Limnology of Blue Mesa, Morrow Point, 

and Crystal Reservoirs, Curecanti 

National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient 

Conditions in Blue Mesa Reservoir, 

Colorado

By Nancy J. Bauch, U.S. Geological Survey, and

Matt Malick, National Park Service

Denver, Colorado

2003

Prepared in cooperation with the

NATIONAL PARK SERVICE

U.S. GEOLOGICAL SURVEY

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

Water-Resources Investigations Report 02–4199
District Chief

U.S. Geological Survey

Box 25046, Mail Stop 415

Denver Federal Center

Denver, CO 80225–0046

For additional information write to:

District Chief

U.S. Geological Survey

Box 25046, Mail Stop 415

Denver Federal Center

Denver, CO 80225–0046

U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification purposes only and does 

not constitute endorsement by the U.S. Geological Survey.

Copies of this report can be purchased 

from:

U.S. Geological Survey

Information Services

Box 25286

Denver Federal Center

Denver, CO 80225
The U.S. Geological Survey (USGS) is committed 

to serve the Nation with accurate and timely scientific 

information that helps enhance and protect the overall 

quality of life, and facilitates effective management 

of water, biological, energy, and mineral resources. 

(http://www.usgs.gov/). Information on the quality 

of the Nation’s water resources is of critical interest to 

the USGS because it is so integrally linked to the longterm availability of water that is clean and safe for 

drinking and recreation and that is suitable for industry, irrigation, and habitat for fish and wildlife. Escalating population growth and increasing demands for 

the multiple water uses make water availability, now 

measured in terms of quantity and quality, even more 

critical to the long-term sustainability of our communities and ecosystems.

The USGS implemented the National WaterQuality Assessment (NAWQA) Program to support 

national, regional, and local information needs and 

decisions related to water-quality management and 

policy. (http://water.usgs.gov/nawqa). Shaped by 

and coordinated with ongoing efforts of other Federal, 

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designed to answer: What is the condition of our 

Nation’s streams and ground water? How are the 

conditions changing over time? How do natural features and human activities affect the quality of streams 

and ground water, and where are those effects most 

pronounced? By combining information on water 

chemistry, physical characteristics, stream habitat, and 

aquatic life, the NAWQA Program aims to provide 

science-based insights for current and emerging water 

issues and priorities. NAWQA results can contribute to 

informed decisions that result in practical and effective 

water-resource management and strategies that protect 

and restore water quality.

Since 1991, the NAWQA Program has implemented interdisciplinary assessments in more than 50 

of the Nation’s most important river basins and aquifers, referred to as Study Units. (http://water.usgs.gov/

nawqa/nawqamap.html). Collectively, these Study 

Units account for more than 60 percent of the overall 

water use and population served by public water 

supply, and are representative of the Nation’s major 

hydrologic landscapes, priority ecological resources, 

and agricultural, urban, and natural sources of 

contamination.

Each assessment is guided by a nationally consistent study design and methods of sampling and analysis. The assessments thereby build local knowledge 

about water-quality issues and trends in a particular 

stream or aquifer while providing an understanding 

of how and why water quality varies regionally and 

nationally. The consistent, multi-scale approach helps 

to determine if certain types of water-quality issues are 

isolated or pervasive, and allows direct comparisons of 

how human activities and natural processes affect 

water quality and ecological health in the Nation’s 

diverse geographic and environmental settings. Comprehensive assessments on pesticides, nutrients, volatile organic compounds, trace metals, and aquatic 

ecology are developed at the national scale through 

comparative analysis of the Study-Unit findings. 

(http://water.usgs.gov/nawqa/natsyn.html). 

The USGS places high value on the communication and dissemination of credible, timely, and 

relevant science so that the most recent and available 

knowledge about water resources can be applied in 

management and policy decisions. We hope this 

NAWQA publication will provide you the needed 

insights and information to meet your needs, and 

thereby foster increased awareness and involvement 

in the protection and restoration of our Nation’s 

waters. 

The NAWQA Program recognizes that a national 

assessment by a single program cannot address all 

water-resource issues of interest. External coordination at all levels is critical for a fully integrated 

understanding of watersheds and for cost-effective 

management, regulation, and conservation of our 

Nation’s water resources. The Program, therefore, 

depends extensively on the advice, cooperation, 

and information from other Federal, State, interstate, 

Tribal, and local agencies, non-government organizations, industry, academia, and other stakeholder 

groups. The assistance and suggestions of all are 

greatly appreciated.

Robert M. Hirsch

Associate Director for Water

FOREWORD III

FOREWORD
CONTENTS V

Foreword ................................................................................................................................................................................ III

Abstract.................................................................................................................................................................................. 1

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

Purpose and Scope....................................................................................................................................................... 4

Acknowledgments ....................................................................................................................................................... 4

Description of Study Area ........................................................................................................................................... 4

Precipitation and Reservoir Operations ....................................................................................................................... 6

Previous Investigations ................................................................................................................................................ 8

Data Collection and Analysis Procedures.............................................................................................................................. 10

Sample Collection........................................................................................................................................................ 10

Analysis Methods ........................................................................................................................................................ 11

Laboratory Analysis for Nutrients and Suspended Sediment............................................................................ 11

Nutrient Ratios and Loads ................................................................................................................................. 12

Water-Quality Standards.................................................................................................................................... 14

Phytoplankton and Chlorophyll-a Analysis....................................................................................................... 15

Reservoir Classification Schemes...................................................................................................................... 15

Trend and Correlation Analysis......................................................................................................................... 16

Quality-Control Methods and Analysis ................................................................................................................................. 18

Limnology of Blue Mesa Reservoir....................................................................................................................................... 23

Physical Properties....................................................................................................................................................... 23

Nutrients ...................................................................................................................................................................... 26

Phytoplankton .............................................................................................................................................................. 27

Chlorophyll-a............................................................................................................................................................... 29

Characteristics of Reservoir Inflows............................................................................................................................ 30

Physical Properties and Suspended Sediment ................................................................................................... 30

Nutrients ............................................................................................................................................................ 33

Characteristics of Reservoir Outflow........................................................................................................................... 34

Limnology of Morrow Point Reservoir ................................................................................................................................. 35

Physical Properties....................................................................................................................................................... 35

Nutrients ...................................................................................................................................................................... 38

Phytoplankton .............................................................................................................................................................. 39

Chlorophyll-a............................................................................................................................................................... 40

Characteristics of Reservoir Inflows............................................................................................................................ 41

Physical Properties and Suspended Sediment ................................................................................................... 41

Nutrients ............................................................................................................................................................ 43

Characteristics of Reservoir Outflow........................................................................................................................... 44

Limnology of Crystal Reservoir ............................................................................................................................................ 45

Physical Properties....................................................................................................................................................... 45

Nutrients ...................................................................................................................................................................... 46

Phytoplankton .............................................................................................................................................................. 47

Chlorophyll-a............................................................................................................................................................... 48

Characteristics of Reservoir Inflows............................................................................................................................ 48

Physical Properties and Suspended Sediment ................................................................................................... 48

Nutrients ............................................................................................................................................................ 49

Characteristics of Reservoir Outflow........................................................................................................................... 50

Comparison of Reservoirs, Inflows, and Outflows................................................................................................................ 51

Physical Properties in Reservoirs ................................................................................................................................ 51

Nutrients in Reservoirs ................................................................................................................................................ 53

Phytoplankton in Reservoirs........................................................................................................................................ 53

Chlorophyll-a in Reservoirs......................................................................................................................................... 55

Characteristics of Reservoir Inflows and Outflows ..................................................................................................... 56

Implications for Management...................................................................................................................................... 56

CONTENTS
VI CONTENTS

Retrospective of Nutrient Conditions in Blue Mesa Reservoir ............................................................................................. 57

Physical Properties ...................................................................................................................................................... 57

Nutrients ...................................................................................................................................................................... 58

Phytoplankton.............................................................................................................................................................. 62

Chlorophyll-a............................................................................................................................................................... 62

Nutrient Enrichment .................................................................................................................................................... 63

Summary................................................................................................................................................................................ 64

References ............................................................................................................................................................................. 65

Supplemental Data................................................................................................................................................................. 69

FIGURES

1. Map showing Curecanti National Recreation Area and sampling sites .................................................................... 3

2. Map showing land-use/land-cover classification, Curecanti National Recreation Area watershed.......................... 6

3–27. Graphs showing:

3. Reservoir volume, inflow, and outflow of water for Blue Mesa, Morrow Point, and Crystal 

Reservoirs, 1999................................................................................................................................................. 7

4. Depth profiles of (A) water temperature and dissolved oxygen, and (B) pH and specific conductance, 

Blue Mesa Reservoir, April–November 1999 .................................................................................................... 24

5. Light transparency in Blue Mesa Reservoir, April–November 1999................................................................. 26

6. Nitrogen and phosphorus concentrations in Blue Mesa Reservoir at (A) Iola Basin (site BM1), 

(B) Cebolla Basin (site BM2), and (C) Sapinero Basin (site BM3), April–November 1999............................. 28

7. Phytoplankton density in Blue Mesa Reservoir, April–November 1999 ........................................................... 30

8. Genera richness in Blue Mesa Reservoir, April–November 1999 ..................................................................... 31

9. Phytoplankton community in Blue Mesa Reservoir, April–November 1999 .................................................... 31

10. Percent composition of phytoplankton community by genera, Blue Mesa Reservoir, 

April–November 1999........................................................................................................................................ 32

11. Trophic-state indices for Blue Mesa Reservoir, calculated from Secchi depth, chlorophyll-a, and 

total phosphorus, April–November 1999 ........................................................................................................... 32

12. Depth profiles of (A) water temperature and dissolved oxygen, and (B) pH and specific conductance, 

Morrow Point Reservoir, April–December 1999 ............................................................................................... 36

13. Light transparency in Morrow Point Reservoir, April–December 1999............................................................ 38

14. Nitrogen and phosphorus concentrations in Morrow Point Reservoir, (A) Above Pine Creek (site MP1), 

(B) Kokanee Bay (site MP2), and (C) Hermits Rest (site MP3), April–December 1999 .................................. 40

15. Phytoplankton density in Morrow Point Reservoir, April–December 1999 ...................................................... 42

16. Genera richness in Morrow Point Reservoir, April–December 1999 ................................................................ 42

17. Phytoplankton community in Morrow Point Reservoir, April–December 1999 ............................................... 42

18. Percent composition of phytoplankton community by genera, Morrow Point Reservoir, 

April–December 1999........................................................................................................................................ 43

19. Trophic-state indices for Morrow Point Reservoir, calculated from Secchi depth, chlorophyll-a, 

and total phosphorus, April–December 1999..................................................................................................... 44

20. Depth profiles of water temperature, dissolved oxygen, pH, and specific conductance, Crystal 

Reservoir near Crystal Dam (site CR1), April–December 1999........................................................................ 45

21. Light transparency in Crystal Reservoir near Crystal Dam (site CR1), April–December 1999........................ 46

22. Nitrogen and phosphorus concentrations in Crystal Reservoir near Crystal Dam (site CR1), 

April–December 1999........................................................................................................................................ 47

23. Phytoplankton density in Crystal Reservoir near Crystal Dam (site CR1), April–December 1999 .................. 48

24. Genera richness in Crystal Reservoir near Crystal Dam (site CR1), April–December 1999 ............................ 48

25. Phytoplankton community in Crystal Reservoir near Crystal Dam (site CR1), April–December 1999 ........... 49

26. Percent composition of phytoplankton community by genera, Crystal Reservoir near Crystal Dam 

(site CR1), April–December 1999 ..................................................................................................................... 49

27. Trophic-state indices for Crystal Reservoir near Crystal Dam (site CR1), calculated from Secchi 

depth, chlorophyll-a, and total phosphorus, April–December 1999.................................................................. 50

28. Photograph showing mouth of Cimarron River at Gunnison River, August 1999.................................................... 51
CONTENTS VII

29–32. Graphs showing:

29. Median nutrient concentrations in Curecanti National Recreation Area, April–December 1999 .................... 54

30. Genera richness in Blue Mesa Reservoir for 1975, 1983, 1984, 1985, 1998, and 1999................................... 63

31. Phytoplankton community in Blue Mesa Reservoir for 1975, 1983, 1984, 1985, 1998, and 1999.................. 63

32. Chlorophyll-a concentrations in Blue Mesa Reservoir at Iola Basin (site BM1), 1984–99 ............................. 64

TABLES

1. Sample-collection sites, Curecanti National Recreation Area, April–December 1999 ................................................... 5

2. Water-quality parameters of interest.................................................................................................................................. 10

3. Reporting conventions and reporting values for nutrient constituents ............................................................................. 12

4. Procedures used to aggregate nitrogen data into total nitrogen and dissolved inorganic nitrogen constituents.............. 13

5. Stream classification for reservoir and stream inflow sample-collection sites, Curecanti National 

Recreation Area ................................................................................................................................................................. 14

6. Water-quality standards for stream segments in the Gunnison River Basin..................................................................... 15

7. Information used in seasonal Kendall test for temporal trends......................................................................................... 17

8. Concentrations and absolute differences of nutrients in replicate samples...................................................................... 19

9. Range of absolute differences in replicate samples for individual nutrients.................................................................... 20

10. Estimated sampling variability and confidence intervals around measured nutrient concentrations at 

selected maximum or critical values and mean concentrations for interpretation of environmental data 

for Curecanti National Recreation Area stream inflow sites ............................................................................................ 21

11. Concentrations of nutrients in blank samples ................................................................................................................... 22

12. Nitrogen phosphorus ratios in Blue Mesa, Morrow Point, and Crystal Reservoirs, April–December 1999................... 30

13. Percentage of total inflow into Blue Mesa Reservoir for each sampled inflow site, May–December 1999................... 33

14. Estimated mean annual and monthly discharge and nutrient loads for Gunnison River at County Road 32 

(site BI1), calendar years 1995–99.................................................................................................................................... 34

15. Percentage of total inflow into Morrow Point Reservoir for each sampled inflow site, May–December 1999.............. 44

16. Percentage of total inflow into Crystal Reservoir for each sampled inflow site, May–December 1999......................... 50

17. Estimated mean annual and monthly discharge and nutrient loads for outflow from Crystal Reservoir, 

calendar years 1995–99 ..................................................................................................................................................... 52

18. August and September/October water-quality data for Iola (site BM1) and Sapinero (site BM3) Basins, 

Blue Mesa Reservoir, for 1975, 1983, 1984, 1985, and 1999 .......................................................................................... 58

19. Phytoplankton genera detected in Blue Mesa Reservoir during 1975, 1983, 1984, 1985, 1998, and 1999, 

listed in respective phylum ................................................................................................................................................ 59

20. Results of seasonal Kendall test for temporal trends in Blue Mesa Reservoir inflow and water-quality 

parameters for Iola (site BM1) and Sapinero (site BM3) Basins in Blue Mesa Reservoir, Gunnison River 

at County Road 32 (site BI1), and Lake Fork of the Gunnison River (site BI10)............................................................ 61

21. Mean phytoplankton density in Blue Mesa Reservoir by basin for 1983, 1984, 1985, 1998, and 1999......................... 62

22. Reservoir profile measurements, Blue Mesa Reservoir at Iola Basin (site BM1), April–November 1999..................... 71

23. Reservoir profile measurements, Blue Mesa Reservoir at Cebolla Basin (site BM2), April–November 1999 .............. 72

24. Reservoir profile measurements, Blue Mesa Reservoir at Sapinero Basin (site BM3), April–November 1999............. 74

25. Nitrogen and phosphorus concentrations in Blue Mesa Reservoir, April–November 1999............................................ 76

26. Phytoplankton taxonomic list, Curecanti National Recreation Area, April–December 1999......................................... 78

27. Number of phytoplankton detected in Blue Mesa Reservoir, April–November 1999..................................................... 80

28. Chlorophyll-a concentrations and trophic-state indices, Blue Mesa, Morrow Point, and Crystal Reservoirs, 

April–December 1999 ....................................................................................................................................................... 82

29. Physical properties and suspended sediment (inflows only) for Blue Mesa Reservoir inflow and outflow sites, 

May–December 1999 ........................................................................................................................................................ 83

30. Nitrogen and phosphorus concentrations in Blue Mesa Reservoir inflow and outflow sites, May–December 1999..... 85

31. Reservoir profile measurements, Morrow Point Reservoir above Pine Creek (site MP1), April–December 1999........ 87

32. Reservoir profile measurements, Morrow Point Reservoir at Kokanee Bay (site MP2), April–December 1999........... 88

33. Reservoir profile measurements, Morrow Point Reservoir off Hermits Rest (site MP3), April–December 1999.......... 90

34. Nitrogen and phosphorus concentrations in Morrow Point Reservoir, April–December 1999....................................... 92

35. Number of phytoplankton detected in Morrow Point Reservoir, April–December 1999................................................ 93
VIII CONTENTS

36. Physical properties and suspended sediment (inflows only) for Morrow Point Reservoir inflow and outflow 

sites, May–December 1999 ................................................................................................................................................ 94

37. Nitrogen and phosphorus concentrations in Morrow Point Reservoir inflow and outflow sites, May–December 1999..... 95

38. Reservoir profile measurements, Crystal Reservoir near Crystal Dam (site CR1), April–December 1999 .................... 96

39. Nitrogen and phosphorus concentrations at Crystal Reservoir near Crystal Dam (site CR1), April–December 1999 ... 98

40. Number of phytoplankton detected at Crystal Reservoir near Crystal Dam (site CR1), April–December 1999............. 99

41. Physical properties and suspended sediment (inflows only) for Crystal Reservoir inflow and outflow sites, 

May–December 1999 ......................................................................................................................................................... 100

42. Nitrogen and phosphorus concentrations in Crystal Reservoir inflow and outflow sites, May–December 1999............ 101

CONVERSION FACTORS AND ABBREVIATIONS

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

°F = 1.8 (°C) + 32

Additional Abbreviations

algal units/L algal units per liter

Curecanti NRA Curecanti National Recreation Area

E estimated

LT-MDL long-term method detection level

LRL laboratory reporting level

mg/m3 milligrams per cubic meter

mg/L milligram(s) per liter

MRL minimum reporting level

NAWQA National Water-Quality Assessment

N:P nitrogen:phosphorus

NWQL National Water Quality Laboratory

TSI trophic-state index

UCOL Upper Colorado River Basin Study Unit

μm micrometer

μS/cm microsiemens per centimeter at 25 degrees Celsius

USEPA U.S. Environmental Protection Agency

WY water year (a 12-month period beginning October 1 and ending September 30 of the following year. A water year is 

described by the year in which it ends.)

Multiply By To obtain

acre 4,047 square meter

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

acre-foot per day (acre-ft/d) 0.01428 cubic meter per second

centimeter (cm) 0.3937 inch

cubic foot per second (ft3/s) 0.02832 cubic meter per second

foot (ft) 0.3048 meter (m)

gallon (gal) 3.785 liter (L)

inch 25.4 millimeter

liter (L) 0.2642 gallon (gal)

kilogram (kg) 2.205 pound, avoirdupois

kilograms per day (kg/d) 2.205 pounds, avoirdupois per day

meter (m) 3.2808 foot (ft)

milliliter (mL) 2.642×10–4 gallon (gal)

mile (mi) 1.609 kilometer
 1

Abstract

The U.S. Geological Survey and the 

National Park Service conducted a waterquality investigation in Curecanti National 

Recreation Area in Colorado from April through 

December 1999. Current (as of 1999) limnological 

characteristics, including nutrients, phytoplankton, 

chlorophyll-a, trophic status, and the water quality 

of stream inflows and reservoir outflows, of Blue 

Mesa, Morrow Point, and Crystal Reservoirs were 

assessed, and a 25-year retrospective of nutrient 

conditions in Blue Mesa Reservoir was conducted. 

The three reservoirs are in a series on the Gunnison 

River, with an upstream to downstream order of 

Blue Mesa, Morrow Point, and Crystal Reservoirs. 

Physical properties and water-quality samples were 

collected four times during 1999 from reservoir, 

inflow, and outflow sites in and around the recreation area. Samples were analyzed for nutrients, 

phytoplankton and chlorophyll-a (reservoir sites 

only), and suspended sediment (stream inflows 

only). Nutrient concentrations in the reservoirs 

were low; median total nitrogen and phosphorus 

concentrations were less than 0.4 and 0.06 milligram per liter, respectively. During water-column 

stratification, samples collected at depth had higher 

nutrient concentrations than photic-zone samples. 

Phytoplankton community and density were 

affected by water temperature, nutrients, and 

water residence time. Diatoms were the dominant 

phytoplankton throughout the year in Morrow 

Point and Crystal Reservoirs and during spring 

and early winter in Blue Mesa Reservoir. Bluegreen algae were dominant in Blue Mesa Reservoir 

during summer and fall. Phytoplankton density 

was highest in Blue Mesa Reservoir and lowest 

in Crystal Reservoir. Longer residence times and 

warmer temperatures in Blue Mesa Reservoir were 

favorable for phytoplankton growth and development. Shorter residence times and cooler temperatures in the downstream reservoirs probably limited 

phytoplankton growth and development. Median 

chlorophyll-a concentrations were higher in Blue 

Mesa Reservoir than Morrow Point or Crystal 

Reservoirs. Blue Mesa Reservoir was mesotrophic 

in upstream areas and oligotrophic downstream. 

Both Morrow Point and Crystal Reservoirs were 

oligotrophic. Trophic-state index values were 

determined for total phosphorus, chlorophyll-a, 

and Secchi depth for each reservoir by the Carlson 

method; all values ranged between 29 and 55. Only 

the upstream areas in Blue Mesa Reservoir had 

total phosphorus and chlorophyll-a indices above 

50, reflecting mesotrophic conditions. Nutrient 

inflows to Blue Mesa Reservoir, which were 

derived primarily from the Gunnison River, varied 

on a seasonal basis, whereas nutrient inflows to 

Morrow Point and Crystal Reservoirs, which 

were derived primarily from deep water releases 

from the respective upstream reservoir, were 

steady throughout the sampling period. Total 

phosphorus concentrations were elevated in many 

Limnology of Blue Mesa, Morrow Point, and Crystal 

Reservoirs, Curecanti National Recreation Area, 

during 1999, and a 25-Year Retrospective of Nutrient 

Conditions in Blue Mesa Reservoir, Colorado

By Nancy J. Bauch and Matt Malick
2 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

stream inflows. A comparison of current (as of 

1999) and historical nutrient, chlorophyll-a, and 

trophic conditions in Blue Mesa Reservoir and 

its tributaries indicated that the trophic status in 

Blue Mesa Reservoir has not changed over the 

last 25 years, and more recent nutrient enrichment 

has not occurred.

INTRODUCTION

Curecanti National Recreation Area (Curecanti 

NRA) encompasses three reservoirs on the Gunnison 

River in west-central Colorado (fig. 1). Blue Mesa, 

Morrow Point, and Crystal Reservoirs, collectively 

known as the Wayne N. Aspinall Storage Unit of the 

Colorado River Storage Project, were created in the 

1960’s and 1970’s for water storage, power production, streamflow regulation, and recreation. The 

primary recreational feature of the Aspinall Unit 

is the stocked fishery associated with the three reservoirs, which includes kokanee salmon (Oncorhynchus 

nerka), rainbow trout (Oncorhynchus mykiss), 

brown trout (Salmo trutta), lake trout (Salvelinus 

namaycush), and cutthroat trout (Oncorhynchus 

clarki pleuriticus). Optimal conditions in Blue Mesa 

Reservoir have made it one of the premier kokanee 

salmon fisheries in the Western United States, and 

the fishery-related tourism benefits local economies. 

A healthy aquatic system is needed for the fishery of 

Curecanti NRA to continue into the future.

Population growth and land-use changes 

upstream from Curecanti NRA, as well as reservoir 

operations and transbasin water diversions, have the 

potential to affect water quantity and quality and 

aquatic biology in the three reservoirs. From 1970 

to 1998, the population of Gunnison County (fig. 1) 

increased 76 percent (Colorado Department of Local 

Affairs, 1999), resulting in substantial land-use 

changes in the upper Gunnison River Valley because 

of increased development. Almost 48 percent of the 

Curecanti NRA boundary abuts private property; many 

of these properties have proposed development for 

recreational vehicle campgrounds and single-family 

homes (National Park Service, 1995). Numerous acres 

of ranchland are being converted to urban development. Nutrient levels in Blue Mesa Reservoir, as well 

as in Morrow Point and Crystal Reservoirs, may be 

affected by these land-use changes. Thermal regimes 

in the reservoirs and, ultimately, the productivity 

of the reservoirs also may be adversely affected by 

potential changes in the operation of the Aspinall 

Unit reservoirs to meet proposed downstream streamflow requirements for endangered fish. Changes 

in streamflow caused by reservoir operations and 

water diversions have altered important habitats and 

restricted the range of endangered fish and their access 

to former habitats (Pitlick, 2002). It is not known if 

or how potential transbasin diversions to meet water 

needs of the Front Range of Colorado and the final 

quantification of the National Park Service water right 

for the Black Canyon of the Gunnison National Park 

may affect the quantity and quality of water in the 

three reservoirs. 

While numerous reports are available on the 

water resources of the upper Gunnison River Valley 

and Curecanti NRA, there is a general lack of recent 

information, especially nutrient data and nutrient 

pathways, for the recreation area itself. Intensive 

limnological studies were conducted on Blue Mesa 

Reservoir in 1975 and 1982–85, but no recent intensive investigations pertaining to nutrients in the 

reservoir have been done. Few studies have been 

done on the limnology of Morrow Point and Crystal 

Reservoirs. For all but the major inflow streams, 

little or no physical, chemical, or hydrologic data 

are available. Very little information is available 

on nutrient concentrations in discharges from Blue 

Mesa and Morrow Point Dams.

Nutrients are of prime importance in the 

maintenance of the fisheries and aquatic systems 

of the three reservoirs. Over the last 25 years, 

several studies of the limnology of Blue Mesa 

Reservoir (U.S. Environmental Protection Agency, 

1977; Cudlip and French, 1985) have called for 

continued investigations into nutrient enrichment of 

the Aspinall Unit. The water-resources planning document for Curecanti NRA (Cudlip and others, 1996) 

recognized the importance of biological productivity 

in the reservoirs in meeting the needs of native and 

stocked fish; however, up-to-date information on 

nutrient inflows and outflows and productivity of the 

three reservoirs generally is limited. Finally, recent 

concerns of additional nutrient loading from upstream 

sources because of land-use changes indicated a need 

to compare data describing ambient conditions in Blue 

Mesa Reservoir to data from the 1970’s and 1980’s.
INTRODUCTION 3

BM3

MI3

MI2

BM1

BI8

BI3

Iola Basin

Steuben Creek

Blue Mesa Reservoir

BM2

BI4

BI6

West Elk Creek

Cebolla Basin

Red

Creek

East Elk Creek

South W

BI5

BI7

MP1

BO

Soap Creek

Sapinero

Basin

Pine Creek

MI4

Corral Cr

Curecanti Creek

Kokanee Bay

MP2

Morrow Point

Reservoir

Creek

Gunnison County

MI5

Blue Creek

Montrose County

MO

CI2

MP3

Cimarron Ri ver

Crystal Reservoir

CR1

CurecantiNationalRecreation Area

CI4

C rystal Creek CI3

Mesa

Black Canyon ot the Gunnison

National Park

CO

BI10

BI9

Cebolla Creek

Powderhorn

Location of CurecantiNational Recreation Area

10 MILES

Recreation Area boundarySampling site (see table 1 for site names)

Site located south, off of map

0 8

0 2 10 KILOMETERS

24 6

4 68

Dam

Tributary

MO

County boundary

38°22'30"

107°37'30"

38°30'

107°22'30" 107°07'30"

of the Gunnison Rive EXPLANATION r Lake Fork

Hermits

Rest

Figure 1. Curecanti National Recreation Area and sampling sites.
4 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

To meet these needs, the U.S. Geological 

Survey (USGS), in cooperation with the National 

Park Service (NPS), conducted a study in 1999 

to investigate the limnological characteristics of 

Blue Mesa, Morrow Point, and Crystal Reservoirs, 

including the water quality of stream inflows 

and reservoir outflows.

Purpose and Scope

The purposes of this report are to (1) describe 

the limnological characteristics (physical properties 

and nutrient, phytoplankton, and chlorophyll-a

concentrations) of Blue Mesa, Morrow Point, 

and Crystal Reservoirs in Curecanti NRA in 1999; 

(2) describe 1999 water-quality conditions in stream 

inflows (physical properties, suspended sediment, and 

nutrients) and reservoir outflows (physical properties 

and nutrients) for Blue Mesa, Morrow Point, and 

Crystal Reservoirs; and (3) compare the nutrient, 

phytoplankton, chlorophyll-a, and(or) trophic status 

of Blue Mesa Reservoir and its inflows in 1999 to 

previous levels over the past 25 years with regard 

to nutrient conditions and nutrient enrichment in 

the reservoir. The report describes the spatial and 

temporal distribution of physical properties, nutrients, 

phytoplankton, chlorophyll-a, and trophic status for 

Blue Mesa, Morrow Point, and Crystal Reservoirs; 

physical properties, suspended sediment, and nutrients 

for stream inflows; and physical properties and nutrients for reservoir outflows. Nutrient, phytoplankton, 

chlorophyll-a, and(or) trophic conditions in Blue 

Mesa Reservoir and two of its inflows are compared 

to historical data to investigate nutrient conditions 

and nutrient enrichment with respect to land-use 

changes in the upper Gunnison River Basin. Included 

in the analysis of 1999 phytoplankton data for Morrow 

Point and Crystal Reservoirs is a comparison to 1998 

phytoplankton data.

Acknowledgments

The authors thank Jeff Shellberg (NPS) and 

Adrienne Greve, Jason Gurdak, and Norman Spahr (all 

USGS) for their efforts in collecting water samples for 

this study and Mark Wondzell (NPS), Tony Ranalli, 

and Lonna Frans (both USGS) for their review of the 

manuscript. Thanks also are extended to Mary Kidd 

(editorial review), Sharon Powers (graphics), and 

Joy Monson (layout).

Description of Study Area

Curecanti NRA is located in semiarid westcentral Colorado in Gunnison and Montrose Counties. 

The recreation area begins about 5 mi west of the 

town of Gunnison and extends about 50 mi to the 

west (fig. 1). As the Aspinall Unit of the Colorado 

River Storage Project, Blue Mesa, Morrow Point, and 

Crystal Reservoirs have a combined storage capacity 

of approximately 1,083,126 acre-ft of water (Bureau 

of Reclamation, 1999a). Blue Mesa Reservoir, the 

most upstream reservoir and the largest body of 

water in Colorado, has a maximum storage capacity 

of 940,700 acre-ft and a surface area of 9,180 acres 

at full pool (elevation of 7,519 ft). Morrow Point 

Reservoir, downstream from Blue Mesa Reservoir, has 

a storage capacity of 117,190 acre-ft and a surface area 

of 817 acres at full pool (elevation of 7,160 ft). Crystal 

Reservoir, downstream from Morrow Point Reservoir, 

has a storage capacity of 25,236 acre-ft and a surface 

area of 301 acres at full pool (elevation of 6,700 ft) 

(Bureau of Reclamation, 1999a). Each reservoir 

is used for water storage and the generation of 

hydroelectric power. Crystal Reservoir also acts 

to re-regulate fluctuating flows due to power production. The residence time (the average time needed 

to completely replenish a reservoir’s water volume) 

differs for the three reservoirs and depends on 

each reservoir’s purpose and size. The 1978–99 

average residence time for Blue Mesa Reservoir 

was 202 days; for Morrow Point Reservoir, 36 days; 

and for Crystal Reservoir, 4.5 days (Bureau of 

Reclamation, 1975–99). The operation of the Aspinall 

Unit is controlled by the Bureau of Reclamation, 

whereas the recreational uses of Curecanti NRA are 

administered by the NPS.

Blue Mesa Reservoir’s 98 miles of shoreline 

are bordered by rolling hills with dominant vegetation 

consisting of sagebrush (Artemisia sp.) and Gambel 

oak (Quercus gambelii). The surficial geology 

surrounding Blue Mesa Reservoir consists of sedimentary deposits of Mesozoic age capped with volcanic 

rocks of Cenozoic age. The Gunnison River (site BI1; 

fig. 1, table 1) supplies more than one-half of the 

flow into Blue Mesa Reservoir. A short, free-flowing
INTRODUCTION 5

Table 1. Sample-collection sites, Curecanti National Recreation Area, April–December 1999

[USGS, U.S. Geological Survey]

Site

number

(fig. 1)

USGS station number Site name

BLUE MESA RESERVOIR—RESERVOIR SITES

BM1 382856107050000 Blue Mesa Reservoir below Highway 149 bridge, near Gunnison 

(Iola Basin)

BM2 382829107122200 Blue Mesa Reservoir above Highway 50 bridge, near Sapinero

(Cebolla Basin)

BM3 382831107172600 Blue Mesa Reservoir above Blue Mesa Powerhouse, near Sapinero

(Sapinero Basin)

BLUE MESA RESERVOIR—INFLOW AND OUTFLOW SITES

BI1 383103106594200 Gunnison River at County Road 32 below Gunnison

BI2 382943107015300 Beaver Creek at Highway 50, near Gunnison

BI3 382937107033500 Steuben Creek at Highway 50, near Gunnison

BI4 382900107101600 East Elk Creek above Highway 50, near Sapinero

BI5 382902107140400 Red Creek above Highway 50, near Sapinero

BI6 383028107162200 West Elk Creek above Blue Mesa Reservoir, near Sapinero

BI7 383137107183600 Soap Creek above Blue Mesa Reservoir, near Sapinero

BI8 382807107033900 South Willow Creek above Highway 149, near Gunnison

BI9 381633107054700 Cebolla Creek at bridge southeast of Powderhorn

BI10 381934107133500 Lake Fork of the Gunnison River below Gateview

BO 382712107200100 Blue Mesa Reservoir discharge at Blue Mesa Powerhouse, near Sapinero

MORROW POINT RESERVOIR—RESERVOIR SITES

MP1 382711107201200 Morrow Point Reservoir below Blue Mesa Powerhouse, near Sapinero

(Above Pine Creek)

MP2 382644107271000 Morrow Point Reservoir below Curecanti Needle, near Sapinero

(Kokanee Bay)

MP3 382702107315400 Morrow Point Reservoir above Morrow Point Dam, near Cimarron

(Hermits Rest)

MORROW POINT RESERVOIR—INFLOW AND OUTFLOW SITES

BO 382712107200100 Blue Mesa Reservoir discharge at Blue Mesa Powerhouse, near Sapinero

MI2 382730107232900 Corral Creek at Highway 92, near Sapinero

MI3 09125000 Curecanti Creek near Sapinero

MI4 382702107203900 Pine Creek at Highway 50, near Sapinero

MI5 382418107242600 Blue Creek at Highway 50, near Sapinero

MO 382710107323000 Crystal Reservoir below Morrow Point Dam, near Cimarron

(Morrow Point Reservoir discharge)

CRYSTAL RESERVOIR—RESERVOIR SITE

CR1 383024107371800 Crystal Reservoir near Crystal Dam, near Cimarron

CRYSTAL RESERVOIR—INFLOW AND OUTFLOW SITES

MO 382710107323000 Crystal Reservoir below Morrow Point Dam, near Cimarron

(Morrow Point Reservoir discharge)

CI2 382720107324000 Mesa Creek above Crystal Reservoir, near Cimarron

CI3 383150107333300 Crystal Creek at Highway 92, near Crawford

CI4 09127000 Cimarron River below Squaw Creek, near Cimarron

CO 09128000 Gunnison River below Gunnison Tunnel
6 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

segment of the Gunnison River is located in the 

eastern part of the recreation area upstream from the 

reservoir. Additional primary inflows to Blue Mesa 

Reservoir are Lake Fork of the Gunnison River and 

Cebolla and Soap Creeks (sites BI10, BI9, and BI7, 

respectively; fig. 1, table 1). Other inflows to Blue 

Mesa Reservoir are small, and some are ephemeral. 

The Black Canyon of the Gunnison River begins near 

Blue Mesa Dam and gives rise to the steep cliffs of 

Morrow Point and Crystal Reservoirs. Both reservoirs 

are long and narrow and set deep in the canyon, 

cutting through igneous and metamorphic rock of 

Precambrian age. Curecanti Creek and Blue Creek 

(sites MI3 and MI5, respectively; fig. 1, table 1) are 

primary stream inflows to Morrow Point Reservoir; 

the Cimarron River (site CI4; fig. 1, table 1) is the 

primary stream inflow to the Gunnison River before 

the beginning of Crystal Reservoir. Other stream 

inflows to the two downstream reservoirs provide 

small, often ephemeral, flow. Most of the streamflow 

in the inflows to all three reservoirs results from snowmelt runoff during spring and localized rainshowers. 

The reservoirs’ watershed is dominated by forests and 

rangeland (fig. 2). Agricultural land is located adjacent 

to the Gunnison River and other streams or rivers. The 

town of Gunnison, population of 5,392 in 1998, is 

the major urban center in the watershed (Colorado 

Department of Local Affairs, 1999).

Precipitation and Reservoir Operations

Precipitation in the Gunnison River Basin in 

1999 was variable; there were extended periods of 

dry and wet conditions. Much of the winter season 

of 1999 (January through March) was characterized 

by dry conditions resulting from a persistent high 

pressure system over the Southwestern United States. 

Conditions began to change during April, with precipitation in the basin 230 percent above average for 

the month (Paul Davidson, Bureau of Reclamation, 

written commun., 2000). Precipitation was prevalent 

throughout the summer months, as heavy thunderstorms from the summer monsoon season began 

earlier than usual in July and continued into 

September. Cool temperatures also were prevalent 

during this time. The fall and early winter seasons 

of 1999 in the Gunnison River Basin were very 

dry. Precipitation amounts in October, November, 

and December were between 20 and 60 percent of 

average (Paul Davidson, Bureau of Reclamation, 

written commun., 2000).

The volume of water stored in Blue Mesa 

Reservoir during 1999 reflected the weather and 

runoff conditions (fig. 3). Storage in the first 4.5 months 

of 1999 was relatively constant and ranged between 

535,397 and 577,692 acre-ft (Bureau of Reclamation,

Land-Use/Land-Cover Classification

Urban

Agriculture

Rangeland

Forest

Water

Wetland

Barren

Tundra

EXPLANATION

39° 39°

0 5 1015 KILOMETERS

0 5 10 15 MILES

106°30'

107°30'

107°30'

38° 38°

106°30'

Figure 2. Land-use/land-cover classification, Curecanti National Recreation Area watershed (from Spahr and others, 2000).
INTRODUCTION 7

Blue Mesa Reservoir

2,000

4,000

6,000

8,000

10,000

8,000

9,000

10,000

12,000

14,000

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

0

0

100,000

140,000

120,000

100,000

80,000

60,000

40,000

20,000

200,000

300,000

400,000

500,000

600,000

700,000

800,000

900,000

Crystal Reservoir

0

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

20,000

1999

1999

1999

Reservoir volume (storage) Inflow Outflow Sampling time

0

2,000

4,000

6,000

8,000

10,000

12,000

DAILY MEAN INFLOW OR OUTFLOW, IN ACRE-FEET PER DAY

Morrow Point Reservoir

RESERVOIR VOLUME, IN ACRE-FEET

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

EXPLANATION

Figure 3. Reservoir volume, inflow, and outflow of water for Blue Mesa, Morrow Point, and 

Crystal Reservoirs, 1999.
8 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

1999b). Storage increased during spring and early 

summer with greater precipitation and snowmelt conditions and was near full pool from July into September 

because of monsoon-season rainstorms. Storage 

amounts decreased during fall and early winter, as water 

is usually released from Blue Mesa Reservoir at this 

time of the year to lessen winter icing in the Gunnison 

River where it enters the reservoir by reducing the 

lake level. In contrast to Blue Mesa Reservoir, water 

storage in Morrow Point Reservoir was nearly constant 

all year, with storage ranging between 104,729 and 

118,663 acre-ft (fig. 3) (Bureau of Reclamation, 1999b, 

2000). In general, inflows and outflows for Morrow 

Point Reservoir mirrored each other. Morrow Point 

Reservoir is primarily used as a power-peaking unit for 

power generation, and as such, a constant water level or 

hydraulic head is needed to maximize power production. Storage in Crystal Reservoir in 1999 ranged 

between about 14,000 and 18,578 acre-ft except for 

a 2-week period during September (fig. 3). Storage was 

reduced to a minimum of 4,937 acre-ft on September 17 

for maintenance work on the Crystal Dam penstocks 

(Bureau of Reclamation, 1999b, 2000). As with 

Morrow Point Reservoir, inflows and outflows for 

Crystal Reservoir generally mirrored each other, probably indicating a need for power generation and the 

re-regulation of fluctuating flows. With the increased 

precipitation in the Gunnison River Basin during April 

and early May, the amount of water released from each 

reservoir was increased during May to ensure adequate 

storage in Blue Mesa Reservoir during snowmelt and 

the monsoon season. For all three reservoirs, water is 

drawn through a power-gate slot on the dam face. For 

Blue Mesa Dam, the power-gate slot is located between 

the elevations of 7,358 and 7,376 ft; for Morrow Point 

Dam, between 7,071 and 7,090 ft; and for Crystal Dam, 

between 6,645 and 6,678 ft (Donald K. Phillips, Bureau 

of Reclamation, written commun., 2000). The powergate slot locations result in water being released from 

deep within each reservoir.

