophyll levels in Wapato Lake pump discharges were 

elevated (11 μg/L, table 4).

Clouds and rain during the first week of June (about 

0.8 in. of rain, mostly on June 3) temporarily slowed algal 

photosynthesis in Wapato Lake and downstream in the 

Tualatin River (data available from U.S. Geological Survey, 

2010). Pumping/drainage from Wapato Lake then appeared to 

stop for a couple weeks in mid-June (fig. 11), which may have 

contributed to a slight improvement in water quality—lower 

total phosphorus concentrations—in the Tualatin River at 

Dilley (RM 58.8), downstream of the Wapato Creek inflow 

(table 5).

The early June pumping or drainage from Wapato 

Lake was one potential source of Anabaena to the Tualatin 

River, although drainage from other water bodies, nursery 

ponds, canals, wetlands, or pooled backwaters also may have 

contributed. Many of the small Tualatin River tributaries 

between Gaston and Scholls include small instream ponds. 

On June 11, 1 week after the taste and odor issues were 

first reported, colonies of Anabaena and another colonial 

blue-green algae (Aphanizomenon) were noted in net 

plankton samples from the Tualatin River at Rood Bridge 

(RM 38.4), Jurgens Park (RM 10.8), and Oswego Dam 

(RM 3.4). Enumeration (cell counts) of samples collected 

on June 17 showed 573 Anabaena cells per milliliter in the 

Tualatin River near Scholls (RM 24.5), with similar levels 

(474 cells per mL) downstream of Fanno Creek (RM 9.2), but 

no Anabaena colonies detected at Jurgens Park (RM 10.8) 

(table 6). This suggests that the inoculum for the bloom may 

have been released to the river intermittently, supporting 

the conclusions of the flow data analysis and estimated 

discharges from Wapato Lake (fig. 11). Downstream variations 

in Anabaena abundance also could be due to variability in 

the success of Anabaena to survive and reproduce in the 

Tualatin River (from variations in sunlight, for example), from 

uneven discharge of algae from Wapato Lake during draining 

(possible wind effects that push floating mats toward or away 

from the pumps or the levee breach), and possibly also from 

zooplankton grazing.

Mature Bloom, July 2008

The algal bloom in the Tualatin River grew considerably 

during the first week of July, when weather and flow 

conditions were favorable for algal growth. On July 4–5, the 

DO concentration measured by a USGS water-quality monitor 

at RM 24.5 increased anomalously, above historical conditions 

for that time of year, and indicative of a substantial amount 

of photosynthetic DO production. On July 7, about 1 week 

after the Wapato Lake pumping appeared to increase (fig. 11), 

a CWS sampling crew observed floating mats of algae in the 

Tualatin River at Elsner (RM 16.2), well within the reservoirlike reach of the river that is prone to algal growth. Two days 

later, a surface scum was observed in the Tualatin River by 

USGS staff and members of the Tualatin Riverkeepers group 

at Jurgens Park (RM 10.8), and by USGS staff downstream 

of Stafford Road (RM 5.4). The bloom reached the Oswego 

Dam (RM 3.4) water-quality monitoring site on July 10. A 

reconstructed timeline of events is shown in table 3.

Water samples from July 9 were examined 

microscopically and results showed that the bloom was 

dominated by Anabaena, a colonial blue-green algae that 

often forms blooms and surface scums in nutrient-enriched 

rivers, lakes, and reservoirs (Wehr and Sheath, 2003). Algae 

samples were sent to Aquatic Analysts for rush analysis, who 

confirmed the initial identification as Anabaena flos‐aquae. 

Routine and targeted plankton sampling by USGS starting 

July 9 revealed elevated levels of Anabaena at many sites 

in the lower Tualatin River (table 6). Selected samples were 

analyzed by USGS for the algal toxin microcystin, and 

results confirmed the presence of the toxin at levels below 

the Oregon recreational health-hazard guideline in effect at 

that time (8 μg/L), but one sample exceeded the World Health 

Organization drinking-water guideline of 1 μg/L (table 6). The 

U.S. Environmental Protection Agency (EPA) did not have a 

drinking-water standard for microcystins in 2008.
20 Upstream Factors Affecting Tualatin River Algae, Oregon Table 5. Chlorophyll and total phosphorus data from Clean Water Services for sites in the Tualatin River, Oregon, May–August 2008. (Additional water-quality data from Clean Water Services at these sites are provided in appendix A.) [Sites listed in downstream order. Abbreviations: RM, river mile; μg/L, microgram per liter; mg/L, milligram per liter; JWC, Joint 

Water Commission; TVID, Tualatin Valley Irrigation District; Hwy, Highway; 

–, no data; <, less than]

Constituent

(units) Date

Tualatin River sites

Cherry

Grove

(RM 67.8)

Dilley

(RM 58.8)

JWC/TVID 

Spring Hill 

pumping 

plant

(RM 56.1)

Golf Course 

Road

(RM 51.5)

Hwy 219 

Bridge

(RM 44.4)

Rood

Bridge

(RM 38.4)

Farmington 

(RM 33.3)

Scholls

Bridge

(RM 26.9)

Elsner

(RM16.2)

Boones 

Ferry Road

(RM 8.7)

Stafford 

Road

(RM 5.5)

Oswego 

Dam

(RM 3.4)

Weiss 

Bridge

(RM 0.2)

Chlorophyll-a

(μg/L)

5-05-2008 – – – – 4.5 3.8 3.7 3.8 4.6 6.5 4.4 4.4 5.0

5-12-2008 – – – – 3.8 3.8 3.5 3.4 – 4.3 4.2 5.2 4.2

5-19-2008 – – – – – – 2.4 4.1 4.7 4.0 3.9 5.2 5.3

5-27-2008 – – – – 3.1 2.9 2.8 3.1 3.8 2.2 2.5 2.1 2.9

6-02-2008 – – – – 3.9 2.9 2.4 2.3 3.8 3.3 2.8 2.6 1.8

6-09-2008 – – – – 3.5 4.4 3.8 6.4 5.2 4.4 3.3 3.5 2.7

6-16-2008 – – – – 2.7 2.8 2.6 2.8 4.3 5.6 6.0 8.5 3.7

6-23-2008 – – – – 2.7 3.5 3.2 3.5 7.6 12.0 18.8 19.4 10.2

6-30-2008 – – – – 2.2 2.2 2.5 2.9 4.3 12.7 17.0 14.9 9.1

7-07-2008 – – – – 6.7 8.0 7.3 7.4 65.0 6.3 10.6 12.5 3.7

7-14-2008 – – – – 23.9 31.4 33.0 18.0 82.9 41.1 49.2 24.7 4.1

7-21-2008 – – – – 47.3 49.1 31.6 – 11.4 54.1 29.1 21.8 8.7

7-28-2008 – – – – 46.4 33.2 60.9 – 53.4 25.6 18.9 22.5 19.5

8-04-2008 – – – – 17.9 8.1 10.2 4.7 50.8 14.6 15.8 16.8 10.8

8-11-2008 – – – – 5.6 5.3 3.9 4.8 8.5 7.0 12.5 14.2 10.4

8-18-2008 – – – – 3.4 2.6 2.6 4.4 3.7 8.2 5.3 6.2 1.7

8-25-2008 – – – – 3.5 3.2 3.1 – 1.5 2.3 2.6 3.5 3.1
Bloom Origination, Discovery, and Tracking to Wapato Lake 21

Constituent

(units) Date

Tualatin River sites

Cherry

Grove

(RM 67.8)

Dilley

(RM 58.8)

JWC/TVID 

Spring Hill 

pumping 

plant

(RM 56.1)

Golf Course 

Road

(RM 51.5)

Hwy 219 

Bridge

(RM 44.4)

Rood

Bridge

(RM 38.4)

Farmington 

(RM 33.3)

Scholls

Bridge

(RM 26.9)

Elsner

(RM16.2)

Boones 

Ferry Road

(RM 8.7)

Stafford 

Road

(RM 5.5)

Oswego 

Dam

(RM 3.4)

Weiss 

Bridge

(RM 0.2)

Total phosphorus

(mg/L)

5-05-2008 <0.025 0.043 – 0.048 0.057 0.065 0.065 0.061 0.063 0.074 0.081 – 0.063

5-12-2008 <0.025 0.051 – 0.066 0.073 0.075 0.074 0.078 0.077 0.076 0.078 – 0.078

5-19-2008 – – – – – – 0.153 0.092 0.084 0.092 0.083 – 0.086

5-27-2008 <0.025 0.042 – 0.074 0.102 0.151 0.187 0.273 0.117 0.085 0.086 – 0.106

6-02-2008 <0.025 0.048 – 0.044 0.074 0.087 0.095 0.102 0.114 0.101 0.102 – 0.101

6-04-2008 – – 0.053 – – – – – – – – – –

6-09-2008 <0.025 0.028 – 0.048 0.074 0.071 0.083 0.082 0.091 0.106 0.100 – 0.104

6-11-2008 – – 0.028 – – – – – – – – – –

6-16-2008 <0.025 0.027 – – 0.081 0.071 0.086 0.087 0.079 0.087 0.089 – 0.074

6-18-2008 – – 0.043 0.034 – – – – – – – – –

6-23-2008 <0.025 0.030 – 0.037 0.065 0.078 0.097 0.106 0.091 0.095 0.084 – 0.075

6-25-2008 – – 0.036 – – – – – – – – – –

6-30-2008 <0.025 0.053 – 0.037 0.064 0.057 0.095 0.086 0.081 0.125 0.088 – 0.064

7-02-2008 – – 0.052 – – – – – – – – – –

7-07-2008 <0.025 0.149 – 0.072 0.113 0.078 0.092 0.154 0.101 0.116 0.109 – 0.079

7-09-2008 – – 0.111 – – – – – – – – – –

7-14-2008 <0.025 0.095 – 0.184 0.173 0.172 0.130 0.098 0.109 0.092 0.092 – 0.087

7-16-2008 – – 0.248 – – – – – – – – – –

7-21-2008 <0.025 0.220 – 0.304 0.265 0.273 0.194 – 0.092 0.110 0.083 – 0.069

7-23-2008 – – 0.213 – – – – – – – – – –

7-28-2008 <0.025 0.472 – 0.393 0.256 0.152 0.222 – 0.122 0.117 0.086 – 0.073

7-30-2008 – – 0.158 – – – – – – – – – –

8-04-2008 <0.025 0.036 – 0.070 0.120 0.091 0.108 0.106 0.158 0.101 0.099 – 0.091

8-06-2008 – – 0.032 – – – – – – – – – –

8-11-2008 <0.025 0.034 – 0.045 0.070 0.074 0.078 0.083 0.089 0.092 0.076 – 0.073

8-13-2008 – – 0.029 – – – – – – – – – –

8-18-2008 <0.025 0.025 – 0.048 0.058 0.070 0.081 0.089 0.091 0.115 0.092 – 0.079

8-20-2008 – – 0.034 – – – – – – – – – –

8-25-2008 <0.025 0.028 – 0.046 0.098 0.086 0.121 – 0.116 0.120 0.102 – 0.103

8-27-2008 – – 0.044 – – – – – – – – – –

Table 5. Chlorophyll and total phosphorus data from Clean Water Services for sites in the Tualatin River, Oregon, May–August 2008. (Additional water-quality data from Clean 

Water Services at these sites are provided in appendix A.)—Continued

[Sites listed in downstream order. Abbreviations: RM, river mile; μg/L, microgram per liter; mg/L, milligram per liter; JWC, Joint Water Commission; TVID, Tualatin Valley Irrigation District; Hwy, Highway; 

–, no data; <, less than]
22 Upstream Factors Affecting Tualatin River Algae, Oregon

Table 6. Anabaena flos-aquae cell counts and microcystin algal toxin concentrations for select sites in the 

Tualatin River basin, Oregon, June–August 2008.

