U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2004-5113

National Water-Quality Assessment Program

Water-Quality Assessment of the Yellowstone River Basin, 

Montana and Wyoming—Water Quality of Fixed Sites, 

1999-2001
Front cover photograph: Aerial image of the Crazy Mountains, Montana, northwest of Billings, Montana (used with permission from 

Larry Mayer, larrymayer.com).
Water-Quality Assessment of the 

Yellowstone River Basin, Montana and 

Wyoming—Water Quality of Fixed Sites, 

1999-2001

By Kirk A. Miller, Melanie L. Clark, and Peter R. Wright

Scientific Investigations Report 2004-5113

U.S. Department of the Interior

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

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2005

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iii

FOREWORD

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 ). 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 long-term 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 Water-Quality 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, State, and local agencies, the NAWQA Program is 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 waterresource 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 ). 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).

 Robert M. Hirsch

 Associate Director for Water
iv

Contents

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

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

Purpose and Scope ............................................................................................................................. 2

Description of Study Unit .................................................................................................................... 2

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

Environmental Settings of Fixed Sites ....................................................................................................... 4

Design and Characteristics of the Fixed-Site Network ................................................................. 4

Soda Butte Creek at YNP boundary near Silver Gate, Montana (SB) ....................................... 12

Yellowstone River at Corwin Springs, Montana (YCS) ................................................................ 13

Clarks Fork Yellowstone River at Edgar, Montana (CF) ................................................................ 14

Yellowstone River at Billings, Montana (YB) ................................................................................. 15

Bighorn River at Kane, Wyoming (B) .............................................................................................. 16

Yellowstone River at Forsyth, Montana (YF) .................................................................................. 17

Tongue River at Dayton, Wyoming (T) ............................................................................................ 18

Little Powder River above Dry Creek, near Weston, Wyoming (LP) .......................................... 19

Powder River near Locate, Montana (P) ....................................................................................... 20

Yellowstone River near Sidney, Montana (YS) .............................................................................. 21

Data Collection and Analysis .................................................................................................................... 22

Sampling Methods ............................................................................................................................. 22

Data-Analysis Methods .................................................................................................................... 23

Quality Control .................................................................................................................................... 23

Fixed-Site Water Quality, 1999-2001 ......................................................................................................... 28

Hydrology ............................................................................................................................................ 28

Field Measurements .......................................................................................................................... 28

Fecal-Indicator Bacteria .................................................................................................................. 33

Concentrations .......................................................................................................................... 33

Comparison to Recommended Limits .................................................................................... 34

Temporal Variability .................................................................................................................. 35

Major Ions and Dissolved Solids ..................................................................................................... 37

Water Type ................................................................................................................................. 37

Dissolved Solids ........................................................................................................................ 41

Comparison to Water-Quality Criteria ................................................................................... 41

Temporal Variability .................................................................................................................. 41

Nutrients .............................................................................................................................................. 45

Concentrations .......................................................................................................................... 46

Nitrogen ............................................................................................................................. 46

Phosphorus ....................................................................................................................... 50

Organic Carbon ................................................................................................................ 51

Comparison to Water-Quality Criteria ................................................................................... 52

Temporal Variability .................................................................................................................. 52

Nitrogen ............................................................................................................................. 52

Phosphorus ....................................................................................................................... 55
v

Trace Elements ................................................................................................................................... 55

Iron and Manganese ................................................................................................................ 55

Arsenic ....................................................................................................................................... 55

Copper ........................................................................................................................................ 58

Selenium ..................................................................................................................................... 58

Zinc ........................................................................................................................................ 59

Comparison to Water-Quality Criteria ................................................................................... 59

Pesticides ............................................................................................................................................ 59

Pesticide Use ............................................................................................................................. 62

Frequency of Detections ......................................................................................................... 62

Comparison to Water-Quality Criteria ................................................................................... 64

Temporal Variability .................................................................................................................. 68

Suspended Sediment ........................................................................................................................ 68

Concentrations .......................................................................................................................... 70

Temporal Variability .................................................................................................................. 71

Estimated Loads and Yields ..................................................................................................... 71

Summary ...................................................................................................................................................... 74

References ................................................................................................................................................... 76

Figures

1. Map showing location of the Yellowstone River Basin ......................................................... 3

2. Schematic diagram and map of environmental settings and fixed sites of the 

Yellowstone River Basin ............................................................................................................. 6

3. Annual hydrograph (1999-2001) and photograph for Soda Butte Creek, Montana 

(site SB) ....................................................................................................................................... 12

4. Annual hydrograph (1890-2001) and photograph for the Yellowstone River at 

Corwin Springs, Montana (site YCS) ...................................................................................... 13

5. Annual hydrograph (1922-2001) and photograph for the Clarks Fork Yellowstone 

River, Montana (site CF) ............................................................................................................ 14

6. Annual hydrograph (1929-2001) and photograph for the Yellowstone River at 

Billings, Montana (site YB) ....................................................................................................... 15

7. Annual hydrograph (1952-2001) and photograph for the Bighorn River at Kane, 

Wyoming (site B) ........................................................................................................................ 16

8. Annual hydrograph (1978-2001) and photograph for the Yellowstone River at 

Forsyth, Montana (site YF) ........................................................................................................ 17

9. Annual hydrograph (1920-2001) and photograph for the Tongue River, Wyoming 

(site T) .......................................................................................................................................... 18

10. Annual hydrograph (1973-2001) and photograph for the Little Powder River, 

Wyoming (site LP) ..................................................................................................................... 19

11. Annual hydrograph (1939-2001) and photograph for the Powder River, 

Montana (site P) ......................................................................................................................... 20

12. Annual hydrograph (1967-2001) and photograph for the Yellowstone River near 

Sidney, Montana (site YS) ........................................................................................................ 21
vi

Figures—Continued

 13-19. Graphs showing:

 13. Recovery of pesticide compounds in field matrix spikes for fixed sites in the 

 Yellowstone River Basin, 1999-2001 ................................................................................ 27

 14. Recovery of surrogate compounds in pesticide samples for fixed sites in the 

 Yellowstone River Basin, 1999-2001 ................................................................................ 28

 15. Distribution of samples relative to daily mean streamflow duration for fixed 

 sites in the Yellowstone River Basin, 1999-2001 ............................................................ 30

 16. Statistical summary of water temperature, specific conductance, pH, and 

 dissolved-oxygen concentrations for fixed sites in the Yellowstone River Basin, 

 1999-2001. ............................................................................................................................. 32

 17. Statistical summary of fecal-indicator-bacteria concentrations for fixed sites 

 in the Yellowstone River Basin, 2000-2001 ..................................................................... 34

 18. Fecal-coliform and Escherichia coli relation for fixed sites in the Yellowstone River relation for fixed sites in the Yellowstone River 

 Basin, 2000-2001 ................................................................................................................. 36

 19. Seasonal variations in fecal-indicator-bacteria concentrations for fixed sites 

 in the Yellowstone River Basin, 2000-2001 ..................................................................... 36

20. Trilinear diagram showing major-ion composition and dissolved-solids concentrations for fixed sites in the Yellowstone River Basin, 1999-2001 ..................................... 38

21. Stiff diagrams showing major-ion composition for fixed sites in the Yellowstone 

River Basin, 1999-2001 .............................................................................................................. 39

22-41. Graphs showing:

 22. Statistical summary of concentrations of dissolved calcium, sodium, bicar-

 bonate, and sulfate for fixed sites in the Yellowstone River Basin, 1999-2001 ......... 40

 23. Statistical summary of dissolved-solids concentrations for fixed sites in the 

 Yellowstone River Basin, 1999-2001 ................................................................................ 42

 24. Seasonal variations in dissolved-solids concentrations for fixed sites in the 

 Yellowstone River Basin, 1999-2001 ................................................................................ 43

 25. Annual variations in dissolved-solids concentrations for fixed sites in 

 Yellowstone River Basin, 1999-2001 ................................................................................ 44

 26. Statistical summary of concentrations of selected nutrients for fixed sites in 

 the Yellowstone River Basin, 1999-2001 .......................................................................... 47

 27. Flow-weighted mean dissolved-nitrate concentrations related to A, drainage 

 area; B, forested lands; C, rangeland; and D, agricultural lands on alluvial 

 deposits for fixed sites in the Yellowstone River Basin, 1999-2001 ............................ 48

 28. Flow-weighted mean total-nitrogen concentrations related to A, drainage area; 

B, forested lands; C, rangeland; and D, agricultural lands on alluvial deposits 

 for fixed sites in the Yellowstone River Basin, 1999-2001 ............................................ 49