Previous Investigations

Numerous reports pertaining to water quality 

and aquatic biology in the upper Gunnison River 

Basin and Curecanti NRA are available. These include 

investigations on the Gunnison River before and after 

impoundment; studies on water quality in streams in 

the upper Gunnison River Basin, including inflows 

to the recreation area; reports on the trophic status 

and limnology of Blue Mesa Reservoir; investigations on aquatic biota, including macroinvertebrates, 

phytoplankton, and fish in the recreation area and 

inflow streams; and National Park Service reports 

on water resources of Curecanti NRA. 

Knight and Argyle (1962) studied the Gunnison 

River prior to impoundment. Wiltzius (1965–1967, 

1971, 1974, 1976) investigated fisheries and waterquality properties (temperature, dissolved oxygen, pH, 

specific conductance, turbidity, alkalinity, hardness, 

and ions) before and after impoundment. Reed (1968) 

discussed limnological developments after dam 

completion on the Gunnison River, including blooms 

of blue-green algae that appeared in the reservoir soon 

after filling. 

Boettcher (1971) studied water quality and 

supply at six planned or developed sites in the 

recreation area. Rumberg and others (1978) reported 

that water in the upper Gunnison River Basin, 

including Curecanti NRA inflows, was generally of 

high quality. Aaronson (1982a, 1982b) also investigated water quality in Gunnison River Basin streams. 

Long and others (1995) analyzed data from 1987 to 

1993 for Blue Mesa Reservoir and 11 inflows in the 

recreation area. It was reported that ambient water 

quality appeared to vary more spatially than temporally, and few serious effects from natural or anthropogenic factors were detected. As the major inflow to 

Blue Mesa Reservoir, the Gunnison River had a 

measurable influence on the reservoir due to its 

overall volume, including loadings to the reservoir. 

The Cimarron River had elevated levels of nutrients, 

bacteria, and dissolved solids as compared to other 

inflow streams in the recreation area. A retrieval 

and analysis of surface-water-quality data for 

Curecanti NRA from six U.S. Environmental 

Protection Agency (USEPA) databases for the period 

from 1994 through 1997 indicated generally good 

water quality in surface waters of the study area 

with some effects from natural and human activities 

(National Park Service, 1998a). Spahr and others 

(2000) provided results from 3 years of water-quality 

sampling on the Gunnison River upstream and downstream from Curecanti NRA, starting in October 1995. 

Water quality in the Gunnison River just upstream 

from Blue Mesa Reservoir was representative of 
INTRODUCTION 9

mixed land-use and high-elevation basins. Nitrogen 

concentrations were commonly highest in winter, 

and phosphorus concentrations were greatest during or 

just prior to peak streamflow from snowmelt. Water 

quality in the Gunnison River just downstream from 

Crystal Reservoir was relatively dilute with limited 

variability. No instream water-quality standards 

of the Colorado Department of Public Health and 

Environment (Colorado Department of Public Health 

and Environment, 2001) were exceeded at either 

of the two Gunnison River sites. Gurdak and others 

(2002) conducted an analysis of surface- and groundwater-quality data of the Upper Gunnison River watershed for 1969–99. These properties and constituents 

were measured: in surface and ground water—field 

properties, major ions, nutrients, and trace elements; 

in surface water—suspended sediment, chlorophyll-a, 

biochemical oxygen demand, and fecal coliform; 

and in ground water—radon, pesticides, and volatile 

organic compounds.

The trophic status and limnology of Blue 

Mesa Reservoir has been discussed in numerous 

reports. The U.S. Environmental Protection Agency 

(1977) reported that Blue Mesa Reservoir was 

mesotrophic, with nitrogen limitation during late 

summer and early fall. Blackwell and Boland (1979) 

used Landsat imagery and principal component analysis techniques to study the trophic status of the reservoir. As part of a large lake and reservoir study in the 

1970’s, Sapinero Basin (site BM3; fig. 1, table 1) was 

determined to be oligotrophic in 1975 (Britton and 

Wentz, 1980). Cudlip and French (1985) also reported 

that Sapinero Basin was oligotrophic in 1985, as 

was Cebolla Basin (site BM2; fig. 1, table 1). Iola 

Basin (site BM1; fig. 1, table 1) was reported to be 

mesotrophic. Physical, chemical, and biological data 

for Blue Mesa Reservoir from 1965 through 1985 

were summarized by Cudlip and others (1987). Based 

on data from 1975 and 1983–85, it was suggested that 

the reservoir reached trophic equilibrium without 

passing through a period of decreased productivity; 

the reservoir was mesotrophic in 1985, as in 1975. 

Hickman (1987) analyzed water-quality data from 

1982 through 1985 for trends and determined that 

no gross pollution or deterioration of water quality 

occurred in the reservoir over the time period. Effects 

of changes in reservoir operations on Blue Mesa 

Reservoir were described in a series of reports by 

Johnson and Bergstedt (1994) and Johnson and others 

(1995, 1996, 1997). These reports focused on reservoir 

limnology (physiochemical characteristics, primary 

production, and zooplankton dynamics) and fishery 

investigations. Reservoir thermal ecology, a thermal 

stratification model, and a growth (bioenergetics) 

model for kokanee salmon also were discussed in 

the latter two reports. As a result of the modeling, 

Johnson and others (1997) concluded that Blue Mesa 

Reservoir’s thermal regime was relatively insensitive 

to changes in reservoir operations during normal 

climatic conditions.

Wiltzius (1971, 1974) investigated fish populations in Blue Mesa Reservoir after initial stocking. 

Wiltzius (1976) also reported on the relation of irrigation diversions and reservoirs to temperature and fish 

populations. Stanford and Ward (1983, 1985) investigated the effects of dams and river regulation on the 

Gunnison River. It was reported that seasonal water 

temperatures downstream from the impoundments were 

moderated, and dissolved solids and organic carbon 

were higher downstream. Macroinvertebrates, particularly Plecoptera, Trichoptera, and Ephemeroptera, were 

studied by Stanford and Ward (1989), Hauer and others 

(1989), and Ward and Stanford (1990, 1991). In each 

case, faunal discontinuities resulting from the damming 

of the Gunnison River were observed. McAda and 

Kaeding (1990) reported on changes in the Gunnison 

River from construction of the Aspinall Unit and 

effects on endangered fish species. Colborn (1981) 

investigated amounts of trace elements in aquatic 

insects in Gunnison-area streams. Nehring and 

Anderson (1983) summarized benthic and fishery 

studies in the Gunnison River. The National Park 

Service (1986) gathered data on benthic fauna in 

Blue Mesa Reservoir’s four major inflows and on 

phytoplankton in the reservoir. The benthic organisms 

indicated good water quality in the inflow streams. 

Phytoplankton in Blue Mesa, Morrow Point, and 

Crystal Reservoirs during 1998 were described by the 

National Park Service (1998b). Diatoms and blue-green 

algae were dominant in Blue Mesa Reservoir, while 

diatoms were dominant in Morrow Point and Crystal 

Reservoirs. Phytoplankton data for the 1999 study will 

be compared to phytoplankton data from the 1998 study 

(National Park Service, 1998b). Studies on catostomid 

and salmonid fishes in Curecanti NRA were conducted 

by Middleton (1969) and Wiltzius and Smith (1976), 
10 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

respectively. Analyses of fish tissue for metals were 

conducted by Kunkle and others (1983). Concentrations 

were below levels harmful to human beings. Wise 

(1997) investigated the effects of kokanee salmon 

predation on the abundance and population dynamics of 

its preferred prey species, the zooplankton Daphnia sp., 

in 1994 and 1995, and found that kokanee had very little 

influence on spring Daphnia dynamics.

A water-resources scoping report analyzed 

the water-resource issues facing the recreation area 

(National Park Service, 1995). Waters in the recreation area were determined to be of high quality. 

However, upstream land-use activities, including 

increased urban development, and activities within 

park boundaries were recognized as potentially 

affecting water quality. The influence of changes 

in the operation of the Aspinall Unit on fisheries 

and reservoir trophic dynamics also was discussed. 

As a result of the scoping report, the Water Resources 

Management Plan for Curecanti NRA was developed 

(Cudlip and others, 1996). This document described 

the water resources of the recreation area and issues 

affecting the resources. Eight project statements 

describing research needs in the recreation area 

were included in the management plan, including 

one statement that addressed the lack of information 

on physical and biological dynamics in Morrow Point 

and Crystal Reservoirs.

DATA COLLECTION AND ANALYSIS 

PROCEDURES

The surface-water sampling for this study 

was designed to investigate the limnology of Blue 

Mesa, Morrow Point, and Crystal Reservoirs in 

Curecanti NRA, including nutrient enrichment in 

Blue Mesa Reservoir, and the water quality of stream 

inflows and reservoir outflow for each reservoir. 

Sample Collection

Water-quality samples were collected four times 

from April through December 1999 from reservoir, 

stream inflow, and reservoir outflow sites throughout 

the recreation area (fig. 1, table 1). Exact dates for 

sampling depended on the hydrological cycle. For 

example, the Blue Mesa Reservoir inflow South 

Willow Creek (site BI8; fig. 1, table 1) was sampled 

only during spring because of the lack of water the 

remainder of the year. Water-quality parameters of 

interest for the respective sites are shown in table 2. 

Prior to each sample collection, all sampling equipment was cleaned with a nonphosphate detergent 

and rinsed, in order, with tap water, deionized 

water, a 5-percent solution of hydrochloric acid, 

and deionized water (Shelton, 1994). At each sampling 

site, the equipment also was thoroughly rinsed with 

native water prior to use. All samples were collected 

using high-density polyethylene plastic bottles.

 Water samples were collected from three 

sites in Blue Mesa Reservoir, three sites in Morrow 

Point Reservoir, and one site in Crystal Reservoir 

(fig. 1, table 1). For ease of reporting, site names for 

the sample-collection sites in Blue Mesa and Morrow 

Point Reservoirs hereinafter will be described using the 

shorter names in parentheses in table 1. The reservoir 

sampling network for this study overlaps the sampling 

network operated by Curecanti NRA for their waterquality monitoring program. In 1999, samples were 

collected from each reservoir site after ice-out during 

April, at summer stratification, in fall, and in early 

winter. Onsite measurements included light or Secchidepth transparency and depth profiles of water temperature, dissolved-oxygen concentration, pH, and specific 

conductance. The depth profiles were measured using 

a Hydrolab H20 in-situ water-quality probe. Measurements were taken at 1-m intervals to 20 m and then 

at 5-m intervals. Water-quality samples for the determination of dissolved and total nutrient constituents 

were collected at discrete depths by using a vertically 

suspended, 2.2-L, acrylic Kemmerer sampler. 

Table 2. Water-quality parameters of interest

Site type Water-quality parameters of interest

Reservoir Physical properties,1 nutrients,2

phytoplankton, chlorophyll-a

Reservoir inflows Physical properties,3 nutrients,2

suspended sediment

Reservoir outflow Physical properties,3 nutrients2

1

Water temperature, dissolved-oxygen concentration, pH, specific 

conductance, light transparency. 2

Dissolved ammonia (un-ionized ammonia [NH3] plus ammonium 

[NH4

+]), dissolved nitrite, dissolved nitrate plus nitrite, dissolved and total 

ammonia plus organic nitrogen, dissolved orthophosphate, dissolved and 

total phosphorus. 3

Discharge or streamflow, water temperature, dissolved-oxygen 

concentration, pH, specific conductance.
DATA COLLECTION AND ANALYSIS PROCEDURES 11

For the Morrow Point Reservoir site Above 

Pine Creek, samples were collected near the surface 

during each sampling period, with additional samples 

collected near the bottom of the water column during 

summer, fall, and early winter. Water at this shallow 

site was thoroughly mixed at each sampling.

For the other six reservoir sites, two waterquality samples were collected at each site during 

spring turnover in April, one near the surface and 

the other from mid-depth of the reservoir. During

turnover, the reservoir water was thoroughly mixed, 

and physical and chemical conditions were similar 

throughout the water column. Collecting water-quality 

samples at depth during turnover was done to determine similarities or differences in nutrient concentrations in the water column during turnover. During 

summer stratification, water-quality samples were 

collected at the top and bottom of the epilimnion 

(warm upper stratum) and near the bottom of the 

water column at the six sites. Additional samples 

were collected in Blue Mesa Reservoir from the metalimnion (stratum with maximum rate of temperature 

decrease with depth) during summer stratification. 

During fall, water-quality samples were collected near 

the surface and near the bottom of the water column 

at the six sites. Additional samples were collected 

from the bottom of the photic (light penetration) zone 

during early winter when turnover was occurring to 

determine variability in nutrient concentrations with 

depth during turnover. 

Inflow and outflow samples for each reservoir 

were collected from 10 stream sites for Blue Mesa 

Reservoir, 4 for Morrow Point Reservoir, and 3 for 

Crystal Reservoir (fig. 1, table 1). Samples were 

collected in spring during high flow and in summer, 

fall, and early winter during low flows. Except for the 

spring sampling, sample collection at the stream sites 

was approximately concurrent with sample collection 

at the reservoir sites. For the stream sites, field 

measurements were obtained for streamflow, water 

temperature, dissolved-oxygen concentration, pH, 

and specific conductance. Water-quality samples 

for nutrient and suspended-sediment analysis were 

collected by equal-width-increment sampling using 

techniques described by Shelton (1994). At the 

reservoir-discharge sites downstream from Blue 

Mesa and Morrow Point Dams, water temperature, 

dissolved-oxygen concentration, pH, and specific 

conductance were determined, and water-quality 

samples were collected as grab samples for nutrient 

analysis. While these two sites are named as reservoir 

sites (Blue Mesa Reservoir discharge at Blue Mesa 

Powerhouse, near Sapinero and Crystal Reservoir 

below Morrow Point Dam, near Cimarron) in table 1, 

they are located on free-flowing segments of the 

Gunnison River just upstream from the reservoirs’ 

beginnings. Samples at the Crystal Reservoir outflow 

site at Gunnison River below Gunnison Tunnel were 

collected in the same fashion as the stream sites except 

that no suspended-sediment samples were collected.

Water-quality samples from all sites were 

processed onsite using techniques described by 

Shelton (1994). Samples for the analysis of dissolved 

nutrient constituents were filtered through a 0.45-μm 

membrane filter. Dissolved concentrations were determined for ammonia (un-ionized ammonia [NH3] plus 

ammonium [NH4

+]) (as nitrogen), nitrite (as nitrogen), 

nitrate plus nitrite (as nitrogen), ammonia plus organic 

nitrogen (as nitrogen), orthophosphate (as phosphorus), and phosphorus (as phosphorus). Samples 

for the determination of total ammonia plus organic 

nitrogen (as nitrogen) and total phosphorus (as phosphorus) were unfiltered and preserved with 1 mL of 

sulfuric acid. All samples were stored on ice prior 

to delivery to the USGS National Water Quality 

Laboratory (NWQL) in Lakewood, Colo.

Analysis Methods

Various methods were used to analyze the waterquality data collected in this study. These included laboratory analysis for nutrients and suspended sediment, 

determination of nutrient ratios and loads, comparison 

of 1999 water-quality data to water-quality standards, 

analysis of phytoplankton and chlorophyll-a, description of reservoir classification schemes, and trend and 

correlation analysis.

Laboratory Analysis for Nutrients and 

Suspended Sediment

The nutrient samples were extracted and 

analyzed at the NWQL using methods described 

by Fishman and Friedman (1989), Fishman (1993), 

and the U.S. Environmental Protection Agency (1993). 

Concentrations for ammonia, nitrite, nitrate plus 

nitrite, and orthophosphate were reported in terms 

of minimum reporting levels (MRLs). The MRL is 

defined by the NWQL as the smallest measured 

concentration of a constituent that may be reliably 
12 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

measured using a given analytical method (Timme, 

1995). A constituent detected at a concentration less 

than the MRL or undetected is reported at the MRL 

with a “<” symbol. Concentrations for ammonia plus 

organic nitrogen were reported in terms of the longterm method detection level (LT-MDL) and laboratory 

reporting level (LRL) (Childress and others, 1999). 

The LT-MDL is the lowest concentration of a constituent that is reported by the NWQL and represents that 

value at which the chance of a false positive detection 

is statistically limited to less than or equal to 1 percent. 

The LRL is calculated at two times the LT-MDL and 

represents the value at which the rate of false negatives 

is less than or equal to 1 percent. Concentrations 

detected between the LT-MDL and LRL are reported 

as estimated (E) concentrations. Concentrations for 

dissolved and total phosphorus for samples analyzed 

before October 1, 1999, were reported using MRLs. 

Samples analyzed after September 30, 1999, were 

reported using LT-MDLs and LRLs (Gary Cottrell, 

U.S. Geological Survey, written commun., 2000). The 

reporting conventions and reporting values for the 

different nutrient constituents are given in table 3. For 

this report, the nitrogen data in this study have been 

aggregated into total nitrogen and dissolved inorganic 

nitrogen data to facilitate interpretation and discussion. Concentrations of these two constituents have 

been calculated from ammonia, nitrite, nitrate plus 

nitrite, and ammonia plus organic nitrogen concentrations using the procedures described in table 4. 

Because total nitrogen and dissolved inorganic 

nitrogen concentrations are computed values, there are 

no laboratory reporting levels associated with these 

two constituents. Throughout this report, when total 

nitrogen and dissolved inorganic nitrogen concentrations are described as being less than laboratory 

reporting levels, the reporting levels discussed are 

those for ammonia plus organic nitrogen and nitrate 

plus nitrite, respectively.

Suspended-sediment samples were analyzed at 

the USGS Iowa Sediment Laboratory in Iowa City for 

the determination of concentration, in milligrams per 

liter. Suspended sediments are important in nutrient 

analysis, as a large proportion of phosphorus may 

adhere to the sediment.

Nutrient Ratios and Loads

Phytoplankton (algae) can assimilate only 

three of the several different nutrient (nitrogen and 

phosphorus) compounds available in aquatic ecosystems. The only forms of nitrogen that phytoplankton

can use for growth are nitrate, nitrite, and ammonia 

(inorganic nitrogen), whereas orthophosphate is 

the only form of phosphorus that phytoplankton can 

use for growth (Horne and Goldman, 1994). Nitrogen 

to phosphorus (N:P) ratios can be used to identify 

which of the two nutrients may be growth limiting 

for phytoplankton. In general, a N:P ratio greater 

than 10 (by weight) indicates that phosphorus is the 

limiting nutrient, whereas a ratio less than 10 indicates that nitrogen is limiting (Horne and Goldman, 

1994). A ratio near 10 is in the transition zone 

between phosphorus and nitrogen limitation. In this 

study, N:P ratios were computed using nitrate plus 

nitrite and ammonia concentrations summed as 

inorganic nitrogen and orthophosphate concentrations. Where both concentrations were less than 

the reporting limit, the N:P ratio was not determined. 

In analyzing nutrient data for lakes and reservoirs, 

N:P ratios should be used with caution because the 

ratio for limitation may differ depending on the 

nutrient requirements of the algal genera that are 

present. Among diatoms, for example, Tabellaria sp. 

and Fragilaria sp. reach maximum population densities at orthophosphate concentrations of approximately 0.045 mg/L, while Scenedesmus sp. requires 

a concentration of around 0.5 mg/L (Wetzel, 1983).

Nutrient loads for Gunnison River at County 

Road 32 and Gunnison River near Gunnison Tunnel 

were estimated by the rating-curve method (Cohn 

and others, 1989; Crawford, 1991). Loads were determined for total nitrogen, dissolved inorganic nitrogen,

Table 3. Reporting conventions and reporting values for 

nutrient constituents

[MRL, minimum reporting level; LRL, laboratory reporting level; 

LT-MDL, long-term method detection level; mg/L, milligrams per liter; 

--, not applicable]

Nutrient MRL

(mg/L)

LRL

(mg/L)

LT-MDL

(mg/L)

Ammonia, dissolved 0.002 -- --

Nitrite, dissolved 0.001 -- --

Nitrate plus nitrite, dissolved 0.005 -- --

Ammonia plus organic nitrogen, 

dissolved and total

-- 0.1 0.05

Orthophosphate, dissolved 0.001 -- --

Phosphorus, dissolved 10.004 20.006 30.003

Phosphorus, total 10.004 20.008 30.004

1Reporting level for samples analyzed before October 1, 1999. 2Reporting levels for samples analyzed after September 30, 1999.

3Detection levels for samples analyzed after September 30, 1999.
DATA COLLECTION AND ANALYSIS PROCEDURES 13

Table 4. Procedures used to aggregate nitrogen data into total nitrogen and dissolved inorganic nitrogen constituents[LT-MDL, long-term method detection level; mg/L, milligrams per liter; LRL, laboratory reporting level; MRL, minimum reporting level; ≥, greater than or equal to; <, le

nitrite; NO2, nitrite; ≤, less than or equal to]

Procedures for calculation of total nitrogen and dissolved inorganic nitrogen

TOTAL NITROGEN

Total ammonia plus organic nitrogen

(LT-MDL=0.05 mg/L)

(LRL=0.10 mg/L)

+ Nitrate plus nitrite

(MRL=0.005 mg/L)

= Total nitrogen

(mg/L)

if ≥0.05 and ≥0.005 then Sum of total ammonia plus organic 

nitrogen and nitrate plus nitrite, rounded to one significant figure

if ≥0.05 and <0.005 then Total ammonia plus organic nitrogenif 1<0.10 and <0.005 then <0.10if 1<0.10 and <0.10 then <0.10

DISSOLVED INORGANIC NITROGEN

Nitrate plus nitrite

(NO3+NO2)

(MRL=0.005 mg/L)

+ Ammonia

(MRL=0.002 mg/L)

+ Nitrite

(NO2)

(MRL=0.001 mg/L)

= 

if ≥0.005 and ≥0.002 then if ≥0.005 and <0.002 then if <0.005 and ≥0.005 and ≥0.001 then if <0.005 and ≥0.005 and <0.001 then if <0.005 and <0.002 and <0.001 then if <0.005 and <0.002 and 0.001≤NO2<0.005 then if <0.005 and 0.002≤ammonia<0.005 and 0.001≤NO2<0.005 then if <0.005 and 0.002≤ammonia<0.005 and <0.001 then 

1Procedure applies when total ammonia plus organic nitrogen concentration is reported as ≤0.10 only, not when the data are reported as an actual value between th

inflow data fall under this rule.
14 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

total phosphorus, and dissolved orthophosphate by 

using 1995–99 (calendar year) data from the Upper 

Colorado River Basin (UCOL) National Water-Quality 

Assessment (NAWQA) Program and the USGS 

computer program load_est2 (Charles Crawford, 

U.S. Geological Survey, written commun., 2000). 

Instantaneous sample data and daily streamflow data 

were used to estimate annual and monthly nutrient 

loads, reported as mean load in kilograms per day. 

Because concentrations for some of the nutrients were 

less than the reporting limit, rating-curve parameters 

were estimated by the linear attribution method 

(Chatterjee and McLeash, 1986). Loads could not be 

estimated for other sites due to lack of data for nutrient 

concentrations or streamflow, or both. For example, 

while nutrient data were available for Cebolla Creek, 

sufficient streamflow data were not available for use in 

load calculations. Data collected as part of this study 

were not extensive enough for load determination. 

Estimates of load calculations using these data would 

be subject to large uncertainty.

Water-Quality Standards

Water-quality standards for temperature, 

dissolved oxygen, pH, un-ionized ammonia, nitrite, 

and nitrate have been established by the State of 

Colorado for Blue Mesa, Morrow Point, and Crystal 

Reservoirs and their tributaries (Colorado Department 

of Public Health and Environment, 2001). The numeric 

standards are used to determine the allowable concentrations of various parameters in water and are based on 

a stream-designated use classification for aquatic life, 

recreation, drinking water, and agriculture. Use classifications for the reservoirs and tributaries are listed in 

table 5. For the Gunnison River Basin, the temperature 

standard is a 3°C temperature increase above ambient 

water temperature, taking into account normal diurnal 

and seasonal fluctuations. Standards for dissolved 

oxygen, pH, un-ionized ammonia (chronic), nitrite, 

and nitrate are listed in table 6 (Colorado Department 

of Public Health and Environment, 2001). For reservoirs, the dissolved-oxygen standard only applies to 

the epilimnion and metalimnion strata; the hypolimnion stratum is exempt. Standards for phosphorus 

have not been established by the State of Colorado. 

To control eutrophication in lakes and reservoirs, 

the USEPA has established a recommended concentration limit of 0.05 mg/L for total phosphorus in 

rivers or streams that drain into lakes and reservoirs 

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

New nutrient criteria based on ecoregions and type 

of receiving water are currently being developed 

on a regional scale (U.S. Environmental Protection 

Agency, 1998).

Table 5. Stream classification for reservoir and stream inflow sample-collection sites, Curecanti National Recreation Area

[no., number; UGR, Upper Gunnison River; LGR, Lower Gunnison River; data from Colorado Department of Public Health and Environment, 2001]

Stream segment Basin Segment no. Classification

Gunnison River above Blue Mesa Reservoir inlet

Blue Mesa, Morrow Point, and Crystal Reservoirs

Lake Fork of the Gunnison River

UGR

UGR

UGR

14

25

29

Aquatic life—Cold water, Class 11

Recreation—Class 1a2

Water supply3

Agriculture4

Beaver, Steuben, East Elk, Red, West Elk, Soap, South Willow, 

Cebolla, Pine, Blue, Corral, Curecanti, Mesa, and Crystal 

Creeks; Cimarron River

UGR 26 Aquatic life—Cold water, Class 11

Recreation—Class 25

Water supply3

Agriculture4

Main stem of Gunnison River from outlet of Crystal Reservoir LGR 1 Aquatic life—Cold water, Class 11

Recreation—Class 1a2

Water supply3

Agriculture4

1Aquatic life—Cold water, Class 1: Waters that support a wide variety of cold-water biota. 2

Recreation—Class 1a: Waters where primary contact recreational uses have been documented or are presumed to be present. 3Water supply: Water suitable for water supply.

4Agriculture: Waters suitable for agriculture.

5Recreation—Class 2: Waters where primary contact recreation does not exist and cannot be reasonably expected to exist in the future.
DATA COLLECTION AND ANALYSIS PROCEDURES 15

Phytoplankton and Chlorophyll-a Analysis

Phytoplankton samples were collected using a 

6-inch-diameter conical plankton tow net with a mesh 

size of 153 μm and a sample vial of 50 mL. The net 

was lowered vertically into the water to a depth of 

15 m and rapidly raised to the surface. The 50-mL 

vial was removed from the net and the contents poured 

into a 125-mL sample bottle containing 1 mL of 

Lugol’s solution as a preservative. The sample vial 

was returned to the tow net, and the net was rinsed to 

capture any remaining phytoplankton to the sample 

vial. Again, the 50-mL sample vial was emptied into 

the sample bottle, making a total sample volume of 

100 mL. The samples were stored on ice in the field 

and refrigerated in the dark in the laboratory until 

enumeration and identification.

The phytoplankton samples were analyzed 

by the NPS for taxa presence, abundance, and 

density. Taxa identification was to the genus level. 

Phytoplankton density for each sample was determined using a compound microscope with a 

micrometer disk placed in the eyepiece of the 

10X planachromatic objective and a 1-mL SedgewickRafter (S-R) counting cell. One milliliter of the sample 

was removed from the agitated sample bottle and 

placed into the S-R counting cell. The total number of 

phytoplankton was counted across a strip the length of 

the S-R cell, with three strips counted per sample. For 

samples that were dense (more than 10 phytoplankton 

units per field), the number of phytoplankton in 10 

or more random fields was counted. Each field constituted 1-μm grid. Phytoplankton were counted in 

terms of “algal units.” A filament of multicellular 

phytoplankton was counted as one unit, similar to a 

unicellular phytoplankton. Results for phytoplankton 

counts are discussed in terms of algal units per liter 

(algal units/L).

Chlorophyll-a, the primary photosynthetic 

pigment in algae, is used during photosynthesis to 

convert light energy into the creation of new organic 

matter (Wetzel, 1983). As such, chlorophyll-a concentrations can be used as indicators of primary productivity and trophic status. Chlorophyll-a concentrations 

were determined for the 0–5-m depth interval for 

each reservoir site and sampling event. Chlorophyll-a

samples were collected using a 5-m PVC pipe. The 

pipe was inserted vertically into the water up to the 

5-m mark, and a cord was pulled to stopper the pipe 

end. The collected water was poured in a rinsed 

5-gal bucket, and a 1-L composited subsample was 

collected and stored in the dark on ice in the field. 

The chlorophyll-a samples were analyzed by standard 

method 10200H.2, spectrophotometric determination 

of chlorophyll (American Public Health Association, 

American Water Works Association, and Water 

Pollution Control Federation, 1999).

Reservoir Classification Schemes

 An index developed by Likens (1975) uses 

chlorophyll-a concentrations of phytoplankton to 

determine the trophic level of a lake or reservoir. 

According to Likens (1975), chlorophyll-a concentrations of 0–3 mg/m3

 indicate oligotrophic conditions, 

2–15 mg/m3 constitute mesotrophic conditions, and 

10–500 mg/m3 are associated with eutrophic conditions. Oligotrophic lakes or reservoirs have very low 

nitrogen and phosphorus concentrations and limited 

productivity. Mesotrophic reservoirs have moderate 

concentrations of nitrogen and phosphorus and significant productivity, and eutrophic reservoirs are characterized by high levels of nutrients and organic matter 

and are highly productive for plant growth (North 

American Lake Management Society, 2000).

Another system to classify lakes and reservoirs 

was developed by Carlson (1977). A numeric trophicstate index (TSI) is calculated from Secchi-disc transparency, chlorophyll-a concentrations, or total phosphorus concentrations, using a distinct formula for 

each parameter. The TSI is on a scale of 0 to 100, and 

each major division (10, 20, 30, and so forth) represents a doubling of surface algal biomass (Carlson, 

Table 6. Water-quality standards for stream segments in the 

Gunnison River Basin

[Water-quality standards are from Colorado Department of Public Health 

and Environment, 2001, except for total phosphorus recommendation, 

which is from the U.S. Environmental Protection Agency, 1986; mg/L, 

milligrams per liter]

Water-quality parameters Water-quality standard

Dissolved oxygen 6.0 mg/L

pH 6.5–9.0 standard units

Un-ionized ammonia (chronic) 0.02 mg/L

Nitrite 0.05 mg/L

Nitrate 10 mg/L

Phosphorus, total 10.05 mg/L

1

Recommended concentration limit in rivers and streams that drain 

into lakes and reservoirs.
16 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

1977). The TSI numbers generated from the formulas 

are only an index of the trophic state of a lake or reservoir, not a definition of the trophic state. An index 

can be used in lake or reservoir management. For 

example, the biological conditions of a water body 

can be estimated using different scenarios of total 

phosphorus concentrations. For the classification 

system, Carlson (1977) suggests that priority be 

given to biological parameters, especially the 

chlorophyll-a index in summer, and possibly the 

phosphorus index for times of the year when phosphorus is not the limiting nutrient. In developing the 

chlorophyll-a index, Carlson (1977) used a fluorometric method to determine chlorophyll-a concentrations. Chlorophyll-a concentrations derived from the 

fluorometric method are higher than concentrations 

derived from spectrophotometric methods, such 

as were used in this study. The index values for 

chlorophyll-a in this study are, thus, lower than they 

would be if the fluorometric method had been used. 

Chlorophyll-a indices for Blue Mesa, Morrow Point, 

and Crystal Reservoirs will only be used to compare 

among the three reservoirs. These indices should not 

be used to compare with other reservoirs or in cases 

where the chlorophyll-a analysis method has changed 

over time. Historical chlorophyll-a values cited in this 

report for Blue Mesa Reservoir also were determined 

from spectrophotometric methods.

Trend and Correlation Analysis

Water-chemistry, nutrient, and(or) 

chlorophyll-a data for Iola and Sapinero Basins 

in Blue Mesa Reservoir, Gunnison River at County 

Road 32, and Lake Fork of the Gunnison River 

were tested for temporal trends to determine if 

water quality in the reservoir and the inflows has 

changed over time; these were the only sites in this 

study with extensive historical nutrient data and 

streamflow measurements (inflow streams only) 

that could be used in trends testing. The amount 

of inflow to Blue Mesa Reservoir also was tested 

for temporal trends. For each site, table 7 lists the 

constituents used in the seasonal Kendall test for 

trends, time period of test, source of data, and 

number of seasons used in test.

In the seasonal Kendall test, variations in 

constituent data due to seasonality were accounted 

for by comparing data for the same periods or 

“seasons” (Helsel and Hirsch, 1992). For example, 

dissolved-oxygen concentrations for May of one 

year were compared only with May dissolved-oxygen 

concentrations of other years. The seasonal Kendall 

test for trends determines whether the seasonal Kendall 

tau value, which measures the strength of the monotonic 

relationship between time and some other variable, is 

significantly different from zero at a p-value (significance level) of 0.05. As tau deviates more from zero, 

with zero meaning no trend, the greater is the likelihood 

of a trend. For those sites with trends testing on May 

through September data only that had more than one 

data value for the month, the median value for the 

month was used in the trend test. Because data for 

Iola Basin was available for a period longer than 

10 years, the p-value was corrected for serial correlation. Nutrient concentrations for Gunnison River at 

County Road 32 and Lake Fork of the Gunnison 

River were adjusted for streamflow prior to trend 

testing, as were specific-conductance values for the 

Gunnison River at County Road 32. Trend testing for 

this latter site was divided into two time periods based 

on source of data: 1995–99 for nutrient and streamflow 

data from the UCOL study and from this study, and 

1987–94 for nutrient data from the NPS (site is named 

Gunnison River at Riverway by NPS). Streamflow data 

for the 1987–94 time period were from USGS gaging 

stations Gunnison River near Gunnison (station 

number 09114500) and Tomichi Creek at Gunnison 

(09119000) (http://water.usgs.gov/co/nwis accessed 

December 1, 2001). Daily streamflow data were not 

available for Gunnison River at County Road 32 for 

1987–94, but streamflow at this site is the combined 

flow of the Gunnison River near Gunnison and Tomichi 

Creek. Nutrient data for Lake Fork of the Gunnison 

River were for 1995–99. Streamflow data for this 

site were from USGS gaging station Lake Fork at 

Gateview (09124500) (http://water.usgs.gov/co/nwis 

accessed December 1, 2001). Trend-analysis results are 

presented in the section titled “Retrospective of Nutrient 

Conditions in Blue Mesa Reservoir.”

Care must be used in interpreting trend results. 

A trend that may be statistically significant may not be 

important environmentally in cases when the trend is 

small or the concentrations are very low. Also, trend 

results depend on the period of record and may differ 

for different time periods.

Correlation analyses using the rank Kendall 

correlation coefficient (Kendall’s tau) were undertaken to test for relationships between reservoir
DATA COLLECTION AND ANALYSIS PROCEDURES 17

Table 7. Information used in seasonal Kendall test for temporal trends[Periods are in water years (WY), except for Blue Mesa Reservoir inflow, which is in calendar years; site number refers to table 1 and figure 1; BOR, Bureau of ReclamatCURE, U.S. Geological Survey and National Park Service data collection in 1999; UCOL, Upper Colorado River Basin National Water-Quality Assessment Program; NWInformation System; Gunnison River at Riverway is NPS name for Gunnison River at County Road 32]

Constituent or property Time period (in WY) Source of data 

BLUE MESA RESERVOIR

Inflow amount 1984–99 BOR 

BLUE MESA RESERVOIR AT IOLA (SITE BM1) AND SAPINERO

(SITE BM3) BASINS

pH, specific conductance, Secchi depth, 

total ammonia plus organic nitrogen, total phosphorus, chlorophyll-a

Iola Basin: May through September 1984–99 (pH, Secchi 

depth, specific conductance, chlorophyll-a), May through September 1987–99 (total ammonia plus organic nitrogen, 

total phosphorus)

Sapinero Basin: May through September 1992–99

NPS, CURE 

GUNNISON RIVER AT COUNTY ROAD 32 BELOW GUNNISON

(SITE BI1)

Specific conductance, total ammonia plus 

organic nitrogen, dissolved inorganic nitrogen, total phosphorus, dissolved orthophosphate

1995–99 UCOL, CURE 

Specific conductance, total ammonia plus 

organic nitrogen, total phosphorus

May through September 1987–94 NPS—water quality (Gunnison R

NWIS—streamflow

LAKE FORK OF THE GUNNISON RIVER BELOW GATEVIEW

(SITE BI10)

Total ammonia plus organic nitrogen, 

total phosphorus

1995–99 NPS—water quality

NWIS—streamflow
18 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

parameters (including pH and chlorophyll-a

concentrations, and chlorophyll-a concentrations 

and phytoplankton density) and between total phosphorus and chlorophyll-a concentrations in an inflow 

and reservoir, respectively. As such, the correlation 

analyses were used as an additional tool for understanding reservoir dynamics. Values of pH in a reservoir, for example, vary because of chemical and 

biological factors, especially carbon dioxide in the 

water column. Correlation analyses using pH and 

chlorophyll-a concentrations (as a proxy for carbon 

dioxide use) were done to see if changes in pH were 

related to chlorophyll-a concentrations and, hence, 

carbon dioxide use. Two parameters were correlated 

when the rank Kendall correlation coefficient was 

significantly different from zero at a p-value of 0.05. 

A value of zero indicated that there was no relationship between the two parameters. When two or more 

values of a parameter were available in a month, the 

median value was used in the correlation analysis. 

Flow-adjusted concentrations were used in correlation 

analyses involving specific conductance or nutrients in 

stream inflows.

QUALITY-CONTROL METHODS 

AND ANALYSIS

Quality-control (QC) samples were used 

to assess the variability and bias of water-quality 

data that may be introduced by sample collection, 

processing, storage, and analysis. Replicate and 

field-blank samples were collected and processed 

as QC samples using the same equipment and procedures as the regular or environmental samples in 

order to evaluate the variability and bias of the waterquality data. Replicate and field-blank samples were 

collected for nutrient analysis. Replicate samples 

only were collected for suspended-sediment and 

phytoplankton analyses. Additional information 

on QC procedures and samples is given in Shelton 

(1994).

Replicate samples were used to test for variability, which is the degree of random error in independent measurements of the same quantity (Spahr 

and Boulger, 1997). Replicate samples were collected 

in sequence at a site to yield samples of nearly identical composition. By comparing the analytical results 

of the first sample (environmental sample) with the 

second sample (quality-control sample), the replicates 

provide information on the precision of the concentration values and the consistency in identifying 

the parameter of interest. Replicate samples were 

analyzed by determining the absolute difference 

between the environmental sample and the qualitycontrol sample.