[Anabaena flos-aquae abundance: Oregon Department of Human Service’s public health action level in 2008 was 100,000 cells 

per mL. Microcystins: Samples were analyzed for five microcystin algal toxins (MC-LR, MC-RR, MC-YR, MC-LW, MC-LF) 

using an Abraxis enzyme-linked immunosorbent assay (ELISA) (see Data Sources, Methods, and Quality Assurance/Quality 

Control section). Abbreviations: JWC, Joint Water Commission; TVID, Tualatin Valley Irrigation District; mL, milliliter; μg/L, 

microgram per liter; <, less than laboratory detection limit of 0.1 μg/L; ND, not detected; –, no data]

Sample 

date Site River mile

Anabaena flosaquae abundance 

(cells per mL)

Microcystins

(μg/L)

5-19-2008 Tualatin River at Rood Bridge 38.4 ND –

5-19-2008 Tualatin River at Jurgens Park 10.8 ND –

6-11-2008 Tualatin River at Rood Bridge 38.4 781 –

6-11-2008 Tualatin River at Jurgens Park 10.8 ND –

6-17-2008 Tualatin River near Scholls 24.5 573 –

6-17-2008 Tualatin River at Jurgens Park 10.8 ND –

6-17-2008 Tualatin River downstream of Cook Park 9.7 ND –

6-17-2008 Tualatin River downstream of Fanno Creek 9.2 474 –

6-17-2008 Tualatin River at Stafford 5.4 ND –

6-17-2008 Tualatin River at Oswego Dam 3.4 ND –

6-30-2008 Tualatin River at Rood Bridge 38.4 ND –

6-30-2008 Tualatin River at Jurgens Park 10.8 ND –

7-01-2008 Tualatin River near Scholls 24.5 90 –

7-01-2008 Tualatin River at Jurgens Park 10.8 ND –

7-01-2008 Tualatin River downstream of Cook Park 9.7 ND –

7-01-2008 Tualatin River downstream of Fanno Creek 9.2 1,212 –

7-01-2008 Tualatin River at Stafford 5.4 ND –

7-01-2008 Tualatin River at Oswego Dam 3.4 ND –

7-09-2008 Tualatin River near Scholls 24.5 884 –

7-09-2008 Tualatin River at Jurgens Park 10.8 23,300 2.4

7-09-2008 Tualatin River downstream of Cook Park 9.7 29,858 0.19

7-09-2008 Tualatin River downstream of Fanno Creek 9.2 20,958 –

7-09-2008 Tualatin River at Stafford 5.4 11,505 0.14

7-09-2008 Tualatin River at Oswego Dam 3.4 ND –

7-15-2008 Tualatin River at Rood Bridge 38.4 11,726 –

7-15-2008 Tualatin River at Jurgens Park 10.8 16,734 –

7-16-2008 Tualatin River near Scholls 24.5 6,107 –

7-16-2008 Tualatin River at RM 23.2 23.2 11,036 –

7-16-2008 Tualatin River at RM 21.1 21.1 14,831 –

7-16-2008 Tualatin River at RM 20.4 20.4 3,499 –

7-16-2008 Tualatin River at RM 17.9 17.9 12,638 –

7-16-2008 Tualatin River at RM 17.3 17.3 33,203 –

7-16-2008 Tualatin River at RM 13.5 13.5 10,677 –

7-16-2008 Tualatin River at Jurgens Park 10.8 33,825 <0.1

7-19-2008 Wapato Lake pump discharge 60.5 5,568 –

7-21-2008 Wapato Lake pump discharge 60.5 3,007 –

7-21-2008 Tualatin River at JWC/TVID Spring Hill Pumping Plant 56.1 1,342 –

8-05-2008 Tualatin River at Jurgens Park 10.8 ND –

8-06-2008 Tualatin River near Scholls 24.5 ND –

8-06-2008 Tualatin River downstream of Cook Park 9.7 ND –

8-06-2008 Tualatin River downstream of Fanno Creek 9.2 ND –

8-06-2008 Tualatin River at Stafford 5.4 ND –

8-06-2008 Tualatin River at Oswego Dam 3.4 ND –
Bloom Origination, Discovery, and Tracking to Wapato Lake 23

Meanwhile, TOC concentrations in the upper Tualatin 

River at the Spring Hill pumping plant (JWC’s drinking water 

intake) increased markedly in early July to 5–6 mg/L (fig. 12). 

Detectable levels of taste-and-odor compounds continued 

to be present in Wapato Creek and in the raw and finished 

drinking water at the JWC WTP through August (table 4). 

Enhanced drinking-water treatment with powdered activated 

carbon continued.

Water samples collected by USGS from Wapato Creek 

at Gaston Road on July 19 confirmed that Wapato Lake 

discharges had high concentrations of organic nitrogen 

and chlorophyll-a (330 μg/L), along with substantial 

concentrations of phosphorus and suspended sediment, and 

high oxygen demand (table 7). That sample and additional 

water samples collected by JWC on July 21 from Wapato 

Creek at Gaston Road and from the Tualatin River at the 

Spring Hill pumping plant revealed elevated levels of 

algae and zooplankton, including a moderate abundance 

of Anabaena flos-aquae (tables 8 and 9, appendix B). The 

relative abundance and species composition of algae in 

those samples, especially the dominance of Trachelomonas 

volvocina and Cryptomonas erosa, strongly suggested that 

Wapato Lake discharges were indeed the source of the algal 

material in samples from the Spring Hill pumping plant. 

Although Anabaena flos-aquae comprised less than 3 percent 

of the total algal biovolume in the Wapato Lake discharge 

on those dates, conditions for the growth of this blue-green 

species became more favorable and the bloom increased as it 

moved downstream, with Anabaena becoming more prevalent 

in the lower river (fig. 13).

Table 7. Results of water-quality tests on samples of Wapato Lake pump discharge compared with nearby locations, upper Tualatin 

River basin, July 19 and 21, 2008.

[Sites listed in downstream order. Parameter: BOD5, 5-day biochemical oxygen demand; CBOD5, 5-day carbonaceous biochemical oxygen demand; COD, 

chemical oxygen demand; TSS, total suspended solids. Units: ft3/s, cubic foot per second; kg/d, kilogram per day; μg/L, microgram per liter; mg/L, milligram 

per liter; mL, milliliter. RM, river mile; –, no data; ~, approximately]

Parameter Units

Tualatin River 

at Cherry Grove

(RM 67.8)

Wapato Lake 

pump discharge 

at Gaston Road

Scoggins Creek

(RM 60)

Tualatin River

at Dilley 

(RM 58.8)

Tualatin River 

at the JWC/

TVID Spring Hill 

pumping plant 

(RM 56.1)

July 21 July 19 July 19 July 21 July 21

Flow ft3

/s 50 18 212 285 109

TSS mg/L 0.4 74 3

4 13.2 –

Chlorophyll-a μg/L – 330 – – –

Anabaena flos-aquae cells per mL – 1

5,568 – – 1,342

Total phosphorus mg/L <0.025 2.5 <0.025 0.22 2

0.23

Total phosphorus load kg/d <3 109 <3 153 61

Soluble reactive phosphorus mg/L 0.009 0.47 – – –

Total Keldahl organic nitrogen mg/L 0.064 6.6 – – –

Ammonia-nitrogen mg/L 0.017 0.14 3

0.015 0.042 –

Nitrate-nitrogen mg/L – ~0.01 – – –

Dissolved oxygen mg/L 10.7 3 – 10.6 –

Chloride mg/L – 7.59 – – –

Sulfate mg/L – 0.29 – – –

BOD5 mg/L – 24.5 – – –

CBOD5 mg/L – 18.8 – – –

COD, total mg/L 3.8 146 3

2.6 14.8 –

1

The Anabaena density was 3,007 cells per mL on July 21.

2

Average of two measurements on July 16 and July 23.

3

Data from July 22.
24 Upstream Factors Affecting Tualatin River Algae, Oregon

Table 8. Ten most abundant algal taxa in Wapato Lake pump discharge and abundances downstream in the 

Tualatin River at the JWC/TVID Spring Hill pumping plant, Oregon, July 19 and 21, 2008.

[For a full listing of species abundances, see appendix B. Abbreviations: μm3/mL, cubic micron per milliliter; JWC, Joint Water 

Commission; TVID, Tualatin Valley Irrigation District; RM, river mile]

Scientific name Algal group

Wapato Lake

pump discharge

Spring Hill 

pumping plant

(RM 56.1)

 July 19 July 21 July 21

 Taxon biovolume (μm3/mL)

Trachelomonas volvocina Euglenoid 3,673,423 7,934,593 404,826

Cryptomonas erosa Cryptophyte 3,619,136 5,003,093 418,786

Unidentified flagellate Unknown 1,876,383 1,671,707 5,369

Trachelomonas hispida Euglenoid 584,630 631,400 56,375

Chlamydomonas sp. Green algae 651,444 488,583 52,348

Scenedesmus quadricauda Green algae 537,442 234,520 65,784

Anabaena flos-aquae Blue-green algae 373,049 201,447 89,932

Marssoniella elegans Unknown 0 541,200 96,643

Actinastrum hantzschii Green algae 534,519 0 0

Nitzschia capitellata Diatom 0 324,720 38,657

Table 9. Zooplankton taxa in water samples collected from Wapato Lake pump discharge and downstream in 

the Tualatin River at the JWC/TVID Spring Hill pumping plant, Oregon, July 19 and 21, 2008.