 29. Relations of total-phosphorus and suspended-sediment concentrations for 

 fixed sites in the Yellowstone River Basin, 1999-2001 .................................................. 51

 30. Seasonal statistical summary of LOADEST estimated daily dissolved-nitrate 

 concentrations for fixed sites in the Yellowstone River Basin, 1999-2001 ................ 53

 31. Seasonal statistical summary of LOADEST estimated daily total-nitrogen 

 concentrations for fixed sites in the Yellowstone River Basin, 1999-2001 ................ 54

 32. Seasonal statistical summary of LOADEST estimated daily total-phosphorus 

 concentrations for fixed sites in the Yellowstone River Basin, 1999-2001 ................ 56

 33. Statistical summary of selected trace-element concentrations for fixed sites 

 in the Yellowstone River Basin, 1999-2001 ..................................................................... 57
vii

Figures—Continued

 34. Relation of dissolved-arsenic concentrations and streamflow for fixed sites 

 on the Yellowstone River in the Yellowstone River Basin, 1999-2001 ........................ 58

 35. Pesticide use in the Yellowstone River Basin during 1992 (U.S. Department 

 of Commerce, 1995) ............................................................................................................ 63

 36. Frequency of pesticide detections for fixed sites in the Yellowstone River 

 Basin, 1999-2001 ................................................................................................................. 64

 37. Relation between atrazine concentrations and streamflow for site YF and 

 site YS in the Yellowstone River Basin, 1999-2001. ....................................................... 69

 38. Statistical summary of suspended-sediment concentrations for fixed sites 

 in the Yellowstone River Basin, 1999-2001 ..................................................................... 70

 39. Flow-weighted mean suspended-sediment concentration relation to 

 reservoir-adjusted A, drainage area; B, Tertiary-period sedimentary rocks; 

C, soil-erodibility factor; and D, rangeland for fixed sites in the Yellowstone 

 River Basin, 1999-2001 ....................................................................................................... 72

 40. Seasonal statistical summary of LOADEST estimated daily suspended-

 sediment concentrations for fixed sites in the Yellowstone River Basin, 

 1999-2001 .............................................................................................................................. 73

 41. Suspended-sediment yield related to mean annual precipitation for 

A, 1999-2001; and B, 1999 for fixed sites in theYellowstone River Basin ................... 74

Tables

1. Selected basin characteristics for fixed sites in the Yellowstone River Basin. ................ 8

2. Selected streamflow statistics for fixed sites in the Yellowstone River Basin. ............... 11

3. State water-quality classifications of surface waters, Montana and Wyoming. .......... 11

4. Summary of data collected by constituent grouping and calendar year for fixed 

sites in the Yellowstone River Basin, 1999-2001. .................................................................. 22

5. Statistical summary for concentrations of selected constituents in field equipment 

blank samples for fixed sites in the Yellowstone River Basin, 1999-2001. ........................ 25

6. Statistical summary of the relative percent difference determined for selected 

constituents in replicate samples for fixed sites in the Yellowstone River Basin, 

1999-2001. .................................................................................................................................... 26

7. Fecal-indicator bacteria exceeding U.S. Environmental Protection Agency’s 

recommended limits for a single sample for recreational contact with water for 

fixed sites in the Yellowstone River Basin, 2000-2001. ........................................................ 35

8. Sulfate and dissolved-solids concentrations exceeding U.S. Environmental 

Protection Agency’s Secondary Maximum Contaminant Levels for fixed sites 

in the Yellowstone River Basin, 1999-2001 ............................................................................. 42

9. Trade names, type, reporting levels, drinking-water criteria, and aquatic-life 

criteria for pesticide compounds analyzed by gas chromatography/mass spectrometry method. ........................................................................................................................ 60

10. Statistical summary of detections and concentrations of pesticides for fixed sites 

in the Yellowstone River Basin, 1999-2001. ........................................................................... 65

11. Estimated water year and average total annual suspended-sediment loads and 

reservoir-adjusted yields for fixed sites in the Yellowstone River Basin, 1999-2001. ..... 71
viii

Conversion Factors and Datum

Multiply By To obtain

inch (in.) 25.4 millimeter (mm)

mile (mi) 1.609 kilometer (km)

square mile (mi2) 2.590 square kilometer (km2) 

cubic foot (ft3) 0.02832 cubic meter (m3) 

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

pound (lb) 0.4536 kilogram (kg) 

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

 °F=(1.8×°C)+32

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

 °C=(°F-32)/1.8

Water year is the 12-month period from October 1 through September 30 and is designated by 

the year in which it ends. For example, the water year ending September 30, 1999 is called water 

year 1999.

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

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

Abbreviated Water-Quality Units

col/100 mL colonies per 100 milliliters

ft3/sec cubic feet per second /sec cubic feet per second

mg/L milligrams per liter

μg/g micrograms per gram

μg/L micrograms per liter

μm micrometer

μS/cm microsiemens per centimeter at 25 degrees Celsius

< less than

> greater than

°C degrees Celsius
ix

Abbreviations

B Bighorn River at Kane, Wyoming

CF Clarks Fork Yellowstone River at Edgar, Montana

DOC Dissolved organic carbon

E. coli Escherichia coli

GCMS Gas chromatography and mass spectrometry

IQR Interquartile range

LP Little Powder River above Dry Creek near Weston, Wyoming

MCL Maximum Contaminant Level

MRA Mineral resource area

NAWQA National Water-Quality Assessment Program

NED National Elevation Database

NLCD National Land Cover Data

P Powder River near Locate, Montana

RPD Relative percent difference

RSD4 Risk-specifi c dose associated with an excess cancer risk of 1 in 10,000 for a 

 concentration in drinking water equal to the risk-specifi c dose

RSD5 Risk-specifi c dose associated with an excess cancer risk of 1 in 100,000 for a 

 concentration in drinking water equal to the risk-specifi c dose

SB Soda Butte Creek at Yellowstone National Park boundary near Silver Gate,

 Montana

SMCL Secondary Maximum Contaminant Level

T Tongue River at Dayton, Wyoming

USEPA U.S. Environmental Protection Agency

USFS U.S. Forest Service

USGS U.S. Geological Survey

YELL Yellowstone River Basin Study Unit

YNP Yellowstone National Park

YCS Yellowstone River at Corwin Springs, Montana

YB Yellowstone River at Billings, Montana

YF Yellowstone River at Forsyth, Montana

YS Yellowstone River near Sidney, Montana

Water-Quality Assessment of the Yellowstone River 

Basin, Montana and Wyoming—Water Quality of Fixed 

Sites, 1999-2001

By Kirk A. Miller, Melanie L. Clark, and Peter R. Wright

Abstract

The National Water-Quality Assessment Program of 

the U.S. Geological Survey initiated an assessment in 1997 

of the quality of water resources in the Yellowstone River 

Basin. Water-quality samples regularly were collected during 

1999-2001 at 10 fixed sites on streams representing the major 

environmental settings of the basin. Integrator sites, which are 

heterogeneous in land use and geology, were established on 

the mainstem of the Yellowstone River (4 sites) and on three 

major tributaries—Clarks Fork Yellowstone River (1 site), the 

Bighorn River (1 site), and the Powder River (1 site). Indicator 

sites, which are more homogeneous in land use and geology 

than the integrator sites, were located on minor tributaries 

with important environmental settings—Soda Butte Creek in 

a mineral resource area (1 site), the Tongue River in a forested 

area (1 site), and the Little Powder River in a rangeland area 

(1 site). Water-quality sampling frequency generally was at 

least monthly and included field measurements and laboratory analyses of fecal-indicator bacteria, major ions, dissolved 

solids, nutrients, trace elements, pesticides, and suspended 

sediment.

Median concentrations of fecal coliform and Escherichia 

coli were largest for basins that were predominantly rangeland and smallest for basins that were predominantly forested. 

Concentrations of fecal coliform and Escherichia coli significantly varied by season (p-value <0.001); the smallest median 

concentrations were during January–March and the largest 

median concentrations were during April–June. Fecal-coliform 

concentrations exceeded the U.S. Environmental Protection 

Agency recommended limit for a single sample of 400 colonies per 100 milliliters in 2.6 percent of all samples. Escherichia coli concentrations exceeded the U.S. Environmental 

Protection Agency recommended limit for a single sample of 

298 colonies per 100 milliliters for moderate use, full-body 

contact recreation in 7.6 percent of all samples.

Variations in water type in the basin are reflective of 

the diverse geologic terrain in the Yellowstone River Basin. 