For the nutrient sampling, 63 nutrient replicate 

pairs were studied: 8 different pairs for all nutrients 

except nitrate plus nitrite (7 replicate pairs), with a 

replicate pair consisting of the environmental sample 

and the subsequent quality-control sample. Four replicate pairs each were collected at reservoir and inflow 

sites. The absolute difference was determined for each 

nutrient replicate pair and is listed in table 8 by site 

type. Forty-three percent (27 of 63) of the nutrient 

replicate pairs had no absolute difference; the environmental sample and the quality-control sample had the 

same concentration. For the remaining replicate pairs, 

the absolute differences were low. Excluding the 

ammonia plus organic nitrogen constituents with 

higher reporting levels, only one nitrate plus nitrite 

replicate pair (reservoir site) and one total phosphorus 

replicate pair (inflow site) had absolute differences 

greater than 0.005 mg/L. Concentrations for both 

replicate pairs were elevated, as compared to most 

other replicate pairs. The two absolute differences 

above 0.005 mg/L were not unexpected given the 

random nature of independent measurements and 

the elevated concentrations. Relative percent differences for these two replicate pairs were small, 10 

and 5 percent, respectively. The median absolute 

differences for all nutrients were of the same order 

of magnitude as the reporting level; the median variabilities were very low (table 9). Because inflow 

sites in this study were sampled using procedures 

of the NAWQA Program, sampling variability and 

95-percent confidence intervals could be calculated 

for the inflow sites using NAWQA quality-control 

data (Mueller, 1998). Table 10 lists the procedures 

and results for calculating sampling variability 

and 95-percent confidence intervals for individual 

measurements and mean concentrations. An example 

interpretation is as follows: The critical value for 

total phosphorus is 0.05 mg/L, the recommended 

concentration limit in rivers or streams that drain 

into lakes and reservoirs for control of eutrophication 

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

concentration, the estimated sampling variability is 

0.006 mg/L, and the 95-percent confidence interval 

range is 0.038–0.062 mg/L (table 10). As such, the
QUALITY-CONTROL METHODS AND ANALYSIS 19

Table 8. Concentrations and absolute differences of nutrients in replicate samples

[mg/L, milligrams per liter; <, concentration less than the laboratory reporting level; E, estimated]

Concentration

in replicates

(mg/L)

Absolute

difference

Concentration

in replicates

(mg/L)

Absolute

difference

Concentration

in replicates

(mg/L)

Absolute

difference

Concentration

in replicates

(mg/L)

Absolute

difference

RESERVOIR SITES

Ammonia, dissolved

0.005

0.004 0.001 0.0020.007 0.005 <0.002<0.002 0.000 <0.002<0.002 0.000

Nitrite, dissolved

0.001

<0.001

1

0.001 <0.001

0.001

10.001 0.001

0.001 0.000 <0.001<0.001 0.000

Nitrate plus nitrite, dissolved

20.07

2

0.08

2

0.01 0.073

0.066 0.007 <0.005<0.005 0.000 0.0310.030 0.001

Ammonia plus organic nitrogen, dissolved

0.1

0.1 0.0 0.20.2 0.0 0.10.2 0.1 0.20.2 0.0

Ammonia plus organic nitrogen, total

0.1

0.2 0.1 0.30.2 0.1 0.10.2 0.1 0.10.1 0.0

Orthophosphate, dissolved

0.004

0.003 0.001 0.0280.028 0.000 0.0060.006 0.000 0.0070.008 0.001

Phosphorus, dissolved

<0.004

<0.004 0.000 0.0310.033 0.002 0.0080.009 0.001 0.0130.013 0.000

Phosphorus, total

0.011

0.011 0.000 0.0410.040 0.001 0.0110.012 0.001 0.0200.019 0.001

INFLOW SITES

Ammonia, dissolved

0.010

0.010 0.000 0.0100.013 0.003 <0.0020.005

1

0.005 0.005

<0.002

1

0.005

Nitrite, dissolved

0.002

0.002 0.000 0.0010.002 0.001 <0.0010.001

1

0.001 0.001

0.001 0.000

Nitrate plus nitrite, dissolved

0.030

0.028 0.002 <0.005<0.005 0.000 <0.005<0.005 0.000 0.1400.140 0.000

Ammonia plus organic nitrogen, dissolved

0.3

0.3 0.0 0.20.2 0.0 0.10.1 0.0 E 0.05E 0.07 0.02

Ammonia plus organic nitrogen, total

0.6

0.5 0.1 0.30.3 0.0 0.10.1 0.0 0.10.1 0.0

Orthophosphate, dissolved

0.036

0.036 0.000 0.0610.062 0.001 0.0330.037 0.004 0.0350.036 0.001

Phosphorus, dissolved

0.043

0.044 0.001 0.0680.070 0.002 0.0440.043 0.001 0.0470.049 0.002

Phosphorus, total

0.169

0.178 0.009 0.0950.096 0.001 0.0580.057 0.001 0.0690.072 0.003

1

Zero was substituted for the “less than” value to yield the maximum difference that could have occurred. 2Environmental and quality-control samples were analyzed to two significant figures and not three significant figures, as for low-level nutrients. 

Thus, this replicate pair is not included in the discussion of replicate results.
20 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

potential error in the 0.05-mg/L measurement due to 

sampling variability is ±0.012 mg/L or a relative error 

of ±24 percent. The higher sampling variabilities for 

ammonia plus organic nitrogen and total phosphorus 

being greater than dissolved phosphorus, which is 

greater than orthophosphate, may be due to differences 

in analytical methods and difficulties in obtaining 

representative laboratory subsamples from the unfiltered (total) field samples (Mueller, 1998).

These procedures for estimating sampling variability and 95-percent confidence intervals also could 

be done for other individual nutrient measurements or 

for comparing mean nutrient concentrations among 

inflow sites. For the Curecanti NRA reservoir sites, a 

large quality-control data set similar to the NAWQA 

stream quality-control data was not available, and 

sampling variability and 95-percent confidence intervals for reservoir nutrient concentrations could not be 

calculated.

Field-blank samples were used to test for bias, 

defined as the systematic error inherent in sampling 

and analytical methods (Spahr and Boulger, 1997). 

Blank samples were inorganic-free water that contained 

no detectable concentrations of the nutrients of interest. 

The blank water was processed through the sampling 

equipment and handled and analyzed in the same 

manner as the environmental samples. Because nutrients in this study were analyzed to low concentrations 

in the laboratory, field blanks were useful in determining possible contamination of a sample from 

collection, processing, cleaning, storage, and analysis 

procedures.

Table 9. Range of absolute differences in replicate samples for individual nutrients

[mg/L, milligrams per liter]

Nutrient

Minimum absolute

difference

(mg/L)

Median absolute

difference

(mg/L)

Maximum absolute

difference

(mg/L)

Reporting level

(mg/L)

RESERVOIR SITES

Ammonia, dissolved 0.000 10.001 0.005 0.002

Nitrite, dissolved 0.000 10.001 0.001 0.001

Nitrate plus nitrite, dissolved 0.000 0.001 0.007 0.005

Ammonia plus organic nitrogen, dissolved 0.0 0.0 0.1 0.1

Ammonia plus organic nitrogen, total 0.0 0.1 0.1 0.1

Orthophosphate, dissolved 0.000 10.001 0.001 0.001

Phosphorus, dissolved 0.000 10.001 0.002 20.004

30.006

Phosphorus, total 0.000 0.001 0.001 20.004

30.008

INFLOW SITES

Ammonia, dissolved 0.000 0.004 0.005 0.002

Nitrite, dissolved 0.000 10.001 0.001 0.001

Nitrate plus nitrite, dissolved 0.000 0.000 0.002 0.005

Ammonia plus organic nitrogen, dissolved 0.0 0.0 0.02 0.1

Ammonia plus organic nitrogen, total 0.0 0.0 0.1 0.1

Orthophosphate, dissolved 0.000 0.001 0.004 0.001

Phosphorus, dissolved 0.001 10.002 0.002 20.004

30.006

Phosphorus, total 0.001 0.002 0.009 20.004

30.008

1Rounded concentration.

2

Reporting level for samples analyzed before October 1, 1999.

3Reporting level for samples analyzed after September 30, 1999.
QUALITY-CONTROL METHODS AND ANALYSIS 21

Table 10. Estimated sampling variability and confidence intervals around measured nutrient concentrations at selected maximum or crit

concentrations for interpretation of environmental data for Curecanti National Recreation Area stream inflow sites

[Table modified from Mueller (1998); equations from Mueller (1998); mg/L, milligrams per liter]

Constituent

Maximum or

critical value

(mg/L)

Mean

concentration

(mg/L)

Estimated

sampling

variability1

(mg/L)

Estimated parameter values for

determining sampling variability2

95-perce

B1 B2 B3 For the max

or critical v

Ammonia, dissolved 50.031 0.005 0.004 0.003889 1.302 3.151 0.023–0Nitrate plus nitrite, dissolved 50.17 0.025 0.009 0.008629 2.462 3.020 0.15–0Ammonia plus organic nitrogen, dissolved 50.5 0.145 0.034 0.03346 0.9141 3.769 0.434–0Ammonia plus organic nitrogen, total 50.6 0.189 0.060, 0.011 0.007993 1.633 0.7950 0.483–0Orthophosphate, dissolved 60.05 0.036 0.003, 0.002 0.002076 4.503 0.1549 0.045–0Phosphorus, dissolved 70.05 0.042 0.005 0.004816 2.949 0.6719 0.041–0Phosphorus, total 60.05 0.069 0.006, 0.007 0.005855 3.133 0.2846 0.038–0

1ESV=B1+e(–B2–B3/C). C is maximum or critical value or mean concentration; e is the base of natural logarithms. Results are rounded. When two numbers are liste

is sampling variability for maximum or critical value, and the second number is sampling variability for mean concentration. 2From Mueller (1998).

3CI=C±1.96(ESV). 4CI=C±1.96(ESV/SQRT(77)). (There were a total of 77 inflow measurements.) 5Maximum detected concentration. These values are used because detected concentrations were much lower than water-quality standards (un-ionized ammonia and 

have not been established (ammonia plus organic nitrogen). Values are used here for comparison to other nutrients. 6Critical value recommended to avoid eutrophication (U.S. Environmental Protection Agency, 1986). 7No critical value has been identified. Value used here is for comparison to other nutrients.
22 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

Nine field-blank samples were collected in 

this study. Analytical results are listed in table 11 in 

order of date of collection for reservoir sites, followed 

by inflow sites. The shaded cell represents the one 

ammonia concentration that was greater than twice the 

laboratory reporting level. Concentrations of dissolved 

and total ammonia plus organic nitrogen and dissolved 

and total phosphorus were not detected in the nine 

field-blank samples. Most sites sampled just prior 

to the blank processing had these nutrients detected 

above the respective reporting levels. Therefore, 

the potential for contamination of samples with 

dissolved and total ammonia plus organic nitrogen 

and dissolved and total phosphorus during sample 

collection, processing, cleaning, shipping, and analysis 

procedures was minimal. Ammonia, nitrite, nitrate 

plus nitrite, and orthophosphate were each detected 

in low concentrations in some field-blank samples 

for reservoir and inflow sites (table 11). Blank water 

samples can become contaminated with ammonia 

when exposed to the atmosphere, especially when 

analyzed to low concentrations as was done in this 

study. For some of the blank samples with detections 

of nitrite, the original container of blank water 

contained nitrite at a concentration of 0.001 mg/L, 

the level detected in the field-blank samples. All four 

of the nutrients detected in the field-blank samples 

were detected at very low concentrations, up to a few 

thousandths of a milligram of the respective reporting 

level. These concentrations were within the expected 

instrument or method variance, and no blank corrections were required to be made to the environmental 

data (Gary Cottrell, U.S. Geological Survey, oral 

commun., 2000).

Four replicate pairs were studied for suspendedsediment analysis. Concentrations for the environmental and quality-control samples, respectively, were 

133, 155 mg/L; 6, 6 mg/L; 3, 2 mg/L, and 9, 9 mg/L. 

As such, the absolute difference was low or nonexistent at low concentrations and greater at higher 

concentrations. Most (75 percent) suspended-sediment 

concentrations for the tributaries to the three reservoirs 

were equal to or below 10 mg/L. Based on the replicate data, no adjustments to the suspended-sediment 

concentrations were needed.

For the phytoplankton data, two replicate pairs 

were available for analysis. For some phytoplankton 

genera, higher counts of algal units per liter displayed 

less precision between environmental and qualitycontrol samples, respectively: Asterionella sp., 433, 

158 algal units/L; Tabellaria sp., 108, 53 algal units/L; 

and Melosira sp., 252, 129 algal units/L. For replicate 

pairs with low (less than 5) counts of algal units per 

liter, there was less consistency in the presence or

Table 11. Concentrations of nutrients in blank samples

[Shaded cell represents concentration greater than twice the laboratory reporting level; mg/L, milligrams per liter; <, concentration less than the laboratory 

reporting level; E, estimated]

Ammonia,

dissolved

(mg/L)

Nitrite,

dissolved

(mg/L)

Nitrate

plus nitrite,

dissolved

(mg/L)

Ammonia

plus organic

nitrogen,

dissolved

(mg/L)

Ammonia

plus organic

nitrogen,

total

(mg/L)

Orthophosphate,

dissolved

(mg/L)

Phosphorus,

dissolved

(mg/L)

Phosphorus,

total

(mg/L)

RESERVOIR SITES

<0.002 0.001 1<0.05 <0.1 <0.1 0.001 <0.004 <0.004

0.004 0.001 <0.005 <0.1 E 0.07 <0.001 <0.004 <0.004

0.004 0.001 <0.005 <0.1 <0.1 0.002 <0.006 <0.008

<0.002 <0.001 0.008 <0.1 <0.1 <0.001 <0.006 <0.008

0.002 <0.001 <0.005 <0.1 <0.1 <0.001 <0.006 <0.008

INFLOW SITES

0.005 <0.001 0.008 <0.1 <0.1 0.001 <0.004 <0.004

<0.002 0.001 <0.005 <0.1 <0.1 0.001 <0.004 <0.004

0.003 0.001 <0.005 <0.1 <0.1 0.002 <0.006 <0.008

0.002 <0.001 0.008 <0.1 <0.1 <0.001 <0.006 <0.008

1

Sample was analyzed to two significant figures and not three significant figures, as for low-level nutrients. 
LIMNOLOGY OF BLUE MESA RESERVOIR 23

absence of phytoplankton genera. Phytoplankton that 

were present in only one sample of these replicate pairs 

included Dinobryon sp., Stephanodiscus sp., Navicula

sp., Ceratium sp., Synedra sp., Chlamydomonas sp., 

Pandorina sp., and Staurastrom sp. Phytoplankton typically have a horizontal and vertical spatial distribution 

that is uneven. Uneven distribution can be caused by 

such factors as rapid reproduction, unequal grazing 

by zooplankton, and algal movement (Horne and 

Goldman, 1994). The uneven nature of phytoplankton 

distribution should be considered when interpreting 

the phytoplankton data presented in this report.

LIMNOLOGY OF BLUE MESA RESERVOIR

Reservoir data discussed in this section are listed 

in tables 22–28 of the “Supplemental Data” section at 

the back of this report. Please note that profile measurements in Sapinero Basin did not extend to the bottom of 

the water column in August and October due to inadequate cable length on the Hydrolab water-quality probe.

Physical Properties

Water temperature in Blue Mesa Reservoir 

ranged from 19.3°C at 1 m below the water surface 

to 4.2°C at depth (fig. 4A, tables 22–24). Temperatures 

throughout the water column were coldest during April 

and warmest during August. Water temperatures at the 

1-m depth reflected a downstream gradient pattern, 

as Iola Basin was warmer than Cebolla and Sapinero 

Basins during spring and summer and cooler during 

early winter. Isothermal or mixing conditions were 

present in each basin during spring and early winter and 

also in Iola Basin during fall. Each basin was thermally 

stratified during summer, with stratification continuing 

in Cebolla and Sapinero Basins during fall (fig. 4A). 

Three distinct temperature zones were present in Blue 

Mesa Reservoir: the epilimnion (upper stratum of 

uniformly warm water), metalimnion (thermocline or 

stratum with the greatest rate of temperature decrease 

with depth), and the hypolimnion (deep stratum of 

uniformly cold water). In Cebolla and Sapinero Basins, 

the epilimnion was deeper during fall than summer 

because of cooling and some circulation.

Dissolved-oxygen concentrations in each basin 

were highest (9.2–10.0 mg/L) during April when the 

reservoir was coolest, reflecting the inverse relationship between water temperature and dissolved-oxygen 

concentrations (fig. 4A, tables 22–24). The minimum 

concentrations of 1.5 and 3.6 mg/L occurred at depth 

in Cebolla and Sapinero Basins, respectively, during 

October and November. Although dissolved-oxygen 

concentrations were very low, anoxic conditions 

(dissolved-oxygen concentrations around 0.0 mg/L) 

were not present. Uniform dissolved-oxygen concentrations with depth tended to occur with isothermal 

conditions, whereas concentrations generally 

decreased with depth or were more variable during 

stratification. During summer and fall, dissolvedoxygen concentrations in Cebolla and Sapinero Basins 

were at a minimum in the metalimnion. Dissolvedoxygen concentrations in the epilimnion of each basin 

were above the Colorado water-quality standard of 

6.0 mg/L (table 6), except for one instance in Sapinero 

Basin during fall. Concentrations in the metalimnion 

primarily were below the standard, especially in 

Cebolla and Sapinero Basins during fall with concentrations near 4.0 mg/L or lower (fig. 4A). Although 

below the standard, these values are not uncommon 

for deeper strata in lakes and reservoirs.

In Blue Mesa Reservoir, pH ranged from 7.0 to 

8.4 standard units (fig. 4B, tables 22–24). Seasonally, 

pH in near-surface (0–10 m) waters of the reservoir was 

lowest during early winter and higher at other times of 

the year. The water-column distribution of pH reflected 

thermally stratified or unstratified conditions in the 

reservoir. During isothermal conditions, pH values were 

nearly uniform throughout much of the water column. 

With stratification, pH was fairly uniform in the epilimnion and hypolimnion of each basin and varied in the 

metalimnion (fig. 4B). All pH values were well within 

the Colorado water-quality standard (table 6). For each 

site in Blue Mesa Reservoir, there was no correlation 

between pH values and chlorophyll-a concentrations, as 

measured by the rank Kendall correlation coefficient at 

a significance level of p≤0.05. 

Specific conductance in Blue Mesa Reservoir 

varied from 137 to 228 μS/cm (fig. 4B, tables 22–24). 

These values would indicate dissolved-solids concentrations of 82–137 mg/L, using a conversion factor of 0.6 

for the moderately mineralized water (Hem, 1985). At 

the 1-m depth, specific conductance decreased in a 

downstream direction, with the highest values in Iola 

Basin and the lowest in Sapinero Basin. For each basin, 

specific conductance was at a maximum during spring. 

Specific-conductance values generally were consistent 

throughout the water column in each basin when 

isothermal conditions were present. With stratification,
24 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

80

70

60

50

40

30

20

10

0

DEPTH, IN METERS

TEMPERATURE, IN DEGREES CELSIUS

DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER

April 20, 1999 August 19, 1999 October 6, 1999 November 30, 1999

April 20, 1999 August 19, 1999 October 6, 1999 November 30, 1999

80 0 5 10

5 10 15 0 5 10 0 5 10 0 5 10

0 5 10 15 0 5 10 1 5 10 15 20 5

70

60

50

40

30

20

10

0

DEPTH, IN METERS

Iola Basin (site BM1) Cebolla Basin (site BM2) Sapinero Basin (site BM3)

EXPLANATION

A

Figure 4. Depth profiles of (A) water temperature and dissolved oxygen, and (B) pH and specific 

conductance, Blue Mesa Reservoir, April–November 1999.
LIMNOLOGY OF BLUE MESA RESERVOIR 25

175 200 225 250 125 150 175 200 225 150 175 200 225 175 200 225

October 6, 1999 November 30, 1999

pH, IN STANDARD UNITS

April 20, 1999

80

70

60

50

40

30

20

10

0

7 8 97 8 9 7 6 89 7 6 89

DEPTH, IN METERS

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER 

AT 25 DEGREES CELSIUS

lola Basin (site BM1) Cebolla Basin (site BM2) Sapinero Basin (site BM3)

80

70

60

50

40

30

20

10

0

DEPTH, IN METERS

April 20, 1999 October 6, 1999 August 19, 1999

August 19, 1999

November 30, 1999

EXPLANATION

B

Figure 4. Depth profiles of (A) water temperature and dissolved oxygen, and (B) pH and specific 

conductance, Blue Mesa Reservoir, April–November 1999—Continued.
26 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

though, specific conductance in Cebolla and Sapinero 

Basins was more variable. During August, specific 

conductance in Cebolla Basin was highest in the metalimnion, whereas conductance in Sapinero Basin was 

lowest in the upper two-thirds of the metalimnion and 

then increased in the lower one-third of the metalimnion 

and hypolimnion to values near those in the epilimnion. 

The low specific conductance in Sapinero Basin may 

have been the result of inflow of snowmelt runoff 

moving through the reservoir. Dissolved-solids 

concentrations typically are diluted in snowmelt runoff, 

resulting in lower specific-conductance values. During 

October, conductance in Cebolla and Sapinero Basins 

varied little with depth except for small changes in the 

metalimnion.

Light transparency of the water at the surface 

of Blue Mesa Reservoir varied over the sampling 

period, with the Secchi depth ranging from 3.0 to 

5.0 m (fig. 5, tables 22–24). For each basin, Secchi 

depth was smallest during spring with mixing conditions. Secondary minimum Secchi-depth values

were repeated during fall in Iola Basin because of 

an algal bloom and also in Sapinero Basin. The time 

of maximum Secchi depth varied among the basins. 

Average light transparency (Secchi depth) was lowest 

for Iola Basin (3.6 m) and similar for Cebolla and 

Sapinero Basins, 4.2 and 4.1 m, respectively. Using 

the rule of thumb that the depth of the photic zone is 

3.0 times the Secchi depth (Cole, 1983), the photic zone 

in Blue Mesa Reservoir ranged from 9.0 to 15.0 m.

Nutrients

Concentrations of nitrogen nutrient species in 

Blue Mesa Reservoir were very low throughout the 

study period. Total nitrogen concentrations, calculated 

as the sum of total ammonia plus organic nitrogen 

and dissolved nitrate plus nitrite, ranged from 0.1 to 

0.4 mg/L (fig. 6, table 25). Most total nitrogen was 

in the organic form, which primarily occurs in aquatic 

ecosystems as organic detritus and plant or animal 

nitrogen (Horne and Goldman, 1994). Dissolved 

inorganic nitrogen concentrations, calculated as the 

sum of dissolved ammonia and dissolved nitrate plus 

nitrite, ranged from less than 0.005 to 0.16 mg/L 

(fig. 6, table 25); most was in the nitrate form. Inorganic 

nitrogen concentrations were at a maximum in spring 

near the surface of the photic zone. Summer and fall 

concentrations in the epilimnion were at or below

the reporting level of 0.005 mg/L. During these 

latter times, inorganic nitrogen was essentially fully 

utilized by phytoplankton. Concentrations of dissolved 

inorganic nitrogen in many bottom-water samples were 

higher than the concentrations in the photic zone or 

epilimnion, with some concentrations being greater by 

one or two orders of magnitude (fig. 6). For each basin, 

nitrogen concentrations at depth were highest during 

stratification. These high concentrations may indicate 

the settling of decomposing material from the photic 

zone. Nitrate, nitrite, and un-ionized ammonia concentrations in the reservoir were lower than Colorado 

water-quality standards by at least one or two orders 

of magnitude (table 6). Un-ionized ammonia (NH3) 

concentrations were estimated from the ammonia 

concentrations cited in this report (tables 25, 30, 34, 

37, 39, and 42) using pH, temperature, and an equilibrium constant (U.S. Geological Survey Office of Water 

Quality Technical Memorandum No. 93.12, 1993, URL 

http://water.usgs.gov/admin/memo/QW/qw93.12.html, 

accessed February 7, 2002).

8

6

4

2

0

8

6

4

2

0

lola Basin (site BM1)

1999

8

6

4

2

0

APR JUNE AUG OCT DEC

LIGHT TRANSPARENCY, IN METERS 

BELOW WATER SURFACE

Cebolla Basin (site BM2) 

Sapinero Basin (site BM3)

Secchi depth

EXPLANATION

Figure 5. Light transparency in Blue 

Mesa Reservoir, April–November 1999.
LIMNOLOGY OF BLUE MESA RESERVOIR 27

Concentrations of phosphorus nutrient species 

also were low in Blue Mesa Reservoir throughout 

the study period. Total phosphorus concentrations 

ranged from 0.007 to 0.053 mg/L (fig. 6, table 25). 

Concentrations of dissolved orthophosphate, an 

inorganic phosphorus and the only form of phosphorus available for uptake by phytoplankton, ranged 

from less than the reporting level of 0.001 mg/L to 

0.041 mg/L (fig. 6, table 25). In the upper strata of 

Blue Mesa Reservoir, much of the phosphorus 

was in the organic form and could not be used by 

phytoplankton for growth. Most orthophosphate 

concentrations in the upper strata of the reservoir 

were less than or equal to 0.004 mg/L for the 

entire sampling period, reflecting consumption 

by phytoplankton. This pattern of consistently low 

orthophosphate concentrations throughout the year 

was unlike that for dissolved inorganic nitrogen, 

which had much higher concentrations in spring 

than during summer, fall, and early winter. The orthophosphate that accumulates during winter is usually 

reduced by late spring to levels well below that needed 

by phytoplankton for growth (Horne and Goldman, 

1994). During active cell growth of phytoplankton, 

most of the dissolved inorganic phosphorus that is 

needed for growth is continually recycled back to 

phytoplankton through excretion from fish, zooplankton, and bacterial activity and is in the form of 

soluble phosphate ions (Wetzel, 1983). As with total 

nitrogen and dissolved inorganic nitrogen, the higher 

concentrations of total phosphorus and dissolved 

inorganic phosphorus (orthophosphate) in Blue 

Mesa Reservoir tended to be present in the hypolimnion during stratification (fig. 6), probably resulting 

from the decomposition of organic matter.

N:P ratios were estimated, where possible, 

for each basin in Blue Mesa Reservoir (table 12). 

Dissolved inorganic nitrogen and orthophosphate 

concentrations in near-surface and epilimnion samples 

indicate that phosphorus was the limiting nutrient 

during spring and nitrogen was the limiting nutrient 

during early winter for each basin. Although N:P ratios 

could not be determined for Sapinero Basin during 

summer or for all three basins during fall, nitrogen 

probably was the limiting nutrient. For these instances, 

dissolved inorganic nitrogen concentrations in the nearsurface zone or epilimnion were less than the reporting 

level of 0.005 mg/L, and the corresponding dissolved 

orthophosphate concentrations were greater than or 

equal to the reporting level of 0.001 mg/L. N:P ratios 

could not be determined for Iola and Cebolla Basins 

for summer, as both dissolved inorganic nitrogen and 

orthophosphate concentrations were less than the 

respective reporting levels. For these basins, nitrogen 

and phosphorus were essentially fully utilized by 

biological activity during summer.

Phytoplankton

In Blue Mesa Reservoir, phytoplankton densities 

differed across the sampling period for the three basins. 

Phytoplankton densities were at a minimum in each 

basin during summer when nutrient concentrations were 

low, whereas the time of maximum density differed for 

each basin (fig. 7, table 27). The extreme phytoplankton 

density of 21,930 algal units/L in Iola Basin during 

fall was due almost entirely to the bloom of the bluegreen algae Aphanizomenon sp. This phytoplankton 

and Anabaena sp., another blue-green algae detected 

in Curecanti NRA, are able to convert atmospheric 

nitrogen to ammonia for use as a food source when 

inorganic nitrogen in a lake or reservoir is depleted. The 

inorganic nitrogen concentration in the epilimnion of 

Iola Basin during fall was less than 0.005 mg/L. While 

Aphanizomenon sp. also was dominant or co-dominant 

in Cebolla and Sapinero Basins during fall, the densities 

were much smaller, 707 and 66 algal units/L, respectively. Overall, phytoplankton densities generally were 

highest in Iola Basin and lowest in Sapinero Basin.

Cebolla and Sapinero Basins had mostly similar 

patterns in genera richness (number of genera present) 

as compared to Iola Basin (fig. 8). Genera richness 

in the two downstream basins was greatest during 

October, with the nine genera detected in each basin 

being the most for any site in all three reservoirs. 

Genera richness in Iola Basin was at a minimum during 

fall because of the dominance of the blue-green algae 

Aphanizomenon sp.

The phytoplankton community in Blue Mesa 

Reservoir was dominated by diatoms and blue-green 

algae, with small populations of golden-brown algae, 

green algae, and dinoflagellates present during the 

sampling periods (fig. 9). The major components of 

phytoplankton community succession were mostly 

similar for the three basins (fig. 10). The spring 

phytoplankton community in the reservoir consisted
28 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

primarily of diatoms, with Asterionella being the dominant genus, and smaller populations of golden-brown 

algae. During summer, warmer water temperatures 

and the lack of inorganic nitrogen resulted in the dominance of blue-green algae—Aphanizomenon sp. in 

Iola and Sapinero Basins and Aphanizomenon sp. and 

Anabaena sp. in Cebolla Basin—with diatoms, green 

algae, and a dinoflagellate also present. Aphanizomenon 

sp. was the dominant phytoplankton in Iola Basin 

during fall, almost to the complete exclusion of other 

genera. It also was dominant in Cebolla Basin. 

The phytoplankton community structure in Sapinero 

Basin during fall differed from that in the two upstream 

basins. Aphanizomenon sp. and Tabellaria sp. each 

were about one-third of the population, followed by 

the diatom Fragilaria sp. and the green algae Pandorina

sp. The early winter phytoplankton population in the 

reservoir was dominated by the diatom Melosira sp., 

accounting for least 81 percent of the population in each 

basin, followed by Tabellaria sp.

Apr 20 Aug 19 Oct 6 Nov 30 Apr 20 Aug 19 Oct 6 Nov 30

Apr 20 Aug 19 Oct 6 Nov 30 Apr 20 Aug 19 Oct 6 Nov 30

TOTAL NITROGEN, IN 

MILLIGRAMS PER LITER TOTAL PHOSPHORUS, 

IN MILLIGRAMS PER LITER

DISSOLVED INORGANIC NITROGEN, 

IN MILLIGRAMS PER LITER

DISSOLVED ORTHOPHOSPHATE, 

IN MILLIGRAMS PER LITER

25

50

75

0

DEPTH, IN METERS 25

50

75

0

DEPTH, IN METERS

25

50

75

0

DEPTH, IN METERS

25

50

75

0

DEPTH, IN METERS

0 0.2 0.4 0 0.2 0.4 0 0.2 0.4 0 0.2 0.4 0 0.03 0.06 0 0.03 0.06 0 0.03 0.06 0 0.03 0.06

0 0.2 0 0.2 0.4 0.4 0 0.2 0.4 0 0.2 0.4 0 0.03 0.06 0.06 0 0.03 0 0.03 0.06 0 0.03 0.06

1999

B

Apr 20 Aug 19 Oct 6 Nov 30 Apr 20 Aug 19 Oct 6 Nov 30

Apr 20 Aug 19 Oct 6 Nov 30 Apr 20 Aug 19 Oct 6 Nov 30

TOTAL NITROGEN, IN 

MILLIGRAMS PER LITER

TOTAL PHOSPHORUS, 

IN MILLIGRAMS PER LITER

DISSOLVED INORGANIC NITROGEN, 

IN MILLIGRAMS PER LITER

DISSOLVED ORTHOPHOSPHATE, 

IN MILLIGRAMS PER LITER

25

20

15

10

5

0

DEPTH, IN METERS 25

20

15

10

5

0

DEPTH, IN METERS

25

20

15

10

5

0

DEPTH, IN METERS 25

20

15

10

5

0

DEPTH, IN METERS

0 0.2 0.4 0 0.2 0.4 0 0.2 0.4 0 0.2 0.4 0 0.03 0.06 0 0.03 0.06 0 0.03 0.06 0 0.03 0.06

0 0.2 0.4 0 0.2 0.4 0 0.2 0.4 0 0.2 0.4 0 0.03 0.06 0 0.03 0.06 0 0.03 0.06 0 0.03 0.06

1999

A

EXPLANATION

Concentration greater than 

 or equal to reporting level

Concentration less than 

 reporting level

Figure 6. Nitrogen and phosphorus concentrations in Blue Mesa Reservoir at (A) Iola Basin (site BM1), 

(B) Cebolla Basin (site BM2), and (C) Sapinero Basin (site BM3), April–November 1999.
LIMNOLOGY OF BLUE MESA RESERVOIR 29

Chlorophyll-a

In Blue Mesa Reservoir, chlorophyll-a concentrations ranged from 0.86 mg/m3

 in Cebolla Basin 

to 7.55 mg/m3 in Iola Basin (table 28). The mean 

chlorophyll-a concentration was greatest for Iola Basin 

(4.55 mg/m3), followed by Cebolla Basin (3.93 mg/m3) 

and Sapinero Basin (2.77 mg/m3

). Each basin had 

minimum chlorophyll-a concentrations during August, 

corresponding to the time of lowest phytoplankton 

densities. The time of maximum chlorophyll-a

concentration varied for each basin. In Iola Basin, 

the maximum chlorophyll-a concentration was at 

the same time as maximum phytoplankton density—

both during October when Aphanizomenon sp. was 

blooming; however, there was no statistical correlation. 

Chlorophyll-a concentrations and phytoplankton densities were positively correlated for Cebolla and Sapinero 

Basins, as measured by the rank Kendall correlation 

coefficient at a significance level of p≤0.05. Correlation 

between chlorophyll-a concentration and phytoplankton 

density can differ or be nonexistent, in the case of Iola 

Basin, because the chlorophyll-a content varies among 

algal species and can vary within a single species 

depending on such factors as light intensity or the 

availability of nutrients. Using the mean chlorophyll-a

concentrations listed above and Likens’ (1975) 

chlorophyll-a classification system, Iola and Cebolla 

Basins would be classified as mesotrophic for the 

entire sampling period, and Sapinero Basin would be 

oligotrophic. As a whole, Blue Mesa Reservoir would 

be classified as mesotrophic.

Trophic-state indices (TSI) for total phosphorus, 

chlorophyll-a, and Secchi depth were calculated for 

each basin and sampling event. The total phosphorus 

TSI was highest at times in Iola Basin (34–55) as 

compared to Cebolla (41–51) and Sapinero Basins 

(39–47) (fig. 11, table 28). An upstream to downstream 

gradient also applied to the chlorophyll-a TSI—Iola 

Basin (35–50), Cebolla Basin (29–50), and Sapinero 

Basin (34–45). The Secchi depth TSI was similar 

(37–44) for the three basins. Ideally, TSI values for a 

site should be the same for each index parameter for 

a particular sample. The exception to this in Blue Mesa 

Reservoir occurred in Cebolla Basin in summer, as the 

chlorophyll-a and Secchi depth indices were less than 

the total phosphorus index (fig. 11). This could be due 

to a number of factors, including nutrient limitations, 

predation on phytoplankton, and variable chlorophyll-a

content among algal species.

Apr 20 Aug 19 Oct 6 Nov 30 Apr 20 Aug 19 Oct 6 Nov 30

Apr 20 Aug 19 Oct 6 Nov 30 Apr 20 Aug 19 Oct 6 Nov 30

TOTAL NITROGEN, IN MILLIGRAMS PER LITER TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER

DISSOLVED INORGANIC NITROGEN, 

IN MILLIGRAMS PER LITER

DISSOLVED ORTHOPHOSPHATE, 

IN MILLIGRAMS PER LITER

20

40

60

80

100

120

0

DEPTH, IN METERS 20

40

60

80

100

120

0

20

40

60

80

100

120

0

20

40

60

80

100

120

0

DEPTH, IN METERS

DEPTH, IN METERS

DEPTH, IN METERS

0 0.2 0.4 0 0.2 0.4 0 0.2 0.4 0 0.2 0.4

0 0.2 0 0.2 0.4 0.4 0 0.2 0.4 0 0 0.03 0.06 0 0.03 0.06 0 0.03 0.06 0 0.03 0.06

0 0.03 0.06 0 0.03 0.06 0 0.03 0.06 0 0.03 0.06

0.2 0.4

1999

EXPLANATION

Concentration greater than 

 or equal to reporting level

Concentration less than 

 reporting level

C

Figure 6. Nitrogen and phosphorus concentrations in Blue Mesa Reservoir at (A) Iola Basin (site BM1), (B) Cebolla 

Basin (site BM2), and (C) Sapinero Basin (site BM3), April–November 1999—Continued.
30 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

Characteristics of Reservoir Inflows

The data discussed in this section for Blue 

Mesa Reservoir inflow and outflow sites are listed 

in tables 29–30 in the “Supplemental Data” section 

at the back of this report.

Physical Properties and Suspended Sediment

Streamflow in the Blue Mesa Reservoir 

inflows was dominated by snowmelt runoff during 

spring (table 29). Smaller streamflows at other times 

of the year reflected the gradual melting of annual 

snowfields, precipitation events (primarily thunderstorms in summer), and base flow from ground-water 

discharge. Of the 10 inflow stream sites for Blue 

Mesa Reservoir sampled for this study (fig. 1, 

table 1), the Gunnison River (site BI1) provided 

more than 50 percent of the reservoir inflow for each 

of the four sampling periods, followed by Lake Fork 

of the Gunnison River (site BI10) and Cebolla Creek 

(site BI9) (table 13).

Water temperature in the inflows ranged from 

–0.4 to 16.5°C, and the median was 8.3°C (table 29). 

Temperatures reflected a seasonal cycle, with the 

warmest water during August, followed by May/June or 

October and November/December (the coolest water). 

No one inflow had extremes in water temperature.

0

5,000

10,000

15,000

20,000

25,000

PHYTOPLANKTON 

DENSITY, IN 

ALGAL UNITS 

PER LITER

1999

APR AUG OCT NOV

Iola Basin (site BM1)

Cebolla Basin (site BM2)

Sapinero Basin (site BM3)

EXPLANATION

Figure 7. Phytoplankton density in Blue Mesa 

Reservoir, April–November 1999.

Table 12. Nitrogen phosphorus ratios in Blue Mesa, Morrow Point, and Crystal Reservoirs, April–December 1999

[N:P, nitrogen:phosphorus; nd, not determined]

Date N:P

BLUE MESA RESERVOIR AT IOLA BASIN

(SITE BM1)

MORROW POINT RESERVOIR AT KOKANEE BAY

(SITE MP2)

04/20/99 23 04/21/99 16

08/19/99 nd 08/17/99 nd

10/06/99 nd 10/12/99 3

11/30/99 5 12/01/99 4

BLUE MESA RESERVOIR AT CEBOLLA BASIN

(SITE BM2)

MORROW POINT RESERVOIR OFF HERMITS REST

(SITE MP3)

04/20/99 70 04/21/99 13

08/19/99 nd 08/17/99 nd

10/06/99 nd 10/12/99 3

11/30/99 7 12/01/99 4

BLUE MESA RESERVOIR AT SAPINERO BASIN

(SITE BM3)

CRYSTAL RESERVOIR NEAR CRYSTAL DAM

(SITE CR1)

04/20/99 20 04/20/99 14

08/19/99 nd 08/24/99 nd

10/06/99 nd 10/13/99 2

11/30/99 4 12/02/99 4

MORROW POINT RESERVOIR ABOVE PINE CREEK

(SITE MP1)

04/21/99 16

08/23/99 5

10/12/99 3

12/01/99 4
LIMNOLOGY OF BLUE MESA RESERVOIR 31

Blue Mesa Reservoir inflows were well oxygenated (table 29). Most dissolved-oxygen concentrations 

were within a few percentage points (plus or minus) 

of full saturation for all sampling periods, indicating 

favorable conditions for aquatic organisms. All concentrations were above the Colorado aquatic-life instream 

standard (table 6). The well-oxygenated conditions in 

the tributaries are consistent with dissolved-oxygen 

concentrations found in other high-gradient streams 

in the Southern Rocky Mountains physiographic 

province in Colorado because of generally low water 

temperatures year-round, shallow stream depths, and 

high stream velocities promoting the dissolution of 

oxygen into the stream.

In the inflows, pH indicated slightly basicity 

conditions. Excluding South Willow Creek, Gunnison 

River at County Road 32 and Lake Fork of the Gunnison 

River were the most basic, with median pH values of 

8.0 (table 29). High pH can be of concern because the 

toxicity of un-ionized ammonia to fish increases with 

higher values for pH; however un-ionized ammonia 

concentrations in the Gunnison River and Lake Fork 

were low (undetected or below 0.01 mg/L) and limited 

any chance of un-ionized ammonia toxicity. All pH 

values were within the Colorado instream standard 

(table 6).