[Values are density, in number per cubic meter. Abbreviations: JWC, Joint Water Commission; TVID, Tualatin Valley Irrigation 

District; RM, river mile; sp., species]

Zooplankton taxa Group

Wapato Lake 

pump discharge

(near Tualatin River at RM 60.1)

Tualatin River at the 

JWC/TVID Spring Hill

pumping plant (RM 56.1)

 July 19 July 21 July 21

Cyclopoid copepodites Copepod 384,507 415,790 6,780

Diacyclops thomasi Copepod 209,859 345,614 6,780

Copepod nauplii Copepod 63,380 8,772 0

Daphnia pulicaria Cladoceran 9,859 14,035 0

Difflugia sp. Other zooplankton 8,451 10,526 1,695

Diaptomus reighardi Copepod 9,859 0 0

Bosmina longirostris Cladoceran 4,225 3,509 0

Conochilus unicornis Rotifer 0 5,263 1,695

Daphnia mendotae Cladoceran 5,634 0 0

Oligochaete sp. Other zooplankton 2,817 0 0

Brachionus angularis Rotifer 0 1,754 0

Chydorus sphaericus Cladoceran 1,409 0 0

Keratella irregularis Rotifer 1,409 0 0
0 

5,000 

10,000 

15,000 

20,000 

25,000 

30,000 

35,000 

40,000 

Anabaena flos-aquae abundance, in cells per milliliter 

Tualatin River, July 15–21

Wapato Lake pump discharge, July 19

Wapato Lake pump discharge, July 21 

0 

20 

40 

60 

80 

100 

70 60 50 40 30 20 10 0 

Chlorophyll-a concentration, 

in micrograms per liter (μg/L) 

River mile 

Tualatin River, June 30

Tualatin River, July 14

Tualatin River, July 28 

EXPLANATION

EXPLANATION

330 μg/L

Wapato Lake 

pump discharge, 

July 19 

A

B

Bloom Origination, Discovery, and Tracking to Wapato Lake 25

Figure 13. Longitudinal pattern in 

Anabaena flos-aquae abundance 

(A) and chlorophyll-a concentrations 

(B) in the Tualatin River along with 

measurements from the Wapato 

Lake pump discharge, Oregon, July 

2008. (A) Samples were collected 

during a 7-day period (July 15–21), 

and travel times vary between sites; 

therefore, values are not necessarily 

comparable between sites, but the 

general pattern is valid (see table 6 for 

specific data points). (B) Data are from 

Clean Water Services (see table 5).

tac16-1036_fig12

0 

1 

2 

3 

4 

5 

6 

7 

Total organic carbon, in milligrams per liter 

Month in 2008 

July 10 

July 17 

July 3 

March April May June July

Figure 12. Total organic carbon concentrations in the Tualatin River at the Spring Hill pumping plant (river mile 56.1), 

Oregon, March–July 2008.
26 Upstream Factors Affecting Tualatin River Algae, Oregon

Analysis and Confirmation of Bloom Source

Preliminary evidence pointed to Wapato Lake discharges 

as a potential source of downstream changes in water quality 

and the algal community. To confirm that Wapato Lake pump 

discharges were indeed the cause of the Anabaena bloom 

in the lower Tualatin River, and to determine how the river 

responded to this inoculation of plankton and nutrients, waterquality data from continuous monitors located at Highway 219 

(RM 44.4), near Scholls (RM 24.5), at Cook Park (RM 9.9), 

and at Oswego Dam (RM 3.4) were analyzed, accounting for 

the travel time between those locations. Specific increases in 

the measured DO concentration can be used as tracers for algal 

photosynthesis and an indication of when the bloom reached 

each location. 

The RM 24.5 DO data indicate that a large population 

of algae moved past that site on July 4–5 (figs. 14 and 15). 

The estimated travel time from Wapato Lake to RM 24.5 

is approximately 4–5 days (Carpenter and Rounds, 2013, 

table 3), assuming a water velocity of 0.3–0.4 mi/hr for the 

approximate 250 ft3/s of streamflow in the Tualatin River at 

Dilley at the time (fig. 11). For Wapato Lake discharges to 

have been associated with the bloom at RM 24.5 on July 4, the 

travel-time information suggests that pumping from Wapato 

Lake must have increased on or about June 30. The Wapato 

Creek discharge estimates confirm that pumping from Wapato 

Lake likely increased substantially on that date (fig. 11). 

The arrival of the bloom farther downstream at Cook Park 

(RM 9.9) and Oswego Dam (RM 3.4), again based on DO 

data, corresponds well with the estimated travel times between 

those sites (fig. 15). In addition, USGS monitoring data 

showed nothing unusual in Rock, Dairy, Gales, or Scoggins 

Creeks during this period, which further supports the evidence 

implicating Wapato Lake as the cause of the bloom.

Data from the USGS continuous monitor in the Tualatin 

River near Scholls (RM 24.5) for 1997–2012 show that, except 

for 2008, photosynthetic production of DO by algae never 

has been high enough to achieve supersaturated conditions 

at that site (fig. 14). In 2008, however, supersaturated DO 

conditions occurred at the RM 24.5 site during most of July 

and extending into early August, peaking at greater than 140 

percent of saturation in late July. Under normal conditions, 

small populations of algae enter the reservoir reach from 

upstream. The decreased shading (more light) in the reservoir 

reach causes the algae to grow faster, and a bloom may reach 

substantial levels by the time it travels downstream as far 

as RM 16.2 or farther. These anomalous conditions at RM 

24.5 clearly indicated that a well-developed algal bloom 

was entering the reservoir reach from upstream, rather than 

developing within the reservoir reach.

The 2008 Tualatin River algal bloom was anomalous in 

many ways, but particularly because it included high-biomass 

conditions farther upstream than in normal years. At Rood 

Bridge (RM 38.4), the median and maximum chlorophyll-a

concentrations in July were greater than 30 μg/L and nearly 

50 μg/L in 2008 (fig. 16A), respectively, whereas values at that 

location were less than 5 μg/L in July 2005–07. At Highway 

219 (RM 44.4), chlorophyll-a concentrations in 2008 were 

similar to those at Rood Bridge (table 5). Farther upstream, 

total chlorophyll concentrations in Wapato Creek at Gaston 

Road were substantially higher than at other sites in the upper 

Tualatin River basin in June and July (table 4), with median 

and maximum values of 190 and 675 μg/L, respectively. 

In late July, elevated total chlorophyll levels (13–37 μg/L, 

table 4) also were measured in the Tualatin River at Dilley 

(RM 58.8) and at the Spring Hill pumping plant (RM 56.1). 

Total chlorophyll measurements at other sites upstream of 

the Spring Hill pumping plant, including the Tualatin River 

upstream of the Wapato Creek confluence and other tributary 

streams, clearly show that the Wapato Lake discharge had 

the greatest influence on chlorophyll levels at the Spring Hill 

pumping plant (table 4). In August, measured chlorophyll 

concentrations in Wapato Creek at Gaston Road decreased to 

the 10–14 μg/L range as pumping of the lake decreased and 

stopped. All these data confirm that Wapato Lake discharges 

were a source of high-chlorophyll water that affected 

chlorophyll levels downstream all the way into the reservoir 

reach.

Unusually high total phosphorus concentrations also 

occurred in July 2008 at all sites from Dilley (RM 58.8) 

downstream to the reservoir reach (fig. 16B, table 5), and 

those values were consistent with high total phosphorus 

concentrations discovered in Wapato Lake drainage water 

on July 19 (table 7). The phosphorus data indicate that the 

increase in concentration in the Tualatin River occurred 

between the Cherry Grove (RM 67.8) and Dilley (RM 58.8) 

sampling sites, a reach that includes inputs from Wapato and 

Scoggins Creeks. Data from CWS showed low concentrations 

in Scoggins Creek and Henry Hagg Lake. A mass balance of 

total phosphorus loads in the Tualatin River between Cherry 

Grove and Dilley indicates that the Wapato Lake discharge can 

account for most or all of the increase in phosphorus in that 

river reach, assuming that the total phosphorus concentration 

of 2.5 mg/L in the Wapato Creek sample from July 19 was 

representative, and that Wapato Lake pumping rates were 

similar to those estimated in the analysis shown in figure 11. 

Using a flow of about 21 ft3

/s (about 72 percent of the full 

pumping capacity) from Wapato Creek, phosphorus inputs 

from Wapato Lake would have accounted for about 83 percent 

of the total phosphorus load in the Tualatin River at Dilley on 

July 19, with Scoggins Creek contributing about 8 percent and 

the upper Tualatin River just 2 percent.
tac16-1036_fig14

60 

70 

80 

90 

100 

110 

120 

130 

140 

150 

5-01 6-01 7-01 8-01 9-01 10-01 11-01 12-01 

Dissolved oxygen, in percent saturation 

Date 

10th to 90th percentile, 1997–2012 

25th to 75th percentile, 1997–2012 

Median, 1997–2012 

Measured dissolved oxygen in 2008 

EXPLANATION

40 

60 

80 

100 

120 

140 

1 2 3 4 5 6 7 8 9 10 11 12 13 

Dissolved oxygen, in percent saturation 

Day in July 2008 

RM 24.5

~4 days travel from RM 24.5 to RM 9.9,

bloom arrives on July 8

~2-3 days travel from RM 9.9 to RM 3.4,

bloom arrives on July 10 

Bloom arrives at RM 24.5,

on July 4

EXPLANATION

RM 9.9 RM 3.4 

Figure 14. Comparison of measured dissolved oxygen percent saturation in the Tualatin River near Scholls, Oregon (river mile 24.5) 

in 2008 with long-term conditions in 1997–2012.

Figure 15. Dissolved-oxygen percent saturation in the Tualatin River at river miles (RM) 24.5, 9.9, and 3.4, showing a 

substantial increase in dissolved oxygen associated with the arrival of the Anabaena bloom at each location, Tualatin 

River, Oregon, July 2008. Arrows and red dots indicate when the dissolved oxygen signals reached each monitoring 

location.