The water type of Soda Butte Creek and the Tongue River 

was calcium bicarbonate. These two sites are in forested and 

mountainous areas where igneous rocks and Paleozoic-era and 

Mesozoic-era sedimentary rocks are the dominant geologic 

groups. The water type of the Little Powder River was sodium 

sulfate. The Little Powder River originates in the plains, and 

geology of the basin is nearly homogenous with Tertiaryperiod sedimentary rocks. Water type of the Yellowstone River 

changed from a mixed-cation bicarbonate type upstream to 

a mixed-cation sulfate type downstream. Dissolved-solids 

concentrations ranged from fairly dilute in Soda Butte Creek, 

which had a median concentration of 118 milligrams per 

liter, to concentrated in the Little Powder River, which had a 

median concentration of 2,840 milligrams per liter.

Nutrient concentrations generally were small and reflect 

the relatively undeveloped conditions in the basin; however, 

some correlations were made with anthropogenic factors. 

Median dissolved-nitrate concentrations in all samples from 

the fixed sites ranged from 0.04 milligram per liter to 0.54 milligram per liter. Flow-weighted mean dissolved-nitrate concentrations were positively correlated with increasing agricultural 

land use and rangeland on alluvial deposits upstream from the 

sites and negatively correlated with increasing forested land. 

Ammonia concentrations generally were largest in samples 

collected from the Yellowstone River at Corwin Springs, Montana, which is downstream from Yellowstone National Park 

and receives discharge from geothermal waters that are high 

in ammonia. Median total-phosphorus concentrations ranged 

from 0.007 to 0.18 milligram per liter. Median total-phosphorus concentrations exceeded the U.S. Environmental Protection Agency’s recommended goal of 0.10 milligram per liter 

for preventing nuisance plant growth for samples collected 

from the Bighorn River, Powder River, and Yellowstone River. 

Seasonal variations were observed in nutrient concentrations. 

Dissolved-nitrate concentrations generally were largest during 

October to March when plant uptake of nitrate is lowest. In 

contrast, total-phosphorus concentrations were largest during 

April–June when sediment concentrations, which contribute to 

the total-phosphorus concentrations, are largest.

Concentrations of trace elements generally were small in 

samples for sites in the Yellowstone River Basin. Soda Butte 

Creek, which is in a mineral resource area with historical mining in the basin upstream from the sampling site, did not have 

elevated concentrations of trace elements compared to other 

sites. On the Yellowstone River, median concentrations of dissolved arsenic of 21 micrograms per liter at Corwin Springs, 

Montana, and 10.5 micrograms per liter at Billings, Montana, 
exceeded the drinking-water Maximum Contaminant Level of 

10 micrograms per liter. Geothermal waters from Yellowstone 

National Park are a significant source of arsenic in the Yellowstone River. Concentrations of dissolved selenium were largest 

in the Powder River, ranging from 0.48 microgram per liter to 

4.6 micrograms per liter. Concentrations were smaller than the 

aquatic-chronic criterion of 5 micrograms per liter; however, 

other studies have shown that concentrations of total selenium 

larger than 2 micrograms per liter may produce adverse effects 

on some fish and wildlife species.

Pesticide concentrations generally were small in samples 

for three sites on the Yellowstone River, one site on the Clarks 

Fork Yellowstone River, and one site on the Bighorn River. 

Herbicides were more frequently detected than insecticides. 

Atrazine was the most commonly detected herbicide and was 

detected in 74.8 percent of the samples. Concentrations of 

all compounds generally were smaller than 0.01 microgram 

per liter and substantially smaller than aquatic-life or humanhealth criteria. Mixtures of two or more pesticides were 

detected in 75 percent of the samples.

Suspended-sediment concentrations were seasonally 

variable and were largest during April–June during snowmelt 

runoff. Suspended-sediment concentrations were smallest 

for the fixed sites on Soda Butte Creek and the Tongue River 

because of the resistant geology in the mountainous settings. 

Reservoir-adjusted yields were largest for the Clarks Fork Yellowstone River, Bighorn River, and the Powder River, which 

have large drainage areas with mixed geology that includes 

Tertiary-period sedimentary rocks. On the Yellowstone River, 

suspended-sediment loads increased in the downstream direction.

Introduction

The National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey (USGS) was designed to: 

1) assess the status in quality of the Nation’s water resources, 

2) describe the trends in quality of these resources over time, 

and 3) improve the understanding of natural and anthropogenic influences on the quality of these resources (Hirsch and 

others, 1988). To implement this design, the NAWQA Program initiated more than 50 interdisciplinary assessments of 

the Nation’s most important stream and aquifer systems. These 

systems—referred to as Study Units—include more than 60 

percent of water used by all sectors and populations served by 

public water supplies.

Study-Unit assessments are implemented using a consistent design to allow for comparison of data and results on a 

National scale. As such, a Study-Unit assessment consists of 

four components: retrospective analysis, occurrence and distribution assessment, trends assessment, and detailed studies 

of selected constituents. Within the occurrence and distribution component, physical and chemical properties of dissolved 

and total constituents in streams are assessed at fixed sampling 

sites to address water-column characteristics (Gilliom and others, 1995).

In 1997, the NAWQA Program initiated an assessment 

of the quality of the streams and aquifers for the Yellowstone 

River Basin Study Unit (YELL). The YELL was defined as 

the entire Yellowstone River drainage basin, including the 

Yellowstone River and its major tributaries: Clarks Fork Yellowstone, Wind/Bighorn, Tongue, and Powder Rivers (Miller 

and Quinn, 1997). To assess the status of water-quality conditions in the YELL, 10 fixed sites were established on streams 

representing most of the environmental settings in the Study 

Unit. Water-quality samples generally were collected at least 

monthly at the fixed sites from January 1999 through September 2001 for use in describing the occurrence and distribution 

of water-column characteristics in the YELL.

Purpose and Scope

This report summarizes the environmental settings and 

water-quality characteristics at 10 fixed sites in the YELL in 

Montana and Wyoming. Fixed sites were on Soda Butte Creek 

(1 site), Yellowstone River (4 sites), Clarks Fork Yellowstone 

River (1 site), Bighorn River (1 site), Tongue River (1 site), 

Little Powder River (1 site), and Powder River (1 site). The 

water-quality characteristics described in the report include 

field measurements, fecal-indicator bacteria, major ions, 

dissolved solids, nutrients, trace elements, pesticides, and suspended sediment. Analyses of water-quality data for the fixed 

sites generally are limited to those samples collected during 

the study period from January 1, 1999 through September 30, 

2001. Water-quality characteristics are summarized in the 

context of the fixed-site environmental settings.

Description of Study Unit

The YELL extends from central Wyoming north to 

include most of southeastern Montana and a small part of 

western North Dakota (fig. 1). Drainage area for the YELL is 

about 70,100 square miles (mi2). The entire Yellowstone River 

drainage basin defines the YELL boundaries and includes all 

of the Clarks Fork Yellowstone, Wind/Bighorn, Tongue, and 

Powder River Basins. Topography of the YELL varies from 

mountain ranges and high plateaus, including the Wind River 

Range, Bighorn Mountains, and Absaroka Range, to intermontane basins, such as the Wind River and Bighorn Basins. 

Elevations in the YELL range from more than 13,800 feet 

above the North American Vertical Datum of 1988 (NAVD 88) 

to about 1,900 feet above NAVD 88. Mean annual precipitation ranges from more than 60 inches in the mountains near 

Yellowstone National Park (YNP) to less than 6 inches in parts 

of the Bighorn River Basin (Oregon Climate Service, 1998).

Rangeland is the dominant land use and land cover in the 

YELL, which includes about 47 percent herbaceous grasslands 

and 27 percent shrublands (U.S. Geological Survey, 1992). 

The remaining land uses and land covers include about 

2 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
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Figure 1. Location of the Yellowstone River Basin.

Introduction 3
14 percent forested lands, 9 percent agricultural lands, and 

3 percent other uses. Urban areas compose about 0.2 percent 

of the YELL. Total population of the Yellowstone River Basin 

was about 323,000 during 1990 (Zelt and others, 1999, p. 57). 

About 30 active mines remove low-sulfur coal by surface 

strip-mining methods from the large coal reserves in the 

Tongue and Powder River Basins. Most of the metals mining 

was in the mountainous regions of the Study Unit. Oil and gas 

are produced from reservoirs in the Powder River and Bighorn 

Basins (Miller and Quinn, 1997).