Low to moderate amounts of dissolved solids 

were contributed to Blue Mesa Reservoir by the 

inflows. Ninety percent of the specific-conductance 

values were below 205 μS/cm (table 29), reflecting 

the fact that the inflow drainage basins are primarily 

underlain by weather-resistant igneous and metamorphic rocks. The highest specific-conductance values 

were detected in South Willow Creek, an ephemeral 

stream, and Gunnison River at County Road 32, a 

large drainage that includes urban and agricultural 

lands. Inflow streams on the north side of Blue Mesa

0

2

4

6

8

10

NUMBER OF 

GENERA

APR AUG OCT NOV

1999

Iola Basin (site BM1)

Cebolla Basin (site BM2)

Sapinero Basin (site BM3)

EXPLANATION

PHYTOPLANKTON

Diatoms

Blue-green algae

Golden-brown algae

Green algae

Dinoflagellates

Iola Basin (site BM1)

Cebolla Basin (site BM2)

Sapinero Basin (site BM3)

100,000

10,000

1,000

100

10

1

100,000

10,000

1,000

100

10

1

100,000

10,000

1,000

100

10

1

PHYTOPLANKTON COMMUNITY, 

IN ALGAL UNITS PER LITER

APR AUG OCT NOV

1999

EXPLANATION

Figure 8. Genera richness in Blue Mesa 

Reservoir, April–November 1999.

Figure 9. Phytoplankton community in Blue Mesa Reservoir, 

April–November 1999.
32 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

Anabaena

Aphanizomenon

Asterionella

Ceratium

Dinobryon

Fragilaria

Schroederia + Pandorina

Stephanodiscus

Tabellaria

Other genera

PHYTOPLANKTON GENUS

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

PHYTOPLANKTON COMMUNITY COMPOSITION, IN PERCENT

APR AUG OCT NOV

1999

Iola Basin (site BM1) 

Cebolla Basin (site BM2)

Sapinero Basin (site BM3)

Melosira

EXPLANATION

Secchi depth

Chlorophyll-a

Total phosphorus

EXPLANATION

1999

20

30

40

50

60

70

20

30

40

50

60

70

TROPHIC-STATE INDEX

APR JUNE AUG OCT DEC APR JUNE AUG OCT DEC

Iola Basin (site BM1)

Cebolla Basin (site BM2) Sapinero Basin (site BM3)

20

30

40

50

60

70

Figure 10. Percent composition of phytoplankton community by genera, Blue Mesa 

Reservoir, April–November 1999.

Figure 11. Trophic-state indices for Blue Mesa Reservoir, calculated from Secchi 

depth, chlorophyll-a, and total phosphorus, April–November 1999.
LIMNOLOGY OF BLUE MESA RESERVOIR 33

Reservoir drain mostly undeveloped or wilderness 

lands and contributed few dissolved solids to the reservoir. In most streams, specific conductance was lowest 

during spring because of dilution by snowmelt and 

highest during early winter because most streamflow 

was derived from ground-water discharge.

Concentrations of suspended sediment 

entering Blue Mesa Reservoir from the inflows were 

low overall (median of 5 mg/L) and were not a waterquality concern (table 29). Concentrations were largest 

during spring. Most of the sediment load into the reservoir was supplied by those inflows with higher streamflows and suspended-sediment concentrations. For 

the four sampling periods, almost 95 percent of the 

suspended-sediment load to the reservoir was supplied 

by the three largest tributaries: Gunnison River at 

County Road 32 (59 percent), Lake Fork of the 

Gunnison River (24 percent), and Cebolla Creek 

(12 percent).

Nutrients

Nitrogen concentrations were low in the 

inflows. Concentrations of total nitrogen (the sum 

of dissolved nitrate plus nitrite and total organic 

nitrogen plus ammonia) ranged from 0.05 to 0.5 mg/L 

with the highest concentrations primarily in spring 

during snowmelt (table 30). Median concentrations 

of total nitrogen generally were higher in the larger 

inflows and the small inflow from Red Creek. 

Dissolved inorganic nitrogen concentrations (the 

sum of nitrate plus nitrite and ammonia) in the inflows 

were much lower than total nitrogen, ranging from less 

than 0.005 to 0.088 mg/L (table 30), indicating that 

most of the nitrogen supplied to the reservoir by the 

inflows was organic nitrogen. For most sampling 

periods, nitrate was detected in higher concentrations 

than ammonia and was the dominant form of inorganic 

nitrogen. Maximum concentrations of nitrate and 

ammonia were low, 0.082 and 0.014 mg/L, respectively (table 30). All nitrite, nitrate, and un-ionized 

ammonia concentrations in the inflows to Blue 

Mesa Reservoir were much lower than the Colorado 

instream water-quality standards (table 6). Prior 

sampling at Gunnison River at County Road 32 

showed that the maximum nitrate plus nitrite concentrations commonly occurred prior to peak flows 

from snowmelt runoff in spring. Concentrations were 

diluted by snowmelt and increased again the following 

winter (Spahr and others, 2000).

Total phosphorus concentrations in the 

inflows ranged from 0.022 to 0.2 mg/L (table 30). 

The maximum concentration was in East Elk and Red 

Creeks, both of which drain mostly undeveloped forest 

land. Seventy percent of the inflow samples had total 

phosphorus concentrations above 0.05 mg/L, indicating 

that high concentrations frequently entered the reservoir 

during the four sampling periods. Each inflow had at 

least one sample above 0.05 mg/L, and all or most 

samples from Cebolla Creek and all north-side tributaries (excluding Soap Creek) had concentrations 

exceeding 0.05 mg/L. Higher total phosphorus concentrations in the smaller inflows were unexpected because 

total phosphorus concentrations in mostly forested or 

pristine areas of the Nation generally are less than 

0.02 mg/L (Litke, 1999). Decomposing organic matter 

from beaver ponds located upstream from the inflow 

sampling sites may be the source of the additional total 

Table 13. Percentage of total inflow into Blue Mesa Reservoir for each sampled inflow site, May–December 1999

[Site number refers to table 1 and figure 1; columns may not add to 100 because of rounding; --, no flow in streambed]

Inflow site Percentage of total reservoir inflow

May/June August October November/December

Gunnison River at County Road 32 (site BI1) 59 54 70 72

Beaver Creek (site BI2) 1.3 1.3 0.67 0.59

Steuben Creek (site BI3) 0.81 0.71 0.40 0.52

East Elk Creek (site BI4) 0.59 0.26 0.30 0.66

Red Creek (site BI5) 0.20 0.04 0.10 0.24

West Elk Creek (site BI6) 1.8 0.77 0.62 1.1

Soap Creek (site BI7) 5.4 1.3 1.5 3.3

South Willow Creek (site BI8) 0.07 -- -- --

Cebolla Creek (site BI9) 9.5 16 9.0 7.9

Lake Fork of the Gunnison River (site BI10) 21 26 18 14
34 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

phosphorus. For Beaver, East Elk, and Red Creeks, the 

highest percentage of particulate phosphorus in the 

sample water occurred during fall. For all other stream 

inflows, the highest percentage of particulate phosphorus occurred during spring. Gunnison River at 

County Road 32 and Cebolla Creek were the only 

inflows where particulate phosphorus was more than 

50 percent of the total phosphorus in two or more 

samples. Orthophosphate, the primary component 

of dissolved phosphorus and the form of phosphorus 

used by phytoplankton, was detected in the inflows 

in concentrations ranging from 0.004 to 0.14 mg/L 

(table 30). In general, orthophosphate accounted for 

over 50 percent of total phosphorus in those inflows 

with low suspended-sediment concentrations.

Because phosphorus usually is the limiting 

nutrient in lakes and reservoirs, excessive phosphorus 

in streams can lead to eutrophication in water bodies. 

To control eutrophication, the USEPA established a 

recommended limit for total phosphorus of 0.05 mg/L 

in rivers and streams that enter lakes and reservoirs 

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

most samples from the Blue Mesa Reservoir inflows 

had total phosphorus concentrations above 0.05 mg/L, 

the effects on the reservoir would be small because of 

the relatively small volumes of inflow from the smaller 

streams.

As discussed in the “Data Collection and 

Analysis Methods” section, monthly nutrient loads 

for the Blue Mesa Reservoir inflows could only be 

determined for Gunnison River at County Road 32 

(site BI1). For all other sites, lack of nutrient and 

streamflow data limited monthly load calculations. 

For site BI1, estimated mean annual and monthly 

discharge and loads in kilograms per day for total 

nitrogen, dissolved inorganic nitrogen, total phosphorus, and dissolved orthophosphate for 1995–99 

are listed in table 14. Mean annual and monthly 

loads were highest for total nitrogen and lowest for 

dissolved orthophosphate. Mean monthly loads varied 

seasonally and were largest during the snowmelt 

runoff months of May, June, and July. Loads from 

the other inflows would have a similar pattern of 

seasonal variation.

Characteristics of Reservoir Outflow

Outflow from Blue Mesa Reservoir ranged 

from 1,317 to 3,263 ft3/s for the four sampling periods 

(table 29). Higher releases generally occurred during 

the warmer months (fig. 3). Water temperature ranged 

from 6.0°C during early winter to 12.5°C during fall 

and reflected cold hypolimnetic discharge from the

Table 14. Estimated mean annual and monthly discharge and nutrient loads for Gunnison River at County Road 32 (site BI1), 

calendar years 1995–99

[Site number refers to table 1 and figure 1; acre-ft/d, acre-foot per day; kg/d, kilograms per day]

Month

Mean 

discharge

(acre-ft/d)

Mean load

(kg/d)

Total

nitrogen

Dissolved

inorganic nitrogen

Total

phosphorus

Dissolved

orthophosphate

January 646 160 81 26 15

February 644 210 87 32 16

March 853 360 110 54 21

April 1,696 870 210 140 37

May 4,980 2,900 540 490 87

June 7,049 3,700 640 640 110

July 4,227 1,700 320 270 65

August 2,254 640 150 92 36

September 1,530 330 99 47 26

October 1,193 220 86 33 21

November 867 160 75 24 17

December 720 150 76 23 15

Annual 2,222 950 200 160 39
LIMNOLOGY OF MORROW POINT RESERVOIR 35

reservoir. Dissolved-oxygen concentrations (summer 

and fall only) and pH met Colorado instream waterquality standards (table 6). Dissolved oxygen was 

not measured during spring and early winter because 

of equipment failures. Water released from Blue Mesa 

Reservoir had moderate specific conductance, from 

174 to 200 μS/cm.

The concentration of total nitrogen in the 

Blue Mesa Reservoir outflow was 0.1 mg/L for 

all four sampling periods (table 30). Inorganic 

nitrogen concentrations in the release water were 

low, from 0.012 mg/L during spring to 0.054 mg/L 

during summer. More than one-half of the inorganic 

nitrogen during spring was ammonia, whereas nearly 

all inorganic nitrogen for the remaining sampling 

periods was nitrate. Total phosphorus concentrations 

were consistently low in the reservoir outflow, ranging 

from 0.014 mg/L during spring to 0.021 mg/L during 

fall and early winter (table 30). This is in contrast to 

the higher total phosphorus concentrations detected 

in the reservoir’s stream inflows. Orthophosphate was 

only detected in very low concentrations in the release 

waters. Concentrations ranged from 0.005 mg/L 

during spring to 0.014 mg/L during summer and 

fall.

LIMNOLOGY OF MORROW POINT 

RESERVOIR

Reservoir data discussed in this section are 

located in tables 26, 28 and 31–35 of the “Supplemental 

Data” section at the back of this report.

Physical Properties

Water temperature in Morrow Point Reservoir 

ranged from 15.8°C at 1 m below the water surface to 

3.9°C at depth (fig. 12A, tables 31–33). Water temperatures were influenced by cold water releases from 

Blue Mesa Reservoir and less sunlight reaching the 

waters of Morrow Point Reservoir because of the 

reservoir’s steep canyon walls. The site Above Pine 

Creek (MP1) exhibited isothermal conditions for all 

four sampling periods (fig. 12A, table 31). This site is 

about 0.5 mile downstream from Blue Mesa Dam and 

was characterized by riverine conditions with strong 

flowing current for each sampling period, resulting in 

well-mixed conditions and no thermal or chemical 

stratification. Kokanee Bay and Hermits Rest were 

isothermal during spring and early winter and stratified during summer and fall. At both downstream 

sites, the epilimnion was thin during summer and 

thicker and more pronounced during fall. At Hermits 

Rest, there was a secondary thermal decrease or 

thermal discontinuity deeper in the water column 

during summer. Water temperature in Morrow Point 

Reservoir was cooler than that measured in Blue Mesa 

Reservoir.

Dissolved-oxygen concentrations in Morrow 

Point Reservoir were at a maximum of 10.5 mg/L 

during April when water temperatures were coldest 

and at a minimum of 3.2 mg/L during December at 

depth (fig. 12A, tables 31–33). Anoxic conditions 

were not present. Concentrations were mostly uniform 

throughout the water column during isothermal conditions at Above Pine Creek (all four sampling periods) 

and during April at Kokanee Bay and Hermits Rest. 

For the latter two sites, dissolved-oxygen concentrations decreased at depth for the October and December 

profiles, except for Hermits Rest during October when 

concentrations increased at depth. August concentrations at these two downstream sites were not obtained 

because of faulty equipment. Only one dissolvedoxygen concentration, 5.6 mg/L in the metalimnion 

of Kokanee Bay during October, did not meet the 

Colorado water-quality standard for epilimnion and 

metalimnion strata (table 6).

In Morrow Point Reservoir, pH values ranged 

from 7.0 to 8.5 standard units (fig. 12B, tables 31–33). 

At each site, pH values throughout the water column 

were at maximum levels during spring and decreased 

to minimum levels during fall and early winter. When 

isothermal conditions were present at a site, pH varied 

only slightly with depth. Variability increased at 

Kokanee Bay and Hermits Rest with stratification 

during August but was much less pronounced during 

October stratification. All pH values were well within 

the Colorado water-quality standard (table 6). For each 

site, no significant correlation existed between pH 

values and chlorophyll-a concentrations, as measured 

by the rank Kendall correlation coefficient at a significance level of p≤0.05.

Specific conductance in the reservoir varied 

from 166 to 212 μS/cm (fig. 12B, tables 31–33), 

equivalent to estimated dissolved-solids concentrations of 100–127 mg/L (conversion factor of 0.6; Hem,
36 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER

Above Pine Creek (site MP1) Kokanee Bay (site MP2) Hermits Rest (site MP3)

DEPTH, IN METERS

100

90

80

70

60

50

40

30

20

10

0

TEMPERATURE, IN DEGREES CELSIUS

April 21, 1999 August 23, 1999 October 12, 1999 December 1, 1999

5 10 15 0 5 10 0 5 10 0 5 10

DEPTH, IN METERS

100

90

80

70

60

50

40

30

20

10

0

April 21, 1999 October 12, 1999 August 23, 1999

0 5 10 0 5 10 15 0 5 10 0 5 10 20 15

December 1, 1999

EXPLANATION

A

Figure 12. Depth profiles of (A) water temperature and dissolved oxygen, and (B) pH and 

specific conductance, Morrow Point Reservoir, April–December 1999.
LIMNOLOGY OF MORROW POINT RESERVOIR 37

100

90

80

70

60

50

40

30

20

10

0

DEPTH, IN METERS

175 200 225

100

90

80

70

60

50

40

30

20

10

0

DEPTH, IN METERS

150 175 200 225 150 175 200 225

pH, IN STANDARD UNITS

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER 

AT 25 DEGREES CELSIUS

Above Pine Creek (site MP1) Kokanee Bay (site MP2) Hermits Rest (site MP3)

150 175 200

April 21, 1999 August 23, 1999

April 21, 1999 August 23, 1999

October 12, 1999 December 1, 1999

October 12, 1999 December 1, 1999

7 8 97 8 9 6 7 86 7 8

EXPLANATION

B

Figure 12. Depth profiles of (A) water temperature and dissolved oxygen, and (B) pH and 

specific conductance, Morrow Point Reservoir, April–December 1999—Continued.
38 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

1985). These values would indicate dilute conditions. 

Maximum and minimum specific conductance for 

each site generally occurred during April and August, 

respectively. Each site had mostly uniform specific 

conductance with depth when isothermal conditions 

were present. Specific conductance was more variable 

with depth at Kokanee Bay and Hermits Rest with 

stratification during August and October.

Light transparency in Morrow Point Reservoir 

ranged from 2.5 to 7.3 m (fig. 13, tables 31–33). Transparency was at a minimum at each site during spring 

with mixing conditions and again at Hermits Rest 

during fall. The time of maximum light penetration 

varied. Mean light transparency for the four sampling 

periods increased along a downstream gradient in the 

reservoir, with an average Secchi depth of 3.4 m for 

Above Pine Creek, 4.1 m for Kokanee Bay, and 

5.8 m for Hermits Rest. Transparency at the first site 

was affected by riverine conditions. Using a photiczone/Secchi-depth relationship of 3, the photic zone 

in Morrow Point Reservoir ranged between 7.5 and 

21.9 m. Among the three reservoirs, the largest range 

in light transparency was in Morrow Point Reservoir.

Nutrients

Nitrogen concentrations in Morrow Point 

Reservoir were very low for the study period. Total 

nitrogen concentrations ranged from 0.1 to 0.3 mg/L, 

and many concentrations were equal to or less than 

0.2 mg/L (fig. 14, table 34). Only the fall and early 

winter Kokanee Bay samples had higher total nitrogen 

concentrations at depth than in the photic zone. 

Nitrogen in the reservoir occurred primarily as organic 

nitrogen. Dissolved inorganic nitrogen concentrations 

ranged from less than 0.005 to 0.149 mg/L (fig. 14, 

table 34). The four summer epilimnion samples for 

Kokanee Bay and Hermits Rest were the only samples 

with dissolved inorganic nitrogen concentrations 

below 0.032 mg/L; all four were less than 0.005 mg/L. 

Most dissolved inorganic nitrogen was in the form of 

nitrate. The deeper summer sample at Above Pine 

Creek was the only sample with an ammonia concentration higher than the corresponding nitrate concentration. For one or more sampling events at each site 

in Morrow Point Reservoir, the dissolved inorganic 

nitrogen concentration at depth was higher than the 

corresponding epilimnion or photic zone concentration. All nitrate, nitrite, and un-ionized ammonia 

concentrations in Morrow Point Reservoir were at 

least one order of magnitude lower than Colorado 

instream water-quality standards (table 6).

Total phosphorus concentrations in Morrow 

Point Reservoir also were low, ranging from 0.007 

to 0.024 mg/L (fig. 14, table 34). Concentrations in 

bottom-water samples during stratification were at 

most 0.010 mg/L higher than concentrations in the 

epilimnion. Dissolved orthophosphate concentrations 

also were low in Morrow Point Reservoir, ranging 

from less than the reporting level of 0.001 to 

0.018 mg/L (fig. 14, table 34). Concentrations less 

than or equal to 0.004 mg/L were detected only in the 

epilimnion of Kokanee Bay and Hermits Rest during 

summer. Concentrations also were low for all spring 

samples at the three sites.

Phosphorus was the limiting nutrient for each 

site during spring, and nitrogen was the limiting 

nutrient during fall and early winter (table 12). 

Nitrogen also was the limiting nutrient at Above 

Pine Creek during summer. Nitrogen was probably 

the limiting nutrient in Kokanee Bay during summer 

as inorganic nitrogen concentrations in the epilimnion 

were less than the laboratory reporting level of 

8

6

4

2

0 Above Pine Creek (site MP1)

8

6

4

2

0 Kokanee Bay (site MP2)

Hermits Rest (site MP3)

8

6

4

2

0

APR JUNE AUG OCT DEC

1999

LIGHT TRANSPARENCY, IN METERS BELOW 

WATER SURFACE

Secchi depth

EXPLANATION

Figure 13. Light transparency in Morrow Point 

Reservoir, April–December 1999.
LIMNOLOGY OF MORROW POINT RESERVOIR 39

0.005 mg/L and related orthophosphate concentrations 

were greater than the laboratory reporting level of 

0.001 mg/L. Nutrient limitation could not be determined for Hermits Rest during summer. Concentrations of both inorganic nitrogen and orthophosphate 

in the epilimnion were below the respective laboratory 

reporting levels; inorganic nitrogen and orthophosphate were essentially fully utilized by biological 

activities during summer. The spring and early winter 

limitations of phosphorus and nitrogen, respectively, 

in Morrow Point Reservoir were similar to those in 

Blue Mesa Reservoir.

Phytoplankton

 Phytoplankton density in Morrow Point 

Reservoir varied across the sampling period. Densities were smallest during August when nutrients 

were limited; densities also were low during October 

(fig. 15, table 35). Maximum phytoplankton density 

was during early winter at Above Pine Creek and 

Kokanee Bay and during spring at Hermits Rest. 

Densities generally were lower at Above Pine Creek 

than at the two downstream sites. The highest 

phytoplankton density in Morrow Point Reservoir, 

1,264 algal units/L at Kokanee Bay during early 

winter, was much smaller than the maximum densities 

of 21,930, 5,304, and 3,177 algal units/L for the Blue 

Mesa Reservoir sites. 

There were few patterns to richness in genera 

among the Morrow Point Reservoir sites (fig. 16). 

Genera richness at Above Pine Creek was at a 

minimum during August with only the diatoms 

Melosira sp. and Fragilaria sp. present. Genera richness for Kokanee Bay was constant for spring through 

fall and then decreased during early winter, whereas 

genera richness for Hermits Rest decreased from 

spring to fall. Above Pine Creek had the lowest 

number of genera present for any site in the three 

reservoirs. This probably was due to the fast-flowing, 

riverine conditions that dominate at the site due to its 

proximity to Blue Mesa Dam.

Diatoms were the dominant community 

group throughout the year in Morrow Point Reservoir 

(figs. 17–18). The golden-brown algae Dinobryon sp., 

the green algae Schroederia sp. and Spirogyra sp., 

and the blue-green algae Aphanizomenon sp. were 

present only in small amounts during April, August, 

and(or) October. Dinoflagellates were not detected. 

The diatom Melosira sp. was the most common 

phytoplankton in about 67 percent (8 of 12) of the 

Morrow Point Reservoir samples. In five samples, 

it represented 60 percent or more of the total 

phytoplankton population. When Melosira sp. populations were low during summer at Kokanee Bay and 

during fall at each site, the diatoms Fragilaria sp. and 

Tabellaria sp. were the most common phytoplankton, 

respectively. In contrast to Blue Mesa Reservoir, 

Asterionella sp. and Aphanizomenon sp. were never 

the most dominant species in any sample from 

Morrow Point Reservoir.

Phytoplankton density at Kokanee Bay and 

Hermits Rest differed between 1999 and 1998. Considering spring through fall samples only, densities during 

1999 were at a maximum during spring, a minimum 

during summer, and low during fall, whereas densities 

during 1998 were low during spring, at a maximum 

during summer, and a minimum during fall (National 

Park Service, 1998b). Mean phytoplankton densities 

at Kokanee Bay and Hermits Rest for spring through 

fall were lower during 1999 than during 1998—318 

and 433 algal units/L, respectively, during 1999 as 

compared to 989 and 1,030 algal units/L, respectively, 

during 1998. Phytoplankton density varies from year to 

year in a water body as environmental conditions vary, 

but because of limited phytoplankton data for Morrow 

Point Reservoir, it is not known whether the differences 

in phytoplankton density and distribution between 1999 

and 1998 are significant or are within normal year-toyear variance. 

The dominance of diatoms in Morrow Point 

Reservoir during 1999 also was observed during 

1998 (National Park Service, 1998b). However, 

there were some differences in community structure 

between the two years. The phytoplankton community during the summer of 1998 was dominated by 

Asterionella sp. and Melosira sp.; during 1999, 

Melosira sp. and Fragilaria sp. were prevalent 

during summer and dominant at two of three sites. 

The diatom Stephanodiscus sp. was the only taxon 

present at Kokanee Bay during fall 1998 and also was 

included in the community at Hermits Rest, but it was 

observed only in small populations during 1999. Also, 

a small population of Aphanizomenon sp. was present 

in the reservoir during fall 1999 but was not detected 

during 1998. Yearly fluctuations in species compositions such as these are normal in a water body (Wetzel, 

1983).
40 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

Figure 14. Nitrogen and phosphorus concentrations in Morrow Point Reservoir, (A) Above Pine Creek (site MP1), 

(B) Kokanee Bay (site MP2), and (C) Hermits Rest (site MP3), April–December 1999.

Chlorophyll-a

Chlorophyll-a concentrations in Morrow Point 

Reservoir ranged from 0.91 to 4.39 mg/m3

 (table 28). 

Mean chlorophyll-a concentrations were 2.26 mg/m3

for Above Pine Creek, 2.36 mg/m3

 for Kokanee Bay, 

and 2.34 mg/m3

 for Hermits Rest. All three sites were 

oligotrophic, based on Likens’ classification system 

(Likens, 1975). Chlorophyll-a concentrations at 

Above Pine Creek were smallest during August and 

largest during December. Concentrations at Kokanee 

Bay and Hermits Rest were smallest during October 

and largest during April. The only statistically significant (p≤0.05) correlation was between chlorophyll-a

concentration and phytoplankton density for Above 

Pine Creek. TSI values ranged from 32 to 49 for 

total phosphorus, 30 to 45 for chlorophyll-a, and 31 

to 47 for Secchi depth (fig. 19, table 28). Values for 

a particular site per sampling period were fairly similar 

except for Above Pine Creek during summer and 

fall and for Kokanee Bay and Hermits Rest during

fall.

DISSOLVED INORGANIC 

NITROGEN, IN MILLIGRAMS 

PER LITER

DISSOLVED 

ORTHOPHOSPHATE, IN 

MILLIGRAMS PER LITER

15

10

5

0

15

10

5

0

15

10

5

0

15

10

5

0

DEPTH, IN 

METERS

DEPTH, IN 

METERS

DEPTH, IN 

METERS

DEPTH, IN 

METERS

A

0 0.2 0.4 0 0.2 0.4 0 0.2 0.4 0 0.2 0.4

0 0.2 0.4 0 0.2 0.4 0 0.2 0.4 0 0.2 0.4

0 0.03 0 0.03 0 0.03 0 0.03

0 0.03 0 0.03 0 0.03 0 0.03

TOTAL NITROGEN, IN 

MILLIGRAMS PER LITER

TOTAL PHOSPHORUS, IN 

MILLIGRAMS PER LITER

Apr 21 Aug 23 Oct 12 Dec 1 Apr 21 Aug 23 Oct 12 Dec 1

Apr 21 Aug 23 Oct 12 Dec 1 Apr 21 Aug 23 Oct 12 Dec 1

1999

DISSOLVED INORGANIC 

NITROGEN, IN MILLIGRAMS 

PER LITER

DISSOLVED ORTHOPHOSPHATE, IN 

MILLIGRAMS PER LITER

0

10

20

30

40

50

10

0

20

30

40

50

10

0

20

30

40

50

0

10

20

30

40

50

DEPTH, IN 

METERS

DEPTH, IN 

METERS

DEPTH, IN 

METERS

DEPTH, IN 

METERS

0 0.2 0.4 0 0.2 0.4 0 0.2 0.4 0 0.2 0.4

0 0.2 0.4 0 0.2 0.4 0 0.2 0.4 0 0.2 0.4

0 0.03 0 0.03 0 0.03 0 0.03

0 0.03 0 0.03 0 0.03 0 0.03

TOTAL NITROGEN, IN 

MILLIGRAMS PER LITER

TOTAL PHOSPHORUS, IN 

MILLIGRAMS PER LITER

Apr 21 Oct 12 Dec 1 Aug 17 Apr 21 Aug 17

Apr 21 Oct 12 Dec 1 Aug 17 Apr 21 Oct 12 Dec 1 Aug 17

Oct 12 Dec 1

1999

B

EXPLANATION

Concentration greater than 

 or equal to reporting level

Concentration less than 

 reporting level
LIMNOLOGY OF MORROW POINT RESERVOIR 41

Characteristics of Reservoir Inflows

Data discussed in this section are located in 

tables 36–37 of the “Supplemental Data” section 

at the back of this report.

Physical Properties and Suspended Sediment

Five inflow sources to Morrow Point Reservoir 

were studied: the outflow from Blue Mesa Reservoir 

(site BO) (discussed above in “Characteristics of 

Reservoir Outflow” for Blue Mesa Reservoir) and 

four stream inflows (fig. 1, table 1). For the four 

sampling periods, most (median of 96 percent) of the 

water flowing into Morrow Point Reservoir was water 

released from Blue Mesa Reservoir, with the remainder 

mainly supplied by Blue and Curecanti Creeks 

(table 15). Streamflow in the inflows ranged from 0.18 

to 161 ft3

/s and was highest during spring (table 36).

Water temperature in the stream inflows 

ranged from 0.0° to 17.0°C, and the median was 

6.1°C (table 36). Temperatures varied seasonally. The 

warmest temperatures were during August, followed by 

October and(or) May/June and December (the coolest). 

Blue Creek was consistently cooler than the other 

inflows for all sampling periods except December.

The inflows to Morrow Point Reservoir were 

well oxygenated (table 36). Each inflow was almost 

fully saturated with dissolved oxygen during the four 

sampling periods, indicating favorable conditions for 

aquatic organisms. All dissolved-oxygen concentrations 

met the Colorado instream water-quality standard 

(table 6).

Median pH in the Morrow Point Reservoir 

inflows was 7.9 (table 36). There was little chance 

of un-ionized ammonia toxicity to fish with elevated 

pH, as all dissolved ammonia concentrations were equal 

to or less than 0.01 mg/L. All pH values were within the 

Colorado instream water-quality standard (table 6). 

Median pH in the Morrow Point Reservoir inflows was 

slightly more basic than that in the Blue Mesa Reservoir 

inflows. This may reflect a difference in the geology of 

the inflow watersheds.

Specific conductance in the inflows ranged 

from 48 to 141 μS/cm (table 36). As such, low amounts 

of dissolved solids were supplied to Morrow Point 

Reservoir. Specific conductance in the Morrow Point 

Reservoir inflows was diluted during spring because of 

snowmelt runoff and was more concentrated at other 

times of the year because of ground-water discharge 

(base flow), similar to conditions in the inflows to Blue 

Mesa Reservoir.

DISSOLVED INORGANIC NITROGEN, 

IN MILLIGRAMS PER LITER

DISSOLVED ORTHOPHOSPHATE, IN 

MILLIGRAMS PER LITER

0

25

50

75

100

125

0

25

50

75

100

125

0

25

50

75

100

125

0

25

50

75

100

125

DEPTH, IN METERS

DEPTH, IN METERS

DEPTH, IN METERS

DEPTH, IN METERS

0 0.2 0.4 0 0 0.2 0.2 0.4 0.4 0 0.2 0.4

0 0.2 0.4 0 0.2 0.4 0 0.2 0.4 0 0.2 0.4

0 0.03 0 0.03 0 0.03 0 0.03

0 0.03 0 0.03 0 0.03 0 0.03

TOTAL NITROGEN, IN MILLIGRAMS PER LITER TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER

Apr 21 Oct 12 Dec 1 Aug 17 Apr 21 Aug 17

Apr 21 Oct 12 Dec 1 Aug 17 Apr 21 Oct 12 Dec 1 Aug 17

Oct 12 Dec 1

1999

C

EXPLANATION

Concentration greater than 

 or equal to reporting level

Concentration less than 

 reporting level

Figure 14. Nitrogen and phosphorus concentrations in Morrow Point Reservoir, (A) Above Pine Creek (site MP1), 

(B) Kokanee Bay (site MP2), and (C) Hermits Rest (site MP3), April–December 1999—Continued.
42 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

EXPLANATION

0

200

400

600

800

1,000

1,200

1,400

PHYTOPLANKTON 

DENSITY, IN ALGAL 

UNITS PER LITER

Above Pine Creek (site MP1)

Kokanee Bay (site MP2)

Hermits Rest (site MP3)

1999

APR AUG OCT DEC

Figure 15. Phytoplankton density in Morrow Point Reservoir, April–

December 1999.

Above Pine Creek (site MP1)

Kokanee Bay (site MP2)

Hermits Rest (site MP3)

APR AUG OCT DEC

1999

0

2

4

6

8

10

NUMBER OF 

GENERA

EXPLANATION

Figure 16. Genera richness in Morrow Point Reservoir, April–

December 1999.

10,000

1,000

100

10

1

10,000

1,000

100

10

1

10,000

1,000

100

10

1

PHYTOPLANKTON COMMUNITY, IN ALGAL 

UNITS PER LITER

Above Pine Creek (site MP1)

Kokanee Bay (site MP2)

Hermits Rest (site MP3)

1999

APR AUG OCT DEC

Diatoms

Blue-green algae

Golden-brown algae

Green algae

PHYTOPLANKTON

EXPLANATION

Figure 17. Phytoplankton community in Morrow Point Reservoir, 

April–December 1999.
LIMNOLOGY OF MORROW POINT RESERVOIR 43

Suspended-sediment concentrations in the 

Morrow Point Reservoir inflows were low, ranging 

from 2 to 31 mg/L (table 36) and did not appear to 

affect water quality in the reservoir. Concentrations 

were highest during spring. Most of the suspendedsediment load into Morrow Point Reservoir came from 

Blue Creek (all four sampling periods) and Curecanti 

Creek (spring).

Nutrients

Nitrogen concentrations were low in the 

stream inflows to Morrow Point Reservoir. Concentrations of total nitrogen in the inflows were from 0.07 to 

0.5 mg/L (table 37). Much of the total nitrogen was 

organic nitrogen. Inorganic nitrogen concentrations in 

the inflows ranged from less than 0.005 to 0.14 mg/L 

(table 37). The dominant form of inorganic nitrogen 

varied between ammonia and nitrate for all sampling 

periods except early winter when nitrate was dominant. All nitrate, nitrite, and un-ionized ammonia 

concentrations in the inflows were much lower 

than Colorado instream water-quality standards 

(table 6).

Total phosphorus concentrations ranged from 

0.04 to 0.14 mg/L (table 37). Elevated concentrations 

(above 0.1 mg/L) were detected in Pine Creek. Beaver 

complexes and livestock grazing are both present 

upstream from the Pine Creek sampling site, and 

decomposing organic matter may have contributed to 

the elevated total phosphorus concentrations. Concentrations of total phosphorus in all samples for Curecanti, 

Blue, and Pine Creeks were above the recommended 

limit of 0.05 mg/L to control eutrophication in water 

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

Only Corral Creek had total phosphorus concentrations 

less than 0.05 mg/L. During spring when streamflow 

and suspended-sediment concentrations were high, over

Aphanizomenon

Asterionella

Dinobryon

Fragilaria

Melosira

Navicula

Schroederia

Stephanodiscus

Tabellaria

Other genera

PHYTOPLANKTON GENUS

0

20

40

60

80

100

0

20

40

60

80

100

Above Pine Creek (site MP1) 

0

20

40

60

80

100

Kokanee Bay (site MP2)

Hermits Rest (site MP3)

APR AUG OCT DEC

1999

PHYTOPLANKTON COMMUNITY COMPOSITION, IN PERCENT

EXPLANATION

Figure 18. Percent composition of phytoplankton community by genera, 

Morrow Point Reservoir, April–December 1999.
44 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

50 percent of the total phosphorus in the four inflows 

was particulate phosphorus. Dissolved phosphorus 

was prominent in the inflows during the other three 

sampling periods. Most of the dissolved phosphorus 

was orthophosphate, which ranged in concentration 

from 0.016 to 0.094 mg/L (table 37).

Characteristics of Reservoir Outflow

Two sources were used for information on the 

outflow from Morrow Point Reservoir. Data on the 

amount of water released from the reservoir were 

obtained from the Bureau of Reclamation (1999b, 

2000), whereas physical properties and water-quality 

data were collected on the Gunnison River about 

0.25 mile downstream from Morrow Point Dam at 

the inflow to Crystal Reservoir (site MO, table 1, 

fig. 1). 

Outflow from Morrow Point Reservoir ranged 

from 1,109 to 3,196 ft3

/s for the four sampling periods 

(table 36). Outflow mirrored inflow (fig. 3). The 

outflow tended to vary depending on power generation 

needs. Water temperatures in the outflow from 

Morrow Point Reservoir ranged from 6.0° to 11.2°C 

and reflected cold hypolimnetic releases. Dissolvedoxygen concentrations and pH met Colorado instream 

water-quality standards (table 6). Specific conductance 

varied little in the outflow, ranging from 172 to 

182 μS/cm.

Total nitrogen concentrations in the outflow 

from Morrow Point Reservoir ranged from 0.1 to 

0.3 mg/L (table 37). Inorganic nitrogen concentrations 

were low, ranging from 0.01 mg/L during May to 

0.07 mg/L during August. Almost one-third or greater 

of the inorganic nitrogen during May and August was 

ammonia, whereas over 90 percent of the October and 

December inorganic nitrogen was nitrate. Total phosphorus concentrations were low in the outflow, 

ranging from 0.019 mg/L during December to 

0.034 mg/L during May (table 37). Orthophosphate 

concentrations were consistently low in the outflow, 

from 0.006 mg/L during May to 0.015 mg/L during 

October.

EXPLANATION

20

30

40

50

60

70

20

30

40

50

60

70

TROPHIC-STATE INDEX

Above Pine Creek (site MP1)

Kokanee Bay (site MP2) Hermits Rest (site MP3)

1999

APR JUNE AUG OCT DEC APR JUNE AUG OCT DEC

20

30

40

50

60

70

Secchi depth

Chlorophyll-a

Total phosphorus

Figure 19. Trophic-state indices for Morrow Point Reservoir, calculated from 

Secchi depth, chlorophyll-a, and total phosphorus, April–December 1999.

Table 15. Percentage of total inflow into Morrow Point 

Reservoir for each sampled inflow site, May–December 1999

[Site number refers to table 1 and figure 1; columns may not add to 100 

because of rounding; <, less than]

Inflow site Percentage of total reservoir inflow

May/June August October December

Blue Mesa Reservoir 

discharge (site BO)

85 96 99 97

Corral Creek 

(site MI2)

0.27 0.01 <0.01 0.03

Curecanti Creek 

(site MI3)

7.5 0.63 0.18 0.45

Pine Creek (site MI4) 0.29 0.06 0.05 0.26

Blue Creek (site MI5) 6.9 3.1 0.73 2.1
LIMNOLOGY OF CRYSTAL RESERVOIR 45

LIMNOLOGY OF CRYSTAL RESERVOIR

Reservoir data discussed in this section are 

located in tables 26, 28, and 38–40 of the “Supplemental 

Data” section at the back of this report.

Physical Properties

Water temperature in Crystal Reservoir at 

the site near Crystal Dam ranged from 15.5°C at the 

1- to 3-m depth during August to 4.3°C at depth during 

April (fig. 20, table 38). Cold-water releases from 

Morrow Point Reservoir and reservoir topography 

of steep canyon walls contributed to the cold water 

temperatures. Crystal Reservoir was stratified during 

August and isothermal for the other three sampling 

periods (fig. 20). Two thermal discontinuities were 

present during summer stratification, in the metalimnion and hypolimnion. Isothermal conditions in 

Crystal Reservoir during October were in contrast to 

the October stratification in the two upstream reservoirs. 

The drawdown of Crystal Reservoir on September 17 

may have caused a breakdown in stratification, resulting 

in isothermal conditions during October. 

Dissolved-oxygen concentrations at the site 

near Crystal Dam ranged from 10.3 mg/L during April, 

when water temperatures were coldest, to 3.2 mg/L 

at depth during October (fig. 20, table 38). Anoxic 

conditions did not exist. Dissolved-oxygen concentrations in Crystal Reservoir were mostly uniform with 

depth during mixing conditions in April, October, and 

December, although a significant decrease from 7.0 to 

3.2 mg/L did occur near the bottom of the water column 

during October. During August stratification, dissolvedoxygen concentrations were mostly uniform with depth 

until the lowest one-third of the hypolimnion where 

concentrations decreased in the area of the secondary 

thermal discontinuity. All dissolved-oxygen concentrations in the epilimnion and metalimnion met the 

Colorado water-quality standard (table 6).