Bloom Origination, Discovery, and Tracking to Wapato Lake 27
28 Upstream Factors Affecting Tualatin River Algae, Oregon

tac16-1036_fig16

EXPLANATION

0

10

20

30

40

50

60

70

80

90

Chlorophyll-a concentration, in micrograms per liter

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

Total phosphorus concentration, in milligrams per liter

2005–07

2008

38.4 33.3 26.9 16.2 8.7 5.5 3.4 0.2

River Mile

67.8 58.8 56.1 51.5 44.4 38.4 33.3 26.9 16.2 8.7 5.5 0.2

River Mile

A

B

Outlier

Outlier

75th percentile

90th percentile

10th percentile

50th percentile

 (median)

25th percentile

Interquartile

range 

Figure 16. Comparison of (A) chlorophyll-a and (B) total phosphorus concentrations in the Tualatin River, Oregon, July 2005–07 and 

July 2008.
Upstream Factors Affect Downstream Tualatin River Algae 29

The abundance of zooplankton (particularly copepods, 

table 9), in addition to elevated nutrient concentrations, 

likely was important in producing conditions that led to 

the dominance of blue-green algae in the lower Tualatin 

River during July 2008. Blue-green algal colonies are not 

easily consumed by zooplankton because of their large size 

and mucilaginous coatings (Caramujo and others, 2008). 

Preferential grazing of diatoms and other non-blue-green algae 

by zooplankton would have reduced competition and allowed 

blue-green algae to proliferate (Gulati and DeMott, 1997). The 

mid-July increase in copepods (Carpenter and Rounds, 2013, 

figs. 17 and 18) was due to a large abundance of cyclopoid 

copepods and Diacyclops thomasi that coincided with the 

bloom (table 9). The cyclopoid copepods, in particular, had 

a strong reproductive pulse in the deepest green samples 

containing the greatest abundance of algae (Alan Vogel, 

ZP’s Taxonomic Services, written commun., 2008). The 

algal bloom peaked in mid-July, with the highest measured 

biomass of 82.9 μg/L chlorophyll-a at Elsner (RM 16.2) on 

July 14 (figs. 10, 13B, 16A, table 5). By July 16, zooplankton 

counts downstream of Elsner were exceptionally high (88,000 

organisms per m3

) and samples were composed mostly of 

copepods. 

The algal bloom in the lower Tualatin River ended soon 

after pumping from Wapato Lake mostly ceased (large pump 

turned off) at the end of July (fig. 11), as evidenced by a return 

to normal DO conditions at the water-quality monitor at RM 

24.5 about 5 days later (fig. 14, table 3). Samples collected by 

ODEQ on August 1 confirmed that water-quality conditions 

had returned to more-normal levels in Wapato Creek and 

the Tualatin River at Dilley (table 10). The public health 

advisory was lifted July 25 after it was evident that Anabaena

concentrations in the lower Tualatin River had decreased 

substantially (table 6). 

Upstream Factors Affect Downstream 

Tualatin River Algae

Previous research and modeling of the Tualatin River 

had determined that the most important factors affecting 

algae in the lower river included streamflow (residence 

time), light, water temperature, and, to a lesser degree, 

phosphorus concentrations (Rounds and others, 1999; Rounds, 

2002). Although these factors continue to be important, the 

2008 Wapato Lake algae bloom was instrumental in the 

identification of another important factor: the input of an 

upstream algal inoculum (Carpenter and Rounds, 2013). 

Upstream inocula were determined to be important in the 

San Joaquin River, California, where input of algal cells 

from upstream agricultural sloughs influenced phytoplankton 

assemblages in the slower-moving reach downstream (Leland 

and others, 2001). Similarly, the type and amount of algae 

and zooplankton that enter the reservoir reach of the Tualatin 

River are critical in determining how much and what types of 

algae will grow in the reservoir-like reach downstream to the 

Oswego Dam at RM 3.4. 

Inputs of algal inoculum and zooplankton from upstream, 

as occurred during the 2008 Wapato Lake bloom, clearly 

can have a profound influence on plankton communities that 

develop in the lower Tualatin River. The DO data from the 

RM 24.5 site (fig. 14) showed that an algal bloom was already 

well developed upstream of that site in July 2008—something 

that had not occurred at any time since that monitor was 

installed in 1997 and has not occurred since (through 2015). 

Typically, algae do not have enough time to grow from a small 

population entering the reservoir reach (RM 30) before being 

transported downstream to the monitor location at RM 24.5. 

Algal growth in the reservoir reach normally does not become 

Table 10. Water-quality data from the Oregon Department of Environmental Quality for selected sites in the upper Tualatin 

River basin, Oregon, August 2008.

[Data reproduced from Oregon Department of Environmental Quality (2008). Wapato Creek at Gaston Road: Site includes discharge from the 

Wapato Lake pump station and the adjacent canal. Abbreviations: Hwy, highway; RM, river mile; °C, degrees Celsius; μS/cm, microsiemens per 

centimeter; mg/L, milligrams per liter]

Parameter

Tualatin River at 

Old Hwy 47 Bridge 

near Gaston

(RM 62.3)

Wapato Creek

at Gaston Road

Tualatin River at 

Dilley (downstream 

of the Wapato Creek 

confluence) (RM 58.8)

Water temperature, °C 15.5 17.3 10.3

Specific conductance, μS/cm 77 82 71

Dissolved oxygen, mg/L 8.8 7.1 11.2

Dissolved oxygen, percent saturation 87 73 100

pH, standard units 7.5 7.2 7.3

Total phosphorus, mg/L 0.01 0.09 0.09

Ammonia-nitrogen, mg/L <0.02 0.15 <0.02

Nitrate-nitrogen, mg/L 0.08 0.09 <0.005

Pesticide screens Negative1 Negative1 Negative1

1

All three samples were negative, so no further tests were run.
30 Upstream Factors Affecting Tualatin River Algae, Oregon

substantial until approximately the Elsner site (RM 16.2), 

which is about 2 days travel time downstream of the RM 24.5 

site. Discharges from Wapato Lake on July 19, 2008, included 

extremely high chlorophyll-a concentrations (330 μg/L, 

table 7) and high zooplankton populations (table 9), both of 

which likely had a large influence on the composition and size 

of the algal community that was transported downstream and 

entered the reservoir reach of the river.

Although large inputs of potentially toxic blue-green 

algae are clearly undesirable, some amount of algal inoculum 

delivered to the reservoir reach—preferably in the form of 

diatoms and other beneficial types of algae—is necessary to 

“seed” the river and thereby develop enough biomass and 

produce enough oxygen through photosynthesis to prevent 

low-DO conditions in the lower river (Carpenter and Rounds, 

2013). Inclusion of this upstream inoculum factor into 

water-quality models could improve how well such models 

capture the size of the phytoplankton population in the river 

and, therefore, improve the accuracy of their predictions. For 

example, incorporating this upstream factor into the USGS 

neural network water-quality model of Tualatin River DO 

concentrations (Rounds, 2002) would likely improve its 

predictions and resolve any important year-to-year or seasonto-season variations in the size of the algal community. The 

importance of these upstream data, perhaps as manifested in 

chlorophyll concentrations upstream of the reservoir reach, 

also has ramifications for future monitoring plans.

Implications for Monitoring and 

Management

Blooms of nuisance and potentially toxic and harmful 

blue-green algae have occurred in the Tualatin River from time 

to time since the 1960s (Carpenter and Rounds, 2013, table 1). 

These blooms can cause problems for aquatic life in the river 

by producing high pH conditions and low DO concentrations, 

and may represent a risk to public health, depending on the 

composition and characteristics of the bloom. Some of the 

implications of algal blooms for monitoring and management 

are discussed below.

Public Health Hazards

In the event that blue-green algal blooms produce liver 

or neurotoxins (microcystins and anatoxin, for example), 

they may pose a public health risk to humans and wildlife. 

Blue-green algae blooms have the greatest potential to cause 

hazardous conditions for dogs, in particular, and humans when 

coming into contact with floating mats of high-concentration 

surface scums, such as during the 2008 Tualatin River 

bloom in the lower river reaches (figs. 8, 10). Because of the 

extensive Anabaena surface scums in July 2008, the Oregon 

Department of Human Services issued a public health advisory 

for the lower Tualatin River. Anabaena cell counts were about 

3,000–5,500 cells/mL in Wapato Lake pump discharge in late 

July, whereas concentrations in the Tualatin River downstream 

were much higher, about 11,700 cells/mL at Rood Bridge (RM 

38.4) on July 15 and 33,800 cells/mL on July 16 at Jurgens 

Park (RM 10.8) (table 6, fig. 13A). Health advisories typically 

are issued in Oregon when the combined cell counts from 

potentially toxigenic algae exceed 100,000 cells/mL or when 

extensive surface scums are present (Oregon Health Authority, 

2010). Although the cell counts from this event did not reach 

the 100,000 cells/mL threshold, visible surface scums of 

Anabaena were present during the 2008 bloom. The health 

advisory was lifted on July 25, 2008, after the floating mats 

had largely disappeared and sufficient time was allowed for 

any toxins that may have been present to dissipate.

In addition to water-contact issues, studies have detected 

the presence of algal toxins in crops that were irrigated with 

water containing toxic blue-green algae (Milligan, 2009). This 

represents another potential exposure pathway to humans, and 

one that might merit further study in the future.

Anabaena is known to produce a potent nerve toxin 

(anatoxin-a) and liver toxins (microcystins). Although tests 

were not conducted for the more toxic anatoxin-a, microcystin 

was detected by USGS in a few Tualatin River samples 

at concentrations ranging from 0.14 to 2.4 μg/L (table 6). 

At the time of this study, the EPA had not set any health 

guidelines or concentration restrictions on algal toxins in 

drinking water. One detection of microcystin in the lower 

river, well downstream of drinking water intakes, exceeded 

the World Health Organization drinking water guideline of 

1 μg/L (table 6). None of the samples exceeded the Oregon 

recreational health-hazard guideline for microsystins in effect 

at that time (8 μg/L). When surface scums are present or 

blue-green cell concentrations are high, river managers and 

public-health agencies may need to act swiftly to determine 

the presence and concentrations of any algal toxins and 

communicate the results to water users.

Municipal Water Issues

The 2008 Wapato Lake algae bloom was an important 

reminder that proactive engagement in the watershed is 

important. JWC expended more than $300,000 in extra 

treatment costs during summer 2008, mainly associated with 

the need to add powdered activated carbon to resolve tasteand-odor issues. JWC also donated services and materials to 

the Wapato Improvement District to fully repair the Wapato 

Lake levee.
Implications for Monitoring and Management 31

A massive communications effort began to inform JWC’s 

more than 300,000 customers that the drinking water, although 

it had a foul taste and odor, was not a health risk. During 

this event, hundreds of customer complaints were received, 

several press releases were issued, interviews were granted, 

and print and television stories ran. JWC also serves several 

high-tech industries that rely on consistent water quality, and 

those customers required specialized communications and 

information sharing. Several of these industries had production 

issues during this event, and it is unclear whether the geosmin, 

powdered activated carbon, or a combination of the two 

contributed to the problems.