Streamflow in all the major drainage basins is affected 

by diversions. Although there are no reservoirs on the Yellowstone River, several reservoirs regulate flow in the Wind/

Bighorn and Tongue River drainage basins. About 98 percent 

of the total water used in the Study Unit in 1990 was surface 

water (Miller and Quinn, 1997). Most of this water—about 

99 percent—was used by the agricultural industry for crops 

and livestock. Public supply, mining, power generation, and 

industry made up most of the remaining uses of water in the 

YELL (Miller and Quinn, 1997).

Acknowledgments

USGS hydrologic technicians, in particular Stacy Kinsey, 

and hydrologists that collected water-quality samples and 

streamflow data are gratefully acknowledged; without their 

dedication, this report would not have been possible. All 

the local, State, and Federal agencies that contribute to the 

operation of streamflow gages in the basin are acknowledged. 

Reviews by Kent Becher, Janet Carter, and Norm Spahr 

improved the report. D. Kirk Nordstrom, USGS, is acknowledged for his insight into the water quality of the geothermal 

resources of Yellowstone National Park. David Peterson, 

USGS, is acknowledged for his assistance in evaluating 

nutrients in the Yellowstone River and his direction as project 

chief. Thomas Quinn, formerly USGS, is acknowledged for 

his guidance and support. The compilation and reduction of 

digital geographic data by Ronald Zelt, USGS, and Robert 

Kirkwood, formerly USGS, made possible many of the analyses in this report. In addition, Sue Roberts and Emily Sabado 

are acknowledged for their assistance in the preparation of the 

report.

Environmental Settings of Fixed Sites

Natural and anthropogenic factors, such as geology and 

land use, affect the water quality of streams. These factors can 

be combined to create environmental settings for the drainage 

basins that can be used for designing sampling networks and 

making water-quality assessments (Gilliom and others, 1995). 

This section describes the design and characteristics of the 

fixed-site network for the YELL and the characteristics for 

each of the sites in the network.

Design and Characteristics of the Fixed-Site 

Network

Zelt and others (1999) used three factors in a layered—or 

stratified—approach to create environmental settings that are 

believed to be important in assessing water-quality conditions 

in the YELL (fig. 2). Ecoregions—the first factor—were determined from a modification of mapping by Omernik (1987) 

(U.S. Environmental Protection Agency, 1996). Geology—the 

second factor—was determined from a reduction of multiple 

sources to generalized geologic groups. An additional geologic 

group—mineral resource area (MRA)—was defined for areas 

where minerals (for example, metals, coal deposits, or oil and 

gas fields) occur and (or) extraction activities have occurred 

or are likely to occur. Alluvium and other Quaternary-period 

unconsolidated deposits compose a small component of 

surficial geology and are not included with the consolidated 

geologic groups in table 1; however, these deposits typically 

are close to the stream and may be important to water quality, 

so they are discussed in the text in some places. Land use and 

land cover classification—the third factor—was determined 

from Anderson and others (1976).

The fixed-site network has two general types of sites. 

Integrator sites are used to characterize water quality in larger 

basins with a heterogeneous environmental setting, potentially 

consisting of multiple land covers, land uses, and geologic 

groups in more than one ecoregion. Integrator sites are 

located near the Study Unit outlet and near important confluences. By comparison, indicator sites are used to characterize 

water-quality in smaller basins with a relatively homogeneous 

environmental setting. Indicator sites are selected to represent 

environmental settings that may have an important influence 

on water quality in the YELL.

Of the 10 sites that were established as part of the YELL 

fixed-site network (table 1), 4 integrator sites were established 

on the Yellowstone River to directly describe downstream 

water-quality gradients on the mainstem. Sites were established at Corwin Springs (site YCS) downstream from YNP, 

Billings (site YB) downstream from the Clarks Fork Yellowstone River, Forsyth (site YF) downstream from the Bighorn 

River, and Sidney (site YS) near the mouth. Three additional 

integrator sites were established on major tributaries to augment information from the mainstem integrator sites. A site 

was established near the mouth of the Clarks Fork Yellowstone 

River (site CF) to characterize the contribution of nutrients 

and sediment to the mainstem. A site was established on the 

Bighorn River (site B) to characterize water-quality conditions in the largest and most regulated tributary. A site was 

established near the mouth of the Powder River (site P), which 

is a substantial source of sediment to the mainstem. Three 

indicator sites were established to characterize the water-quality conditions of important environmental settings in more 

homogeneous basins. A site was established on Soda Butte 

Creek (site SB) to characterize water-quality conditions of a 

MRA; on the Tongue River (site T) to characterize water-quality conditions for forested land; and on the Little Powder River 

4 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
(site LP) to characterize water-quality conditions for rangeland.

Environmental settings also were used to help determine sampling frequency and select constituents for analysis. 

Basic fixed sites were sampled monthly during the study with 

additional samples collected during extreme flows. Intensive 

fixed sites were sampled monthly during the study with additional samples collected during extreme flows and during the 

growing season where agriculture was an important land use. 

Fixed-site type for each site is listed in table 1. Constituents 

selected for analysis may be targeted to assess a specific land 

use. For example, trace elements may be analyzed in samples 

collected from basins where a MRA is a part of the environmental setting, but not analyzed in samples collected from a 

forested basin.

The simple one-, two-, or three-letter identifiers that 

were defined for each site are used in text, figures, and tables 

throughout the report for the benefit of the reader. Shading 

used in figures corresponds to the site groups (table 1) of 

mainstem integrator (gray shading), major tributary integrator (blue shading), and minor tributary indicator (white or no 

shading).

The land use and land cover distributions in table 1 were 

determined using the National Land Cover Data (NLCD) 

(U.S. Geological Survey, 1992). General differences between 

the NLCD and the Anderson and others (1976) classifications 

are described by the U.S. Geological Survey (1992). For land 

use and land cover information over small areas in the YELL, 

the NLCD probably is more accurate than the previous data, 

because of enhanced spatial resolution and updated mapping 

techniques as well as being more contemporaneous with this 

study. Because of the generalized, composite nature of the 

stratification process, however, differences between the land 

use and land cover data and the resulting differences in the 

environmental settings at the basin scale for the YELL are 

small. In this report, rangeland is the combined area of the 

shrubland and herbaceous grassland land covers.

Land-use and land-cover classifications are general 

descriptors of land characteristics that often are interpreted 

differently. Such interpretations can exclude detailed characteristics that are important in water-quality assessments. For 

example, rangelands typically are associated with minimal use 

as well as livestock grazing of native grasslands. In the YELL, 

however, land uses on rangelands also include vegetation 

management to improve forage and dispersed development 

of oil and gas. Similarly, in addition to the natural conditions 

in forested lands, forest uses also include logging, livestock 

grazing, and recreational activities. In addition, for rangelands 

as well as forested lands, increasing low-density, unsewered 

domestic development is a changing land use in the YELL. 

Finally, some land uses that do not compose a large percentage 

of any given basin can be important in water-quality assessments. For example, much of the agricultural land uses in the 

YELL are concentrated near water sources because of the 

semi-arid climate.

Environmental Settings of Fixed Sites 5

Other basin or stream characteristics are useful in 

describing the environmental setting of the fixed sites. Areaweighted mean basin elevations (table 1) were determined 

using the National Elevation Database (NED) (U.S. Geological Survey, 1999) and other digital spatial data. Area-weighted 

mean annual and monthly precipitation values were calculated using digital spatial data by Daly and others (1994) and 

Oregon Climate Service (1998). Streamflow statistics for the 

fixed sites were determined using gaging-station data from 

USGS databases (table 2). Because of the short period of 

record (1999-2001) for site SB, the streamflow statistics might 

not be representative of historical or future streamflows. These 

streamflow data are available from the USGS on the Internet at 

http://waterdata.usgs.gov/nwis/sw. Stream classifications and 

corresponding quality or use classifications that are used by 

the States of Montana and Wyoming for regulatory concerns 

were simplified for this report and are listed in table 3. The 

stream classifications and supporting uses are described with 

the environmental setting for the site.
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Figure 2. Schematic diagram and map of environmental settings and fixed sites of the Yellowstone River Basin.

6 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
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Figure 2. Continued.

Environmental Settings of Fixed Sites 7
Table 1. Selected basin characteristics for fixed sites in the Yellowstone River Basin.