In Crystal Reservoir, pH ranged from 7.2 to 

8.4 standard units (fig. 20, table 38). Throughout the 

water column, pH was higher during April and August 

than during October and December. During isothermal 

or mixing conditions, pH was mostly uniform with 

depth or varied only by a few tenths of a unit. The 

pH distribution during summer reflected thermal 

stratifications, with decreases in the metalimnion and 

lowest one-third of the hypolimnion. All pH values 

were within the Colorado water-quality standard 

(table 6). There was no correlation between pH values 

and chlorophyll-a concentrations, as measured by the 

rank Kendall correlation coefficient at a significance 

level of p≤0.05. Values of pH in Crystal Reservoir were 

similar to those detected in Blue Mesa and Morrow 

Point Reservoirs.

APRIL

AUGUST

OCTOBER

DECEMBER

60

50

40

30

20

10

DEPTH, IN METERS

DISSOLVED OXYGEN,

IN MILLIGRAMS 

PER LITER

TEMPERATURE, IN

DEGREES CELSIUS pH, IN 

STANDARD UNITS

SPECIFIC

CONDUCTANCE,

IN MICROSIEMENS

PER CENTIMETER

AT 25 DEGREES

CELSIUS

0 EXPLANATION

0 5 10 15 0 5 10 15 6 7 8 9 100 150 200 250 20

Figure 20. Depth profiles of water temperature, dissolved oxygen, pH, and specific conductance, Crystal Reservoir 

near Crystal Dam (site CR1), April–December 1999.
46 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

Specific conductance in Crystal Reservoir 

ranged from 183 to 243 μS/cm (fig. 20, table 38), 

indicating dissolved-solids concentrations of about 

110 to 146 mg/L (conversion factor of 0.6; Hem, 

1985). Specific conductance was higher during 

spring and summer than later in the year. During 

isothermal conditions, specific conductance was 

mostly uniform with depth. With stratification during 

August, specific conductance increased sharply in 

the deepest 20 m of the reservoir; this increase was 

unique among all Curecanti NRA reservoir sites. 

The increase in Crystal Reservoir was located in the 

area of the hypolimnion secondary thermal discontinuity and may be the result of water of high specific 

conductance in the reservoir’s main stream inflow, 

the Cimarron River, flowing along the bottom of the 

reservoir. Specific conductance in Crystal Reservoir 

was higher than that in Blue Mesa or Morrow Point 

Reservoirs.

Light transparency in Crystal Reservoir ranged 

from 3.0 to 5.5 m for the spring through fall sampling 

periods (fig. 21, table 38)) and averaged 4.0 m. The 

early winter Secchi depth was not recorded. Transparency was at a minimum during spring and at a 

maximum during summer. With the photic zone 

estimated as three times the Secchi depth, the photic 

zone at the Crystal Reservoir site ranged between 9.0 

and 16.5 m.

Nutrients

Total nitrogen concentrations in Crystal 

Reservoir at the site near Crystal Dam ranged from 

0.1 to 0.4 mg/L (fig. 22, table 39). Most nitrogen in 

Crystal Reservoir was organic nitrogen. Concentrations of dissolved inorganic nitrogen in the reservoir 

ranged from 0.009 to 0.19 mg/L (fig. 22, table 39). 

Only the summer samples from the epilimnion had 

concentrations less than or equal to 0.010 mg/L. 

All other samples had concentrations greater than 

or equal to 0.039 mg/L. Much of the dissolved 

inorganic nitrogen in the photic zone during spring, 

fall, and early winter occurred as nitrate. Nitrate 

was undetected in the epilimnion during summer, and 

more of the dissolved inorganic nitrogen occurred as 

ammonia. In Crystal Reservoir, maximum concentrations for both total nitrogen and dissolved inorganic 

nitrogen occurred at depth during summer stratification and were much greater than the corresponding 

epilmnion concentrations. All nitrate, nitrite, and unionized ammonia concentrations in the reservoir were 

well within the Colorado water-quality standards 

(table 6). Concentrations of total nitrogen in Crystal 

Reservoir were similar to those detected in Blue 

Mesa and Morrow Point Reservoirs, whereas concentrations of dissolved inorganic nitrogen in Crystal 

Reservoir were higher than those in the two upstream 

reservoirs.

Total phosphorus concentrations in Crystal 

Reservoir were low, ranging between 0.009 and 

0.057 mg/L (fig. 22, table 39). The only concentration 

greater than 0.023 mg/L was in the summer bottomwater sample during stratification. Dissolved orthophosphate concentrations in the reservoir also were 

low, ranging from less than the reporting level of 0.001 

to 0.02 mg/L (fig. 22, table 39). Concentrations below 

the laboratory reporting level only were in the summer 

epilimnion samples. Spring, fall, and early winter 

concentrations of both total phosphorus and dissolved 

orthophosphate were mostly uniform with depth and 

reflected the unstratified conditions in the water 

column. With stratification, concentrations were 

higher in the hypolimnion than in other parts of the 

water column.

Phosphorus was the limiting nutrient in 

Crystal Reservoir during spring, whereas nitrogen 

was the limiting nutrient during fall and early winter 

(table 12). During summer, phosphorus probably 

was the limiting nutrient because inorganic nitrogen 

concentrations were 0.009 or 0.010 mg/L and orthophosphate concentrations were less than the reporting 

limit of 0.001 mg/L.

8

6

4

2

0

1999

APR JUNE AUG OCT DEC

LIGHT TRANSPARENCY, 

IN METERS BELOW 

WATER SURFACE

EXPLANATION

Secchi depth

Figure 21. Light transparency in Crystal Reservoir near 

Crystal Dam (site CR1), April–December 1999.
LIMNOLOGY OF CRYSTAL RESERVOIR 47

Phytoplankton

Phytoplankton density in Crystal Reservoir was 

nearly constant for the April, October, and December 

samples, when densities ranged from 175 to 183 algal 

units/L, and reached a maximum level of 393 algal 

units/L during August (fig. 23, table 40). Genera richness in the reservoir was greatest during summer and 

lowest during early winter (fig. 24).

The pattern of phytoplankton density in 

Crystal Reservoir (fig. 23) differed from that in Blue 

Mesa (fig. 7) and Morrow Point Reservoirs (fig. 15). 

Both Blue Mesa and Morrow Point Reservoirs 

had minimum phytoplankton density during 

August, whereas Crystal Reservoir had maximum 

phytoplankton density during August. Algal density in 

Crystal Reservoir, from 175 to 393 algal units/L, was 

much smaller and much less variable than that in Blue 

Mesa and Morrow Point Reservoirs, which had densities of 26 to 21,930 algal units/L and 19 to 1,264 algal 

units/L, respectively. These differences in density 

among the three reservoirs may be related to residence 

time, water temperature, and nutrients. The first two 

factors, in particular, decreased along an upstream-todownstream gradient among the reservoirs.

The phytoplankton community in Crystal 

Reservoir in 1999 was dominated by diatoms 

(figs. 25–26). Diatoms made up about 98, 85, 

and 95 percent of the phytoplankton community 

during spring, summer, and fall, respectively, and 

were the only phytoplankton detected during early 

winter. Melosira sp. was the dominant diatom genera 

in all samples except summer, when Asterionella sp. 

was dominant. Other phytoplankton present in 

small amounts during spring, summer, and(or) fall 

were the golden-brown algae Dinobryon sp., the 

green algae Schroederia sp., the dinoflagellate 

Ceratium sp., and the blue-green algae 

Aphanizomenon sp.

Historical phytoplankton data for this site, 

which are available only for fall 1998, revealed 

the presence of five diatom genera (Melosira, 

Fragilaria, Stephanodiscus, Synedra, and Navicula), 

four green algae genera (Gloeocystis, Eudorina, 

Closteridium, and Oedogonium), and the 

dinoflagellate Ceratium (National Park Service, 

1998b). The first two diatoms and Ceratium were 

the only phytoplankton in common for fall 1998 

and fall 1999.

Figure 22. Nitrogen and phosphorus concentrations in Crystal Reservoir near Crystal Dam 

(site CR1), April–December 1999.

DISSOLVED INORGANIC NITROGEN, IN 

MILLIGRAMS PER LITER DISSOLVED ORTHOPHOSPHATE, 

IN MILLIGRAMS PER LITER

0

10

20

30

40

50

60

0

10

20

30

40

50

60

0

10

20

30

40

50

60

0

10

20

30

40

50

60

DEPTH, IN METERS

DEPTH, IN METERS DEPTH, IN METERS

DEPTH, IN METERS

0 0.2 0.4 0 0.2 0.4 0 0.2 0.4 0 0.2 0.4

0 0.2 0.4 0 0.2 0.4 0 0.2 0.4 0 0.2 0.4

0 0.03 0 0.03 0 0.03 0 0.03 0.06 0.06 0.06 0.06

0 0.03 0 0.03 0 0.03 0 0.03 0.06 0.06 0.06 0.06

TOTAL NITROGEN, IN MILLIGRAMS PER LITER TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER

Apr 20 Oct 13 Dec 2 Aug 24 Apr 20 Aug 24

Apr 20 Oct 13 Dec 2 Aug 24 Apr 20 Oct 13 Dec 2 Aug 24

Oct 13 Dec 2

1999

EXPLANATION

Concentration greater 

 than or equal to 

 reporting level

Concentration less 

 than reporting level
48 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

Chlorophyll-a

Chlorophyll-a concentrations near Crystal 

Dam ranged from 2.01 to 3.32 mg/m3 (table 28). The 

mean concentration of 2.64 mg/m3 would indicate 

oligotrophy (Likens, 1975). Chlorophyll-a concentrations in Crystal Reservoir were at a minimum during 

August and at a maximum during December. No 

correlation existed between chlorophyll-a concentration and phytoplankton density. TSI values ranged 

from 36 to 49 for total phosphorus, 37 to 42 for 

chlorophyll-a, and 35 to 44 for Secchi depth (fig. 27, 

table 28). Indices for all three parameters were very 

similar during spring and summer and tended to 

diverge slightly during fall. 

Characteristics of Reservoir Inflows

Data discussed in this section are located 

in tables 41–42 of the “Supplemental Data” section 

at the back of this report.

Physical Properties and Suspended Sediment

Four inflow sources were investigated for 

Crystal Reservoir: the outflow from Morrow 

Point Reservoir (site MO) (discussed above in 

“Characteristics of Reservoir Outflow” for Morrow 

Point Reservoir) and the stream inflows Cimarron 

River and Mesa and Crystal Creeks (sites CI4, CI2, 

and CI3, respectively) (fig. 1, table 1). Most (median 

of 97 percent) of the water flowing into Crystal 

Reservoir during the four sampling periods was 

outflow from Morrow Point Reservoir. The remainder 

was mainly supplied by the Cimarron River (table 16). 

Discharge in the three stream tributaries ranged from 

0.11 to 194 ft3

/s, and except during spring snowmelt, 

streamflow in Crystal and Mesa Creeks was less than 

1 ft3

/s (table 41).

Water temperature in the inflows to Crystal 

Reservoir ranged from 0.0° to 16.8°C, and the median 

was 8.4°C (table 41). Temperatures reflected a seasonal 

cycle, with the warmest water generally during August, 

followed by cooler water during May/June and October, 

and the coolest water during December. Crystal Creek 

was the exception to this, as its warmest water was in 

May.

The stream inflows to Crystal Reservoir generally were well oxygenated (table 41). Most dissolvedoxygen concentrations for all four sampling periods 

were at or near 100-percent saturation, indicating good 

conditions for aquatic organisms. The exception 

to high saturation values was Crystal Creek during 

October with 72-percent saturation. Dissolved-oxygen 

concentrations in each inflow met the Colorado 

aquatic-life instream standard (table 6).

The median pH in the Crystal Reservoir inflows 

was 8.2 (table 41). There was little possibility of unionized ammonia toxicity to fish at these pH values 

because all dissolved ammonia concentrations were 

at or below 0.01 mg/L. All pH values were within the 

Colorado instream standard (table 6). The median pH 

in the inflows to Crystal Reservoir was higher than 

that detected in inflows to Blue Mesa and Morrow 

Point Reservoirs.

Specific conductance in the three inflows to 

Crystal Reservoir ranged from 48 to 449 μS/cm 

(table 41). Both Cimarron River and Crystal Creek 

had high values of specific conductance; median 

specific-conductance values for these two inflows 

were 402 and 418 μS/cm, respectively. Both inflows 

drain agricultural lands that include deposits of 

Mancos Shale, a highly erodible Upper Cretaceous

0

2

4

6

8

10

NUMBER OF 

GENERA

APR AUG OCT DEC

1999

Figure 23. Phytoplankton density in Crystal 

Reservoir near Crystal Dam (site CR1), April–

December 1999.

Figure 24. Genera richness in Crystal 

Reservoir near Crystal Dam (site CR1), 

April–December 1999.

0

100

200

300

400

500

PHYTOPLANKTON

DENSITY, IN 

ALGAL UNITS

PER LITER

1999

APR AUG OCT DEC
LIMNOLOGY OF CRYSTAL RESERVOIR 49

saline, marine sedimentary rock. Crystal Creek is 

subject to water withdrawals for irrigation and may be 

dry at certain times of the year. The Cimarron River 

has substantial streamflow throughout the year and, 

therefore, has a larger effect on the quality of water 

in Crystal Reservoir than does Crystal Creek. In 

Crystal Reservoir, there was a substantial increase 

in specific conductance, about 50 μS/cm, in the lower 

hypolimnion during stratification in August. More 

dense water from the Cimarron River may sink to the 

reservoir bottom and cause the high specific conductance at depth. Sampling along the length of the 

reservoir would be needed to verify this. Specific 

conductance in the inflows to Crystal Reservoir was 

higher than that in most inflows to Blue Mesa and 

Morrow Point Reservoirs.

Suspended-sediment concentrations in the three 

Crystal Reservoir inflows ranged from 1 to 133 mg/L 

(table 41). Suspended sediment is not a water-quality 

concern in Mesa and Crystal Creeks but is a concern 

in the Cimarron River. The median suspendedsediment concentration in the river was 36 mg/L, 

and concentrations especially were elevated during 

June and August. The June concentration of 133 mg/L 

was highest among all reservoir inflows in Curecanti 

NRA. A sediment plume could easily be seen during 

the spring, summer, and fall sampling periods at the 

point where the Cimarron River enters the Gunnison 

River (fig. 28), just upstream from Crystal Reservoir. 

As such, the Cimarron River supplied almost all of 

the sediment load to Crystal Reservoir for the four 

sampling periods.

Nutrients

Total nitrogen concentrations in the stream 

inflows to Crystal Reservoir ranged from 0.1 to 

0.6 mg/L (table 42). Most total nitrogen in the inflows 

was dissolved organic nitrogen. Except for Mesa 

Creek and the Cimarron River during December, 

dissolved inorganic nitrogen accounted for less than 

one-third of total nitrogen. Inorganic nitrogen concentrations in the inflows were from less than 0.005 to 

0.18 mg/L (table 42). Most inorganic nitrogen in Mesa

1,000

100

10

1

PHYTOPLANKTON 

COMMUNITY, IN 

ALGAL UNITS 

PER LITER

PHYTOPLANKTON

1999

APR AUG OCT DEC

Diatoms

Blue-green algae

Golden-brown algae

Green algae

Dinoflagellates

EXPLANATION

PHYTOPLANKTON GENUS

Asterionella

Ceratium

Fragilaria

Melosira

Navicula

Schroederia

Tabellaria

Other genera 0

20

40

60

80

100

APR AUG OCT DEC

1999

PHYTOPLANKTON 

COMMUNITY

COMPOSITION, 

IN PERCENT

EXPLANATION

Figure 25. Phytoplankton community in Crystal Reservoir near Crystal Dam 

(site CR1), April–December 1999.

Figure 26. Percent composition of phytoplankton community by genera, Crystal 

Reservoir near Crystal Dam (site CR1), April–December 1999.
50 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

Creek and the Cimarron River was nitrate, whereas 

ammonia was dominant in Crystal Creek during 

August and October. All nitrate, nitrite, and un-ionized 

ammonia concentrations met Colorado instream 

water-quality standards (table 6). Concentrations of 

total nitrogen and dissolved inorganic nitrogen in the 

inflows to Crystal Reservoir were the highest among 

all inflows to the recreation area.

Total phosphorus concentrations in the three 

inflows ranged from 0.027 to 0.17 mg/L (table 42). 

Elevated concentrations (above 0.1 mg/L) were 

detected in the Cimarron River. At least one-half of 

the samples for Crystal Creek and Cimarron River 

had total phosphorus concentrations exceeding the 

recommended limit of 0.05 mg/L to control eutrophication in water bodies (U.S. Environmental Protection 

Agency, 1986). Most total phosphorus in Crystal 

Creek occurred as dissolved phosphorus, whereas 

the percentage of total phosphorus in Mesa Creek 

and the Cimarron River as either particulate or 

dissolved phosphorus was related to streamflow and 

suspended-sediment concentration. When the latter 

two parameters were elevated, particulate phosphorus 

was the primary form of total phosphorus. Most 

dissolved phosphorus in the inflows was orthophosphate. Orthophosphate concentrations were low, 

ranging from 0.011 to 0.052 mg/L (table 42).

Characteristics of Reservoir Outflow

Two sources were used for information on the 

outflow from Crystal Reservoir. Data on the amount 

of water released from the reservoir were obtained 

from the Bureau of Reclamation (1999b, 2000), 

whereas physical properties and water-quality data 

collected at the Gunnison River below Gunnison 

Tunnel site (site CO), about 2 miles downstream from 

Crystal Dam, were used to represent the quality of the 

water released from the reservoir. The major hydrologic feature between Crystal Dam and the sampling 

site, the Gunnison Tunnel, routed water away from the 

Gunnison River during the irrigation season.

The amount of water released from Crystal 

Reservoir ranged from 1,209 to 3,824 ft3/s for the 

four sampling periods (table 41). Abrupt changes 

in discharge throughout the year reflected the regulation of water released from Crystal Dam (fig. 3). 

Water temperature in the Gunnison River below the 

Gunnison Tunnel ranged from 6.5° to 11.5°C, reflecting 

cold hypolimnetic releases from Crystal Reservoir. 

Dissolved-oxygen concentrations and pH were 

within Colorado instream standards (table 6). Specificconductance values in the river were around 190 μS/cm. 

Suspended-sediment samples were not collected at the 

Gunnison River below Gunnison Tunnel site in 1999; 

however, sampling between 1994 and 1998 indicated 

that suspended-sediment concentrations at the site were 

low (median of 3 mg/L) (Spahr and others, 2000).

20

30

40

50

60

70

80

TROPHIC-STATE 

INDEX

1999

APR JUNE AUG OCT DEC

EXPLANATION

Secchi depth

Chlorophyll-a

Total phosphorus

Figure 27. Trophic-state indices for Crystal Reservoir near Crystal 

Dam (site CR1), calculated from Secchi depth, chlorophyll-a, and 

total phosphorus, April–December 1999.

Table 16. Percentage of total inflow into Crystal Reservoir 

for each sampled inflow site, May–December 1999

[Site number refers to table 1 and figure 1; columns may not add to 100 

because of rounding; <, less than]

Inflow site Percentage of total reservoir inflow

May/June August October December

Morrow Point 

Reservoir 

outflow 

(site MO)

93 96 98 98

Mesa Creek 

(site CI2)

1.0 0.02 <0.01 0.02

Crystal Creek 

(site CI3)

0.09 <0.01 <0.01 0.01

Cimarron River 

(site CI4)

5.7 4.3 2.4 2.3
COMPARISON OF RESERVOIRS, INFLOWS, AND OUTFLOWS 51

Total nitrogen concentrations in the Gunnison 

River below the Gunnison Tunnel site ranged from 

0.1 to 0.4 mg/L, with the maximum concentration 

occurring during May (table 42). Inorganic nitrogen 

concentrations in the river were low, ranging between 

0.018 mg/L during May to 0.083 mg/L during 

December. Nitrate was the primary component of 

inorganic nitrogen, especially during August, October, 

and December. Total phosphorus concentrations ranged 

from 0.022 to 0.07 mg/L in the outflow from Crystal 

Reservoir (table 42) and were more variable than those 

from the upstream reservoirs. Orthophosphate concentrations were similar, however, to the upstream reservoir 

outflows and ranged from 0.007 to 0.015 mg/L.

Nutrient loads in the outflow from Crystal 

Reservoir were estimated using nutrient concentrations from the Gunnison River below Gunnison Tunnel 

site and water released from Crystal Reservoir. Mean 

annual loads for 1995–99 were highest for total nitrogen 

and lowest for dissolved orthophosphate (table 17). 

Nutrient loads in the Crystal Reservoir outflow were 

greatest in May–July, similar to those for the Gunnison 

River at County Road 32 site (site BI1) upstream from 

Blue Mesa Reservoir. For other months of the year, the 

amount of nutrient loading in the outflow from Crystal 

Reservoir was more consistent than the amount of 

loading in the upstream Gunnison River at County 

Road 32 site and reflected continual water releases 

from Crystal Dam rather than seasonal streamflow 

patterns at the upstream Gunnison River site.

COMPARISON OF RESERVOIRS, 

INFLOWS, AND OUTFLOWS

Physical properties, nutrients, phytoplankton, 

and chlorophyll-a for Blue Mesa, Morrow Point, and 

Crystal Reservoirs will be compared, as will physical 

properties and nutrients in stream inflows and reservoir outflows. Possible implications for management 

also will be discussed.

Physical Properties in Reservoirs

Blue Mesa, Morrow Point, and Crystal 

Reservoirs had temperature characteristics common to 

lakes and reservoirs in temperate latitudes. Each reservoir had isothermal conditions and vertical mixing of 

water during spring and early winter and thermal stratification during summer. Major differences in water 

temperature between the reservoirs—Blue Mesa being 

the warmest with the greatest range in temperature 

and Crystal being the coolest with smallest range 

in temperature—were related to the presence or 

absence of an impoundment in close, upstream 

proximity to each reservoir. The nearest major dam 

upstream from Blue Mesa Reservoir is Taylor Park 

Reservoir, 37 miles distant, and is too far removed 

to have an effect on temperatures in the Gunnison 

River as it enters Blue Mesa Reservoir. Temperatures 

in the Gunnison River at County Road 32, for 

example, ranged between 0.0° and 13.3°C for the four 

sampling periods. Inflow temperatures to Blue Mesa 

Reservoir reflected the seasonal hydrologic cycle 

rather than effects from upstream impoundments. 

By comparison, the temperature of water released 

from Blue Mesa and Morrow Point Dams ranged 

between 6.0° and 12.5°C. As a result of receiving 

deep outflow water from adjacent upstream impoundments, spring and early winter temperatures in 

Morrow Point and Crystal Reservoirs were warmer

Figure 28. Mouth of Cimarron River at Gunnison 

River, August 1999. Photograph by Nancy 

Bauch.
52 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

than would have occurred without the upstream 

impoundment, and summer temperatures were cooler. 

Water temperature in Morrow and Crystal Reservoir 

also was affected by the reservoirs’ location in the 

Black Canyon of the Gunnison River. The steep sides 

and narrowness of the canyon limit the amount of solar 

radiation absorbed by each reservoir.

Thermal stratification was present at each 

reservoir site during summer, except for Morrow Point 

Reservoir Above Pine Creek. Stratification continued 

into fall for Blue Mesa Reservoir at Cebolla and 

Sapinero Basins and in Morrow Point Reservoir at 

Kokanee Bay and Hermits Rest. A secondary thermal 

discontinuity was present during summer at Hermits 

Rest and in Crystal Reservoir at the site near Crystal 

Dam.

Dissolved-oxygen concentrations in each reservoir were inversely related to water temperature, with 

the highest median photic-zone concentration occurring in the cooler Crystal Reservoir and the lowest 

median photic-zone concentration occurring in the 

warmer Blue Mesa Reservoir. In Blue Mesa Reservoir, 

decreases in dissolved-oxygen concentration were 

in the metalimnion of Cebolla and Sapinero Basins 

during August and October stratification. For both 

basins, dissolved-oxygen concentrations were at a 

minimum in the metalimnion 40 m below the water 

surface during August, with an additional minimum 

at 19 m in Sapinero Basin, and between 35 and 50 m 

below the water surface during October. The deeper 

metalimnetic oxygen minimums may be related to the 

power-gate slot openings on Blue Mesa Dam, as the 

dissolved-oxygen minimums during August were situated just above the power-gate slot openings, and the 

fall minimums were within the power-gate slot openings. As noted by Ford (1990), because stratification 

in a reservoir prevents vertical mixing, the zone of 

outflow or water removal may extend the length of the 

reservoir. This outflow zone may be reflected by the 

dissolved-oxygen minimums in Cebolla and Sapinero 

Basins of Blue Mesa Reservoir. The metalimnetic 

minimums during October also may be related to 

phytoplankton decomposition. As dead phytoplankton 

fall from the epilimnion, they can accumulate in the 

metalimnion because the cooler, more dense water 

found there slows the rate of sinking through the water 

column. The amount of oxygen depletion through 

bacterial respiration is greatest in the metalimnion 

because of the longer period of time the sinking 

phytoplankton spend in this region of higher viscosity, 

leading to a metalimnetic oxygen minimum. This 

mechanism for metalimnetic oxygen depletion has 

been observed in another Colorado River reservoir, 

Lake Powell in Utah (Stanford and Ward, 1991). The 

metalimnetic dissolved-oxygen minimum observed 

in Blue Mesa Reservoir in 1999 also was detected in 

Table 17. Estimated mean annual and monthly discharge and nutrient loads for outflow from Crystal Reservoir, 

calendar years 1995–99

[acre-ft/d, acre-foot per day; kg/d, kilograms per day]

Month

Mean

discharge

(acre-ft/d)

Mean load

(kg/d)

Total

nitrogen

Dissolved

inorganic nitrogen

Total

phosphorus

Dissolved

orthophosphate

January 2,339 550 270 63 38

February 2,195 510 230 57 36

March 3,066 780 310 100 50

April 4,077 1,100 390 140 66

May 6,183 1,800 580 270 100

June 6,844 2,000 640 330 120

July 7,170 2,200 720 380 130

August 4,370 1,200 370 160 70

September 3,639 920 320 120 58

October 3,444 870 340 110 55

November 2,775 670 300 80 45

December 2,813 690 320 82 45

Annual 4,076 1,100 400 160 68
COMPARISON OF RESERVOIRS, INFLOWS, AND OUTFLOWS 53

previous years (Johnson and Bergstedt, 1994; Johnson 

and others, 1995, 1996, 1997). The exact mechanism 

of the metalimnetic dissolved-oxygen minimum in 

Blue Mesa Reservoir is unknown.

Nutrients in Reservoirs

Similarities and differences in nutrient 

concentrations in the three reservoirs were observed, 

as shown by seasonal median concentrations in the 

epilimnion/photic zone and hypolimnion (near 

bottom) for each reservoir (fig. 29). Except for the 

summer near-bottom sample from Crystal Resevoir, 

seasonal median concentrations of total nitrogen in 

Morrow Point and Crystal Reservoirs were less than or 

equal to those in Blue Mesa Reservoir. Some median 

concentrations of total nitrogen were higher at depth 

during stratified conditions and probably were due to 

the settling of organic detritus from above. The high 

median concentration at depth in Crystal Reservoir 

during summer also may have resulted from dense 

Cimarron River water sinking to the bottom of the 

reservoir. For inorganic nitrogen, seasonal median 

concentrations in photic-zone and near-bottom 

samples were nearly similar within each reservoir 

during mixing conditions (fig. 29). In Blue Mesa and 

Morrow Point Reservoirs, median inorganic nitrogen 

concentrations in epilimnion samples were less than 

the reporting limit of 0.005 mg/L during summer, indicating full utilization by biota. Inorganic nitrogen was 

not fully utilized in Crystal Reservoir during summer, 

reflecting the possibility that phosphorus may have 

been the limiting factor. Excluding some Blue Mesa 

Reservoir samples during stratification, median 

inorganic nitrogen concentrations at the different 

depths were higher in Morrow Point and Crystal 

Reservoirs than in Blue Mesa Reservoir for each 

sampling period. Median total phosphorus concentrations in the three reservoirs were similar or nearly 

similar except during stratification (fig. 29). Results 

for dissolved orthophosphate were mostly similar to 

results for dissolved inorganic nitrogen. Median orthophosphate concentrations during summer, though, 

were less than the reporting limit in Blue Mesa and 

Crystal Reservoirs.

In each reservoir, the limiting nutrient during 

spring was phosphorus and the limiting nutrient during 

early winter was nitrogen. In Blue Mesa and Morrow 

Point Reservoirs, nitrogen was probably the limiting 

nutrient during summer for some sites, whereas for 

other sites the limiting nutrient during summer could 

not be determined because both inorganic nitrogen and 

orthophosphate concentrations were less than laboratory reporting levels. Phosphorus probably was the 

limiting nutrient in Crystal Reservoir during summer. 

During fall, nitrogen was limiting in Morrow Point 

and Crystal Reservoirs and probably was the limiting 

nutrient in Blue Mesa Reservoir.

Phytoplankton in Reservoirs

The size and structure of the phytoplankton 

community in each reservoir fluctuated throughout 

the sampling period due to physical, chemical, and 

biological factors. These include water residence time, 

water temperature, sunlight, thermal stratification, 

nutrients, and characteristics of phytoplankton 

species. In particular, the phytoplankton communities 

in Morrow Point and Crystal Reservoirs were affected 

more by water residence time and water temperature 

than in Blue Mesa Reservoir. Phytoplankton density 

generally was less in Morrow Point and Crystal 

Reservoirs than in Blue Mesa Reservoir, and residence 

times were in weeks and days for Morrow Point and 

Crystal Reservoirs, respectively, and in months for 

Blue Mesa Reservoir. Water residence time has been 

shown to strongly influence phytoplankton abundance, 

as algal abundance increases with residence time 

(Soballe and Kimmel, 1987). The short residence 

times in Morrow Point and Crystal Reservoirs could 

limit the time phytoplankton had to reproduce and, 

thus, could limit the population size. Phytoplankton 

growth and development in these two reservoirs also 

could have been limited by lower water temperatures. 

Most of the water supplied to Morrow Point and 

Crystal Reservoirs was from cold, deep discharges 

from the upstream impoundment. Temperatures in 

Morrow Point and Crystal Reservoirs usually were 

less than those in Blue Mesa Reservoir because of the 

short residence times and the lack of solar radiation to 

warm the cold, deep-discharge inflow waters.

 As with other lakes or reservoirs in temperate 

latitudes, there were general patterns in the composition 

of phytoplankton communities in the three Curecanti 

NRA reservoirs. In oligotrophic Morrow Point and 

Crystal Reservoirs, most of the phytoplankton biomass 

was supplied by diatoms. Blue-green algae accounted 

for only a small amount of the phytoplankton biomass
54 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

DISSOLVED ORTHOPHOSPHATE

MEDIAN CONCENTRATION, IN MILLIGRAMS PER LITER

TOTAL PHOSPHORUS

DISSOLVED INORGANIC NITROGEN

TOTAL NITROGEN

SPRING SUMMER FALL EARLY WINTER

0.5

0.4

0.3

0.2

0.1

0

0.20

0.15

0.10

0.05

0.06

0.04

0.02

0.03

0.02

0.01

0

0

0

EXPLANATION

Blue Mesa Reservoir

Morrow Point Reservoir

Crystal Reservoir

Less than detection

Solid color: Photic zone or epilimnion

Stripes: near bottom

Figure 29. Median nutrient concentrations in Curecanti National Recreation Area, 

April–December 1999.
COMPARISON OF RESERVOIRS, INFLOWS, AND OUTFLOWS 55

in these reservoirs with lower productivity. This pattern 

is typical of lakes and reservoirs in temperature latitudes 

of the Northern Hemisphere (Watson and others, 1997). 

In the more nutrient-rich Blue Mesa Reservoir, especially Iola Basin, blue-green algae replaced diatoms 

as the dominant phytoplankton during August 

and October. Green algae never were the primary 

phytoplankton group in any of the three reservoirs. 

The amount of green algae generally is small in north 

temperate-latitude lakes or reservoirs because the rate 

of increase in green algae biomass with increasing total 

phosphorus is much slower than diatoms or blue-green 

algae (Watson and others, 1997). The dinoflagellate 

Ceratium sp. was present in the reservoirs at certain 

times in small amounts. Even though Ceratium sp. 

can regulate their position in the water column to 

that which is favorable for nutrients and sunlight, 

dinoflagellates, in general, are only a small part of the 

phytoplankton biomass in lakes or reservoirs of north 

temperate latitudes.

Patterns in community composition with respect 

to individual genera depended partly on characteristics 

of the particular phytoplankton. In each reservoir, 

diatoms were dominant during April, and Melosira sp. 

and Asterionella sp. were the primary genera. Among 

diatoms, Melosira sp. are characterized as a winterspring species, as they survive in a resting stage in 

reservoir sediment during nonbloom periods and are 

resuspended from the sediment during spring turnover 

(Horne and Goldman, 1994). This mechanism would 

account for the early season presence of Melosira sp.

in the Curecanti NRA reservoirs. During spring, 

diatoms are able to grow faster and thus outcompete 

other algae, and Asterionella sp. grows the fastest 

among the diatoms. In many lakes and reservoirs, 

Melosira sp. are at a maximum before the spring 

dominance of Asterionella sp. (Horne and Goldman, 

1994). Because Melosira sp. are heavy diatoms with 

thick silica walls, they require mixing conditions to be 

resuspended from sediment and to remain in the water 

column. Once stratification begins, Melosira sp. sink 

and again reside in the sediment.

Factors that eventually limit the growth of 

diatoms into the summer are the depletion of nutrients 

in the epilimnion, water temperature, grazing by zooplankton, and parasitism. Limiting nutrients may be 

nitrogen, phosphorus, and silica, the latter used for 

cell walls. Phytoplankton populations in Blue Mesa 

Reservoir (mainly blue-green algae and diatoms) 

and Morrow Point Reservoir (mainly diatoms) 

were at a minimum during August when inorganic 

nitrogen concentrations in most surface water were 

below detection and essentially fully depleted by 

biological activities. In contrast, the Crystal Reservoir 

phytoplankton population, primarily diatoms, was at a 

maximum during August. Inorganic nitrogen was not 

fully utilized, and phosphorus was probably the 

limiting nutrient.

During October, the bloom of blue-green 

algae Aphanizomenon sp. occurred in Blue Mesa 

Reservoir because inorganic nitrogen concentrations 

in surface waters were again below detection and higher 

water temperatures prevailed. Aphanizomenon sp. can 

fix atmospheric nitrogen for use as a food source when 

inorganic nitrogen in a water body is extinguished. 

Aphanizomenon sp. thrive in warm water and reproduce 

faster than diatoms in higher water temperatures (Horne 

and Goldman, 1994). Additionally, blue-green algae can 

regulate their position in the water column to take 

maximum advantage of environmental conditions.

Diatoms were dominant in Morrow and Crystal 

Reservoirs during October because inorganic nitrogen 

(median of 0.054 mg/L) was available in surface water, 

and cooler water temperatures were present. Straskraba 

and Budejovice (1990) reported similar results for a 

downstream reservoir receiving hypolimnetic releases 

from an upstream reservoir: a shift in phytoplankton 

composition from eutrophic assemblages with 

blooms of blue-green algae toward oligotrophic 

assemblages with more diatoms, and a decrease in 

primary productivity. Primary productivity in Morrow 

Point and Crystal Reservoirs, as reflected by median 

chlorophyll-a concentrations at each site, was significantly (p<0.04) lower than in Blue Mesa Reservoir. 

With fall turnover and the end of stratification in each 

reservoir, Melosira sp. became the primary diatom.

Chlorophyll-a in Reservoirs

Mean chlorophyll-a concentrations in the three 

reservoirs were highest in the most upstream area of 

the recreation area. The highest mean chlorophyll-a

concentrations were detected in Blue Mesa Reservoir, 

the most upstream reservoir, and in Iola and Cebolla 

Basins, the most upstream basins in the Blue Mesa 

Reservoir. Using mean chlorophyll-a concentrations 

and Likens’ (1975) classification system, Blue Mesa 
56 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

Reservoir was mesotrophic and Morrow Point and 

Crystal Reservoirs were oligotrophic. TSI values for 

total phosphorus, chlorophyll-a, and Secchi depth 

ranged between 29 and 55. For the first two indices, 

only Iola and Cebolla Basins had values of 50 or 

greater, reflecting the higher trophic states in the 

basins.

Characteristics of Reservoir Inflows 

and Outflows

Inflow to Blue Mesa Reservoir was based on a 

seasonal cycle, whereas most inflow to Morrow Point 

and Crystal Reservoirs depended largely on operations 

at each upstream impoundment since most flow into 

these reservoirs was outflow from the respective 

upstream impoundment. Water temperature in the 

stream inflows for each reservoir reflected a seasonal 

cycle; the warmest temperatures generally were during 

August, and the coolest temperatures were during 

November/December. Water temperatures in the 

outflow from Blue Mesa and Morrow Point Reservoirs 

were warmest during October, followed by August, 

May/June, and December (the coolest). Minimum and 

maximum temperatures in the outflow were moderated 

when compared to minimum and maximum temperatures in the stream inflows. Dissolved-oxygen concentrations in the inflows were favorable for aquatic 

organisms, and toxicity of un-ionized ammonia to 

fish was not indicated. All dissolved oxygen, pH, 

and nitrogen values in the inflows and outflows 

were within water-quality standards for the State of 

Colorado (table 6). Total phosphorus concentrations 

were elevated (above 0.05 mg/L) in many of the 

inflows to the three reservoirs. Most elevated concentrations, however, were detected in smaller inflows 

that contributed little water to the reservoirs, and the 

resulting small total phosphorus loads in these inflows 

would not be a water-quality concern. Only one 

outflow sample, Gunnison River below Gunnison 

Tunnel for August, had a total phosphorus concentration above 0.05 mg/L.

Most nutrient loading into Blue Mesa Reservoir, 

represented by Gunnison River at County Road 32, 

occurred during spring snowmelt (table 14). Nutrient 

loading into Morrow Point and Crystal Reservoirs 

depended largely on operations of each upstream 

impoundment. Using estimated nutrient loads in 

outflow from Crystal Dam as a proxy for nutrient 

loads in outflow from Blue Mesa and Morrow Point 

Dams, nutrient loads into Morrow Point and Crystal 

Reservoirs were moderated when compared to 

seasonal inflow loads that would occur with the 

absence of the upstream impoundment(s). Nutrient 

loads into these two downstream reservoirs were 

smaller during spring snowmelt than would be 

expected with seasonal inflows and were higher 

during the rest of the year. Limnological studies of 

other reservoir systems have indicated that nutrient 

availability for phytoplankton production may 

increase or decrease in reservoirs downstream from 

deep-discharge impoundments (Elser and Kimmel, 

1985). It appears that Blue Mesa Reservoir acts 

somewhat as a sink for phosphorus, as phosphorus 

concentrations in most inflows were higher than 

concentrations in the outflow. For Morrow Point and 

Crystal Reservoirs, it appears that the upstream dam 

discharges increased the availability of total nitrogen 

and dissolved inorganic nitrogen during summer, fall, 

and early winter. Phosphorus concentrations generally 

were similar in the inflows and outflows for both 

Morrow Point and Crystal Reservoirs.

Implications for Management

With water temperature and residence time 

appearing to affect productivity of the reservoirs 

and nutrient inflow to Morrow Point and Crystal 

Reservoirs affected by conditions in the upstream 

reservoir, the question arises as to how a change in 

current reservoir operations will affect productivity 

in all three reservoirs in terms of water temperature, 

residence time, and nutrient inflows. Johnson and 

others (1997) reported that the thermal structure in 

Blue Mesa Reservoir appears to be insensitive to operation changes under normal climatic conditions and 

that reservoir managers have much leeway in different 

operations without affecting kokanee salmon growth. 

However, effects of operation changes on nutrient 

dynamics were not studied. Reservoir operations 

can affect reservoir productivity in a variety of ways, 

including changes in nutrient loading and recycling, 

water-temperature changes, alterations in productivity 

levels with different temperatures, changes in the 

volume of stratification layers, and changes in density 

of organisms in each layer (Johnson and others, 1997). 