After the 2008 algae bloom, a broad coalition of 

managers and regulators crafted a water-quality management 

plan for the Wapato Lake area that requires any major 

pumping from the lake to be completed by May 1 of each 

year. This limit was set in an effort to prevent ponded 

conditions during warm weather that facilitate the growth of 

large amounts of algae that might be pumped downstream 

(Oregon Department of Environmental Quality, 2009). Better 

communication among the various parties, data transmission 

showing when the Wapato pumps are operating, and realtime monitoring of organic-matter concentrations and other 

parameters at the JWC WTP have improved the real-time 

management of drinking-water quality. Prior to the 2008 

Wapato Lake algae bloom, JWC had a proactive watershed 

monitoring program, but since then JWC has become more 

active in identifying and monitoring upstream threats to source 

water quality.

Organic carbon from peat soils and algae blooms can 

be another threat to drinking-water quality because organic 

matter in some WTPs has been associated with the formation 

of toxic disinfection by-products such as chloroform. JWC 

and its partner agencies closely monitor their water for 

various disinfection by-products at the WTP and within the 

drinking-water distribution system. In 2008, JWC modified 

the treatment process to decrease contact time between any 

organic matter and chlorine, which resulted in a decrease in 

disinfection by-product levels in the finished water. JWC has 

been monitoring the upper Tualatin River basin for precursors 

to disinfection by-product formation since 2007 to alert and 

inform WTP operators and water-quality staff.

Wetland Management

Draining seasonal wetlands such as Wapato Lake has 

the potential to negatively affect downstream water quality. 

The specific effects depend on a number of factors including 

the amount, timing, and quality of the discharge, as well as 

the flow or dilutive capacity of the receiving river at the time 

of discharge. Although draining of Wapato Lake typically is 

done during winter and spring when Tualatin River flows are 

high, delays until summer such as what occurred in 2008 can 

cause a myriad of problems for water users. To avoid similar 

events in the future, it is important to better understand the 

processes and conditions that combine to cause large algal 

blooms as well as high concentrations of organic carbon and 

nutrients in wetlands like Wapato Lake, and then to ensure 

that management options exist to avoid discharging such water 

downstream to the Tualatin River.

In 2010, a group of agencies came together to help 

avert a potential repeat of the water-quality issues attributed 

in 2008 to Wapato Lake. During winter of 2010, the largest 

pump at the Wapato Lake pump house was inoperable and 

the capacity of the smaller pump was insufficient to pump out 

the lake before summer. To avoid a repeat of the 2008 event, 

the lake had to be drained by May 1, before favorable bloom 

conditions (low flows and warm weather) could develop. To 

accomplish this, extra pumps from CWS, the U.S. Army Corp 

of Engineers, and the City of Portland were used over the 

course of 2 months to drain Wapato Lake. Conditions were 

monitored closely by CWS, JWC, USGS, TVID, ODEQ, 

U.S. Fish and Wildlife Service, and others, and no significant 

bloom occurred that year (Bonn, 2010; U.S. Geological 

Survey, 2010). 

The source of the nitrogen and phosphorus that fueled 

the 2008 Wapato Lake bloom includes groundwater seepage, 

agricultural fertilizer, and nutrients leached from the rich 

wetland soils. Peat soils typically contain large quantities 

of carbon, nitrogen, and phosphorus, which is stored in the 

accumulated soil biomass (Snyder and Morace, 1997). When 

these soils are drained, or particularly when drained and tilled, 

the organic matter oxidizes and liberates the carbon, nitrogen, 

and phosphorus, which then can affect water quality through 

stimulation of algal growth. 

The oxidation of peat soils also can result in general land 

subsidence in which a large mass of the soil profile essentially 

disappears through decomposition of accumulated organic 

matter (Snyder and Morace, 1997). This type of subsidence 

has occurred at Wapato Lake, resulting in an unquantified 

amount of subsidence that is likely several feet, but possibly 

as much as 6–8 ft (Christy, 2015). As a result, the land surface 

is lower and would hold a deeper lake now compared to the 

period prior to 1895 when the lake was first drained. This 

change in the land surface may present some challenges and 

opportunities for future management and restoration of the 

Wapato Lake area.

Wetlands can be used effectively to improve water 

quality, removing nutrients and suspended sediment if 

managed properly. The U.S. Fish and Wildlife Service is 

working to determine effective strategies for the future 

restoration and management of the Wapato Lake area. The 

fact that wetland discharges can have both positive and 

negative effects on the Tualatin River suggests that enhanced 

and coordinated management of publicly owned wetlands at 

Wapato Lake, Jackson Bottom, Fernhill Wetlands, and (or) 

the wetlands of the Tualatin River National Wildlife Refuge 

may be beneficial to all. Management of wetlands to provide a 

beneficial algal inocula (diatoms, for instance) to the Tualatin 

River could also provide benefits downstream by enhancing 

food webs and providing some photosynthetic oxygen 

production while avoiding the problems associated with bluegreen algae.
32 Upstream Factors Affecting Tualatin River Algae, Oregon

Managing Dissolved Oxygen

Although excessively large algal blooms are not desirable 

and may contribute to violations of water-quality standards, 

some level of algal biomass and photosynthesis is critical 

for sustaining food webs and minimum DO concentrations 

in the Tualatin River. When algal biomass declines and 

photosynthetic production of oxygen decreases, oxygen 

demands and high water temperatures often combine to 

produce low DO concentrations in the lower Tualatin River 

that sometimes do not meet State of Oregon water-quality 

standards, a condition that may last for weeks or even months 

during the low-flow period (Carpenter and Rounds, 2013). 

The discharge permit for CWS treatment facilities 

requires CWS to consider instream DO concentrations as 

feedback to their allowable discharge limits throughout the 

critical summer season. If weekly mean DO levels decrease 

to less than 6.7 mg/L in the lower river, CWS managers must 

meet stringent ammonia treatment levels at the WWTFs 

because the river has little ability to assimilate ammonia 

loads when DO concentrations are low. For water-quality 

management purposes, CWS has some flexibility to release 

relatively cool, high-quality water from upstream reservoirs 

to mitigate water-quality problems in the lower river. For 

example, CWS uses higher streamflow targets for flow 

augmentation (upstream reservoir releases) during late 

summer and early autumn to offset the anticipated effects of 

oxygen demands and potential low-DO conditions late in the 

low-flow season. Once it became clear that the 2008 algal 

bloom was severe, CWS increased its upstream reservoir 

releases to increase the percentage of flow augmentation 

water in the river. Although it was critical in 2008 to increase 

river flow to flush out the hazardous blue-green algae, such 

reservoir releases also dilute any beneficial phytoplankton 

populations and can thereby impede the recovery of 

photosynthesis and DO production that is critical for offsetting 

sediment oxygen demands (Carpenter and Rounds, 2013). 

In the Tualatin River system, a delicate balance exists 

between flow management, natural flow, algal growth and 

photosynthesis, DO concentrations, and general water quality.

Water-Quality and Plankton Monitoring and 

Models

The 2008 Wapato Lake algae bloom presents an 

opportunity to evaluate the current monitoring strategy and 

network for detecting similar problems, should they occur 

in the future. Although the existing data-collection network 

provided the necessary information to hone in on the source 

of the 2008 bloom, now that it is apparent that the plankton 

community in the upper basin can have profound effects on 

downstream populations, additional monitoring in the upper 

part of the basin may be warranted. Plankton monitoring 

has not been done in the upper reaches (upstream of RM 

38.4) of the Tualatin River in recent years, mainly because 

algal densities tend to be small there, but now it is clear that 

such monitoring would help to track algal population levels 

seasonally and longitudinally. JWC has begun quarterly 

plankton monitoring at several sites in the upper Tualatin 

River basin between Gaston and the Spring Hill pumping 

plant. Perhaps the results of that type of monitoring could 

be used to trigger more extensive monitoring and sample 

collection when necessary.

One of the best ways to improve the accuracy and 

predictive capabilities of water-quality models of the lower 

river is to better define the size and type of the plankton 

community entering the reservoir reach from upstream sources 

such as wetlands, reservoirs, and other habitats. The primary 

objective of such monitoring would be to better understand 

the type and amount of algae being delivered to the reservoir 

reach. Similar plankton sampling could be conducted at 

nursery ponds, wetlands, and other water bodies that may 

discharge to the Tualatin River, especially ones with a history 

of algal blooms.

Another valuable monitoring strategy would be the 

addition of total chlorophyll to the suite of parameters 

monitored continuously in the Tualatin River near Scholls 

(RM 24.5) or even farther upstream at Spring Hill (RM 56.1). 

In fact, JWC began monitoring a suite of parameters in their 

raw water from the Tualatin River at the Spring Hill pumping 

plant after the 2008 event, including chlorophyll. It is possible 

to use chlorophyll data from well-calibrated instream sensors 

to determine when a water sample should be collected and 

analyzed for plankton communities; such sensors may provide 

the necessary and timely information on the amount and type 

of algae arriving at drinking-water intakes or entering the 

reservoir reach of the river so that flow management and other 

strategies can be fine-tuned.

Summary and Conclusions

During July 2008, a large bloom of Anabaena flos-aquae

(primarily) and Aphanizomenon flos-aquae occurred in the 

lower Tualatin River, prompting the Oregon Department of 

Human Services (now the Oregon Health Authority) to issue 

a public health advisory for recreational water contact on July 

12 for the reach extending from Jurgens Park (RM 10.8) to the 

river mouth. This bloom formed a thick surface scum along 

the margins and backwater areas of that reach. Anabaena

can produce potent nerve and liver toxins (anatoxin-a and 

microcystin), and although tests were not performed for the 

more toxic compound (anatoxin-a), microcystin was detected 

at concentrations ranging from 0.14 to 2.4 μg/L in the lower 

river. At the same time in June and July, taste and odor issues 

due to geosmin occurred in municipal water produced by the 

Joint Water Commission from water withdrawn from the upper 

Tualatin River at RM 56.1. Extra treatment with powdered 

activated carbon was added at the water treatment plant, and 

upstream monitoring was enhanced to identify the source of 

the issues.
References Cited 33

After reports of the taste-and-odor issues and discovery 

of the bloom in the lower river—and on the basis of water 

sample data, continuous monitoring data, estimated travel 

times, and mass balance calculations—the source of the waterquality problems was traced upstream to the Wapato Lake 

agricultural area adjacent to and southeast of Gaston, Oregon, 

in the upper part of the Tualatin River basin. Because of a 

breach in one of the Wapato Lake levees during a December 

2–3, 2007 storm, the low-lying area was flooded to a much 

greater extent than normal and could not be drained until 

summer after water levels receded or until the levee was 

patched. Normally, the lake would have been pumped out 

in spring so that the lakebed could be farmed in summer. 