[NAVD 88, North American Vertical Datum of 1988; YNP, Yellowstone National Park; p€, Precambrian crystalline; PZ, Paleozoic and Mesozoic sedimentary; Ks, Cretaceous sedimentary; Ts, Tertiary sedimentary; KTv, Cretaceous and Tertiary volcanic; KTQv, Cretaceous, Tertiary, and Quaternary volcanic]

Site

report 

identifier 

(fig. 2)

Station 

number Station name

Drainage area 

(square 

miles)1

Mean basin 

elevation 

(feet above 

NAVD 88) Site group 

Fixed-site 

type

Predominant environmental characteristics 

(percent of drainage area)

Mean annual 

precipitation 

(inches)4 Ecoregion2

Simplified 

geologic 

groups2

Land use and 

land cover3

SB 06187915 Soda Butte Creek 

at YNP boundary, near Silver Gate, Mont.

 31.2 8,900 Minor 

tributary indicator

Basic 

indicator (mineral resource area)

Middle Rocky 

Mountains (100)

KTv (68), 

PZ (31), p€(1)

Evergreen 

forest (77), Transitional (9), Shrubland (9), Herbaceous grassland (3)

38

YCS 06191500 Yellowstone 

River at Corwin Springs, Mont.

 2,619 8,300 Mainstem 

integrator

Basic integrator Middle Rocky Mountains (100) KTQv (77), p€(8), 

PZ (5), Ks (2)

Evergreen 

forest (49), Transitional (23), Shrubland (11), Herbaceous grassland (9)

32

CF 06208500 Clarks Fork Yellowstone River 

at Edgar, Mont.

 2,022 6,300 Major 

tributary integrator

Basic integrator Middle Rocky Mountains (47), 

Wyoming Basin (40), Northwestern Great Plains (13)

Ts (33), 

Ks (19), KTv (18), p€(18), PZ (11)

Shrubland (42), 

Evergreen forest (27), Herbaceous grassland (19), Transitional (3)

22 

YB 06214500 Yellowstone 

River at Billings, Mont.

 11,805 6,500 Mainstem 

integrator

Basic integrator Middle Rocky Mountains (55), 

Northwestern Great Plains (24), Montana Valley and Foothill Prairies (13), Wyoming Basin (7)

KTv (35), 

Ks (22), p€ (16), Ts (15), PZ (5), KTQv (5)

Herbaceous 

grassland (33), Evergreen forest (31), Shrubland (15), Transitional (6)

24

8 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
Site

report 

identifier 

(fig. 2)

Station 

number Station name

Drainage area 

(square 

miles)1

Mean basin 

elevation 

(feet above 

NAVD 88) Site group 

Fixed-site 

type

Predominant environmental characteristics 

(percent of drainage area)

Mean annual 

precipitation 

(inches)4 Ecoregion2

Simplified 

geologic 

groups2

Land use and 

land cover3

B 06279500 Bighorn River at 

Kane, Wyo.

 15,762 6,400 Major 

tributary integrator

Intensive 

integrator

Wyoming Basin 

(74), Middle Rocky Mountains (26)

Ts (43), 

Ks (23), PZ (18), p€ (9), KTQv (6)

Shrubland (60), 

Herbaceous grassland (25), Evergreen forest (9), Pasture/hay (2)

14

YF 06295000 Yellowstone 

River at Forsyth, Mont.

 40,146 5,800 Mainstem 

integrator

Intensive 

integrator

Wyoming Basin 

(35), Middle Rocky Mountains (33), Northwestern Great Plains (27), Montana Valley and Foothill Prairies (4)

Ks (34), 

Ts (27), KTv (16), PZ (13), p€ (8), KTQv (1)

Herbaceous 

grassland (36), Shrubland (33), Evergreen forest (17), Small grains (3)

18

T 06298000 Tongue River 

near Dayton, Wyo.

 206 8,500 Minor 

tributary indicator

Basic 

indicator (forested)

Middle Rocky 

Mountains (100)

PZ (53), 

p€(46)

Evergreen forest 

(60), Herbaceous grassland (23), Shrubland (7), Deciduous forest (5)

27

LP 06324970 Little Powder 

River above Dry Creek, near Weston, Wyo.

 1,237 4,100 Minor 

tributary indicator

Basic indicator (rangeland) Northwestern Great Plains (100) Ts (100) Herbaceous grassland (81), Shrubland (11), 

Evergreen forest (3), Small grains (1), Emergent herbaceous wetlands (1)

14

Table 1. Selected basin characteristics for fixed sites in the Yellowstone River Basin—Continued.

Environmental Settings of Fixed Sites 9
Site

report 

identifier 

(fig. 2)

Station 

number Station name

Drainage area 

(square 

miles)1

Mean basin 

elevation 

(feet above 

NAVD 88) Site group 

Fixed-site 

type

Predominant environmental characteristics 

(percent of drainage area)

Mean annual 

precipitation 

(inches)4 Ecoregion2

Simplified 

geologic 

groups2

Land use and 

land cover3

P 06326500 Powder River 

near Locate, Mont.

 13,068 4,600 Major 

tributary integrator

Basic integrator Northwestern Great Plains (88), 

Middle Rocky Mountains (7), Wyoming Basin (5) 

Ts (65), 

Ks (24), PZ (7), p€ (4)

Herbaceous 

grassland (59), Shrubland (29), Evergreen forest (6), Small grains (1), Fallow (1), Pasture/hay (1)

14

YS 06329500 Yellowstone 

River near Sidney, Mont.

 69,083 5,000 Mainstem 

integrator

Intensive 

integrator

Northwestern Great 

Plains (55), Middle Rocky Mountains (22), Northwestern Great Plains (21), Montana Valley and Foothill Prairies (2)

Ts (48), 

Ks (26), KTv (9), PZ (9), p€ (6)

Herbaceous 

grassland (47), Shrubland (27), Evergreen forest (13), Small grains (3), Fallow (3)

17

1Source U.S. Geological Survey National Water Information System.2Modified from Zelt and others, 1999; only the four largest (by total basin area) geologic groups are listed.3Modified from U.S. Geological Survey, 1992; only the four largest (by total basin area) land use/land cover classifications are listed.4Modified from Oregon Climate Service, 1998.

Table 1. Selected basin characteristics for fixed sites in the Yellowstone River Basin—Continued.

10 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
Table 2. Selected streamflow statistics for fixed sites in the Yellowstone River Basin.

Site report 

identifier 

(fig. 2)

Period 

of record 

(water 

years)1

Mean annual 

streamflow

(cubic feet

per second)

Streamflow percent exceedance 

(cubic feet per second)

Annual runoff

10th 50th 90th (acre- feet)

SB 1999-2001 52.7 203 8.2 1.8 38,000

YCS 1890-2001 3,125 8,490 1,400 760 2,264,000

CF 1922-2001 1,035 2,850 470 275 749,800

YB 1929-2001 6,996 17,700 3,730 2,180 5,069,000

B 1930-2001 2,160 23,000 22,100 21,400 1,565,000

YF 1978-2001 10,800 22,900 7,380 4,600 7,822,000

T 1920-2001 180 479 73 48 130,100

LP 1973-2001 21.8 35 3.0 .03 15,780

P 1939-2001 583 1,370 241 42 422,300

YS 1911-2001 12,550 327,000 38,740 35,000 9,095,000

1

Based on complete water years. May include intervening water years with no record.

2

Based on period of record after regulation began by Boysen Reservoir, water years 1952-2001.

3

Based on period of record after Bighorn Lake reached operational level, water years 1967-2001.

Table 3. State water-quality classifications of surface waters, Montana and Wyoming.

Class Quality or use Comments

Montana1

A Very high quality 3Montana surface-water classification includes a 

nondegredataion policy for “Outstanding Resource 

Waters”

B High quality Majority of surface waters in Montana.

C Low quality Same uses as class B waters except unsuitable for 

drinking.

I Impaired Generally unsuitable for any use.

Wyoming2

1 Outstanding waters Includes all waters in Teton and Yellowstone National 

Parks and designated wilderness areas.

2 Fisheries and drinking waters Known to support or have the potential to support fish 

populations or drinking water supplies.

3 Aquatic life other than fish Basic default classification for all waters; provides 

minimum protection for aquatic life and recreation 

uses.

4 Agriculture, industry, recreation, and 

wildlife

Aquatic life not protected.

1

Source: Bryan and Kakuk, 1997.

2

Source: Wyoming Department of Environmental Quality, 2001a.

3

Bryan and Kakuk, p. 11, 1997.

Environmental Settings of Fixed Sites 11
Figure 3. Annual hydrograph (1999-2001) and photograph for Soda Butte 

Creek, Montana (site SB).

Photograph from U.S. Geological Survey files.