For the Aspinall Unit, it cannot be predicted how 
RETROSPECTIVE OF NUTRIENT CONDITIONS IN BLUE MESA RESERVOIR 57

reservoir productivity will change under different 

operational schemes because it is not known how 

much each particular effect—for example, a change 

in nutrient dynamics—affects productivity. This would 

require a nutrient modeling study. Use of Carlson’s 

TSI, though, can give some qualitative ideas on how 

various changes in total phosphorus, chlorophyll-a, 

and Secchi depth may or may not affect algal biomass.

Analysis and interpretation of data collected 

during this study and historical data highlighted 

several issues concerning sample collection. As 

discussed previously, there is a lack of nutrient and(or) 

streamflow data for most inflows and outflows that are 

needed for determining loads and conducting trend 

analysis. This 1999 study is one of the few studies 

where most inflows and outflows have been sampled; 

these samples indicated elevated total phosphorus 

concentrations in many inflows and fairly consistent 

nutrient concentrations in the reservoir outflows for 

the four sampling periods. Many of the smaller 

inflows, however, contribute little to the reservoirs, 

especially when compared to the largest tributaries and 

dam releases, and may only need to be sampled occasionally. To get an accurate estimate of nutrient loads 

and the movement of nutrients through the reservoir 

system, however, the outflows need to be sampled 

more frequently than seasonally. Ideally, the samples 

should be collected as near to the dam as possible, 

with no major inflows between the dam and the 

sampling site, rather than farther downstream. Also, 

streamflow should be measured at the larger inflows 

whenever being sampled. Little to no historical information is available on silica concentrations in the 

reservoirs or inflows and outflows. Because silica is 

an important nutrient for diatoms and can be a large 

component of cellular walls, it would be beneficial 

to have temporal and spatial information on silica 

concentrations in the recreation area.

RETROSPECTIVE OF NUTRIENT 

CONDITIONS IN BLUE MESA 

RESERVOIR

To assess whether water quality in Blue Mesa 

Reservoir has changed over time, data collected for 

this study during 1999 were compared to historical 

reservoir data for 1975, 1983, 1984, 1985, and 1998 

(tables 18 and 19). Data that were compared included 

physical properties (pH, specific conductance, and 

Secchi depth collected just below the water surface), 

nutrients, phytoplankton, and chlorophyll-a. Testing 

for temporal trends was conducted for the sites and 

data listed in table 7. To reduce seasonality in the 

data comparisons and trend testing, data for the same 

months or seasons were compared; for example, August 

to August and late September to early October for 

the different years. Trends were examined with the 

seasonal Kendall test. Cebolla Basin is excluded from 

the comparisons and trend testing of annual data for 

physical properties and nutrients because the basin 

was not sampled at a consistent location over time. 

Phytoplankton and chlorophyll-a data for this site for 

1975 and 1983–85 are included in the following discussion. Stream inflow sites that were examined were 

Gunnison River at County Road 32 and Lake Fork of 

the Gunnison River. Only the most important results 

for comparisons and trends testing are presented here.

Physical Properties

Values of pH in Iola Basin generally were 

lower during August and September in the mid-1980’s 

when compared to data for 1975 and 1999 (table 18); 

however, no statistically significant (p≤0.05) trend in 

pH was detected for Iola Basin for 1984–99 (table 20). 

Values of pH in Sapinero Basin in the mid-1980’s 

were slightly lower or equal to pH values for 1975 

and 1999 (table 18). A statistically significant upward 

trend in pH was indicated for 1992–99 (table 20). 

In a water body, pH varies because of chemical and 

biological factors, especially the distribution of carbon 

dioxide in the water column (Wetzel, 1983). During 

photosynthesis, carbon dioxide is utilized as an energy 

source, reducing carbon concentrations and increasing 

pH. Greater carbon dioxide use and, thus, higher 

values of pH would be expected with increased algal 

density. Phytoplankton density was elevated in Blue 

Mesa Reservoir during the mid-1980’s, but only the 

September 1984 pH values were elevated (table 18).

Specific-conductance values for both Iola and 

Sapinero Basins generally were higher during 1999 

when compared to data for 1975, 1983, 1984, and 

1985 (table 18). The only statistically significant trend 

result for specific conductance was for Iola Basin for 

1984–99; increasing values over time were indicated 

(table 20). Trend results for specific conductance in 

the Gunnison River at County Road 32, the major
58 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

inflow to Iola Basin, indicated increasing values 

for 1987–94 and no trend for 1995–99. No trend was 

present in the amount of inflow entering Blue Mesa 

Reservoir for 1984–99. The upward trend in specific 

conductance in Iola Basin for 1984–99 may be related 

to the upward trend in specific conductance in the 

Gunnison River at County Road 32 for 1987–94.

Secchi depth was lowest in Iola Basin during 

August and September 1975. A statistically significant (p≤0.05) trend result for 1984–99 indicated 

increasing values of Secchi depth in Iola Basin over 

time (table 20). Secchi depth can vary depending 

on biota and particulate and dissolved matter in the 

photic zone. For Iola Basin, no correlation was present 

between Secchi depth and specific conductance 

for 1984–99, even though an upward trend for that 

time period was indicated for both properties. The 

August 1975 Secchi depth in Sapinero Basin also 

was lower than in other years (table 18). More recently, 

no trend in Secchi depth in Sapinero Basin was indicated for 1992–99 (table 20).

Nutrients

Total ammonia plus organic nitrogen concentrations were identical or nearly identical in Iola and 

Sapinero Basins during late summer through early 

fall for 1975 and 1999 (table 18). Total phosphorus 

concentrations during late summer through early fall 

in the two basins were higher during 1984 than during 

1975 or 1999 (table 18). Dissolved orthophosphate 

concentrations in Iola and Sapinero Basin also were 

higher during August 1983 and(or) August 1984. Total 

ammonia plus organic nitrogen and total phosphorus 

data for both basins were tested for trends. A statistically significant (p≤0.05) result for total phosphorus in 

Sapinero Basin indicated a decrease in concentration 

for 1992–99 (table 20).

Results of the seasonal Kendall test for trends 

in nutrient data for Gunnison River at County Road 32 

and Lake Fork of the Gunnison River indicated that 

the only statistically significant (p≤0.05) trend present 

was an upward trend in total phosphorus concentration

Table 18. August and September/October water-quality data for Iola (site BM1) and Sapinero (site BM3) Basins, Blue Mesa 

Reservoir, for 1975, 1983, 1984, 1985, and 1999

[Site number refers to table 1 and figure 1; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter; --, no data; <, less than; data for 1975 are from 

U.S. Environmental Protection Agency (1977); data for 1983–85 are from the National Park Service]

Date

pH

(standard

units)

Specific

conductance

(μS/cm)

Secchi

depth

(meters)

Total ammonia plus

organic nitrogen

(mg/L)

Total

phosphorus

(mg/L)

Dissolved

orthophosphate

(mg/L)

BLUE MESA RESERVOIR AT IOLA BASIN

(SITE BM1)

August 1975 8.4 187 2.54 0.4 0.014 0.003

August 1984 18.0 1138 13.38 -- 10.05 10.020

August 1985 8.0 155 4.00 0.05 -- --

August 1999 8.3 203 4.5 0.2 0.008 <0.001

September 1975 8.7 158 2.74 0.3 0.020 0.002

September 1983 7.4 160 3.60 -- -- --

September 1984 8.6 1130 4.00 -- 10.06 1<0.010

September 1985 7.5 -- 3.50 -- -- --

October 1999 8.2 204 3.0 0.3 0.033 0.002

BLUE MESA RESERVOIR AT SAPINERO BASIN

(SITE BM3)

August 1975 8.0 156 1.27 0.2 0.012 0.002

August 1983 -- -- -- <1.00 <0.05 0.017

August 1984 18.0 1135 13.75 -- 10.03 10.010

August 1985 7.6 155 4.00 -- -- --

August 1999 8.2 184 4.5 0.2 0.013 0.001

September 1975 8.4 124 3.51 0.2 0.015 0.002

September 1983 7.6 180 3.00 -- -- --

September 1984 18.4 1130 14.00 -- 10.10 1<0.010

September 1985 -- -- --

October 1999 7.9 179 3.5 0.1 0.011 0.006

1

Median value.
RETROSPECTIVE OF NUTRIENT CONDITIONS IN BLUE MESA RESERVOIR 59

Table 19. Phytoplankton genera detected in Blue Mesa Reservoir during 1975, 1983, 1984, 1985, 1998, and 1999, listed in respective p[Data for 1975 and 1983–85 are from Cudlip and others (1987); data for 1998 are from National Park Service (1998b)] 

Phytoplankton 1975 1983 1984 1985 1998 1999 Phytoplankton 1975 1983 1984 

Phylum Bacillariophyta

(Diatoms)

Phylum Chlorophyta

(Green algae)

Achnanthes

X Ankistrodesmus

X

X

Amphipleura

X Asterococcus

X

Amphora

X Botryococcus

X

X

Asterionella

X

X

X

X

X

X Chaetophora

X

Biddulphia

X Characium

X

Cocconeis

X

X

X Chlamydomonas

X

X

Coscinodiscus

X Chlorococcum

Cyclotella

X

X Chlorogonium

X

Cymatopleura

X Closteriopsis

X

Cymbella

X

X Closterium

X

Diatoma

X Coelastrum

X

Epithemia

X Eudorina

X

X

Fragilaria

X

X

X

X

X

X Gloeococcus

X

Gomphonema

X

X Gloeocystis

X

Hannaea

X

X

X Gongrosira

X

Mastogloia

X Gonium

X

Melosira

X

X

X

X

X Kirchneriella

X

Navicula

X

X

X

X Mougeotia

X

X

Nitzschia

X

X

X Nannochloris

X

Pinnularia

X Octocystis

X

X

Rhoicosphenia

X Octosporiella

X

X

Rhopalodia

X Oedogonium

X

X

Stephanodiscus

X

X

X

X

X

X Oocystis

X

X

X

Surirella

X Palmellopsis

X

Synedra

X

X

X

X Pandorina

X

Tabellaria

X Pediastrum

X

X
60 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado Phylum Chlorophyta (green algae)—Continued Phylum Chrysophyta (Golden-brown algae) Quadrigula

X

Chromulina

X Scenedesmus

X

Chrysamoeba

X

X Schroederia

X

X

X

Chrysochromulina

X Sphaerocystis

X

X

Dinobryon

X

X

X Spirogyra

X

X

Mallomonas

X Spondylosium

X

Synura

X Staurastrum

X

X

X

Phylum Cryptophyta

(Cryptomonad algae)

Stigeoclonium

X

Chroomonas

X Tetraedron

X

Cryptomonas

X

X

X

X Ulothrix

X

X

Phylum Cyanophyta

(Blue-green algae)

Volvox

X

X

Anabaena

X

X

X

X

X Volvulina

X

X

Aphanizomenon

X

X

X

X

X

X

Aphanothece

X

X

Dactylococcopsis

X

Gomphosphaeria

X

Microcystis

X

X

X

Nostoc

X

Oscillatoria

X

Pseudoanabaena

X

Phylum Euglenophyta

(Euglenoid algae)

Colacium

X

X

Euglena

X

X

X

Phylum Pyrrophyta

(Dinoflagellates)

Ceratium

X

X

X

X

Phylum Xanthophyta

(Yellow-green algae)

Tribonema

X

X

Table 19. Phytoplankton genera detected in Blue Mesa Reservoir during 1975, 1983, 1984, 1985, 1998, and 1999, listed in respective p[Data for 1975 and 1983–85 are from Cudlip and others (1987); data for 1998 are from National Park Service (1998b)] 

Phytoplankton 1975 1983 1984 1985 1998 1999 Phytoplankton 1975 1983 1984 
RETROSPECTIVE OF NUTRIENT CONDITIONS IN BLUE MESA RESERVOIR 61

for Gunnison River at County Road 32 for 1987–94 

(table 20). This did not appear to affect Blue Mesa 

Reservoir, as no trend was present in total phosphorus 

concentrations for Iola Basin (the basin nearest to 

the Gunnison River inflow) for 1987–99. Also, there 

was no correlation between total phosphorus concentrations in the Gunnison River at County Road 32 and 

chlorophyll-a concentrations in Iola Basin for 1984–99. 

Data on total phosphorus concentrations for the major 

inflow to Sapinero Basin, Lake Fork of the Gunnison 

River, are only available for 1995–99, and no trend 

was indicated for those data. The downward trend in 

total phosphorus concentration in Sapinero Basin for 

1992–99 does not appear to be related to total phosphorus concentrations in Lake Fork of the Gunnison 

River.

Table 20. Results of seasonal Kendall test for temporal trends in Blue Mesa Reservoir inflow and water-quality parameters 

for Iola (site BM1) and Sapinero (site BM3) Basins in Blue Mesa Reservoir, Gunnison River at County Road 32 (site BI1), and 

Lake Fork of the Gunnison River (site BI10)

[Site number refers to table 1 and figure 1; periods are in water years, except for Blue Mesa Reservoir inflow, which is in calendar years; p-value is the 

significance level of the test; BOR, Bureau of Reclamation; NPS, National Park Service; CURE, U.S. Geological Survey and National Park Service data 

collection in 1999; μS/cm, microsiemens per centimeter at 25 degrees Celsius; m, meter; mg/L, milligrams per liter; slopes are listed only for statistically 

significant trend results; UCOL, Upper Colorado River Basin National Water-Quality Assessment Program]

Parameter Period Source of data Slope p-Value Trend direction

BLUE MESA RESERVOIR

Inflow 1984–99 BOR 0.510 None

BLUE MESA RESERVOIR AT IOLA BASIN

(SITE BM1)

Dissolved oxygen 1984–99 NPS, CURE 0.078 None

pH 1984–99 NPS, CURE 0.980 None

Specific conductance 1984–99 NPS, CURE 4.78 μS/cm per year 0.008 Upward

Secchi depth 1984–99 NPS, CURE 0.080 m per year 0.009 Upward

Chlorophyll-a 1984–99 NPS, CURE 0.689 None

Ammonia plus organic nitrogen, total 1987–99 NPS, CURE 0.328 None

Total phosphorus 1987–99 NPS, CURE 0.573 None

BLUE MESA RESERVOIR AT SAPINERO BASIN

(SITE BM3)

Dissolved oxygen 1992–99 NPS, CURE 0.441 None

pH 1992–99 NPS, CURE 0.042 standard units 

per year

<0.001 Upward

Specific conductance 1992–99 NPS, CURE 0.423 None

Secchi depth 1992–99 NPS, CURE 0.404 None

Chlorophyll-a 1992–99 NPS, CURE 0.423 None

Ammonia plus organic nitrogen, total 1992–99 NPS, CURE 0.698 None

Total phosphorus 1992–99 NPS, CURE –0.018 mg/L per year 0.003 Downward

GUNNISON RIVER AT COUNTY ROAD 32

(SITE BI1)

Specific conductance 1995–99 UCOL, CURE 0.514 None

1987–94 NPS 7.80 μS/cm per year <0.001 Upward

Ammonia plus organic nitrogen, total 1995–99 UCOL, CURE 0.695 None

1987–94 NPS 0.319 None

Dissolved inorganic nitrogen 1995–99 UCOL, CURE 0.896 None

Total phosphorus 1995–99 UCOL, CURE 0.240 None

1987–94 NPS 0.028 mg/L per year <0.001 Upward

Dissolved orthophosphate 1995–99 UCOL, CURE 0.896 None

LAKE FORK OF THE GUNNISON RIVER

(SITE BI10)

Ammonia plus organic nitrogen, total 1995–99 UCOL, CURE 0.462 None

Total phosphorus 1995–99 UCOL, CURE 0.806 None
62 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

Table 21. Mean phytoplankton density in Blue Mesa Reservoir by basin for 1983, 1984, 1985, 1998, and 1999

[Site number refers to table 1 and figure 1; algal units/L, algal units per liter; data for 1983–85 are from Cudlip and others (1987); data for 1998 are from National Park Service 

(1998b)]

Date

Iola Basin

(site BM1)

(algal units/L)

Cebolla Basin

(site BM2)

(algal units/L)

Sapinero Basin

(site BM3)

(algal units/L)

1983: July, August 86,000 66,000 69,000

1984: July–September 3,290,000 386,000 239,000

1985: July–September 8,484,000 4,846,000 16,000

1998: June, July, September 12,091 1,861 3,054

1999: April, August, October 7,919 1,422 1,135

As stated previously, all three basins in Blue 

Mesa Reservoir during 1999 were limited in phosphorus during April and nitrogen during November, 

with possible nitrogen limitation in Sapinero Basin 

during summer and all three basins during fall. 

The results for spring and summer of 1999 can be 

compared with historical data for the same seasons. 

The limitation of phosphorus during spring 1999 

mirrors the phosphorus limitation noted during May 

and June 1983, 1984, and 1985 (Cudlip and French, 

1985). While nitrogen probably was the limiting 

nutrient in Sapinero Basin during summer 1999, 

historical data indicate variability in nutrient limitation 

during summer. For 1983 and 1984, nitrogen was the 

limiting nutrient during July, and phosphorus was 

limiting during August. Opposite results prevailed 

for 1985 with phosphorus limitation during July 

and nitrogen limitation during August. Nitrogen 

was the limiting nutrient during August 1975 

(U.S. Environmental Protection Agency, 1977).

Phytoplankton

Differences in phytoplankton over time in Blue 

Mesa Reservoir can be examined in terms of density, 

genera richness and community structure, and community succession. Mean phytoplankton densities in 

the three basins were lower during 1999 than those 

during 1983, 1984, 1985, and 1998 (table 21), and 

densities were lower during 1998 than during the 

mid-1980’s (National Park Service, 1998b). This 

decrease in mean phytoplankton density over time 

may be related to genera richness and nutrients. In 

comparing phytoplankton data for Blue Mesa Reservoir 

for 1975, 1983, 1984, 1985, 1998, and 1999, genera 

richness was greatest during the mid-1980’s (fig. 30, 

table 19). Genera of green algae were most common 

during 1983 and 1984, whereas diatoms were dominant 

during 1985 (fig. 31). The mid-1980’s were wet years 

in the Gunnison River Basin. Inflows to Blue Mesa 

Reservoir during 1983, 1984, and 1985 were higher 

than those for 1975, 1998, and 1999. The range in 

maximum daily peak inflows during the mid-1980’s 

was 8,328–16,084 ft3/s, whereas the range for 1975, 

1998, and 1999 was 4,754–7,346 ft3

/s (Bureau of 

Reclamation, 1975–99). Greater inflows into Blue Mesa 

Reservoir during the mid-1980’s would have increased 

dissolved nutrient and suspended-sediment loads and 

provided additional nutrients for phytoplankton, 

possibly resulting in an increase in mean phytoplankton 

density and number of genera present in the reservoir.

The phytoplankton community succession 

observed during 1999 was similar to that during 

the mid-1980’s and 1998 (Cudlip and others, 1987; 

National Park Service, 1998b). Diatoms were the 

dominant phytoplankton during the cooler spring and 

early summer months, whereas the blue-green algae 

Aphanizomenon sp. was dominant during the warmer 

late summer and fall months. One difference between 

the 1999 data and historical data was that the diatom 

Tabellaria, a prominent genus during 1999, was not 

observed during the mid-1980’s or 1998. It is normal 

for species composition to fluctuate from year to year 

in a water body, as long as the system is not seriously 

disturbed (Wetzel, 1983).

Chlorophyll-a

Finally, current and historical data for 

Blue Mesa Reservoir can be compared in terms of 

chlorophyll-a and trophic status of the reservoir. Mean 

chlorophyll-a concentrations for the 0–15 m interval in 

Iola, Cebolla, and Sapinero Basins were determined 

for the July–October 1985 monthly samples, and the
RETROSPECTIVE OF NUTRIENT CONDITIONS IN BLUE MESA RESERVOIR 63

trophic status was determined using Likens’ (1975) 

index. Iola Basin was classified as mesotrophic with 

a mean chlorophyll-a concentration of 4.84 mg/m3; 

Cebolla Basin, oligotrophic, 2.58 mg/m3

; and 

Sapinero Basin, oligotrophic, 1.41 mg/m3 (Cudlip 

and French, 1985). In comparing these 1985 results to 

the sampling results of August and October 1999, the 

trophic status of the basins did not change between 

1985 and 1999. Iola Basin remained mesotrophic with 

a mean chlorophyll-a concentration of 4.54 mg/m3

for August and October 1999. Cebolla Basin remained 

oligotrophic with a mean chlorophyll-a concentration 

of 1.49 mg/m3 for the same months of 1999. This 

latter value, however, was lower than the chlorophyll-a

concentration of 2.58 mg/m3

 recorded during 1985 

and may be due to the difference in the number of 

months used in the mean calculations (July–October 

for 1985 and August and October for 1999) and to 

year-to-year variability in monthly chlorophyll-a

concentrations. Sapinero Basin was again oligotrophic with a mean chlorophyll-a concentration 

of 1.46 mg/m3 for August and October 1999. Cudlip 

and others (1987) summarized chlorophyll-a data 

for 1982–85 and reported that Blue Mesa Reservoir 

was mesotrophic over the 3-year time period. 

The reservoir also was mesotrophic during 1975 

(U.S. Environmental Protection Agency, 1977) and 

1999. Although the trophic status of the reservoir 

remained constant over time and mean chlorophyll-a

concentrations were similar between 1985 and 1999, 

the annual variability in chlorophyll-a concentration 

was much greater for Iola Basin after 1985 (fig. 32). 

Annual chlorophyll-a data for Sapinero Basin do 

not begin until 1992.

Nutrient Enrichment

Results of the comparison and trend-analysis 

examination of historical and current (as of 1999) data 

for Blue Mesa Reservoir indicate that nutrient enrichment is not occurring in the reservoir. For Iola Basin, 

no trends were detected in total ammonia plus organic 

nitrogen and total phosphorus concentrations for 

1987–99, even though an upward trend in total phosphorus was detected in the Gunnison River at County 

Road 32 for 1987–94. For Sapinero Basin, no trend was 

detected in total ammonia plus nitrogen concentrations 

for 1992–99, whereas there was a downward trend 

in total phosphorus concentrations for the same time 

period. No trend was detected in these two nutrients 

in the Lake Fork of the Gunnison River for 1995–99. 

A comparison of chlorophyll-a data did not indicate an 

increase in reservoir productivity. Finally, the trophic 

status of the reservoir during 1999 was similar to that 

observed during 1975 and the mid-1980’s. It does not 

appear that increasing development and land-use 

changes in the upper Gunnison River Basin have 

affected nutrient levels in Blue Mesa Reservoir. While 

in some cases a bloom of Aphanizomenon sp. can indicate eutrophic conditions, the Aphanizomenon sp.

NUMBER OF 

GENERA

0

10

20

30

40

50

60

70

YEAR

1975 1983 1984 1985 1998 1999

Figure 30. Genera richness in Blue 

Mesa Reservoir for 1975, 1983, 1984, 

1985, 1998, and 1999.

Blue-green algae

Cryptomonad algae

Diatoms

Dinoflagellates

Euglenoid algae

Golden-brown algae

Green algae

Yellow-green algae

PHYTOPLANKTON PHYLUM

1975 1983 1984 1985 1998 1999

YEAR

PHYTOPLANKTON 

COMMUNITY, IN 

NUMBER OF GENERA

PER PHYLUM

0

10

20

30

40 EXPLANATION

Figure 31. Phytoplankton community in Blue Mesa Reservoir for 1975, 1983, 1984, 1985, 1998, and 

1999.
64 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, 

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

bloom observed in Iola Basin during fall 1999 probably 

was related more to favorable environmental conditions 

and biological factors (including warm water, ability to 

fix atmospheric nitrogen, and regulation of position in 

the water column) than excess nutrients. A bloom of 

Aphanizomenon sp. in Iola Basin is not a unique occurrence; a bloom was observed as early as 1967 (Wiltzius, 

1974).

SUMMARY

To assess the current (as of 1999) limnological 

characteristics of Blue Mesa, Morrow Point, and 

Crystal Reservoirs and to carry out a 25-year retrospective of nutrient conditions in Blue Mesa Reservoir, the 

U.S. Geological Survey and the National Park Service 

conducted a water-quality investigation from April 

through December 1999. Samples were collected from 

reservoir, inflow, and outflow sites four times during 

1999. Reservoir samples for nutrient analysis were 

collected from multiple depths at three sites on Blue 

Mesa and Morrow Point Reservoirs and at one site on 

Crystal Reservoir. Phytoplankton and chlorophyll-a

samples were collected in the reservoirs from nearsurface waters. Total nitrogen and phosphorus concentrations in the reservoirs were low. Median concentrations were less than 0.4 and 0.06 milligram per liter, 

respectively. Nutrient concentrations for most summer 

and fall samples collected at depth were greater than 

photic-zone samples. The phytoplankton community 

and density in each reservoir were affected by water 

temperature, nutrients, and water residence time. In 

each reservoir, diatoms dominated with cooler water 

temperatures—during spring and early winter in 

Blue Mesa Reservoir and throughout the year in 

Morrow Point and Crystal Reservoirs. Seasonally, 

both Blue Mesa and Morrow Point Reservoirs had 

their lowest phytoplankton densities during summer 

when inorganic nitrogen was not detected and was 

fully utilized by biota. Density in Crystal Reservoir 

was highest during summer when orthophosphate was 

fully utilized and inorganic nitrogen was not. With low 

inorganic nitrogen concentrations and warmer temperatures in Blue Mesa Reservoir during summer and fall, 

blue-green algae were the dominant phytoplankton. 

Spatially, phytoplankton abundance was highest in Blue 

Mesa Reservoir and lowest in Crystal Reservoir. In Blue 

Mesa Reservoir, the longer residence time (greater than 

6 months) and warmer water temperatures presented 

favorable conditions for phytoplankton growth and 

development. In Morrow and Crystal Reservoirs, low 

phytoplankton abundance was probably due to short 

residence times and cooler water temperatures. The 

short residence times of weeks and days, respectively, 

would limit the time phytoplankton had to reproduce 

and would limit the population size. Also, the short 

residence times would not be long enough to allow 

the deep-discharge waters to warm, and cooler water 

temperatures would limit phytoplankton growth and 

development. Chlorophyll-a concentrations in the 

reservoirs reflected productivity levels. The mean 

chlorophyll-a concentration was higher in Blue Mesa 

Reservoir than Morrow and Crystal Reservoirs. Using 

the classification system developed by Likens (1975), 

the trophic status of Blue Mesa Reservoir varied along 

an upstream-to-downstream gradient, with mesotrophic 

conditions and more productive waters in the upstream 

portions of the reservoir and oligotrophic conditions 

downstream. Both Morrow and Crystal Reservoirs were 

oligotrophic. Trophic-state indices for total phosphorus, 

chlorophyll-a, and Secchi depth ranged between 29 

and 55. Only Iola and Cebolla Basins in Blue Mesa 

Reservoir had total phosphorus and chlorophyll-a

indices above 50, reflecting the mesotrophic conditions in the two basins. Because there are no major 

Chlorophyll-a

EXPLANATION

YEAR

CHLOROPHYLL-a, IN 

MILLIGRAMS PER 

CUBIC METER

0

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

199419951996

1997

19981999

5

10

15

20

25

Figure 32. Chlorophyll-a concentrations in Blue Mesa Reservoir at Iola Basin (site BM1), 1984–99.
REFERENCES 65

impoundments directly upstream from Blue Mesa 

Reservoir, nutrient inflows to the reservoir varied 

seasonally, with a lower nutrient supply occurring 

after spring snowmelt. For Morrow Point and Crystal 

Reservoirs, there was a steady inflow of nutrients during 

the sampling period. Nutrient concentrations in the 

deep-discharge waters from the respective upstream 

impoundment were fairly consistent for all four 

sampling events, and nutrient concentrations in the two 

reservoirs were mostly dependent on upstream reservoir 

conditions rather than seasonal stream inflows. Among 

the physical properties and nutrient constituents studied 

for the inflows for all three reservoirs, only total phosphorus concentrations were elevated; other parameters 

including dissolved oxygen, pH, and nitrogen constituents were within water-quality standards for the State of 

Colorado. Total phosphorus loads, however, would be 

low in most stream inflows because of small streamflow 

amounts. For Blue Mesa Reservoir, a comparison of 

1999 and historical chlorophyll-a and nutrient data 

revealed that productivity in the reservoir has not 

changed over time, and the reservoir has not become 

more enriched with nutrients.

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SUPPLEMENTAL DATA
SUPPLEMENTAL DATA 71

Table 22. Reservoir profile measurements, Blue Mesa Reservoir at Iola Basin (site BM1), April–November 1999

[Site number refers to table 1 and figure 1; C, Celsius; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

APRIL 20, 1999, SECCHI-DISC DEPTH, 3.0 METERS AUGUST 19, 1999, SECCHI-DISC DEPTH, 4.5 METERS

1 5.7 9.7 8.3 225 1 19.3 6.8 8.3 203

2 5.7 9.6 8.3 227 2 19.0 6.9 8.3 204

3 5.7 9.6 8.3 226 3 19.0 6.8 8.3 202

4 5.7 9.6 8.3 228 4 18.9 7.0 8.2 203

5 5.7 9.6 8.3 227 5 18.9 6.8 8.3 204

6 5.7 9.5 8.3 227 6 18.8 6.9 8.3 204

7 5.7 9.5 8.3 227 7 18.7 6.7 8.3 205

8 5.7 9.5 8.3 226 8 18.7 6.5 8.2 205

9 5.7 9.5 8.3 224 9 18.6 6.4 8.2 203

10 5.7 9.4 8.3 225 10 18.4 6.3 8.2 205

11 5.7 9.5 8.3 226 11 17.0 6.0 8.0 201

12 5.6 9.4 8.3 227 12 16.6 6.0 8.0 202

13 5.6 9.3 8.3 226 13 16.2 5.9 8.0 202

14 5.5 9.2 8.3 227 14 16.0 5.8 7.9 202

15 5.5 9.2 8.3 227 15 15.7 5.6 7.9 202

16 5.5 9.2 8.3 224 16 15.4 5.5 7.8 202

17 15.2 5.3 7.8 204

18 15.1 5.6 7.8 204

19 14.9 4.3 7.7 206

20 14.4 4.0 7.6 209

21.4 14.4 3.8 7.6 210

OCTOBER 6, 1999, SECCHI-DISC DEPTH, 3.0 METERS NOVEMBER 30, 1999, SECCHI-DISC DEPTH, 4.0 METERS

1 14.2 7.6 8.2 204 1 6.7 8.7 7.7 191

2 14.2 7.6 8.2 204 2 6.7 8.7 7.7 191

3 14.2 7.6 8.2 204 3 6.7 8.7 7.7 191

4 14.2 7.6 8.2 204 4 6.6 8.7 7.7 191

5 14.2 7.6 8.3 204 5 6.5 8.6 7.7 192

6 14.2 7.6 8.2 204 6 6.5 8.6 7.7 192

7 14.2 7.6 8.2 205 7 6.4 8.6 7.7 192

8 14.2 7.5 8.2 204 8 6.3 8.5 7.7 192

9 14.1 7.6 8.2 204 9 6.3 8.5 7.7 192

10 14.1 7.6 8.2 204 10 6.3 8.5 7.7 193

11 14.1 7.6 8.3 204 11 6.2 8.5 7.7 193

12 14.1 7.6 8.2 205 12 6.2 8.5 7.7 192

13 14.1 7.6 8.3 205 13 5.9 8.6 7.6 196

14 14.1 7.6 8.3 204 14 5.6 8.7 7.6 198

15 14.1 7.6 8.3 204 15 5.4 8.7 7.6 199

16 14.1 7.6 8.3 205 16 4.8 8.7 7.6 204

17 14.1 7.6 8.3 205 17 4.4 8.5 7.4 209

18 14.1 7.6 8.3 205

19 14.1 7.5 8.2 205

20 14.0 7.4 8.2 205

21 10.8 7.6 7.9 215
72 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999,

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

Table 23. Reservoir profile measurements, Blue Mesa Reservoir at Cebolla Basin (site BM2), April–November 1999

[Site number refers to table 1 and figure 1; C, Celsius; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

APRIL 20, 1999, SECCH-DISC DEPTH, 3.0 METERS AUGUST 19, 1999, SECCHI-DISC DEPTH, 5.0 METERS

1 5.1 10.0 8.4 221 1 19.0 6.5 8.2 190

2 5.0 10.0 8.4 220 2 19.0 6.5 8.2 191

3 5.0 10.0 8.4 218 3 19.0 6.5 8.2 189

4 5.0 9.9 8.4 220 4 19.0 7.0 8.2 189

5 5.0 9.9 8.4 218 5 19.0 7.1 8.3 190

6 5.0 9.9 8.4 218 6 19.0 7.0 8.3 192

7 5.0 9.9 8.4 219 7 19.0 7.0 8.3 191

8 5.0 9.8 8.4 219 8 19.0 7.0 8.3 191

9 5.0 9.8 8.4 221 9 19.0 6.9 8.3 192

10 5.0 9.8 8.4 220 10 17.3 5.6 7.9 202

11 5.0 9.8 8.4 219 11 16.8 5.4 7.8 203

12 5.0 9.7 8.4 218 12 16.3 5.2 7.7 205

13 5.0 9.7 8.4 219 13 16.0 5.1 7.7 206

14 5.0 9.7 8.4 219 14 15.8 5.0 7.7 204

15 5.0 9.7 8.4 220 15 15.5 5.0 7.6 200

16 5.0 9.7 8.4 218 16 15.3 4.9 7.6 204

17 4.9 9.7 8.4 219 17 15.2 4.8 7.6 209

18 4.9 9.7 8.4 219 18 14.8 4.7 7.6 195

19 4.9 9.7 8.4 218 19 14.6 4.7 7.6 199

20 4.9 9.7 8.4 220 20 14.4 4.8 7.6 193

25 4.8 9.6 8.4 219 25 12.7 5.2 7.6 185

30 4.8 9.6 8.4 219 30 11.2 5.0 7.6 188

35 4.7 9.6 8.4 219 35 10.3 4.4 7.5 191

40 4.7 9.6 8.4 218 40 9.2 4.1 7.5 196

45 4.7 9.6 8.4 217 45 7.8 4.3 7.5 196

50 4.6 9.5 8.4 218 50 7.2 4.5 7.5 196

55 7.0 4.5 7.5 196

60 6.8 4.2 7.5 196

60.9 6.8 4.2 7.4 196
SUPPLEMENTAL DATA 73

Table 23. Reservoir profile measurements, Blue Mesa Reservoir at Cebolla Basin (site BM2), April–November 

1999—Continued

[Site number refers to table 1 and figure 1; C, Celsius; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

OCTOBER 6, 1999, SECCHI-DISC DEPTH, 5.0 METERS NOVEMBER 30, 1999, SECCHI-DISC DEPTH, 4.0 METERS

1 14.5 6.8 8.0 197 1 7.6 8.9 7.8 191

2 14.4 6.8 8.0 197 2 7.6 8.7 7.8 191

3 14.4 6.8 8.0 197 3 7.7 8.7 7.8 191

4 14.4 6.7 8.0 197 4 7.7 8.8 7.8 190

5 14.4 6.6 8.0 197 5 7.6 8.9 7.8 190

6 14.4 6.7 8.0 197 6 7.7 8.9 7.8 191

7 14.4 6.7 8.0 198 7 7.7 8.9 7.8 191

8 14.4 6.6 8.0 197 8 7.7 8.4 7.8 191

9 14.4 6.6 8.0 197 9 7.7 8.1 7.8 191

10 14.4 6.6 8.0 197 10 7.7 8.0 7.8 191

11 14.4 6.6 8.0 197 11 7.7 8.0 7.8 191

12 14.4 6.6 8.0 198 12 7.7 8.0 7.8 191

13 14.4 6.6 8.0 198 13 7.6 8.0 7.8 191

14 14.4 6.6 8.0 197 14 7.6 8.0 7.8 191

15 14.4 6.6 8.0 198 15 7.7 8.0 7.8 191

16 14.4 6.6 8.0 198 16 7.7 8.0 7.8 191

17 14.4 6.5 8.0 198 17 7.7 8.0 7.8 191

18 14.4 6.6 8.0 198 18 7.6 7.9 7.8 191

19 14.4 6.6 8.0 198 19 7.6 8.0 7.8 191

20 14.4 6.6 8.0 197 20 7.6 8.0 7.8 191

25 14.4 6.6 8.0 197 25 7.6 8.0 7.8 191

30 13.8 6.0 7.9 203 30 7.3 7.9 7.8 192

35 13.0 4.3 7.5 205 35 7.0 7.9 7.8 193

40 11.8 2.0 7.2 212 40 6.6 7.9 7.7 194

45 8.8 1.5 7.1 208 45 6.4 7.9 7.7 195

50 7.4 2.6 7.1 205 50 6.3 7.8 7.7 195

55 7.2 2.3 7.0 206 54.3 6.3 6.9 7.7 196

56 7.2 2.1 7.2 207
74 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999,

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

Table 24. Reservoir profile measurements, Blue Mesa Reservoir at Sapinero Basin (site BM3), April–November 1999

[Site number refers to table 1 and figure 1; C, Celsius; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

APRIL 20, 1999, SECCHI-DISC DEPTH, 3.5 METERS AUGUST 19, 1999, SECCHI-DISC DEPTH, 4.5 METERS

1 5.1 9.8 8.4 213 1 18.9 7.8 8.2 184

2 4.8 9.8 8.4 213 2 18.9 6.8 8.3 183

3 4.7 9.8 8.4 212 3 18.9 6.8 8.3 185

4 4.7 9.7 8.4 214 4 18.8 6.8 8.3 186

5 4.6 9.7 8.4 213 5 18.8 6.9 8.3 184

6 4.6 9.6 8.4 213 6 18.7 6.8 8.3 186

7 4.5 9.6 8.3 213 7 18.7 6.8 8.3 185

8 4.5 9.6 8.3 214 8 18.7 6.9 8.3 185

9 4.5 9.5 8.3 214 9 18.6 6.8 8.3 184

10 4.5 9.6 8.3 213 10 18.5 6.6 8.2 185

11 4.5 9.5 8.3 214 11 17.6 5.6 8.0 177

12 4.5 9.5 8.3 211 12 16.7 5.6 7.9 161

13 4.5 9.5 8.3 213 13 16.0 5.7 7.8 151

14 4.4 9.5 8.3 214 14 15.4 6.1 7.8 146

15 4.4 9.5 8.3 212 15 15.3 5.9 7.8 145

16 4.4 9.5 8.3 213 16 15.2 5.4 7.7 144

17 4.4 9.5 8.3 211 17 14.9 5.6 7.7 142

18 4.4 9.5 8.3 211 18 14.8 5.5 7.8 143

19 4.4 9.5 8.3 212 19 14.8 5.2 7.7 157

20 4.4 9.5 8.3 214 20 14.6 6.0 7.6 146

25 4.4 9.4 8.3 212 25 13.2 5.8 7.6 137

30 4.3 9.4 8.3 212 30 11.2 6.0 7.7 145

35 4.3 9.4 8.3 212 35 10.4 5.8 7.7 166

40 4.3 9.4 8.3 211 40 9.3 5.2 7.6 187

45 4.3 9.4 8.3 212 45 8.0 5.8 7.6 186

50 4.2 9.4 8.3 212 50 7.1 5.9 7.7 195

55 4.2 9.4 8.3 212 55 6.6 6.6 7.7 193

60 4.2 9.4 8.3 212 60 6.3 6.9 7.8 192

65 4.3 9.3 8.3 212 65 6.1 6.7 7.8 193

70 6.0 6.6 7.8 194

73 5.9 6.7 7.8 193
SUPPLEMENTAL DATA 75

Table 24. Reservoir profile measurements, Blue Mesa Reservoir at Sapinero Basin (site BM3), April–November 

1999—Continued

[Site number refers to table 1 and figure 1; C, Celsius; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