Drainage water entering the Tualatin River through Wapato 

Creek at RM 60.1 had elevated concentrations of organic 

matter and phosphorus and contained a rich inoculum of 

algae including Anabaena flos-aquae and Aphanizomenon 

flos-aquae. Wapato Lake discharges also contained high 

abundances of zooplankton (primarily copepods) that 

continued to thrive and multiply downstream in the lower 

Tualatin River during the bloom, likely affecting the algal 

population through selective grazing and resulting in strong 

dominance by blue-green algae. 

The 2008 Wapato Lake algal bloom demonstrated the 

importance of upstream factors in influencing downstream 

water quality in the Tualatin River. Although the algal biomass 

in the upper river may not have been exceptionally high, the 

bloom multiplied as it traveled downstream, reaching more 

than 33,000 cells/mL of Anabaena flos-aquae and more than 

80 μg/L chlorophyll-a in the reservoir-like section of the lower 

river where conditions for algal growth are more favorable. 

Clearly, the amount and type of plankton entering this reach—

in addition to flow, light, temperature, and nutrients—are 

important in determining the type and amount of algae that 

grow in the lower river where the photosynthetic production of 

DO is critical for maintaining minimum oxygen levels. 

Future monitoring of potential plankton inocula sources 

in the upper part of the Tualatin River basin using continuous 

monitoring and targeted sampling for chlorophyll and species 

identification could inform predictive models and enhance the 

real-time network to give water-quality managers additional 

time to respond to events similar to the 2008 Wapato Lake 

algae bloom. Current management and future restoration of the 

Wapato Lake area by the U.S. Fish and Wildlife Service will 

benefit from the lessons learned from the 2008 events. Given 

the potential importance of wetlands as sources of plankton to 

downstream river reaches, it may be helpful for managers of 

these resources to share information and potentially coordinate 

their management of the many wetlands in the Tualatin River 

basin, to help prevent future problems associated with bluegreen algae blooms and to enhance water quality throughout 

the river system.

Acknowledgments

This study was completed as part of a long-term scientific 

collaboration between USGS and Clean Water Services 

(CWS). The authors thank the staff of the CWS WaterQuality Laboratory for collecting samples and producing 

data that were helpful to this study. Deanna Conners and Ken 

Kauffman at the Oregon Department of Human Services, 

Public Health Division, provided useful information and 

expertise on blue-green algae and potential threats to public 

health. Brian Wegener and several volunteers from the 

Tualatin Riverkeepers helped to document the Anabaena

bloom with photographs and observations, and disseminated 

valuable information to the public regarding the potential 

health hazards of the bloom. Conversations with Alan Milligan 

(Oregon State University) were helpful for understanding 

additional public health issues related to algal toxins. Thanks 

also to all of the people and organizations that came together 

to address the problems associated with the 2008 Wapato Lake 

algae bloom.

References Cited

American Public Health Association, 1992, Standard 

methods for examination water and wastewater (17th 

ed.): Washington, D.C., American Public Health 

Association, American Water Works Association, and Water 

Environment Federation [variously paged].

Berger, C.J., 1993, Water quality modeling of the Tualatin 

River: Portland, Oreg., Portland State University, M.S. 

Thesis, Technical Report EWR-001-94, 152 p.

Bonn, B.A., 2008, 2008 Annual Report—Tualatin River Flow 

Management Technical Committee: Prepared for Clean 

Water Services and Oregon Water Resources Department, 

District 18 Watermaster, 42 p. plus appendixes, accessed 

April 24, 2013, at http://www.co.washington.or.us/

Watermaster/SurfaceWater/tualatin-river-flow-technicalcommittee-annual-report.cfm.

Bonn, B.A., 2010, 2010 Annual Report—Tualatin River Flow 

Management Technical Committee: Prepared for Clean 

Water Services and Oregon Water Resources Department, 

District 18 Watermaster, 42 p. plus appendixes, accessed 

April 24, 2013, at http://www.co.washington.or.us/

Watermaster/SurfaceWater/tualatin-river-flow-technicalcommittee-annual-report.cfm.
34 Upstream Factors Affecting Tualatin River Algae, Oregon

Bonn, B.A., and Rounds, S.A., 2010, Use of stable isotopes 

of carbon and nitrogen to identify sources of organic 

matter to bed sediments of the Tualatin River, Oregon: 

U.S. Geological Survey Scientific Investigations Report 

2010-5154, 58 p. [Also available at http://pubs.usgs.gov/

sir/2010/5154/.]

Caramujo, M., Boschker, H.T.S., and Admiraal, W., 2008, 

Fatty acid profiles of algae mark the development 

and composition of harpacticoid copepods: Journal of 

Freshwater Biology, v. 53, p. 77–90.

Carpenter, K.D., and Rounds, S.A., 2013, Plankton 

communities and summertime declines in algal abundance 

associated with low dissolved oxygen in the Tualatin River, 

Oregon: U.S. Geological Survey Scientific Investigations 

Report 2013–5037, 76 p. [Also available at http://pubs.usgs.

gov/sir/2013/5037/.]

Carter, L.M., Petersen, R.R., and Roe, D.K., 1976, An 

assessment of the effects of low-flow augmentation and 

improved sewage treatment on the lower reaches of the 

Tualatin River during the dry weather season of 1976: 

Portland, Oreg., Portland State University, Department of 

Environmental Sciences and Research, 85 p.

Cass P.L., and Miner, J.R., 1993, The historical Tualatin 

River Basin: Oregon Water Resources Research Institute, 

Oregon State University, Tualatin River Basin Water 

Resources Management Report Number 7, 59 p., accessed 

August 27, 2015, at https://ir.library.oregonstate.edu/xmlui/

handle/1957/735.

Christy, J.A., 2015, Historical conditions at Wapato Lake, 

Washington and Yamhill Counties, Oregon: Portland, Oreg., 

Portland State University, Oregon Biodiversity Information 

Center, Institute for Natural Resources, 7 p. 

Clean Water Services, 2006, Clean Water Services Watershed 

Monitoring Plan: Hillsboro, Oreg., Clean Water Services, 

53 p.

Clean Water Services, 2010, Wapato Lake—Protecting water 

quality while transitioning to a National Wildlife Refuge: 

Wapato Lake briefing paper, Clean Water Services, 4 p.

Fischer, W.J., Garthwaite, I., Miles, C.O., Ross, K.M., Aggen, 

J.B., Chamberlin, A.R., Towers, N.A., and Dietrich, D.R., 

2001, Congener-independent immunoassay for microcystins 

and nodularins: Environmental Science and Technology, 

v. 35, p. 4849–4856.

Gottler, R., Calles, J., Westerhoff, P., and Abbaszadegan, 

M., 2007, Addressing concerns about tastes and odors and 

cyanotoxins in tap water: Denver, American Water Works 

Association Research Foundation, 132 p.

Green, G.L., 1982, Soil survey of Washington County, 

Oregon: U.S. Department of Agriculture, Soil Conservation 

Service, in cooperation with the Oregon Agricultural 

Experiment Station, 138 p. plus maps.

Gulati, R.D., and DeMott, W.R., 1997, The role of food 

quality for zooplankton—Remarks on the state-of-the art, 

perspectives and priorities: Journal of Freshwater Biology, 

v. 38, p. 753–768.

Izaguirre, G., Hwang, C.J., Krasner, S.W., and McGuire, M.J., 

1982, Geosmin and 2-methylisoborneol from cyanobacteria 

in three water supply systems: Applied and Environmental 

Microbiology, v. 43, p. 708–714.

Leland, H.V., Brown, L.R., and Mueller, D.K., 2001, 

Distribution of algae in the San Joaquin River, California, in 

relation to nutrient supply, salinity and other environmental 

factors: Freshwater Biology, v. 46, p. 1139–1167.

Milligan, A.J., 2009, Potential impact of cyanobacteria on crop 

plants, in Pscheidt, J.W., and Ocamb, C.M., eds., 2009 PNW 

Plant Disease Management Handbook: Extension Services 

of Oregon State University, Washington State University 

and University of Idaho, p. 38–39.

Oregon Department of Environmental Quality, 2008, 

Wapato Lake region water quality study report—August 

1, 2008 sampling results: Portland, Oreg., Department of 

Environmental Quality, 9 p.

Oregon Department of Environmental Quality, 2009, Wapato 

Lake Water-Quality Management Plan (WQMP) for the 

Wapato Improvement District: Portland, Oreg., Department 

of Environmental Quality, 18 p.

Oregon Department of Environmental Quality and Unified 

Sewerage Agency, 1982, Tualatin River water quality 

1970–1979—Appendices: Portland, Oreg., Department of 

Environmental Quality [variously paged]. 

Oregon Health Authority, 2010, Oregon Harmful Algae Bloom 

Surveillance (HABS) Program—Public health advisory 

guidelines, harmful algae blooms in freshwater bodies: 

Oregon Health Authority, 23 p., accessed April 17, 2013, 

at http://public.health.oregon.gov/HealthyEnvironments/

Recreation/HarmfulAlgaeBlooms/Documents/

HABPublicHealthAdvisoryGuidelines.10.10.12.pdf.

Risley, J., 2000, Effects of hypothetical management 

scenarios on simulated water temperatures in the Tualatin 

River, Oregon: U.S. Geological Survey Water-Resources 

Investigations Report 00–4071, Supplement to WaterResources Investigations Report 97–4071, 110 p. [Also 

available at http://or.water.usgs.gov/pubs_dir/Online/

Pdf/00-4071.pdf.]
References Cited 35

Rounds, S.A., 2002, Development of a neural network model 

for dissolved oxygen in the Tualatin River, Oregon, in

Proceedings of the Second Federal Interagency Hydrologic 

Modeling Conference, July 29–August 1, 2002, Las Vegas, 

Nevada: Subcommittee on Hydrology of the Interagency 

Advisory Committee on Water Information, 13 p., accessed 

December 16, 2013, at http://or.water.usgs.gov/tualatin/

ann_proceedings.pdf.

Rounds, S.A., and Doyle, M.C., 1997, Sediment oxygen 

demand in the Tualatin River basin, Oregon, 1992–96: U.S. 

Geological Survey Water-Resources Investigations Report 

97-4103, 19 p. [Also available at http://pubs.er.usgs.gov/

publication/wri974103.]

Rounds, S.A., and Wood, T.M., 2001, Modeling water quality 

in the Tualatin River, Oregon, 1991–1997: U.S. Geological 

Survey Water-Resources Investigations Report 01-4041, 

53 p. [Also available at http://pubs.er.usgs.gov/publication/

wri014041.]