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Soda Butte Creek at YNP boundary near Silver Gate, Montana (SB)

Soda Butte Creek is located in the Absaroka Range 

of southwestern Montana where it flows west-southwest 

into YNP and Wyoming to its confluence with the Lamar 

River, a tributary to the Yellowstone River. Site SB (fig. 2) 

is downstream from Silver Gate, Montana, at the boundary of YNP. The drainage area for the site is located entirely 

within the Middle Rocky Mountains ecoregion. Mean basin 

elevation is the highest of the fixed-site basins (8,900 feet 

above NAVD 88), with elevations ranging from more than 

11,000 feet above NAVD 88 in the headwaters to about 

7,300 feet above NAVD 88 near site SB. Mean annual precipitation of 38 inches in the Soda Butte Creek Basin is the highest for the fixed-site basins. The geologic groups generally are 

composed of mostly Cretaceous- and Tertiary-period volcanic 

rocks and Paleozoic-era and Mesozoic-era sedimentary rocks 

(Elliott, 1979). About 33 percent of the basin upstream from 

site SB was included by Zelt and others (1999) in the MRA 

geologic group, which is predominantly associated with the 

Paleozoic-era and Mesozoic-era sedimentary rocks, based on 

descriptions of historical and recent metals mining and other 

mineral resource assessments.

About 77 percent of the land cover of the basin upstream 

from site SB is evergreen forest (table 1). An important 

historical land use in the basin has been the mining of gold, 

silver, copper, and other metals. Ore from the McLaren Mine 

was processed at a mill located next to Soda Butte Creek until 

1953 (Boughton, 2001). Much of the mining occurred at or 

near timberline in the upper part of the basin. Disposal of mine 

tailings included an in-channel impoundment in the headwaters of Soda Butte Creek. Subsequent exploration continued 

until 1996 when private mining interests were bought out by 

the U.S. Government (U.S. Forest Service, 2003). The communities of Cooke City and Silver Gate, Montana (fig. 1), 

which have a combined population of 140 people (U.S. Census 

Bureau, 2000), are located in the basin along Soda Butte 

Creek.

The hydrology of site SB is characteristic of small 

streams with headwaters in the mountainous areas of the 

YELL. Annual streamflows are dominated by a snowmelt 

peak of moderate duration during late spring through early 

summer with low variability in daily mean streamflow 

throughout the year (fig. 3). Compared to rainstorms in the 

basins and plains areas, mountain snowpacks are relatively 

consistent in spatial extent and between years, resulting in low 

variability in annual streamflows (Miller, 1999).

Soda Butte Creek upstream from site SB is classified by 

the State of Montana as Class B waters (Montana Department 

of Environmental Quality, 2002a). Soda Butte Creek upstream 

from site SB to a tailings impoundment is listed as only 

partially supporting aquatic life and cold-water fishes because 

of metals from abandoned mining activities (Montana Department of Environmental Quality, 2002b).

12 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
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Figure 4. Annual hydrograph (1890-2001) and photograph for the Yellowstone River at Corwin Springs, Montana (site YCS). Photograph by Gregory K. Boughton, U.S. Geological Survey

Yellowstone River at Corwin Springs, Montana (YCS)

The headwaters of the Yellowstone River are near the 

Continental Divide in the Absaroka Range of northwestern 

Wyoming and from there the river generally flows northnorthwest into YNP, through Yellowstone Lake and the 

Grand Canyon of the Yellowstone, and into Montana. Site 

YCS (fig. 2) is located at Corwin Springs about 8 miles (mi) 

north of the Wyoming-Montana state line and about 550 river 

miles upstream from the confluence with the Missouri River 

(Shields and others, 2001). The basin upstream from the site is 

located entirely within the Middle Rocky Mountains ecoregion. Elevations in the basin range from more than 12,100 

feet above NAVD 88 in the headwaters to about 5,100 feet 

above NAVD 88 near site YCS. Mean annual precipitation 

for the basin is about 32 inches; most of the annual precipitation occurs as snow during the winter months, with November 

through January accumulations equaling about 30 percent of 

the total annual precipitation. The geologic groups in the basin 

upstream from site YCS are composed mostly of Cretaceous-, 

Tertiary-, and Quaternary-period volcanic rocks (77 percent). 

YNP and the surrounding region are considered an active volcanic area; Yellowstone Lake is located in a collapsed caldera 

measuring 45 mi by 30 mi (U.S. Geological Survey, 2003b; 

Yellowstone National Park, 2001).

About 49 percent of the land cover of the basin upstream 

from site YCS is evergreen forest and about 23 percent is 

classified as transitional (table 1). The transitional classification includes areas of sparse vegetative cover that are in the 

process of changing from one land cover to another. Examples 

include forest clearcuts and changes due to natural causes (for 

example, fire). During 1988, forest fires burned large areas 

of YNP and the surrounding region. About 46 percent of the 

basin upstream from site YCS was within the perimeters of 

these fires (Yellowstone National Park, 1995).

The hydrology of site YCS is characteristic of large 

streams with headwaters in the mountainous areas of the 

YELL. Annual streamflows are dominated by a single snowmelt peak of moderate duration during late spring through 

early summer with low variability in daily mean streamflow 

throughout the year (fig. 4). Compared to rainstorms in the 

basins and plains areas, mountain snowpacks vary little in 

spatial extent and between years, resulting in low variability in 

annual streamflows (Miller, 1999). Annual mean streamflow 

at site YCS is about 25 percent of the annual mean streamflow 

at site YS near the mouth; however, drainage area at site YCS 

accounts for only about 4 percent of the drainage area at site 

YS.

In YNP, the Yellowstone River and its tributaries are 

classified by the States of Wyoming and Montana as Class 1 

and A waters, respectively, because all waters within national 

parks and wilderness areas are classified as such (Wyoming 

Department of Environmental Quality, 2001a; Montana 

Department of Environmental Quality, 2002a). The Yellowstone River downstream from YNP to site YCS is classified by 

the State of Montana as Class B waters (Montana Department 

of Environmental Quality, 2002a).

Environmental Settings of Fixed Sites 13
Figure 5. Annual hydrograph (1922-2001) and photograph for the Clarks Fork 

Yellowstone River, Montana (site CF). Photograph by Gregory K. Boughton, U.S. Geological Survey

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Clarks Fork Yellowstone River at Edgar, Montana (CF)

The Clarks Fork Yellowstone River flows east-southeast from its headwaters in the Beartooth Mountains and the 

Absaroka Range of southwestern Montana and northwestern Wyoming before flowing north-northeast to its confluence with the Yellowstone River. Site CF (fig. 2) is located 

at Edgar, Montana, about 22 river miles upstream from the 

confluence (Shields and others, 2001). The drainage area for 

the site is located mostly within the Middle Rocky Mountains 

(47 percent; upper part of the basin) and Wyoming Basin 

(40 percent; lower part of the basin) ecoregions. Elevations in 

the basin range from more than 12,500 feet above NAVD 88 

in the headwaters to about 3,500 feet above NAVD 88 near 

site CF. Annual precipitation in the basin varies substantially, 

ranging from about 65 inches at the higher elevations in the 

western part of the basin to about 7 inches in the east-central 

part of the basin. Precambrian-era crystalline rocks (18 percent 

of the drainage area) and Cretaceous- and Tertiary-period 

volcanic rocks (18 percent) are the dominant geologic groups 

in the upper part of the basin in the Middle Rocky Mountains 

ecoregion. Cretaceous- (19 percent) and Tertiary-period (33 

percent) sedimentary rocks are the dominant geologic groups 

in the lower part of the basin in the Wyoming Basin ecoregion.

The dominant land cover in the basin upstream from site 

CF is rangeland, which includes shrubland and herbaceous 

grassland (table 1). Most of the rangeland is in the lower part 

of the basin in the Wyoming Basin ecoregion. The agricultural 

land cover generally is in the lower part of the basin near the 

streams (fig. 2). About 16 percent of the alluvial deposits in 

the basin have agricultural uses on them; 53 percent of all 

agricultural land uses in the basin are on alluvial deposits. The 

dominant land cover in the upper part of the basin in the Middle Rocky Mountains ecoregion is evergreen forest (table 1).

The hydrology of site CF is characteristic of large streams 

with headwaters in the mountainous areas of the YELL. 

Annual streamflows are dominated by a single snowmelt peak 

of moderate duration during late spring through early summer (fig. 5). Variability in daily mean streamflow during the 

spring, summer, and fall months is larger at site CF than other 

snowmelt-dominated streams because of the variability in 

rainstorms in the lower part of the basin. Irrigation withdrawals in the lower part of the basin also affect variability in daily 

mean streamflow.