OCTOBER 6, 1999, SECCHI-DISC DEPTH, 3.5 METERS NOVEMBER 30, 1999, SECCHI-DISC DEPTH, 5.0 METERS

1 14.3 6.4 7.9 179 1 8.2 7.3 7.5 187

2 14.3 6.4 7.9 179 2 8.1 7.4 7.5 188

3 14.2 6.3 7.8 180 3 8.1 7.4 7.5 187

4 14.2 6.2 7.8 180 4 8.1 7.3 7.5 188

5 14.2 6.1 7.8 180 5 8.1 7.3 7.6 188

6 14.2 6.1 7.8 181 6 8.1 7.3 7.6 188

7 14.2 6.0 7.8 181 7 8.1 7.3 7.5 188

8 14.2 6.0 7.8 180 8 8.1 7.2 7.6 188

9 14.2 6.0 7.8 180 9 8.1 7.2 7.6 188

10 14.2 6.1 7.8 180 10 8.1 7.2 7.6 188

11 14.2 6.1 7.8 180 11 8.1 7.2 7.6 188

12 14.2 6.1 7.8 180 12 8.1 7.2 7.6 188

13 14.1 6.1 7.8 180 13 8.1 7.2 7.6 188

14 14.1 6.1 7.7 181 14 8.1 7.1 7.6 188

15 14.1 6.1 7.8 180 15 8.1 7.2 7.6 187

16 14.1 6.1 7.8 181 16 8.1 7.3 7.6 187

17 14.1 6.0 7.8 181 17 8.1 7.2 7.6 187

18 14.1 6.0 7.7 181 18 8.1 7.2 7.6 187

19 14.1 6.0 7.7 181 19 8.1 7.2 7.6 187

20 14.1 6.0 7.7 182 20 8.1 7.2 7.6 187

25 14.1 6.0 7.7 182 25 8.1 7.2 7.6 187

30 14.0 5.8 7.7 182 30 8.1 7.1 7.6 188

35 13.1 3.8 7.3 194 35 8.0 6.9 7.6 189

40 11.4 4.0 7.2 186 40 8.0 6.8 7.5 190

45 8.6 4.1 7.2 199 45 7.8 6.6 7.5 192

50 7.4 4.3 7.2 203 50 7.7 6.3 7.4 193

55 6.6 5.8 7.3 202 55 6.7 4.6 7.1 195

60 6.3 6.1 7.4 202 60 6.4 4.8 7.1 194

65 6.1 6.3 7.4 201 65 6.2 5.0 7.1 195

68.5 6.0 6.4 7.4 201 70 6.0 4.9 7.1 196

75 5.9 4.5 7.0 197

79 5.8 3.6 7.0 198
76 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999,

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado Table 25. Nitrogen and phosphorus concentrations in Blue Mesa Reservoir, April–November 1999 [Site number refers to table 1 and figure 1; <, less than; E, estimated] Date Time Sampling depth (feet) Concentration, in milligrams per liter Nitrogen, ammonia, dissolved Nitrogen, un-ionized ammonia, dissolved1 Nitrogen, nitrite, dissolved Nitrogen, nitrate + nitrite, dissolved Nitrogen, nitrate, dissolved2 Nitrogen, inorganic, dissolved3 Nitrogen, ammonia + organic, dissolved Nitrogen, ammonia + organic, total Nitrogen, total4 

p

d

BLUE MESA RESERVOIR AT IOLA BASIN (SITE BM1) 04/20/99 0845 2 0.002 <0.001 <0.001 0.07 0.07 0.07 0.1 0.2 0.3 

0900 26 0.003 <0.001 <0.001 0.07 0.07 0.07 0.1 0.2 0.3 

08/19/99 1310 2 <0.002 <0.001 <0.001 <0.005 <0.005 <0.005 0.2 0.2 0.2 <

1350 17 <0.002 <0.001 <0.001 <0.005 <0.005 <0.005 0.2 0.2 0.2 <1400 35 <0.002 <0.001 0.001 <0.005 <0.005 <0.005 0.2 0.2 0.2 1420 76 0.002 <0.001 <0.001 0.073 0.073 0.075 0.2 0.3 0.4 

10/06/99 1025 2 <0.002 <0.001 <0.001 <0.005 <0.005 <0.005 0.2 0.3 0.3 

1035 68 <0.002 <0.001 <0.001 <0.005 <0.005 <0.005 0.1 0.2 0.2 

11/30/99 0840 2 <0.002 <0.001 <0.001 0.005 0.005 0.005 <0.1 0.2 0.2 

0851 16 <0.002 <0.001 <0.001 0.008 0.008 0.008 <0.1 0.2 0.2 0900 55 0.002 <0.001 <0.001 0.015 0.015 0.017 E 0.1 0.1 0.1 

BLUE MESA RESERVOIR AT CEBOLLA BASIN (SITE BM2) 04/20/99 0955 2 0.004 <0.001 <0.001 0.07 0.07 0.07 0.1 0.2 0.3 

1010 90 0.004 <0.001 <0.001 0.08 0.08 0.08 0.1 0.2 0.3 

08/19/99 0830 2 <0.002 <0.001 <0.001 <0.005 <0.005 <0.005 0.1 0.2 0.2 <

0840 17 0.003 <0.001 <0.001 <0.005 <0.005 <0.005 0.1 0.2 0.2 <0850 37 0.004 <0.001 0.001 <0.005 <0.005 <0.005 0.1 0.2 0.2 0930 208 0.003 <0.001 0.001 0.14 0.139 0.14 0.1 0.1 0.2 

10/06/99 1120 2 <0.002 <0.001 0.001 <0.005 <0.005 <0.005 0.2 0.2 0.2 

1140 164 0.002 <0.001 0.001 0.16 0.159 0.16 0.2 0.2 0.4 

11/30/99 0945 2 <0.002 <0.001 <0.001 0.007 0.007 0.007 E 0.09 0.1 0.1 

0950 16 <0.002 <0.001 <0.001 0.006 0.006 0.006 0.1 0.2 0.2 <1010 187 0.004 <0.001 <0.001 0.008 0.008 0.012 0.2 0.2 0.2 
SUPPLEMENTAL DATA 77

BLUE MESA RESERVOIR AT SAPINERO BASIN

(SITE BM3)

04/20/99 1055 2 0.005 <0.001 0.001 0.07 0.069 0.08 0.1 0.1 0.2 

1125 100 0.004 <0.001 <0.001 0.08 0.08 0.08 0.1 0.2 0.3 

08/19/99 1020 2 0.005 <0.001 0.001 <0.005 <0.005 0.006 0.2 0.2 0.2 

1040 18 0.003 <0.001 0.001 <0.005 <0.005 <0.005 0.1 0.2 0.2 1100 37 0.004 <0.001 <0.001 <0.005 <0.005 <0.005 0.2 0.2 0.2 1135 330 0.002 <0.001 <0.001 0.11 0.11 0.11 50.2 50.1 0.2 

10/06/99 1230 2 <0.002 <0.001 0.001 <0.005 <0.005 <0.005 0.1 0.1 0.1 

1300 318 <0.002 <0.001 0.001 0.099 0.098 0.099 0.1 0.2 0.3 

11/30/99 1045 2 <0.002 <0.001 <0.001 0.031 0.031 0.031 60.3 60.2 60.2 

1055 16 <0.002 <0.001 <0.001 0.031 0.031 0.031 60.2 60.1 60.1 1115 278 <0.002 <0.001 <0.001 0.11 0.11 0.11 0.1 E 0.1 E 0.2 

1Calculated from the ammonia concentrations and pH, temperature, and an equilibrium constant (U.S. Geological Survey Office of Water Quality Technical Memo

http://water.usgs.gov/admin/memo/QW/qw93.12.html, accessed February 7, 2002).

2Dissolved nitrate plus nitrite minus nitrite.3Calculated as the sum of dissolved ammonia and dissolved nitrate plus nitrite. See table 4.4Calculated as the sum of total ammonia plus organic nitrogen and dissolved nitrate plus nitrite. See table 4.5Based on variability in the laboratory method, there is no significant difference between the concentration of (1) dissolved ammonia plus organic nitrogen and (2) 

(D.K. Mueller, U.S. Geological Survey, oral commun., 2002).

6Based on variability in the laboratory method, there is no significant difference between the concentration of (1) dissolved ammonia plus organic nitrogen, (2) total 

(3) total nitrogen (D.K. Mueller, U.S. Geological Survey, oral commun., 2002).

Table 25. Nitrogen and phosphorus concentrations in Blue Mesa Reservoir, April–November 1999—Continued[Site number refers to table 1 and figure 1; <, less than; E, estimated]

Date Time

Sampling

depth

(feet)

Concentration, 

in milligrams per liter

Nitrogen,

ammonia,

dissolved

Nitrogen,

un-ionized

ammonia,

dissolved1

Nitrogen,

nitrite,

dissolved

Nitrogen,

nitrate +

nitrite,

dissolved

Nitrogen,

nitrate,

dissolved2

Nitrogen,

inorganic,

dissolved3

Nitrogen,

ammonia +

organic,

dissolved

Nitrogen,

ammonia +

organic,

total

Nitrogen,

total4

p

d
78 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999,

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

Table 26. Phytoplankton taxonomic list, Curecanti National Recreation Area, April–December 1999

[Site number refers to table 1 and figure 1]

Phylum Family Genus

BLUE MESA RESERVOIR AT IOLA BASIN 

(SITE BM1)

Bacillariophyta Coscinodiscaceae Melosira

Bacillariophyta Fragilariaceae Asterionella

Bacillariophyta Fragilariaceae Fragilaria

Bacillariophyta Fragilariaceae Tabellaria

Bacillariophyta Naviculaceae Navicula

Chlorophyta Chlorococcaceae Schroederia

Chrysophyta Dinobryaceae Dinobryon

Cyanophyta Nostocaceae Anabaena

Cyanophyta Nostocaceae Aphanizomenon

Pyrrophyta Ceratiaceae Ceratium

BLUE MESA RESERVOIR AT CEBOLLA BASIN 

(SITE BM2)

Bacillariophyta Coscinodiscaceae Melosira

Bacillariophyta Coscinodiscaceae Stephanodiscus

Bacillariophyta Fragilariaceae Asterionella

Bacillariophyta Fragilariaceae Fragilaria

Bacillariophyta Fragilariaceae Synedra

Bacillariophyta Fragilariaceae Tabellaria

Bacillariophyta Naviculaceae Navicula

Chlorophyta Hydrodictyaceae Pandorina

Chrysophyta Dinobryaceae Dinobryon

Cyanophyta Nostocaceae Anabaena

Cyanophyta Nostocaceae Aphanizomenon

Pyrrophyta Ceratiaceae Ceratium

BLUE MESA RESERVOIR AT SAPINERO BASIN 

(SITE BM3)

Bacillariophyta Coscinodiscaceae Melosira

Bacillariophyta Coscinodiscaceae Stephanodiscus

Bacillariophyta Fragilariaceae Asterionella

Bacillariophyta Fragilariaceae Fragilaria

Bacillariophyta Fragilariaceae Synedra

Bacillariophyta Fragilariaceae Tabellaria

Bacillariophyta Naviculaceae Navicula

Chlorophyta Chlamydomonadaceae Chlamydomonas

Chlorophyta Chlorococcaceae Schroederia

Chlorophyta Hydrodictyaceae Pandorina

Chrysophyta Dinobryaceae Dinobryon

Cyanophyta Nostocaceae Aphanizomenon

Pyrrophyta Ceratiaceae Ceratium

MORROW POINT RESERVOIR ABOVE PINE CREEK 

(SITE MP1)

Bacillariophyta Coscinodiscaceae Melosira

Bacillariophyta Coscinodiscaceae Stephanodiscus

Bacillariophyta Fragilariaceae Asterionella

Bacillariophyta Fragilariaceae Fragilaria

Bacillariophyta Fragilariaceae Tabellaria

Bacillariophyta Naviculaceae Navicula

Cyanophyta Nostocaceae Aphanizomenon
SUPPLEMENTAL DATA 79

MORROW POINT RESERVOIR AT KOKANEE BAY 

(SITE MP2)

Bacillariophyta Coscinodiscaceae Melosira

Bacillariophyta Coscinodiscaceae Stephanodiscus

Bacillariophyta Fragilariaceae Asterionella

Bacillariophyta Fragilariaceae Fragilaria

Bacillariophyta Fragilariaceae Tabellaria

Bacillariophyta Naviculaceae Navicula

Chlorophyta Chlorococcaceae Schroederia

Chrysophyta Dinobryaceae Dinobryon

Cyanophyta Nostocaceae Aphanizomenon

MORROW POINT RESERVOIR OFF HERMITS REST 

(SITE MP3)

Bacillariophyta Coscinodiscaceae Melosira

Bacillariophyta Coscinodiscaceae Stephanodiscus

Bacillariophyta Fragilariaceae Asterionella

Bacillariophyta Fragilariaceae Fragilaria

Bacillariophyta Fragilariaceae Tabellaria

Bacillariophyta Naviculaceae Navicula

Chlorophyta Gamophyceae Spirogyra

Cyanophyta Nostocaceae Aphanizomenon

CRYSTAL RESERVOIR NEAR CRYSTAL DAM 

(SITE CR1)

Bacillariophyta Coscinodiscaceae Melosira

Bacillariophyta Coscinodiscaceae Stephanodiscus

Bacillariophyta Fragilariaceae Asterionella

Bacillariophyta Fragilariaceae Fragilaria

Bacillariophyta Fragilariaceae Tabellaria

Bacillariophyta Naviculaceae Navicula

Chlorophyta Chlorococcaceae Schroederia

Chrysophyta Dinobryaceae Dinobryon

Cyanophyta Nostocaceae Aphanizomenon

Pyrrophyta Ceratiaceae Ceratium

Table 26. Phytoplankton taxonomic list, Curecanti National Recreation Area, April–December 1999—Continued

[Site number refers to table 1 and figure 1]

Phylum Family Genus
80 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999,

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

Table 27. Number of phytoplankton detected in Blue Mesa Reservoir, April–November 1999[Algal units/L, algal units per liter; site number refers to table 1 and figure 1]

Phylum Family Genus Algal units/L Phylum Family 

BLUE MESA RESERVOIR AT IOLA BASIN 

(SITE BM1)

April 20, 1999 October 6, 1999

Bacillariophyta Coscinodiscaceae Melosira 77 Bacillariophyta Fragilariaceae ABacillariophyta Fragilariaceae Asterionella 821 Bacillariophyta Fragilariaceae TBacillariophyta Fragilariaceae Fragilaria 129 Cyanophyta Nostocaceae ABacillariophyta Fragilariaceae Tabellaria 209 Cyanophyta Nostocaceae AChrysophyta Dinobryaceae Dinobryon 338 November 30, 1999

August 18, 1999 Bacillariophyta Coscinodiscaceae M

Bacillariophyta Coscinodiscaceae Melosira 3 Bacillariophyta Fragilariaceae ABacillariophyta Fragilariaceae Tabellaria 3 Bacillariophyta Fragilariaceae TBacillariophyta Naviculaceae Navicula 7 Bacillariophyta Naviculaceae NChlorophyta Chlorococcaceae Schroederia 3 Cyanophyta Nostocaceae ACyanophyta Nostocaceae Anabaena 10Cyanophyta Nostocaceae Aphanizomenon 223Pyrrophyta Ceratiaceae Ceratium 3

BLUE MESA RESERVOIR AT CEBOLLA BASIN 

(SITE BM2)

April 20, 1999 October 6, 1999

Bacillariophyta Coscinodiscaceae Melosira 157 Bacillariophyta Coscinodiscaceae MBacillariophyta Fragilariaceae Asterionella 1,459 Bacillariophyta Fragilariaceae ABacillariophyta Fragilariaceae Fragilaria 501 Bacillariophyta Fragilariaceae FBacillariophyta Fragilariaceae Tabellaria 1,110 Bacillariophyta Fragilariaceae SChrysophyta Dinobryaceae Dinobryon 21 Bacillariophyta Fragilariaceae T

August 18, 1999 Chrysophyta Dinobryaceae D

Bacillariophyta Coscinodiscaceae Melosira 3 Cyanophyta Nostocaceae ABacillariophyta Coscinodiscaceae Stephanodiscus 3 Cyanophyta Nostocaceae ABacillariophyta Fragilariaceae Tabellaria 3 Pyrrophyta Ceratiaceae CCyanophyta Nostocaceae Anabaena 7 November 30, 1999Cyanophyta Nostocaceae Aphanizomenon 7 Bacillariophyta Coscinodiscaceae MPyrrophyta Ceratiaceae Ceratium 3 Bacillariophyta Fragilariaceae A

Bacillariophyta Fragilariaceae FBacillariophyta Fragilariaceae TBacillariophyta Naviculaceae NChlorophyta Hydrodictyaceae P
SUPPLEMENTAL DATA 81

BLUE MESA RESERVOIR AT SAPINERO BASIN 

(SITE BM3)

April 20, 1999 October 6, 1999

Bacillariophyta Coscinodiscaceae Melosira 877 Bacillariophyta Coscinodiscaceae MBacillariophyta Fragilariaceae Asterionella 1,507 Bacillariophyta Fragilariaceae ABacillariophyta Fragilariaceae Fragilaria 414 Bacillariophyta Fragilariaceae FBacillariophyta Fragilariaceae Tabellaria 376 Bacillariophyta Fragilariaceae SChrysophyta Dinobryaceae Dinobryon 3 Bacillariophyta Fragilariaceae T

August 18, 1999 Chlorophyta Chlamydomonadaceae C

Bacillariophyta Coscinodiscaceae Stephanodiscus 3 Chlorophyta Hydrodictyaceae PChlorophyta Chlorococcaceae Schroederia 3 Cyanophyta Nostocaceae ACyanophyta Nostocaceae Aphanizomenon 24 Pyrrophyta Ceratiaceae CPyrrophyta Ceratiaceae Ceratium 3 November 30, 1999

Bacillariophyta Coscinodiscaceae MBacillariophyta Fragilariaceae ABacillariophyta Fragilariaceae TBacillariophyta Naviculaceae N

Table 27. Number of phytoplankton detected in Blue Mesa Reservoir, April–November 1999—Continued[Algal units/L, algal units per liter; site number refers to table 1 and figure 1]

Phylum Family Genus Algal units/L Phylum Family 
82 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999,

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

Table 28. Chlorophyll-a concentrations and trophic-state indices, Blue Mesa, Morrow Point, and Crystal Reservoirs, 

April–December 1999

[mg/m3, milligrams per cubic meter; TP, total phosphorus; CHa, chlorophyll-a; SD, Secchi depth; site number refers to table 1 and figure 1; --, no data]

Date Chlorophyll-a

(mg/m3)

Trophic-state index1

Date Chlorophyll-a

(mg/m3)

Trophic-state index1

TP CHa SD TP CHa SD

BLUE MESA RESERVOIR AT IOLA BASIN 

(SITE BM1)

MORROW POINT RESERVOIR AT KOKANEE BAY 

(SITE MP2)

04/20/99 4.56 47 45 44 04/21/99 3.17 44 42 44

08/19/99 1.52 34 35 38 08/17/99 2.47 36 40 36

10/06/99 7.55 55 50 44 10/12/99 1.45 49 34 42

11/30/99 4.56 46 45 40 12/01/99 2.37 48 39 38

BLUE MESA RESERVOIR AT CEBOLLA BASIN 

(SITE BM2)

MORROW POINT RESERVOIR OFF HERMITS REST 

(SITE MP3)

04/20/99 6.98 41 50 44 04/21/99 4.39 43 45 37

08/19/99 0.86 51 29 37 08/17/99 1.68 32 36 31

10/06/99 2.12 43 38 37 10/12/99 0.91 47 30 37

11/30/99 5.75 43 48 40 12/01/99 2.38 47 39 34

BLUE MESA RESERVOIR AT SAPINERO BASIN 

(SITE BM3)

CRYSTAL RESERVOIR NEAR CRYSTAL DAM 

(SITE CR1)

04/20/99 3.97 39 44 42 04/20/99 3.07 45 42 44

08/19/99 1.42 41 34 38 08/24/99 2.01 36 37 35

10/06/99 1.50 39 35 42 10/13/99 2.18 49 38 42

11/30/99 4.18 47 45 37 12/02/99 3.32 47 42 --

MORROW POINT RESERVOIR ABOVE PINE CREEK 

(SITE MP1)

04/21/99 3.14 48 42 47

08/23/99 0.95 48 30 45

10/12/99 1.26 49 33 40

12/01/99 3.69 47 43 40

1Calculation of trophic-state indices (from Carlson, 1977): 

TP = 10×[6–{ln(48/total phosphorus concentration in mg/m3)/ln2}]

CHa = 10×(6–[{2.04–(0.68×ln chlorophyll-a concentration)}/ln2])

SD = 10×[6–(ln Secchi depth/ln2)]
SUPPLEMENTAL DATA 83

Table 29. Physical properties and suspended sediment (inflows only) for Blue Mesa Reservoir inflow and outflow sites, 

May–December 1999

[ft3/s, cubic feet per second; C, Celsius; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius; site number refers to table 1 

and figure 1; --, no data]

Date Time Discharge

(ft3/s)

Width

(feet)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

Suspended

sediment

(mg/L)

GUNNISON RIVER AT COUNTY ROAD 32 BELOW GUNNISON 

(SITE BI1)

05/26/99 0845 2,920 154 7.6 8.8 8.0 191 80

08/25/99 0810 974 140 13.3 7.7 7.9 212 10

10/21/99 1100 544 112 3.9 10.6 8.0 214 0.9

12/06/99 1500 330 105 0.0 11.3 8.5 241 5

BEAVER CREEK AT HIGHWAY 50, NEAR GUNNISON 

(SITE BI2)

06/01/99 1600 62.0 25.0 13.0 7.6 7.8 74 6

08/12/99 1350 24.5 25.5 15.2 7.5 7.7 67 5

10/04/99 1550 5.24 10.7 10.0 8.3 7.8 93 1

12/06/99 1115 2.68 8.0 0.0 11.0 7.7 98 1

STEUBEN CREEK AT HIGHWAY 50, NEAR GUNNISON 

(SITE BI3)

05/27/99 1600 40.0 15.5 7.8 9.3 7.4 59 8

08/11/99 1340 12.8 15.0 12.5 8.0 7.6 57 4

10/04/99 1430 3.13 10.3 6.5 9.2 7.6 81 1

11/30/99 1535 2.40 10.0 0.0 11.2 7.9 83 2

EAST ELK CREEK ABOVE HIGHWAY 50, NEAR SAPINERO 

(SITE BI4)

05/26/99 1500 29.0 10.5 10.0 8.6 7.6 62 12

08/12/99 1130 4.70 10.1 13.5 7.7 8.0 98 12

10/05/99 0825 2.30 11.8 5.0 9.8 7.6 111 2

11/29/99 1515 3.02 8.1 0.1 10.8 8.0 91 15

RED CREEK ABOVE HIGHWAY 50, NEAR SAPINERO 

(SITE BI5)

05/26/99 1300 10.0 5.5 9.0 8.8 7.9 73 13

08/09/99 1320 0.77 2.0 16.5 6.9 7.8 159 10

10/04/99 1220 0.76 3.3 8.3 8.9 8.0 171 5

12/06/99 1300 1.10 5.1 0.2 10.8 7.8 135 6

WEST ELK CREEK ABOVE BLUE MESA RESERVOIR, NEAR SAPINERO 

(SITE BI6)

06/02/99 0935 89.0 26.0 5.5 9.6 7.5 54 9

08/18/99 0925 14.0 17.0 9.1 8.9 7.8 73 10

10/06/99 1430 4.84 15.6 9.4 8.4 8.2 85 0.9

11/30/99 1230 5.19 12.0 –0.4 10.9 7.5 81 3

SOAP CREEK ABOVE BLUE MESA RESERVOIR, NEAR SAPINERO 

(SITE BI7)

05/25/99 1530 269 29 9.5 8.7 7.8 70 72

08/12/99 0845 23.0 28.0 10.3 8.6 8.0 120 7

10/05/99 1040 12.0 25.4 2.8 10.4 8.3 125 2

12/07/99 1440 15.2 24.5 0.0 11.0 7.8 131 2

SOUTH WILLOW CREEK ABOVE HIGHWAY 149, NEAR GUNNISON 

(SITE BI8)

06/01/99 1230 3.40 7.5 12.2 7.7 8.3 409 1
84 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999,

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

CEBOLLA CREEK AT BRIDGE SOUTHEAST OF POWDERHORN 

(SITE BI9)

06/01/99 0845 468 34.0 5.5 9.4 7.6 81 93

08/11/99 1030 285 36.0 10.0 8.6 7.6 114 23

10/11/99 1250 70 34.0 7.5 9.4 7.9 111 3

12/08/99 0915 36 30.0 0.0 10.8 7.8 133 3

LAKE FORK OF THE GUNNISON RIVER BELOW GATEVIEW 

(SITE BI10)

05/31/99 1230 1,050 124 9.0 8.9 7.6 115 90

08/18/99 1330 481 101 13.5 8.2 8.0 134 7

10/11/99 1505 137 67.0 10.5 8.5 8.1 158 3

12/08/99 1145 64 49.0 0.0 -- 8.0 182 4

BLUE MESA RESERVOIR DISCHARGE AT BLUE MESA POWERHOUSE, NEAR SAPINERO 

(SITE BO)

06/02/99 1215 21,836 -- 6.5 -- 8.1 200 --

08/16/99 1500 22,436 -- 9.1 8.0 7.7 174 --

10/05/99 1355 23,263 -- 12.5 7.6 7.6 176 --

12/08/99 1415 21,317 -- 6.0 -- 8.0 190 --

1Width at bridge.

2Outflow from Blue Mesa Reservoir. Value is mean value for the day.

Table 29. Physical properties and suspended sediment (inflows only) for Blue Mesa Reservoir inflow and outflow sites, 

May–December 1999—Continued

[ft3/s, cubic feet per second; C, Celsius; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius; site number refers to table 1 

and figure 1; --, no data]

Date Time Discharge

(ft3/s)

Width

(feet)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

Suspended

sediment

(mg/L)
SUPPLEMENTAL DATA 85

Table 30. Nitrogen and phosphorus concentrations in Blue Mesa Reservoir inflow and outflow sites, May–December 1999[Site number refers to table 1 and figure 1; <, less than; E, estimated]

Date Time

Concentration, 

in milligrams per liter

Nitrogen,

ammonia,

dissolved

Nitrogen,

un-ionized

ammonia,

dissolved1

Nitrogen,

nitrite,

dissolved

Nitrogen,

nitrate +

nitrite,

dissolved

Nitrogen,

nitrate,

dissolved2

Nitrogen,

inorganic,

dissolved3

Nitrogen,

ammonia +

organic,

dissolved

Nitrogen,

ammonia +

organic,

total

Nitrogen,

total4

Or

phos

diss

GUNNISON RIVER AT COUNTY ROAD 32 BELOW GUNNISON 

(SITE BI1)

05/26/99 0845 0.006 <0.001 0.001 0.047 0.046 0.053 0.2 0.5 0.5 008/25/99 0810 0.006 <0.001 0.001 0.035 0.034 0.041 0.2 0.2 0.2 010/21/99 1100 <0.002 <0.001 0.002 0.014 0.012 0.014 0.1 0.2 0.2 012/06/99 1500 <0.002 <0.001 0.001 0.047 0.046 0.047 E 0.06 0.1 0.1 0

BEAVER CREEK AT HIGHWAY 50, NEAR GUNNISON 

(SITE BI2)

06/01/99 1600 0.007 <0.001 <0.001 <0.005 <0.005 0.007 0.2 0.2 0.2 008/12/99 1350 0.005 <0.001 0.001 <0.005 <0.005 0.006 50.2 5<0.1 5<0.1 010/04/99 1550 <0.002 <0.001 <0.001 <0.005 <0.005 <0.005 0.1 0.1 0.1 012/06/99 1115 <0.002 <0.001 <0.001 <0.005 <0.005 <0.005 5E 0.09 5E 0.06 5E 0.06 0

STEUBEN CREEK AT HIGHWAY 50, NEAR GUNNISON 

(SITE BI3)

05/27/99 1600 0.006 <0.001 <0.001 0.008 0.008 0.014 0.2 0.3 0.3 008/11/99 1340 0.006 <0.001 0.001 <0.005 <0.005 0.007 5E 0.09 5E 0.08 5E 0.08 010/04/99 1430 <0.002 <0.001 <0.001 <0.005 <0.005 <0.005 0.1 0.2 0.2 011/30/99 1535 <0.002 <0.001 <0.001 0.006 0.006 0.006 5<0.1 5E 0.07 5E 0.08 0

EAST ELK CREEK ABOVE HIGHWAY 50, NEAR SAPINERO 

(SITE BI4)

05/26/99 1500 0.004 <0.001 0.001 0.008 0.007 0.012 0.2 0.3 0.3 008/12/99 1130 0.006 <0.001 0.002 0.008 0.006 0.014 50.1 5<0.1 5<0.1 010/05/99 0825 <0.002 <0.001 <0.001 <0.005 <0.005 <0.005 0.1 0.2 0.2 011/29/99 1515 <0.002 <0.001 <0.001 0.005 0.005 0.005 5<0.1 5E 0.06 5E 0.06 0

RED CREEK ABOVE HIGHWAY 50, NEAR SAPINERO 

(SITE BI5)

05/26/99 1300 0.004 <0.001 0.001 0.008 0.007 0.012 0.2 0.3 0.3 008/09/99 1320 0.014 <0.001 0.002 0.015 0.013 0.029 0.2 0.3 0.3 010/04/99 1220 <0.002 <0.001 <0.001 <0.005 <0.005 <0.005 0.2 0.2 0.2 012/06/99 1300 0.003 <0.001 0.001 0.006 0.005 0.009 50.1 5E 0.08 5E 0.08 0

WEST ELK CREEK ABOVE BLUE MESA RESERVOIR, NEAR SAPINERO 

(SITE BI6)

06/02/99 0935 0.008 <0.001 <0.001 <0.005 <0.005 0.008 0.1 0.1 0.1 008/18/99 0925 0.002 <0.001 0.001 0.007 0.006 0.009 E 0.09 0.1 0.1 010/06/99 1430 <0.002 <0.001 <0.001 <0.005 <0.005 <0.005 E 0.09 0.1 0.1 011/30/99 1230 <0.002 <0.001 <0.001 0.017 0.017 0.017 5<0.1 5E 0.05 5E 0.07 0
86 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999,

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado SOAP CREEK ABOVE BLUE MESA RESERVOIR, NEAR SAPINERO (SITE BI7) 05/25/99 1530 0.003 <0.001 0.001 0.01 0.099 0.01 0.2 0.3 0.3 0

08/12/99 0845 <0.002 <0.001 0.001 <0.005 <0.005 <0.005 5E 0.08 5E 0.05 5E 0.05 010/05/99 1040 <0.002 <0.001 <0.001 <0.005 <0.005 <0.005 0.1 0.1 0.1 012/07/99 1440 <0.002 <0.001 <0.001 <0.005 <0.005 <0.005 <0.1 <0.1 <0.1 0

SOUTH WILLOW CREEK ABOVE HIGHWAY 149, NEAR GUNNISON (SITE BI8) 06/01/99 1230 0.011 <0.001 <0.001 <0.005 <0.005 0.011 0.4 0.4 0.4 0

CEBOLLA CREEK AT BRIDGE SOUTHEAST OF POWDERHORN (SITE BI9) 06/01/99 0845 0.007 <0.001 0.001 0.021 0.020 0.028 0.2 0.4 0.4 0

08/11/99 1030 0.012 <0.001 0.001 0.025 0.024 0.037 50.2 5E 0.09 5E 0.1 010/11/99 1250 <0.002 <0.001 <0.001 <0.005 <0.005 <0.005 0.1 0.1 0.1 012/08/99 0915 0.002 <0.001 0.001 0.083 0.082 0.085 E 0.07 0.1 0.2 0

LAKE FORK OF THE GUNNISON RIVER BELOW GATEVIEW (SITE BI10) 05/31/99 1230 <0.002 <0.001 0.001 0.031 0.030 0.031 E 0.1 0.2 0.2 0

08/18/99 1330 0.005 <0.001 0.001 <0.005 <0.005 0.006 50.1 5E 0.08 5E 0.08 010/11/99 1505 0.006 <0.001 0.001 <0.005 <0.005 0.007 5E 0.1 5E 0.08 5E 0.08 012/08/99 1145 0.009 <0.001 0.001 0.079 0.078 0.088 6<0.1 6E 0.07 E 0.1 0

BLUE MESA RESERVOIR DISCHARGE AT BLUE MESA POWERHOUSE, NEAR SAPINERO (SITE BO)

06/02/99 1215 0.007 <0.001 0.001 0.005 0.004 0.012 50.2 50.1 50.1 008/16/99 1500 <0.002 <0.001 0.001 0.054 0.053 0.054 50.1 5E 0.09 5E 0.1 010/05/99 1355 <0.002 <0.001 0.001 0.048 0.047 0.048 50.2 50.1 50.1 012/08/99 1415 <0.002 <0.001 <0.001 0.036 0.036 0.036 E 0.09 0.1 0.1 0

1Calculated from the ammonia concentrations and pH, temperature, and an equilibrium constant (U.S. Geological Survey Office of Water Quality Technical Memo

http://water.usgs.gov/admin/memo/QW/qw93.12.html, accessed February 7, 2002). 2Nitrate plus nitrite minus nitrite.

3Calculated as the sum of dissolved ammonia and dissolved nitrate plus nitrite. See table 4.4Calculated as the sum of total ammonia plus organic nitrogen and dissolved nitrate plus nitrite. See table 4. 5Based on variability in the laboratory method, there is no significant difference between the concentration of (1) dissolved ammonia plus organic nitrogen, (2) total 

(3) total nitrogen (D.K. Mueller, U.S. Geological Survey, oral commun., 2002). 6Based on variability in the laboratory method, there is no significant difference between the concentration of (1) dissolved ammonia plus organic nitrogen and (2) 

(D.K. Mueller, U.S. Geological Survey, oral commun., 2002).

Table 30. Nitrogen and phosphorus concentrations in Blue Mesa Reservoir inflow and outflow sites, May–December 1999—Continued[Site number refers to table 1 and figure 1; <, less than; E, estimated]

Date Time

Concentration, 

in milligrams per liter

Nitrogen,

ammonia,

dissolved

Nitrogen,

un-ionized

ammonia,

dissolved1

Nitrogen,

nitrite,

dissolved

Nitrogen,

nitrate +

nitrite,

dissolved

Nitrogen,

nitrate,

dissolved2

Nitrogen,

inorganic,

dissolved3

Nitrogen,

ammonia +

organic,

dissolved

Nitrogen,

ammonia +

organic,

total

Nitrogen,

total4

O

pho

diss
SUPPLEMENTAL DATA 87

Table 31. Reservoir profile measurements, Morrow Point Reservoir above Pine Creek (site MP1), April–December 1999

[Site number refers to table 1 and figure 1; C, Celsius; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

APRIL 21, 1999, SECCHI-DISC DEPTH, 2.5 METERS OCTOBER 12, 1999, SECCHI-DISC DEPTH, 4.0 METERS

1 4.4 10.5 8.2 212 1 11.7 7.1 7.3 183

2 4.4 10.4 8.2 211 2 11.7 7.0 7.3 182

3 4.4 10.4 8.2 210 3 11.7 7.0 7.3 183

4 4.4 10.5 8.2 211 4 11.5 7.0 7.4 183

5 4.4 10.5 8.2 210 5 11.4 7.0 7.4 184

6 4.4 10.5 8.3 211 6 11.4 7.0 7.4 184

7 4.4 10.5 8.3 209 7 11.4 7.0 7.3 184

8 4.4 10.5 8.3 209 8 11.3 6.9 7.3 184

9 4.4 10.5 8.3 210 9 11.3 7.0 7.3 184

9.5 11.3 7.0 7.3 184

AUGUST 23, 1999, SECCHI-DISC DEPTH, 2.9 METERS DECEMBER 1, 1999, SECCHI-DISC DEPTH, 4.0 METERS

1 10.0 7.6 7.6 172 1 7.7 8.1 7.2 187

2 10.0 7.6 7.6 172 2 7.7 8.1 7.3 187

3 10.0 7.6 7.6 173 3 7.7 8.2 7.3 187

4 10.0 7.5 7.6 170 4 7.7 8.2 7.3 187

5 9.9 7.6 7.6 171 5 7.7 8.2 7.4 187

6 9.9 7.6 7.6 173 6 7.7 8.1 7.4 187

7 10.0 7.5 7.6 174 7 7.7 8.1 7.4 187

8 10.0 7.5 7.6 170 8 7.7 8.1 7.4 187

9 9.9 7.5 7.6 174 9 7.7 8.0 7.4 187

10 9.9 7.5 7.6 173 10 7.7 7.9 7.4 187

11 9.9 7.5 7.6 172 11 7.7 7.9 7.4 187

12 9.9 7.5 7.6 173 12 7.7 7.9 7.4 187

12.6 9.9 7.4 7.6 175 12.5 7.7 7.8 7.4 187
88 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999,

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

Table 32. Reservoir profile measurements, Morrow Point Reservoir at Kokanee Bay (site MP2), April–December 1999

[Site number refers to table 1 and figure 1; C, Celsius; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius; --, no data]

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

APRIL 21, 1999, SECCHI-DISC DEPTH, 3.0 METERS AUGUST 17, 1999, SECCHI-DISC DEPTH, 5.3 METERS

1 5.3 10.2 8.2 205 1 15.8 -- 8.2 168

2 5.2 10.3 8.2 206 2 15.1 -- 8.2 168

3 5.1 10.2 8.3 204 3 14.2 -- 8.2 168

4 5.0 10.2 8.2 205 4 12.5 -- 8.0 166

5 5.0 10.2 8.2 205 5 11.4 -- 7.9 166

6 5.0 10.2 8.2 207 6 10.8 -- 7.8 168

7 5.0 10.2 8.2 205 7 10.5 -- 7.8 168

8 5.0 10.2 8.2 206 8 10.2 -- 7.7 169

9 5.0 10.1 8.2 204 9 10.0 -- 7.7 170

10 4.9 10.1 8.2 204 10 9.9 -- 7.7 170

11 4.9 10.1 8.2 205 11 9.8 -- 7.7 172

12 4.9 10.1 8.2 204 12 9.8 -- 7.7 171

13 4.9 10.1 8.2 205 13 9.7 -- 7.7 173

14 4.9 10.2 8.2 204 14 9.6 -- 7.7 172

15 4.9 10.2 8.2 204 15 9.6 -- 7.7 173

16 4.9 10.1 8.2 204 16 9.6 -- 7.7 172

17 4.9 10.1 8.2 204 17 9.5 -- 7.7 172

18 5.0 10.1 8.2 204 18 9.5 -- 7.7 173

19 4.9 10.2 8.2 204 19 9.5 -- 7.7 171

20 5.0 10.1 8.2 204 20 9.4 -- 7.6 171

25 4.8 10.4 8.2 204 25 9.3 -- 7.6 174

30 4.6 10.5 8.2 207 30 8.9 -- 7.6 177

35 4.6 10.4 8.2 206

38.2 4.6 10.3 8.2 204
SUPPLEMENTAL DATA 89

Table 32. Reservoir profile measurements, Morrow Point Reservoir at Kokanee Bay (site MP2), April–December 

1999—Continued

[Site number refers to table 1 and figure 1; C, Celsius; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius; --, no data]

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

OCTOBER 12, 1999, SECCHI-DISC DEPTH, 3.5 METERS DECEMBER 1, 1999, SECCHI-DISC DEPTH, 4.5 METERS

1 11.7 6.6 7.5 181 1 7.0 8.2 7.4 184

2 11.8 6.6 7.5 181 2 7.0 8.2 7.4 184

3 11.7 6.6 7.5 181 3 7.0 8.1 7.4 184

4 11.7 6.6 7.5 180 4 7.0 8.1 7.3 184

5 11.7 6.6 7.4 180 5 7.0 8.1 7.3 184

6 11.7 6.6 7.4 180 6 7.0 8.1 7.4 184

7 11.7 6.5 7.4 180 7 7.1 8.1 7.4 184

8 11.7 6.5 7.4 180 8 7.0 8.0 7.4 184

9 11.7 6.5 7.4 180 9 7.0 8.0 7.4 184

10 11.7 6.5 7.4 180 10 7.0 8.1 7.4 184

11 11.7 6.5 7.4 180 11 7.0 8.0 7.4 184

12 11.7 6.5 7.4 180 12 7.0 8.0 7.4 184

13 11.7 6.6 7.4 180 13 7.0 8.0 7.4 184

14 11.7 6.5 7.4 180 14 7.0 8.0 7.4 185

15 11.7 6.6 7.4 180 15 7.0 8.0 7.4 185

16 11.6 6.5 7.4 180 16 7.0 8.0 7.4 184

17 11.5 6.5 7.4 179 17 7.0 8.0 7.4 184

18 11.5 6.5 7.4 179 18 7.0 8.0 7.4 185

19 11.4 6.5 7.4 178 19 7.0 8.0 7.4 184

20 11.1 6.5 7.4 176 20 7.0 7.9 7.4 184

25 10.9 6.4 7.4 176 25 7.0 8.0 7.4 185

30 7.9 5.6 7.2 185 30 7.0 7.9 7.4 184

35 6.1 6.0 7.2 190 35 6.6 7.1 7.2 184

40 5.9 6.2 7.2 191 38.9 6.4 3.2 7.1 193

45 5.8 6.2 7.2 191

50 5.8 6.2 7.2 192

53.2 5.8 3.5 7.0 209
90 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999,