Rounds, S.A., Wood, T.M., and Lynch, D.D., 1999, Modeling 

discharge, temperature, and water quality in the Tualatin 

River, Oregon: U.S. Geological Survey Water-Supply Paper 

2465-B, 121 p. [Also available at http://pubs.er.usgs.gov/

pubs/wsp/wsp2465B.]

Snyder, D.T., and Morace, J.L., 1997, Nitrogen and 

phosphorus loading from drained wetlands adjacent 

to Upper Klamath and Agency Lakes, Oregon: U.S. 

Geological Survey Water-Resources Investigations Report 

97-4059, 67 p. [Also available at http://pubs.er.usgs.gov/

usgspubs/wri/wri974059.]

Sullivan, A.B., and Rounds, S.A., 2005, Modeling 

hydrodynamics, temperature and water quality in Henry 

Hagg Lake, Oregon, 2000–2003: U.S. Geological Survey 

Scientific Investigations Report 2004-5261, 38 p. [Also 

available at http://pubs.usgs.gov/sir/2004/5261/.]

U.S. Census Bureau, 2012, State and county quick facts for 

Washington County, Oregon: U.S. Census Bureau, accessed 

September 23, 2013, at http://quickfacts.census.gov/qfd/

states/41/41067.html.

U.S. Fish and Wildlife Service, 2007, Tualatin River 

National Wildlife Refuge Wapato Lake Unit addition—

Land conservation plan and environmental assessment: 

Portland, Oreg., U.S. Fish and Wildlife Service, 68 p. plus 

appendixes, accessed August 27, 2015, at http://www.fws.

gov/pacific/planning/main/docs/OR/Wapato/Final%20

LCP%20EA/2%20Wapato%20FONSI%20EA%20LCP.pdf.

U.S. Geological Survey, 2010, USGS Data Grapher and 

Data Tabler: U.S. Geological Survey Web site, accessed 

December 12, 2012, at http://or.water.usgs.gov/grapher/.

U.S. Geological Survey, 2013, Standard Reference Sample 

project: U.S. Geological Survey Web site, accessed January 

29, 2013, at http://bqs.usgs.gov/srs/.

U.S. Geological Survey, 2015a, National Water Information 

System—Current conditions for Oregon: U.S. Geological 

Survey data base, accessed August 27, 2015, at http://

waterdata.usgs.gov/or/nwis/current/?type=quality&group_

key=huc_cd.

U.S. Geological Survey, 2015b, Tualatin River Basin 

Monitoring Sites: U.S. Geological Survey data base, 

accessed August 27, 2015, at http://or.water.usgs.gov/

tualatin/monitors/.

Wehr, J.D., and Sheath, R.G., eds., 2003, Freshwater algae of 

North America—Ecology and classification: San Diego, 

Calif., Academic Press, 918 p.
36 Upstream Factors Affecting Tualatin River Algae, Oregon

This page left intentionally blank
Appendixes

Appendixes A and B contain additional supporting data that are pertinent to this study. Appendix A includes water-quality data (chemical oxygen demand, 

dissolved oxygen, ammonia-nitrogen, total suspended solids, and turbidity) collected by Clean Water Services at Tualatin River sites in May–August 2008. Appendix B includes additional algal taxa data from samples collected from the Wapato pump discharge and from the Spring Hill pumping plant site in late July 2008.Appendix A. Additional Water-Quality Data from Clean Water Services for Selected Sites in the Tualatin River, Oregon, 

May–August 2008. 

Sites listed in downstream order. Abbreviations: RM, river mile; mg/L, milligram per liter; JWC, Joint Water Commission; TVID, Tualatin Valley Irrigation District; Hwy, Highway; NTU, Nephelometric Turbidity Unit; <, less than; –, no data.

Constituent

(units) Date

Tualatin River sites

Cherry

Grove

(RM 67.8)

Dilley

(RM 58.8)

JWC/TVID 

Spring Hill 

pumping 

plant

(RM 56.1)

Golf Course 

Road

(RM 51.5)

Hwy 219 

Bridge

(RM 44.4)

Rood

Bridge

(RM 38.4)

Farmington 

(RM 33.3)

Scholls

Bridge

(RM 26.9)

Elsner

(RM16.2)

Boones 

Ferry 

Road

(RM 8.7)

Stafford 

Road

(RM 5.5)

Oswego 

Dam

(RM 3.4)

Weiss 

Bridge

(RM 0.2)

Chemical oxygen 

demand(mg/L)

5-05-2008 <2.5 5.0 6.0 4.5 5.2 6.1 6.0 6.6 5.4 6.5 7.4 – 5.8

5-12-2008 <2.5 5.1 – 4.5 5.0 5.6 6.2 7.4 – 6.1 6.3 – 7.7

5-19-2008 – – – – – – 7.8 8.3 6.2 8.2 8.5 – 7.6

5-27-2008 <2.5 5.2 – 6.0 7.6 8.8 9.6 10.8 9.4 10.3 9.3 – 10.9

6-02-2008 <2.5 9.1 4.8 6.5 5.2 6.2 7.5 8.0 9.2 8.4 10.5 – 8.6

6-09-2008 <2.5 5.4 – 5.6 6.8 7.2 9.0 12.1 10.8 12.3 11.0 – 12.2

6-16-2008 3.2 7.3 – – 6.4 6.2 11.4 9.1 9.7 10.5 11.8 – 11.36-18-2008 – – – 3.3 – – – – – – – – –

6-23-2008 2.9 4.9 – 3.9 6.7 7.9 9.8 9.8 9.4 9.1 10.6 – 10.56-30-2008 <2.5 8.2 – 4.8 6.2 5.0 7.8 7.2 7.9 16.3 11.9 – 11.17-07-2008 <2.5 16.8 8.5 7.8 8.6 8.0 9.4 10.0 17.7 9.9 10.4 – 10.47-14-2008 4.1 9.1 – 15.9 15.8 16.3 15.5 16.9 21.4 13.1 14.2 – 16.07-21-2008 3.8 14.8 – 21.5 19.1 20.5 15.7 – 12.1 17.5 14.1 – 20.6

7-28-2008 <2.5 29.9 – 26.3 21.0 12.1 19.6 – 19.6 15.1 14.6 – 13.78-04-2008 2.7 3.7 5.1 6.3 10.7 6.4 11.3 10.0 21.6 14.2 15.9 – 13.7

8-11-2008 3.7 4.6 – 5.6 7.7 6.9 8.1 10.3 11.9 10.9 13.9 – 15.2

8-18-2008 4.7 4.9 – 4.4 5.7 5.5 8.7 9.7 8.5 10.5 11.5 – 10.98-25-2008 3.0 4.2 – 6.6 7.7 6.4 11.0 – 11.4 13.3 8.4 – 9.1

Appendixes 37
38 Upstream Factors Affecting Tualatin River Algae, Oregon Constituent (units) Date Tualatin River sites Cherry Grove (RM 67.8) Dilley (RM 58.8) JWC/TVID Spring Hill pumping plant (RM 56.1) Golf Course Road (RM 51.5) Hwy 219 Bridge (RM 44.4) Rood Bridge (RM 38.4) Farmington (RM 33.3) Scholls Bridge (RM 26.9) Elsner (RM16.2) Boones Ferry Road (RM 8.7) Stafford Road (RM 5.5) Oswego Dam (RM 3.4) Weiss Bridge (RM 0.2) Dissolved oxygen (mg/L) 5-05-2008 12.6 11.3 10.8 10.8 11.5 10.6 10.1 9.8 10.0 10.0 9.9 9.4 9.8 5-12-2008 13.6 11.2 – 10.6 10.7 10.4 10.0 10.2 – 10.3 9.2 9.4 10.8 5-19-2008 – – – – – – 8.2 9.1 8.4 7.9 8.4 8.8 10.1 5-27-2008 11.9 11.2 – 10.4 9.4 9.1 8.8 10.1 8.5 9.9 9.5 9.7 8.7 6-02-2008 11.6 9.8 9.8 9.5 9.1 8.6 8.3 8.8 8.1 7.7 8.0 7.2 9.8 6-09-2008 11.8 10.3 – 10.2 9.8 9.9 9.5 9.7 8.9 9.3 9.1 9.0 9.3 6-16-2008 11.5 9.8 – – 9.2 8.7 8.5 9.0 8.2 8.3 8.8 8.0 10.4 6-18-2008 – – – 9.6 – – – – – – – – – 6-23-2008 12.2 11.1 – 10.3 12.9 8.9 8.9 8.1 8.2 7.4 8.6 8.0 10.3 6-30-2008 10.9 11.5 – 10.3 9.8 9.1 8.7 7.8 6.0 6.5 8.0 8.0 9.7 7-07-2008 11.6 10.3 10.4 – 9.2 9.1 8.5 8.3 – – – – 8.5

7-14-2008 11.9 12.0 – 11.5 9.2 9.0 8.9 8.5 12.0 10.3 11.8 11.2 10.87-21-2008 10.7 10.6 – 9.7 9.5 9.5 9.2 – 7.7 10.0 9.3 9.6 9.3

7-28-2008 11.1 10.2 – 9.8 9.1 8.5 9.0 – 10.5 9.1 8.5 8.6 9.0

8-04-2008 14.9 11.0 10.6 9.9 9.4 9.0 8.4 8.0 9.1 7.4 8.5 8.9 8.4

8-11-2008 11.0 11.0 – 10.3 9.5 9.2 8.4 9.5 7.5 8.7 8.5 8.7 8.7

8-18-2008 9.4 10.0 – 9.6 8.7 8.1 7.4 7.6 5.3 5.2 6.2 5.7 7.98-25-2008 10.4 10.2 – 9.3 8.4 8.1 7.6 – 7.8 7.4 7.0 7.5 9.0

Ammonianitrogen

(mg/L)

5-05-2008 <0.01 0.012 0.011 0.015 0.019 0.083 0.338 0.351 0.288 0.471 0.456 – 0.3065-12-2008 0.019 0.020 – 0.028 0.027 0.053 0.309 0.169 – 0.274 0.260 – 0.164

5-19-2008 – – – – – – 0.075 0.061 0.041 0.074 0.062 – 0.037

5-27-2008 0.011 0.023 – 0.020 0.041 0.064 0.045 0.044 0.041 0.162 0.118 – 0.0796-02-2008 0.013 0.024 0.022 0.019 0.028 0.042 0.057 0.052 0.049 0.104 0.116 – 0.059