The upper reaches of the Clarks Fork Yellowstone River 

in Wyoming are the State’s only reaches with National Wild 

and Scenic Rivers designation (Interagency Coordinating 

Council, 2003) and are classified by the State of Wyoming as 

Class 1 waters. The Clarks Fork Yellowstone River upstream 

from site CF is classified by the State of Montana as Class 

B waters (Montana Department of Environmental Quality, 

2002a). From the headwaters to the state line, the river is listed 

as only partially supporting aquatic life and cold-water fishes, 

because of metals from abandoned mining activities (Wyoming Department of Environmental Quality, 2002, Montana 

Department of Environmental Quality, 2002b).

14 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
Figure 6. Annual hydrograph (1929-2001) and photograph for the Yellowstone 

River at Billings, Montana (site YB). Photograph from U.S. Geological Survey files ���������������������� ������������������������

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Yellowstone River at Billings, Montana (YB)

From site YCS, the Yellowstone River flows north to 

Livingston, Montana, then east through southern Montana 

to Billings, Montana, about 360 river miles upstream from 

the confluence with the Missouri River (Shields and others, 

2001). Billings, Montana, the largest city in the YELL with a 

population of 89,847 (U.S. Census Bureau, 2000), is located 

at site YB (fig. 2). The drainage area for the site is located 

mostly within the Middle Rocky Mountains (55 percent) 

ecoregion. Mean basin elevation is about 6,500 feet above 

NAVD 88, with elevations ranging from more than 12,500 feet 

above NAVD 88 in the headwaters to about 3,100 feet above 

NAVD 88 near site YB. Mean annual precipitation for the 

basin is about 24 inches, ranging from about 65 inches at the 

higher elevations in the basin to about 7 inches in the Clarks 

Fork Yellowstone River part of the basin. The geologic groups 

in the basin upstream from site YB are composed mostly of 

Cretaceous- and Tertiary-period volcanic rocks (35 percent 

of the basin). Cretaceous-period sedimentary rocks compose 

22 percent of the total basin.

Land cover in the basin upstream from site YB is dominated by rangeland and forested land (table 1). About 33 percent of the drainage area land cover is herbaceous grassland 

and 15 percent is shrubland (table 1). The percentage of forested land decreases and the percentage of rangeland increases 

downstream along the Yellowstone River between sites YCS 

and YB as proportionally less of the total drainage area is from 

mountain areas and more is from basin and plains areas. Land 

cover adjacent to streams in the basin upstream from site YB 

is mostly rangeland. About 44 percent of the land cover on 

alluvial deposits in the basin is herbaceous grasslands and 

shrublands. Agricultural land uses are more prevalent adjacent 

to streams than for the distant parts of the basin. About 13 percent of the alluvial deposits in the basin have agricultural uses 

on them.

The hydrology of site YB is characteristic of large 

streams with headwaters in the mountainous areas of the 

YELL. Annual streamflows are dominated by a single snowmelt peak of moderate duration during late spring through 

early summer with low variability in daily mean streamflow 

throughout the year (fig. 6). Annual mean streamflow at 

site YB is about 56 percent of the annual mean streamflow at 

site YS near the mouth; drainage area at site YB accounts for 

only about 17 percent of the drainage area at site YS.

The Yellowstone River at site YB is classified by the 

State of Montana as Class B waters (Montana Department 

of Environmental Quality, 2002a). The Yellowstone River 

downstream from Billings is listed as only partially supporting warm-water fishery probably because of habitat alterations 

(Montana Department of Environmental Quality, 2002b).

Environmental Settings of Fixed Sites 15
Photograph from U.S. Geological Survey files

Figure 7. Annual hydrograph (1952-2001) and photograph for the Bighorn 

River at Kane, Wyoming (site B). ���������������������� ������������������������

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Bighorn River at Kane, Wyoming (B)

The headwaters for the Bighorn River are the streams 

in the mountains rimming the southern, eastern, and western 

margins of the basin. The principal headwater stream—the 

Wind River—flows east-southeast from the Continental Divide 

in Wyoming into the Wind River Basin before flowing north 

into Boysen Reservoir and through Wind River Canyon. Near 

the mouth of Wind River Canyon at Wedding of the Waters, 

the Wind River becomes the Bighorn River and flows north 

through the Bighorn Basin and into Bighorn Lake (a reservoir) 

and Bighorn Canyon National Recreation Area. Site B (fig. 2) 

is located at Kane, Wyoming, about 0.5 mi upstream from the 

normal highwater line for Bighorn Lake (Swanson and others, 2001). The drainage area for site B is mostly within the 

Wyoming Basin (74 percent) ecoregion (table 1). Elevations in 

the basin range from more than 13,800 feet above NAVD 88 

in the Wind River Range to about 3,700 feet above NAVD 88 

near site B. Annual mean precipitation varies with elevation, 

ranging from about 47 inches in the western mountains of the 

basin to less than 6 inches in the central part of the Bighorn 

Basin. The geologic groups in the basin upstream from site B 

are composed mostly of Tertiary-period sedimentary rocks 

(43 percent of the drainage area), which occur mostly in the 

central, lower-elevation parts of the Wind River and Bighorn 

Basins. Cretaceous-period and Paleozoic- and Mesozoic-era 

sedimentary rocks are exposed on the flanks of the mountain 

uplifts at the basin margins.

The dominant land cover in the basin upstream from 

site B is rangeland. About 60 percent of the drainage area land 

cover is shrubland and 25 percent is herbaceous grassland 

(table 1). Evergreen forest land cover is at higher elevations 

in the basin in contrast to agricultural covers, which generally are located in the lower elevations of the basin. About 

70 percent of the land cover on alluvial deposits in the basin is 

herbaceous grasslands and shrublands. About 16 percent of the 

alluvial deposits in the basin have agricultural uses on them. 

About 74 percent of all agricultural land uses in the basin are 

on alluvial deposits.

Streamflows in the Bighorn River are affected substantially by modifications in the form of releases from Boysen 

Reservoir as well as irrigation diversions and return flows. 

Streamflow statistics for the period of record following regulation by Boysen Reservoir (water years 1952-2001) show the 

effects of streamflow modification in the large variability in 

streamflows during the summer months (fig. 7). Annual mean 

streamflow at site B is about 17 percent of the annual mean 

streamflow at site YS near the mouth of the Yellowstone 

River; drainage area at site B accounts for about 23 percent of 

the drainage area at site YS.

The Bighorn River is classified as Class 2 waters (Wyoming Department of Environmental Quality, 2001a). A reach 

of the Bighorn River downstream from Greybull, Wyoming, to 

an undetermined distance upstream from Kane, Wyoming, is 

classified as impaired for contact recreation because of fecalcoliform bacteria (Wyoming Department of Environmental 

Quality, 2002).

16 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
Figure 8. Annual hydrograph (1978-2001) and photograph for the Yellowstone 

River at Forsyth, Montana (site YF).

Photograph from U.S. Geological Survey files

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Yellowstone River at Forsyth, Montana (YF)

The Yellowstone River flows east-northeast from site 

YB through southern Montana. Site YF (fig. 2) is located at 

Forsyth, Montana, downstream from the confluence with the 

Bighorn River and about 240 river miles upstream from the 

confluence with the Missouri River (Shields and others, 2001). 

The basin upstream from site YF is located mostly within the 

Wyoming Basin (35 percent), Middle Rocky Mountains (33 

percent), and Northwestern Great Plains (27 percent) ecoregions. Mean basin elevation is about 5,800 feet above NAVD 

88, with elevations ranging from more than 13,800 feet above 

NAVD 88 in the Wind River Range to about 2,500 feet above 

NAVD 88 near site YF. Mean annual precipitation for the 

basin is about 18 inches. The geologic groups in the basin 

upstream from site YF are dominated by Cretaceous-period 

and Tertiary-period sedimentary rocks that generally extend 

over the basins and plains, including the area along the mainstem of the Yellowstone River and the lower-elevation areas in 

the Wind River and Bighorn Basins. The volcanic rocks that 

dominated the geologic groups of the Yellowstone River Basin 

at site YCS and site YB compose less than 16 percent of the 

basin at site YF.