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

Table 33. Reservoir profile measurements, Morrow Point Reservoir off Hermits Rest (site MP3), April–December 1999

[Site number refers to table 1 and figure 1; C, Celsius; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius; --, no data]

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

APRIL 21, 1999, SECCHI-DISC DEPTH, 5.0 METERS AUGUST 17, 1999, SECCHI-DISC DEPTH, 7.3 METERS

1 4.8 10.1 8.2 205 1 15.2 -- 8.5 170

2 4.6 10.2 8.2 203 2 15.2 -- 8.3 170

3 4.5 10.1 8.2 204 3 14.9 -- 8.3 170

4 4.5 10.1 8.2 204 4 14.5 -- 8.3 170

5 4.5 10.1 8.2 203 5 13.7 -- 8.2 169

6 4.5 10.0 8.2 204 6 13.4 -- 8.2 169

7 4.5 10.0 8.2 202 7 11.4 -- 8.0 171

8 4.5 10.0 8.2 203 8 10.4 -- 7.9 172

9 4.5 10.0 8.2 204 9 10.1 -- 7.8 173

10 4.5 10.0 8.2 205 10 10.0 -- 7.8 173

11 4.4 10.0 8.2 203 11 9.9 -- 7.8 173

12 4.4 9.9 8.2 205 12 9.7 -- 7.8 173

13 4.4 9.9 8.2 204 13 9.7 -- 7.8 172

14 4.4 9.9 8.2 203 14 9.7 -- 7.7 172

15 4.4 9.9 8.2 202 15 9.7 -- 7.7 174

16 4.4 9.9 8.2 204 16 9.6 -- 7.7 172

17 4.4 9.9 8.2 202 17 9.5 -- 7.7 173

18 4.4 9.9 8.2 204 18 9.4 -- 7.7 173

19 4.3 9.9 8.2 203 19 9.4 -- 7.7 173

20 4.3 9.9 8.2 204 20 9.4 -- 7.7 174

25 4.3 9.8 8.2 203 25 9.3 -- 7.7 173

30 4.3 9.8 8.2 201 30 9.0 -- 7.7 175

35 4.2 9.8 8.2 202 35 7.1 -- 7.7 183

40 4.2 9.8 8.2 202 40 5.8 -- 7.7 186

45 4.2 9.7 8.2 201 45 5.6 -- 7.7 187

50 4.1 9.7 8.2 202 50 5.5 -- 7.7 186

55 4.1 9.7 8.2 201 55 5.4 -- 7.7 185

60 4.0 9.7 8.1 200 60 5.2 -- 7.8 186

65 3.9 9.7 8.1 201 65 5.0 -- 7.8 185

70 4.0 9.7 8.1 200 69.5 4.9 -- 7.8 186

73 4.0 9.6 8.1 201
SUPPLEMENTAL DATA 91

Table 33. Reservoir profile measurements, Morrow Point Reservoir off Hermits Rest (site MP3), April–December 

1999—Continued

[Site number refers to table 1 and figure 1; C, Celsius; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius; --, no data]

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

OCTOBER 12, 1999, SECCHI-DISC DEPTH, 5.0 METERS DECEMBER 1, 1999, SECCHI-DISC DEPTH, 6.0 METERS

1 11.7 6.9 7.5 179 1 6.6 8.1 7.4 181

2 11.6 6.9 7.5 179 2 6.6 8.1 7.4 181

3 11.6 6.9 7.5 179 3 6.6 8.0 7.4 181

4 11.6 6.9 7.5 179 4 6.6 8.1 7.4 181

5 11.6 6.9 7.5 179 5 6.6 8.1 7.4 181

6 11.6 6.8 7.5 179 6 6.6 8.1 7.4 181

7 11.6 6.8 7.5 179 7 6.6 8.1 7.4 181

8 11.6 6.9 7.5 179 8 6.6 8.0 7.4 181

9 11.6 6.9 7.5 179 9 6.6 8.0 7.4 181

10 11.5 6.8 7.5 179 10 6.6 8.0 7.4 181

11 11.5 6.8 7.5 179 11 6.6 8.0 7.4 181

12 11.5 6.8 7.5 179 12 6.6 8.0 7.4 181

13 11.5 6.8 7.5 179 13 6.6 8.0 7.4 181

14 11.5 6.8 7.5 179 14 6.6 8.0 7.4 181

15 11.5 6.8 7.5 179 15 6.6 8.0 7.4 181

16 11.5 6.8 7.5 179 16 6.6 8.0 7.4 181

17 11.5 6.8 7.5 179 17 6.6 8.0 7.4 181

18 11.5 6.8 7.5 179 18 6.6 8.0 7.4 181

19 11.5 6.8 7.5 179 19 6.6 7.9 7.4 181

20 11.5 6.8 7.5 179 20 6.6 8.0 7.4 181

25 11.5 6.8 7.5 179 25 6.6 8.0 7.4 181

30 11.3 6.7 7.5 178 30 6.6 7.9 7.4 181

35 6.7 6.9 7.4 188 35 6.6 7.9 7.5 181

40 5.9 6.9 7.3 190 40 6.6 7.9 7.5 181

45 5.8 7.0 7.3 190 45 6.6 7.9 7.5 181

50 5.8 7.0 7.3 190 50 6.6 7.8 7.5 181

55 5.7 7.3 7.3 190 55 6.6 7.9 7.5 181

60 5.5 7.5 7.3 191 60 6.6 7.8 7.5 181

65 5.4 7.6 7.4 191 65 5.7 6.8 7.2 186

70 5.1 7.8 7.4 191 70 5.5 7.0 7.2 187

73.5 5.0 7.9 7.4 191 75 5.3 7.0 7.2 187

80 5.0 6.7 7.2 189

85 4.8 6.5 7.2 190

90 4.8 6.2 7.2 190

95 4.7 5.6 7.2 191

99.8 4.7 5.5 7.0 192
92 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999,

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

Table 34. Nitrogen and phosphorus concentrations in Morrow Point Reservoir, April–December 1999[Site number refers to table 1 and figure 1; <, less than; E, estimated; --, no data]

Date Time

Sampling

depth

(feet)

Concentration,

in milligrams per liter

Nitrogen,

ammonia,

dissolved

Nitrogen,

un-ionized

ammonia,

dissolved1

Nitrogen,

nitrite,

dissolved

Nitrogen,

nitrate +

nitrite,

dissolved

Nitrogen,

nitrate,

dissolved2

Nitrogen,

inorganic,

dissolved3

Nitrogen,

ammonia +

organic,

dissolved

Nitrogen,

ammonia +

organic,

total

Nitrogen,

total4

Or

phos

diss

MORROW POINT RESERVOIR ABOVE PINE CREEK 

(SITE MP1)

04/21/99 1155 2 0.004 <0.001 0.001 0.08 0.079 0.08 0.1 0.2 0.3 008/23/99 1445 2 0.01 <0.001 0.001 0.056 0.055 0.07 0.2 0.2 0.3 0

1500 43 0.095 <0.001 0.001 0.054 0.053 0.149 0.2 0.2 0.3 0

10/12/99 0940 2 0.007 <0.001 0.001 0.042 0.041 0.049 0.1 0.1 0.1 0

1000 31 0.005 <0.001 0.001 0.048 0.047 0.053 0.1 0.1 0.1 0

12/01/99 0940 2 <0.002 <0.001 <0.001 0.032 0.032 0.032 E 0.09 0.1 0.1 0

0950 46 <0.002 <0.001 <0.001 0.032 0.032 0.032 E 0.07 0.1 0.1 0

MORROW POINT RESERVOIR AT KOKANEE BAY 

(SITE MP2)

04/21/99 1055 2 0.003 <0.001 0.001 0.08 0.079 0.08 0.2 0.2 0.3 0

1125 60 0.004 <0.001 <0.001 0.08 0.08 0.08 0.1 0.2 0.3 0

08/17/99 1335 3 0.004 <0.001 <0.001 <0.005 <0.005 <0.005 0.1 0.1 0.1 0

1425 14 0.002 <0.001 <0.001 <0.005 <0.005 <0.005 0.1 0.3 0.3 01440 100 0.002 <0.001 <0.001 0.04 0.04 0.04 50.2 50.1 50.1 0

10/12/99 1045 2 0.005 <0.001 0.002 0.037 0.035 0.042 0.1 0.1 0.1 0

1055 138 0.011 <0.001 0.001 0.072 0.071 0.083 0.1 0.1 0.2 0

12/01/99 1030 2 <0.002 <0.001 <0.001 0.039 0.039 0.039 E 0.07 0.1 0.1 0

1040 16 <0.002 <0.001 <0.001 0.038 0.038 0.038 <0.1 0.1 0.1 01050 146 <0.002 <0.001 <0.001 0.067 0.067 0.067 <0.1 E 0.09 E 0.2 0

MORROW POINT RESERVOIR OFF HERMITS REST 

(SITE MP3)

04/21/99 0925 2 0.002 <0.001 0.001 0.09 0.089 0.09 0.1 0.1 0.2 0

1000 150 0.003 <0.001 0.001 0.09 0.089 0.09 0.1 0.1 0.2 0

08/17/99 0900 2 <0.002 <0.001 <0.001 <0.005 <0.005 <0.005 0.1 0.1 0.1 <0

1115 21.5 <0.002 <0.001 <0.001 <0.005 <0.005 <0.005 0.1 0.2 0.2 01215 280 <0.002 <0.001 0.001 0.043 0.042 0.043 50.2 50.1 50.1 0

10/12/99 1220 2 0.017 <0.001 0.001 0.037 0.036 0.054 0.1 0.1 0.1 0

1235 344 -- -- -- -- -- -- -- -- 

12/01/99 1200 2 <0.002 <0.001 <0.001 0.045 0.045 0.045 E 0.05 0.1 0.1 0

1210 16 <0.002 <0.001 <0.001 0.043 0.043 0.043 E 0.09 0.1 0.1 01225 346 0.021 <0.001 <0.001 0.037 0.037 0.058 E 0.07 0.1 0.1 <0

1Calculated from the ammonia concentrations and pH, temperature, and an equilibrium constant (U.S. Geological Survey Office of Water Quality Technical Mem

http://water.usgs.gov/admin/memo/QW/qw93.12.html, accessed February 7, 2002). 2Nitrate plus nitrite minus nitrite.

3Calculated as the sum of dissolved ammonia and dissolved nitrate plus nitrite. See table 4. 4Calculated as the sum of total ammonia plus organic nitrogen and dissolved nitrate plus nitrite. See table 4. 5Based on variability in the laboratory method, there is no significant difference between the concentration of (1) dissolved ammonia plus organic nitrogen, (2) tota

and (3) total nitrogen (D.K. Mueller, U.S. Geological Survey, oral commun., 2002).
SUPPLEMENTAL DATA 93

Table 35. Number of phytoplankton detected in Morrow Point Reservoir, April–December 1999[Algal units/L, algal units per liter; site number refers to table 1 and figure 1]

Phylum Family Genus Algal units/L Phylum Family Genu

MORROW POINT RESERVOIR ABOVE PINE CREEK 

(SITE MP1)

April 21, 1999 October 7, 1999

Bacillariophyta Coscinodiscaceae Melosira 167 Bacillariophyta Coscinodiscaceae Melosira Bacillariophyta Coscinodiscaceae Stephanodiscus 3 Bacillariophyta Coscinodiscaceae StephanoBacillariophyta Fragilariaceae Asterionella 150 Bacillariophyta Fragilariaceae Tabellaria Bacillariophyta Fragilariaceae Fragilaria 66 Bacillariophyta Naviculaceae Navicula Bacillariophyta Fragilariaceae Tabellaria 77 Cyanophyta Nostocaceae AphanizoBacillariophyta Naviculaceae Navicula 14 December 1, 1999

August 17, 1999 Bacillariophyta Coscinodiscaceae Melosira 

Bacillariophyta Coscinodiscaceae Melosira 16 Bacillariophyta Fragilariaceae AsterioneBacillariophyta Fragilariaceae Fragilaria 3 Bacillariophyta Fragilariaceae Fragilaria 

Bacillariophyta Fragilariaceae Tabellaria 

MORROW POINT RESERVOIR AT KOKANEE BAY 

(SITE MP2)

April 21, 1999 October 7, 1999

Bacillariophyta Coscinodiscaceae Melosira 345 Bacillariophyta Coscinodiscaceae Melosira Bacillariophyta Coscinodiscaceae Stephanodiscus 10 Bacillariophyta Fragilariaceae AsterioneBacillariophyta Fragilariaceae Asterionella 209 Bacillariophyta Fragilariaceae Fragilaria Bacillariophyta Fragilariaceae Fragilaria 139 Bacillariophyta Fragilariaceae Tabellaria Bacillariophyta Fragilariaceae Tabellaria 146 Bacillariophyta Naviculaceae Navicula Chrysophyta Dinobryaceae Dinobryon 7 Cyanophyta Nostocaceae Aphanizo

August 17, 1999 December 1, 1999

Bacillariophyta Coscinodiscaceae Melosira 3 Bacillariophyta Coscinodiscaceae Melosira Bacillariophyta Fragilariaceae Asterionella 3 Bacillariophyta Fragilariaceae AsterioneBacillariophyta Fragilariaceae Fragilaria 10 Bacillariophyta Fragilariaceae Fragilaria Bacillariophyta Naviculaceae Navicula 7 Bacillariophyta Fragilariaceae Tabellaria Chlorophyta Chlorococcaceae Schroederia 3Chrysophyta Dinobryaceae Dinobryon 3

MORROW POINT RESERVOIR OFF HERMITS REST 

(SITE MP3)

April 21, 1999 October 7, 1999

Bacillariophyta Coscinodiscaceae Melosira 741 Bacillariophyta Coscinodiscaceae Melosira Bacillariophyta Coscinodiscaceae Stephanodiscus 7 Bacillariophyta Fragilariaceae Fragilaria Bacillariophyta Fragilariaceae Asterionella 188 Bacillariophyta Fragilariaceae Tabellaria Bacillariophyta Fragilariaceae Fragilaria 132 Cyanophyta Nostocaceae AphanizoBacillariophyta Fragilariaceae Tabellaria 136 December 1, 1999Chlorophyta Gamophyceae Spirogyra 7 Bacillariophyta Coscinodiscaceae Melosira 

August 17, 1999 Bacillariophyta Fragilariaceae Asterione

Bacillariophyta Coscinodiscaceae Melosira 14 Bacillariophyta Fragilariaceae Fragilaria Bacillariophyta Fragilariaceae Asterionella 3 Bacillariophyta Fragilariaceae Tabellaria Bacillariophyta Fragilariaceae Fragilaria 7Bacillariophyta Fragilariaceae Tabellaria 3Bacillariophyta Naviculaceae Navicula 3
94 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999,

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

Table 36. Physical properties and suspended sediment (inflows only) for Morrow Point Reservoir inflow and outflow sites, 

May–December 1999

[ft3/s, cubic feet per second; C, Celsius; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius; site number refers to table 1 

and figure 1; --, no data]

Date Time Discharge

(ft3/s)

Width

(feet)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

Suspended

sediment

(mg/L)

BLUE MESA RESERVOIR DISCHARGE AT BLUE MESA POWERHOUSE, NEAR SAPINERO

(SITE BO)

06/02/99 1215 11,836 -- 6.5 -- 8.1 200 --

08/16/99 1500 12,436 -- 9.1 8.0 7.7 174 --

10/05/99 1355 13,263 -- 12.5 7.6 7.6 176 --

12/08/99 1415 11,317 -- 6.0 -- 8.0 190 --

CORRAL CREEK AT HIGHWAY 92, NEAR SAPINERO 

(SITE MI2)

05/25/99 0900 5.90 8.0 6.2 9.2 7.6 66 16

08/26/99 1515 0.29 2.1 15.0 7.4 7.9 96 9

10/14/99 1305 0.18 2.0 9.7 8.6 7.9 91 4

12/07/99 1245 0.38 1.4 0.0 11.0 8.0 83 10

CURECANTI CREEK NEAR SAPINERO 

(SITE MI3)

05/25/99 1200 161 32.0 6.0 9.2 7.6 48 25

08/26/99 1220 16 20 17.0 7.5 8.1 100 6

10/14/99 1105 5.80 15 6.0 9.5 8.0 97 2

12/07/99 1100 6.14 13 0.0 10.3 7.8 96 3

PINE CREEK AT HIGHWAY 50, NEAR SAPINERO 

(SITE MI4)

06/02/99 1420 6.30 11.0 12.5 8.0 8.2 101 19

08/10/99 1330 1.60 4.5 14.5 7.6 7.9 141 9

10/05/99 1350 1.56 6.1 8.2 8.9 8.3 137 6

12/08/99 1350 3.50 6.6 0.0 -- 8.1 116 9

BLUE CREEK AT HIGHWAY 50, NEAR SAPINERO 

(SITE MI5)

06/03/99 0830 148 30.5 4.0 9.6 7.6 53 31

08/10/99 1115 79.0 29.0 11.2 8.2 7.6 62 16

10/07/99 0840 24.0 26.0 5.0 9.1 7.4 73 5

12/02/99 0950 27.5 27.0 0.0 10.8 7.7 68 8

MORROW POINT RESERVOIR OUTFLOW

05/27/99 -- 23,196 -- -- -- -- -- --

08/24/99 -- 22,135 -- -- -- -- -- --

10/07/99 -- 23,071 -- -- -- -- -- --

12/09/99 -- 21,109 -- -- -- -- -- --

MORROW POINT RESERVOIR DISCHARGE 

(SITE MO)

05/27/99 0915 -- -- 7.8 9.6 8.3 177 --

08/24/99 1310 -- -- 9.9 8.2 7.7 175 --

10/07/99 1435 -- -- 11.2 6.9 7.9 172 --

12/09/99 1150 -- -- 6.0 12.0 8.1 182 --

1

Outflow from Blue Mesa Reservoir. Value is mean value for the day.

2

Mean value for the day.
SUPPLEMENTAL DATA 95

Table 37. Nitrogen and phosphorus concentrations in Morrow Point Reservoir inflow and outflow sites, May–December 1999[Site number refers to table 1 and figure 1; <, less than; E, estimated]

Date Time

Concentration, 

in milligrams per liter

Nitrogen,

ammonia,

dissolved

Nitrogen,

un-ionized

ammonia,

dissolved1

Nitrogen,

nitrite,

dissolved

Nitrogen,

nitrate +

nitrite,

dissolved

Nitrogen,

nitrate,

dissolved2

Nitrogen,

inorganic,

dissolved3

Nitrogen,

ammonia +

organic

Nitrogen,

ammonia +

organic,

total

Nitrogen,

total4

Ortho

phosph

dissolv

BLUE MESA RESERVOIR DISCHARGE AT BLUE MESA POWERHOUSE, NEAR SAPINERO

(SITE BO)

06/02/99 1215 0.007 <0.001 0.001 0.005 0.004 0.012 50.2 50.1 50.1 0.0008/16/99 1500 <0.002 <0.001 0.001 0.054 0.053 0.054 50.1 5E 0.09 5E 0.1 0.0110/05/99 1355 <0.002 <0.001 0.001 0.048 0.047 0.048 50.2 50.1 50.1 0.0112/08/99 1415 <0.002 <0.001 <0.001 0.036 0.036 0.036 E 0.09 0.1 0.1 0.01 

CORRAL CREEK AT HIGHWAY 92, NEAR SAPINERO

(SITE MI2)

05/25/99 0900 0.004 <0.001 <0.001 0.019 0.019 0.023 0.2 0.4 0.4 0.0108/26/99 1515 0.004 <0.001 0.001 0.012 0.011 0.016 0.2 0.2 0.2 0.0210/14/99 1305 0.012 <0.001 0.001 <0.005 <0.005 0.013 E 0.1 0.2 0.2 0.0212/07/99 1245 <0.002 <0.001 <0.001 0.063 0.063 0.063 E 0.08 0.1 0.2 0.02

CURECANTI CREEK NEAR SAPINERO

(SITE MI3)

05/25/99 1200 0.004 <0.001 0.001 0.022 0.021 0.026 0.2 0.3 0.3 0.0108/26/99 1220 0.01 <0.001 0.001 <0.005 <0.005 0.01 0.2 0.3 0.3 0.0610/14/99 1105 0.005 <0.001 0.001 <0.005 <0.005 0.006 0.1 0.1 0.1 0.0412/07/99 1100 <0.002 <0.001 0.001 0.012 0.011 0.012 E 0.06 E 0.06 E 0.07 0.02

PINE CREEK AT HIGHWAY 50, NEAR SAPINERO

(SITE MI4)

06/02/99 1420 0.009 <0.001 0.001 0.007 0.006 0.016 0.3 0.5 0.5 0.0508/10/99 1330 0.007 <0.001 0.001 0.014 0.013 0.021 0.1 0.1 0.1 0.0910/05/99 1350 <0.002 <0.001 <0.001 0.005 0.005 0.005 0.1 0.2 0.2 0.0612/08/99 1350 0.005 <0.001 0.001 0.14 0.139 0.14 E 0.05 0.1 0.2 0.03

BLUE CREEK AT HIGHWAY 50, NEAR SAPINERO

(SITE MI5)

06/03/99 0830 0.009 <0.001 0.001 0.014 0.013 0.023 0.2 0.3 0.3 0.0208/10/99 1115 0.006 <0.001 0.001 <0.005 <0.005 0.007 50.1 5E 0.09 5E 0.09 0.0410/07/99 0840 0.002 <0.001 0.001 <0.005 <0.005 <0.005 0.1 0.2 0.2 0.0312/02/99 0950 <0.002 <0.001 <0.001 0.041 0.041 0.041 <0.1 E 0.09 E 0.1 0.03

MORROW POINT RESERVOIR DISCHARGE

(SITE MO)

05/27/99 0915 0.004 <0.001 0.001 0.01 0.009 0.01 0.1 0.2 0.2 0.0008/24/99 1310 0.02 <0.001 0.005 0.051 0.046 0.07 0.1 0.2 0.3 0.0110/07/99 1435 <0.002 <0.001 0.001 0.063 0.062 0.063 0.1 0.2 0.3 0.0112/09/99 1150 0.005 <0.001 <0.001 0.048 0.048 0.053 50.1 5E 0.07 5E 0.1 0.01

1Calculated from the ammonia concentrations and pH, temperature, and an equilibrium constant (U.S. Geological Survey Office of Water Quality Technical Memo

http://water.usgs.gov/admin/memo/QW/qw93.12.html, accessed February 7, 2002).

2Nitrate plus nitrite minus nitrite.3Calculated as the sum of dissolved ammonia and dissolved nitrate plus nitrite. See table 4.4Calculated as the sum of total ammonia plus organic nitrogen and dissolved nitrate plus nitrite. See table 4.5Based on variability in the laboratory method, there is no significant difference between the concentration of (1) dissolved ammonia plus organic nitrogen, (2) tota

and (3) total nitrogen (D.K. Mueller, U.S. Geological Survey, oral commun., 2002).
96 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999,

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

Table 38. Reservoir profile measurements, Crystal Reservoir near Crystal Dam (site CR1), April–December 1999

[Site number refers to table 1 and figure 1; C, Celsius; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

APRIL 20, 1999, SECCHI-DISC DEPTH, 3.0 METERS AUGUST 24, 1999, SECCHI-DISC DEPTH, 5.5 METERS

1 5.1 10.3 8.2 215 1 15.5 8.6 8.4 193

2 5.0 10.3 8.2 215 2 15.5 8.6 8.4 193

3 5.0 10.2 8.2 213 3 15.5 8.6 8.4 195

4 5.0 10.2 8.2 215 4 15.4 8.6 8.4 193

5 4.9 10.2 8.2 214 5 15.4 8.6 8.4 193

6 4.8 10.2 8.2 211 6 15.1 8.6 8.4 194

7 4.7 10.2 8.2 214 7 15.0 8.6 8.4 193

8 4.6 10.1 8.2 213 8 14.0 8.9 8.3 195

9 4.5 10.2 8.2 214 9 11.6 8.5 8.1 189

10 4.5 10.2 8.2 212 10 11.4 8.4 8.0 191

11 4.4 10.1 8.2 212 11 11.1 8.2 7.9 195

12 4.4 10.1 8.2 214 12 10.9 8.2 7.9 196

13 4.4 10.1 8.2 214 13 10.8 8.1 8.0 194

14 4.5 10.1 8.2 213 14 10.7 8.1 7.9 193

15 4.4 10.1 8.2 213 15 10.7 8.1 7.9 194

16 4.4 10.1 8.2 212 16 10.7 8.1 7.9 193

17 4.4 10.1 8.2 212 17 10.6 8.1 7.9 191

18 4.4 10.1 8.2 214 18 10.5 8.0 7.9 190

19 4.4 10.1 8.2 214 19 10.4 8.0 7.9 188

20 4.4 10.1 8.2 215 20 10.4 8.0 7.9 189

25 4.4 10.1 8.2 215 25 10.3 7.9 7.9 191

30 4.4 10.0 8.2 217 30 10.2 7.8 8.0 193

35 4.3 10.1 8.2 219 35 10.0 7.5 8.0 196

40 8.4 6.1 7.9 211

45 6.1 4.9 7.7 239

49.3 6.2 3.4 7.6 243
SUPPLEMENTAL DATA 97

Table 38. Reservoir profile measurements, Crystal Reservoir near Crystal Dam (site CR1), April–December 

1999—Continued

[Site number refers to table 1 and figure 1; C, Celsius; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

Depth

(meters)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

(standard

units)

Specific

conductance

(μS/cm)

OCTOBER 13, 1999, SECCHI-DISC DEPTH, 3.5 METERS DECEMBER 2, 1999, NO DATA FOR SECCHI-DISC DEPTH

1 11.3 7.4 7.4 186 1 6.0 9.0 7.3 188

2 11.2 7.4 7.4 185 2 6.0 8.8 7.3 187

3 11.1 7.4 7.4 185 3 6.0 8.9 7.3 188

4 11.1 7.4 7.4 185 4 6.0 8.9 7.3 187

5 11.1 7.4 7.4 185 5 6.0 8.8 7.3 187

6 11.1 7.4 7.4 185 6 6.0 8.6 7.3 187

7 11.1 7.4 7.4 185 7 6.0 8.7 7.3 188

8 11.1 7.3 7.4 185 8 6.0 8.8 7.3 188

9 11.1 7.3 7.4 185 9 6.0 8.8 7.3 188

10 11.1 7.3 7.5 186 10 6.0 8.5 7.3 187

11 11.1 7.3 7.6 185 11 6.0 8.6 7.3 187

12 11.1 7.3 7.6 185 12 6.0 8.6 7.3 188

13 11.1 7.3 7.5 185 13 6.0 8.5 7.3 188

14 11.1 7.2 7.5 185 14 6.0 8.5 7.3 188

15 11.1 7.3 7.5 185 15 6.0 8.5 7.3 188

16 11.1 7.3 7.5 185 16 6.0 8.6 7.3 188

17 11.1 7.2 7.5 185 17 6.0 8.5 7.3 188

18 11.1 7.2 7.5 185 18 6.0 8.5 7.3 187

19 11.1 7.3 7.5 185 19 6.0 8.5 7.3 187

20 11.0 7.2 7.5 185 20 6.0 8.4 7.3 187

25 11.0 7.2 7.5 185 25 6.0 8.5 7.3 187

30 11.0 7.2 7.5 185 30 6.0 8.4 7.3 189

35 11.0 7.2 7.4 185 35 6.0 8.4 7.4 188

40 10.9 7.0 7.4 183 40 6.0 8.4 7.4 188

44.4 10.5 3.2 7.2 184 45 6.0 8.5 7.4 192

50 6.0 8.4 7.4 193

52.8 6.0 8.0 7.2 196
98 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999,

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado Table 39. Nitrogen and phosphorus concentrations at Crystal Reservoir near Crystal Dam (site CR1), April–December 1999 [Site number refers to table 1 and figure 1; <, less than; E, estimated] Date Time Sampling depth (feet) Concentration, in milligrams per liter Nitrogen, ammonia, dissolved Nitrogen, un-ionized ammonia1 Nitrogen, nitrite, dissolved Nitrogen, nitrate + nitrite, dissolved Nitrogen, nitrate, dissolved2 Nitrogen, inorganic, dissolved3 Nitrogen, ammonia + organic, dissolved Nitrogen, ammonia + organic, total Nitrogen, total4 O

pho

dis

04/20/99 1530 2 0.003 <0.001 0.001 0.1 0.099 0.1 0.1 0.2 0.3 

1630 42 0.003 <0.001 0.001 0.1 0.099 0.1 0.1 0.1 0.2 

08/24/99 0930 2 0.008 <0.001 0.001 <0.005 <0.005 0.009 0.2 0.2 0.2 <

1005 26 0.009 <0.001 0.001 <0.005 <0.005 0.010 0.2 0.2 0.2 <1055 175 0.01 <0.001 0.002 0.18 0.178 0.19 0.2 0.2 0.4 

10/13/99 1150 2 0.004 <0.001 0.001 0.04 0.039 0.04 0.1 0.1 0.1 

1200 154 0.009 <0.001 0.001 0.044 0.043 0.053 50.2 50.1 50.1 

12/02/99 1235 2 <0.002 <0.001 <0.001 0.039 0.039 0.039 E 0.09 0.2 0.2 

1250 16 <0.002 <0.001 <0.001 0.041 0.041 0.041 E 0.06 0.1 0.1 1305 170 0.003 <0.001 <0.001 0.044 0.044 0.047 <0.1 0.1 0.1 

1Calculated from the ammonia concentrations and pH, temperature, and an equilibrium constant (U.S. Geological Survey Office of Water Quality Technical Mem

http://water.usgs.gov/admin/memo/QW/qw93.12.html, accessed February 7, 2002). 2Nitrate plus nitrite minus nitrite.

3Calculated as the sum of dissolved ammonia and dissolved nitrate plus nitrite. See table 4. 4Calculated as the sum of total ammonia plus organic nitrogen and nitrate plus nitrite. See table 4. 5Based on variability in the laboratory method, there is no significant difference between the concentration of (1) dissolved ammonia plus organic nitrogen, (2) tot

and (3) total nitrogen (D.K. Mueller, U.S. Geological Survey, oral commun., 2002).
SUPPLEMENTAL DATA 99

Table 40. Number of phytoplankton detected at Crystal Reservoir near Crystal Dam (site CR1), April–December 1999[Site number refers to table 1 and figure 1; Algal units/L, algal units per liter]

Phylum Family Genus Algal units/L Phylum Family 

April 20, 1999 October 13, 1999

Bacillariophyta Coscinodiscaceae Melosira 87 Bacillariophyta Coscinodiscaceae MeBacillariophyta Fragilariaceae Asterionella 31 Bacillariophyta Fragilariaceae AsBacillariophyta Fragilariaceae Fragilaria 24 Bacillariophyta Fragilariaceae FrBacillariophyta Fragilariaceae Tabellaria 35 Bacillariophyta Fragilariaceae TaBacillariophyta Naviculaceae Navicula 3 Cyanophyta Nostocaceae ApChrysophyta Dinobryaceae Dinobryon 3 Pyrrophyta Ceratiaceae Ce

August 16, 1999 December 2, 1999

Bacillariophyta Coscinodiscaceae Melosira 17 Bacillariophyta Coscinodiscaceae MeBacillariophyta Coscinodiscaceae Stephanodiscus 7 Bacillariophyta Fragilariaceae AsBacillariophyta Fragilariaceae Asterionella 209 Bacillariophyta Fragilariaceae FrBacillariophyta Fragilariaceae Fragilaria 31 Bacillariophyta Fragilariaceae TaBacillariophyta Naviculaceae Navicula 70Chlorophyta Chlorococcaceae Schroederia 17Chrysophyta Dinobryaceae Dinobryon 14Pyrrophyta Ceratiaceae Ceratium 28
100 Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999,

and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Colorado

Table 41. Physical properties and suspended sediment (inflows only) for Crystal Reservoir inflow and outflow sites, 

May–December 1999

[ft3/s, cubic feet per second; C, Celsius; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius; site number refers to table 1 

and figure 1; --, no data; E, estimated]

Date Time Discharge

(ft3/s)

Width

(feet)

Temperature

(degrees C)

Dissolved

oxygen

(mg/L)

pH

standard

(units)

Specific

conductance

(μS/cm)

Suspended

sediment

(mg/L)

MORROW POINT RESERVOIR OUTFLOW

05/27/99 -- 13,196 -- -- -- -- -- --

08/24/99 -- 12,135 -- -- -- -- -- --

10/07/99 -- 13,071 -- -- -- -- -- --

12/09/99 -- 11,109 -- -- -- -- -- --

MORROW POINT RESERVOIR DISCHARGE 

(SITE MO)

05/27/99 0915 -- -- 7.8 9.6 8.3 177 --

08/24/99 1310 -- -- 9.9 8.2 7.7 175 --

10/07/99 1435 -- -- 11.2 6.9 7.9 172 --

12/09/99 1150 -- -- 6.0 12.0 8.1 182 --

MESA CREEK ABOVE CRYSTAL RESERVOIR, NEAR CIMARRON 

(SITE CI2)

05/27/99 0935 36.0 16.0 6.2 9.4 7.7 48 9

08/24/99 1420 E 0.41 -- 16.8 7.7 8.2 131 4

10/07/99 1345 E 0.19 -- 8.6 9.1 8.2 143 3

12/09/99 1215 E 0.18 -- 0.0 11.5 8.1 130 2

CRYSTAL CREEK AT HIGHWAY 92, NEAR CRAWFORD 

(SITE CI3)

05/24/99 1400 3.10 12.0 16.8 7.2 8.3 227 5

08/26/99 0930 0.11 1.70 14.6 7.8 8.1 413 1

10/14/99 0925 0.11 2.10 3.2 8.9 8.0 444 1

12/07/99 0900 0.16 2.20 0.0 7.8 7.8 422 3

CIMARRON RIVER BELOW SQUAW CREEK, NEAR CIMARRON 

(SITE CI4)

06/03/99 1130 194 43.0 10.0 9.1 8.2 266 133

08/10/99 0845 97.0 30.0 13.0 7.9 8.2 449 56

10/07/99 1130 75.0 26.0 8.2 9.9 8.4 391 16

12/09/99 0925 26.0 28.0 0.0 11.5 8.3 413 2

CRYSTAL RESERVOIR OUTFLOW 

05/26/99 -- 13,824 -- -- -- -- -- --

08/24/99 -- 12,044 -- -- -- -- -- --

10/13/99 -- 11,726 -- -- -- -- -- --

12/02/99 -- 11,209 -- -- -- -- -- --

GUNNISON RIVER BELOW GUNNISON TUNNEL 

(SITE CO)

05/26/99 1315 -- 122 8.6 9.6 8.4 188 --

08/24/99 1340 -- 108 11.5 8.6 9.0 195 --

10/13/99 0930 -- 110 11.0 8.5 8.0 187 --

12/02/99 1225 -- -- 6.5 9.7 8.3 186 --

1Mean value for the day.
SUPPLEMENTAL DATA 101

Table 42. Nitrogen and phosphorus concentrations in Crystal Reservoir inflow and outflow sites, May–December 1999[Site number refers to table 1 and figure 1; <, less than; E, estimated]

Date Time

Concentration, 

in milligrams per liter

Nitrogen,

ammonia,

dissolved

Nitrogen,

un-ionized

ammonia,

dissolved1

Nitrogen,

nitrite,

dissolved

Nitrogen,

nitrate +

nitrite,

dissolved

Nitrogen,

nitrate,

dissolved2

Nitrogen,

inorganic,

dissolved3

Nitrogen,

ammonia +

organic,

dissolved

Nitrogen,

ammonia +

organic,

total

Nitrogen,

total4

Or

phos

diss

MORROW POINT RESERVOIR DISCHARGE 

(SITE MO)

05/27/99 0915 0.004 <0.001 0.001 0.01 0.009 0.01 0.1 0.2 0.2 0.08/24/99 1310 0.02 <0.001 0.005 0.051 0.046 0.07 0.1 0.2 0.3 0.10/07/99 1435 <0.002 <0.001 0.001 0.063 0.062 0.063 0.1 0.2 0.3 0.12/09/99 1150 0.005 <0.001 <0.001 0.048 0.048 0.053 50.1 5E 0.07 5E 0.1 0.

MESA CREEK ABOVE CRYSTAL RESERVOIR, NEAR CIMARRON 

(SITE CI2)

05/27/99 0935 0.006 <0.001 0.001 0.094 0.093 0.100 0.2 0.3 0.4 0.08/24/99 1420 0.016 <0.001 0.001 0.058 0.057 0.074 0.2 0.4 0.5 0.10/07/99 1345 0.003 <0.001 0.001 0.028 0.027 0.031 0.1 0.1 0.1 0.12/09/99 1215 <0.002 <0.001 0.001 0.079 0.078 0.079 6E 0.09 6E 0.07 E 0.1 0.

CRYSTAL CREEK AT HIGHWAY 92, NEAR CRAWFORD 

(SITE CI3)

05/24/99 1400 0.005 <0.001 0.001 0.007 0.006 0.012 0.5 0.6 0.6 0.08/26/99 0930 0.031 0.001 0.004 0.014 0.010 0.045 0.4 0.5 0.5 0.10/14/99 0925 0.011 <0.001 0.001 0.005 0.004 0.016 0.2 0.3 0.3 0.12/07/99 0900 <0.002 <0.001 0.001 <0.005 <0.005 <0.005 0.3 0.3 0.3 0.

CIMARRON RIVER BELOW SQUAW CREEK, NEAR CIMARRON

(SITE CI4)

06/03/99 1130 0.01 <0.001 0.002 0.03 0.028 0.04 0.3 0.6 0.6 0.08/10/99 0845 0.006 <0.001 0.001 0.056 0.055 0.062 60.2 60.1 0.2 0.10/07/99 1130 <0.002 <0.001 0.001 0.037 0.036 0.037 0.2 0.3 0.3 0.12/09/99 0925 0.005 <0.001 0.002 0.17 0.168 0.18 E 0.09 0.1 0.3 0.

GUNNISON RIVER BELOW GUNNISON TUNNEL 

(SITE CO)

05/26/99 1315 0.005 <0.001 0.001 0.013 0.012 0.018 0.1 0.4 0.4 0.08/24/99 1340 0.004 <0.001 <0.001 0.037 0.037 0.041 50.2 50.1 50.1 0.10/13/99 0930 <0.002 <0.001 0.001 0.034 0.033 0.034 0.1 0.1 0.1 0.12/02/99 1225 <0.002 <0.001 <0.001 0.083 0.083 0.083 <0.1 0.1 0.2 0.

1Calculated from the ammonia concentrations and pH, temperature, and an equilibrium constant (U.S. Geological Survey Office of Water Quality Technical Memo

http://water.usgs.gov/admin/memo/QW/qw93.12.html, accessed February 7, 2002).

2Nitrate plus nitrite minus nitrite.3Calculated as the sum of dissolved ammonia and dissolved nitrate plus nitrite. See table 4.4Calculated as the sum of total ammonia plus organic nitrogen and dissolved nitrate plus nitrite. See table 4.5Based on variability in the laboratory method, there is no significant difference between the concentration of (1) dissolved ammonia plus organic nitrogen, (2) tot

and (3) total nitrogen (D.K. Mueller, U.S. Geological Survey, oral commun., 2002).

6Based on variability in the laboratory method, there is no significant difference between the concentration of (1) dissolved ammonia plus organic nitrogen and (2) 

(D.K. Mueller, U.S. Geological Survey, oral commun., 2002).