6-09-2008 <0.01 0.012 – 0.020 0.019 0.029 0.029 0.027 0.029 0.090 0.069 – 0.088

6-16-2008 0.012 0.020 – – 0.029 0.040 0.047 0.039 0.043 0.062 0.098 – 0.0386-18-2008 – – – 0.019 – – – – – – – – –

6-23-2008 0.020 0.024 – 0.020 0.030 0.043 0.049 0.057 0.039 0.017 0.013 – 0.0206-30-2008 0.015 0.042 – 0.017 0.025 0.031 0.055 0.038 0.048 0.026 0.027 – 0.039

7-7-2008 0.015 0.088 0.052 0.026 0.024 0.022 0.049 0.072 0.021 0.406 0.509 – 0.140

7-14-2008 0.017 0.101 – 0.089 0.036 0.013 0.020 0.018 0.014 0.035 0.020 – 0.0247-21-2008 0.017 0.042 – 0.022 0.012 0.011 0.014 – 0.030 0.072 0.070 – 0.0577-28-2008 0.013 0.012 – 0.011 0.013 0.015 0.020 – 0.021 0.056 0.047 – 0.0398-04-2008 0.025 0.050 0.044 0.044 0.017 0.028 0.030 0.064 0.017 0.056 0.062 – 0.045

8-11-2008 0.013 0.040 – 0.025 0.023 0.023 0.037 0.046 0.037 0.072 0.039 – 0.039

8-18-2008 0.021 0.024 – 0.012 0.023 0.031 0.041 0.058 0.065 0.059 0.065 – 0.056

8-25-2008 <0.01 0.029 – 0.013 0.021 0.031 0.038 – 0.056 0.076 0.084 – 0.053

Appendix A. Additional Water-Quality Data from Clean Water Services for Selected Sites in the Tualatin River, Oregon, 

May–August 2008.—Continued
Constituent

(units) Date

Tualatin River sites

Cherry

Grove

(RM 67.8)

Dilley

(RM 58.8)

JWC/TVID 

Spring Hill 

pumping 

plant

(RM 56.1)

Golf Course 

Road

(RM 51.5)

Hwy 219 

Bridge

(RM 44.4)

Rood

Bridge

(RM 38.4)

Farmington 

(RM 33.3)

Scholls

Bridge

(RM 26.9)

Elsner

(RM16.2)

Boones 

Ferry 

Road

(RM 8.7)

Stafford 

Road

(RM 5.5)

Oswego 

Dam

(RM 3.4)

Weiss 

Bridge

(RM 0.2)

Total suspended 

solids (mg/L)

5-05-2008 2.8 10.8 10.0 9.6 16.0 18.8 11.6 9.2 8.4 8.4 7.6 – 4.8

5-12-2008 1.2 7.6 – 10.0 12.0 10.0 9.2 6.8 – 5.6 4.4 – 4.4

5-19-2008 – – – – – – 10.0 9.2 6.4 6.8 5.2 – 4.8

5-27-2008 2.4 10.0 – 17.2 21.6 28.0 19.2 42.4 12.8 8.8 6.8 – 9.66-02-2008 1.2 5.2 7.2 6.0 10.4 10.8 11.2 8.8 8.4 7.6 6.4 – 6.46-09-2008 5.6 7.2 – 7.2 12.0 11.6 13.2 10.8 9.6 10.4 6.4 – 7.6

6-16-2008 1.2 6.0 – – 13.6 7.6 10.4 10.0 6.8 10.4 6.0 – 6.0

6-18-2008 – – – 5.6 – – – – – – – – –

6-23-2008 2.4 6.4 – 5.2 11.6 7.2 9.6 10.8 8.8 8.0 8.8 – 4.4

6-30-2008 2.0 13.6 – 11.2 14.4 7.2 9.2 8.8 3.2 14.4 5.2 – 4.8

7-07-2008 0.8 12.8 9.6 12.4 28.8 11.2 11.2 10.0 10.4 9.2 6.8 – 2.4

7-14-2008 0.8 8.8 – 13.2 14.4 15.2 13.6 12.0 16.8 11.6 11.6 – 11.2

7-21-2008 0.4 13.2 – 17.6 20.4 15.2 11.2 – 8.0 16.8 8.8 – 4.8

7-28-2008 0.9 23.7 – 28.5 20.9 14.1 15.7 – 12.5 13.7 10.9 – 4.9

8-04-2008 1.2 6.8 8.4 5.6 11.6 9.2 8.8 12.4 13.2 9.2 7.6 – 7.2

8-11-2008 0.4 7.2 – 7.2 10.4 10.8 8.0 10.4 5.2 6.4 5.6 – 6.8

8-18-2008 0.8 10.4 – 13.2 12.8 13.6 12.0 7.6 5.2 8.4 5.6 – 4.88-25-2008 1.2 6.0 – 8.8 10.0 5.6 9.6 – 4.4 9.2 5.2 – 6.8

Turbidity (NTU) 5-05-2008 2.5 9.4 9.4 7.9 9.1 8.9 8.8 7.9 7.3 6.7 6.2 – 5.1

5-12-2008 1.6 7.8 – 7.8 7.7 8.7 7.9 4.9 – 4.1 4.5 – 4.6

5-19-2008 – – – – – – 7.9 6.3 4.1 3.9 4.2 – 3.6

5-27-2008 1.9 11 – 16 18 33 37 73 7.1 5.4 5.5 – 7.4

6-02-2008 1.0 6.3 6.8 5.9 8.6 9.5 8.9 7.3 8.5 7.8 6.1 – 5.6

6-09-2008 2.6 8.1 – 8.3 8.6 9.8 12 16 10 9.8 8.8 – 7.0

6-16-2008 1.0 6.5 – – 4.9 5.4 7.5 9.1 7.0 7.5 5.1 – 4.7

6-18-2008 – – – 4.4 – – – – – – – – –

6-23-2008 1.4 9.2 – 8.4 9.2 8.2 8.8 8.2 7.5 7.4 6.2 – 5.0

6-30-2008 1.5 12 – 9.6 11 8.9 9.3 8.0 4.5 12 5.5 – 4.3

7-07-2008 1.6 14 11 11 14 10 9.8 10 12 8.0 6.0 – 4.4

7-14-2008 1.5 9.7 – 12 13 12 11 9.1 14 11 9.4 – 8.3

7-21-2008 1.0 13 – 15 15 14 11 – 7.7 13 7.3 – 4.0

7-28-2008 1.0 21 – 18 16 11 13 – 10 11 9.4 – 4.4

8-04-2008 1.2 7.6 11 7.9 10 9.2 9.3 12 11 8.6 9.3 – 5.7

8-11-2008 1.0 7.4 – 8.1 7.8 6.2 6.2 7.8 6.7 5.8 4.9 – 3.1

8-18-2008 1.6 7.5 – 11 13 14 11 11 8.2 9.7 6.8 – 3.1

8-25-2008 1.4 7.8 – 8.4 9.3 7.2 9.3 – 7.1 11 6.4 – 5.3

Appendix A. Additional Water-Quality Data from Clean Water Services for Selected Sites in the Tualatin River, Oregon, 

May–August 2008.—Continued

Appendixes 39
40 Upstream Factors Affecting Tualatin River Algae, Oregon

This page left intentionally blank
Appendixes 41

Appendix B. Biovolume of Algal Taxa in Water Samples Collected from Wapato Lake 

Pump Discharge and Downstream in the Tualatin River at the Spring Hill Pumping 

Plant, Oregon, July 19–21, 2008

Taxon biovolumes in cubic microns per milliliter. Abbreviations: RM, river mile; sp, species; JWC, Joint Water 

Commission; TVID, Tualatin Valley Irrigation District.

Algal taxa Algal group

Wapato Lake pump discharge

(near Tualatin River at RM 60.1)

Tualatin River at the 

JWC/TVID Spring Hill 

pumping plant 

(RM 56.1)

July 19 July 21 July 21

Anabaena flos-aquae Blue-green algae 373,049 201,447 89,932

Aphanizomenon flos-aquae Blue-green algae 175,389 0 1,691

Cryptomonas erosa cryptophyte 3,619,136 5,003,093 418,786

Rhodomonas minuta cryptophyte 16,704 12,027 2,148

Cyclotella meneghiniana Diatom 0 114,253 10,201

Cyclotella pseudostelligera Diatom 0 76,219 1,745

Nitzschia acicularis Diatom 155,901 0 7,517

Nitzschia capitellata Diatom 0 324,720 38,657

Nitzschia palea Diatom 150,333 162,360 4,832

Stephanodiscus hantzschii Diatom 0 144,320 15,463

Phacus sp. Euglenoid 97,438 0 0

Trachelomonas hispida Euglenoid 584,630 631,400 56,375

Trachelomonas volvocina Euglenoid 3,673,423 7,934,593 404,826

Actinastrum hantzschii Green algae 534,519 0 0

Ankistrodesmus falcatus Green algae 62,639 60,133 4,027

Chlamydomonas sp. Green algae 651,444 488,583 52,348

Crucigenia quadrata Green algae 0 25,557 2,282

Pediastrum duplex Green algae 0 81,781 0

Pediastrum tetras Green algae 0 72,160 0

Scenedesmus acuminatus Green algae 66,815 36,080 32,214

Scenedesmus quadricauda Green algae 537,442 234,520 65,784

Sphaerocystis schroeteri Green algae 155,901 0 22,550

Tetrastrum staurogeniaforme Green algae 60,133 0 5,799

Marssoniella elegans Unknown 0 541,200 96,643

Unidentified flagellate Unknown 1,876,383 1,671,707 5,369

Achnanthes minutissima Diatom 0 0 1,342

Euglena sp. Euglenoid 0 0 15,570

Gomphonema angustatum Diatom 0 0 4,832

Navicula graciloides Diatom 0 0 11,678

Nitzschia communis Diatom 0 0 1,208

Rhoicosphenia curvata Diatom 0 0 3,141

Scenedesmus sp. Green algae 0 0 5,369

Synedra rumpens Diatom 0 0 3,758

Trachelomonas cylindrica Euglenoid 0 0 21,476

Total abundance 12,791,279 17,816,154 1,407,563

Publishing support provided by the U.S. Geological Survey

 Science Publishing Network, Tacoma Publishing Service Center

For more information concerning the research in this report, contact the

Director, Oregon Water Science Center

U.S. Geological Survey

2130 SW 5th Avenue

Portland, Oregon 97201

http://or.water.usgs.gov
Rounds and others—Upstream Factors Affecting Tualatin River Algae, Oregon—Scientific Investigations Report 2015–5178

ISSN 2328-0328 (online)

http://dx.doi.org/10.3133/sir20155178