The dominant land cover in the basin upstream from 

site YF is rangeland. About 36 percent of the drainage area 

land cover is herbaceous grassland and another 33 percent 

is shrubland (table 1). The shift in land cover from forested 

land to rangeland along the Yellowstone River between sites 

YCS and YB continues between sites YB and YF. Land cover 

adjacent to streams in the basin upstream from site YF also is 

dominated by rangeland; about 57 percent of the land cover 

on alluvial deposits in the basin is herbaceous grasslands and 

shrublands. Agricultural land uses are more prevalent adjacent 

to streams than for the distant parts of the basin; about 19 percent of the alluvial deposits in the basin have agricultural uses 

on them.

The hydrology of site YF is similar to the upstream 

site YB, where annual streamflows are dominated by a single 

snowmelt peak of moderate duration during late spring 

through early summer with low variability in daily mean 

streamflow throughout the year (fig. 8). The larger drainage 

area at site YF results in lower variability in streamflows at YF 

compared to YB. Annual mean streamflow at site YF is about 

86 percent of the annual mean streamflow at site YS near the 

mouth; drainage area at site YF accounts for about 58 percent 

of the drainage area at site YS.

The Yellowstone River at site YF is classified by the 

State of Montana as Class B waters (Montana Department 

of Environmental Quality, 2002a). The Yellowstone River in 

this area only partially supports warm water fishery, possibly 

because of habitat alteration from stream modification and 

dam construction (Montana Department of Environmental 

Quality, 2002b). 

Environmental Settings of Fixed Sites 17
Photograph by Gregory K. Boughton, U.S. Geological Survey

Figure 9. Annual hydrograph (1920-2001) and photograph for the Tongue 

River, Wyoming (site T). ���������������������� ������������������������

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Tongue River at Dayton, Wyoming (T)

The Tongue River flows east-northeast from the northeast 

flank of the Bighorn Mountains in northern Wyoming and 

through the plains of southeastern Montana to its confluence 

with the Yellowstone River at Miles City, Montana. Site T 

(fig. 2) is located near Dayton, Wyoming, at the mouth of a 

canyon; the drainage area for the site is located entirely within 

the Middle Rocky Mountains ecoregion (table 1). Mean basin 

elevation is about 8,500 feet above NAVD 88, with elevations ranging from more than 10,800 feet above NAVD 88 

in the headwaters to about 4,100 feet above NAVD 88 near 

site T. Mean annual precipitation for the basin is about 27 

inches, with about 34 percent of the total annual precipitation occurring on average during April through June. The 

geologic groups are composed of Precambrian-era crystalline 

rocks (46 percent) in the headwaters of the basin and upturned 

Paleozoic- and Mesozoic-era sedimentary rocks (53 percent) 

in the lower reaches of the basin. Included in these sedimentary units are carbonate rocks such as the Madison Limestone. 

Dissolution of these carbonates along fault zones and fold 

fractures has developed karstic features in some areas.

The dominant land cover in the basin upstream from 

site T is forested land (table 1). About 60 percent of the drainage area land cover is evergreen forest and 5 percent is deciduous forest. Other land cover in the basin includes rangeland 

(about 30 percent). The U.S. Forest Service (USFS) manages 

about 98 percent of the lands in the basin for multiple uses, 

including logging, grazing, and recreation (U.S. Bureau of 

Land Management, 2002).

The hydrology of site T is characteristic of streams with 

headwaters in the mountainous areas of the YELL. Annual 

streamflows are dominated by a single mountain snowmelt peak of moderate duration during late spring through 

early summer with low variability in daily mean streamflow 

throughout the remainder of the year (fig. 9). Compared to 

rainstorms in the basins and plains areas, mountain snowpacks 

are relatively consistent in spatial extent and between years, 

resulting in low variability in annual streamflows (Miller, 

1999). Streamflows resulting from spring rain events upstream 

from site T generally are attenuated because of the low intensity and moderate duration of those events as well as geologic 

features. Streamflows at site T also are influenced by karstic 

features in the basin.

The Tongue River upstream from site T is classified by 

the State of Wyoming as Class 1 waters. A tributary to the 

Tongue River was previously listed as only partially supporting aquatic life because of residual chlorine in waste-water 

discharge from a USFS facility in the basin (Wyoming Department of Environmental Quality, 1998).

18 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
Photograph from U.S. Geological Survey files Figure 10. Annual hydrograph (1973-2001) and photograph for the Little 

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Little Powder River above Dry Creek, near Weston, Wyoming (LP)

The Little Powder River flows north through the plains 

of northeastern Wyoming and southeastern Montana to its confluence with the Powder River. Site LP (fig. 2) is located about 

5 mi south of the Wyoming-Montana state line. The drainage 

area for the site is located entirely within the Northwestern 

Great Plains ecoregion (table 1). Mean basin elevation is about 

4,100 feet above NAVD 88, with elevations ranging from 

about 4,900 feet above NAVD 88 to about 3,400 feet above 

NAVD 88 near site LP. Mean annual precipitation for the 

basin is about 14 inches; about 39 percent of the total annual 

precipitation occurs on average during May and June. The 

geologic groups for the basin are composed of flat to gently 

dipping Tertiary-age sandstones, shales, coal beds, and clinker. 

Clinker refers to sedimentary rocks that have been thermally 

altered by fires in underlying coal beds. These distinctive 

red-colored rocks that cap topographic highs cover about 

1,600 mi2 in northeastern Wyoming and southeastern Montana, much of which includes the Tongue and Powder Rivers 

of the Yellowstone River Basin. Clinker is characterized by 

high permeability and infiltration rates and large transmissivity 

and storage values (Heffern and Coates, 1997, 1999; Bartos 

and Ogle, 2002).

The dominant land cover in the basin upstream from 

site LP is rangeland (fig 2). About 81 percent of the drainage area land cover is herbaceous grassland and 11 percent is 

shrubland (table 1). Important land uses of these rangelands 

include grazing by livestock and wildlife, oil and gas development, and surface coal mining. Land cover adjacent to streams 

in the basin upstream from site LP also is dominated by rangeland. About 72 percent of the land cover on alluvial deposits in 

the basin is herbaceous grasslands and shrublands.

The hydrology of site LP generally is characteristic of 

small streams with headwaters in the plains areas of the YELL 

and streamflow is highly variable. Isolated precipitation events 

can substantially influence average daily mean streamflows. 

Annual streamflows at site LP consist of a plains (lowland) 

snowmelt peak during late winter through early spring 

(fig. 10). Several short to moderate duration rainstorm peaks 

are superimposed on the snowmelt peak and throughout the 

remainder of the summer. The hydrology of site LP is unique 

in some respects when compared to similar streams in the 

YELL. The occurrences and properties of clinker is important 

to the hydrology of site LP, attenuating streamflows from 

rainfall and snowmelt runoff, maintaining streamflows during 

low-flow periods, functioning as local aquifers, recharging underlying regional aquifers, and generally resulting in 

improved water quality (Lowry and Rankl, 1987; Heffern and 

Coates, 1997, 1999; Bartos and Ogle, 2002).

The Little Powder River is classified by the State of 

Wyoming as Class 2 waters (Wyoming Department of Environmental Quality, 2001a). A reach of the Little Powder River 

upstream from the Wyoming-Montana state line to an undetermined distance upstream is classified as threatened for contact 

recreation because of fecal-coliform bacteria (Wyoming 

Department of Environmental Quality, 2002).

Environmental Settings of Fixed Sites 19
Photograph from U.S. Geological Survey files

Figure 11. Annual hydrograph (1939-2001) and photograph for the Powder 

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Powder River near Locate, Montana (P)

Headwaters for the Powder River are in the plains and 

mountains of central and north-central Wyoming. The Powder 

River flows north through the plains of northeastern Wyoming and southeastern Montana to its confluence with the 

Yellowstone River. Site P (fig. 2) is near Locate, Montana, 

about 25 mi east of Miles City, Montana, and 29 river miles 

upstream from the confluence with the Yellowstone River 

(Shields and others, 2001). The drainage area for the site 

predominantly is located within the Northwestern Great Plains 

(88 percent) ecoregion (table 1). Mean elevation in the basin 

is about 4,600 feet above NAVD 88 and ranges from more 

than 13,100 feet above NAVD 88 in the Bighorn Mountains 

to about 2,400 feet above NAVD 88 near site P. Mean annual 

precipitation for the basin is about 14 inches. The geologic 

groups for the basin include flat to gently dipping Tertiaryperiod sedimentary rocks that compose 65 percent of the 

drainage area. Cretaceous-period sedimentary rocks compose 

24 percent of the drainage area. Like the Little Powder River 

Basin, clinker exists in the basin, particularly along the eastern 

margin of the basin. Paleozoic- and Mesozoic-era sedimentary 

rocks and Precambrian-era crystalline rocks are exposed in the 

mountains along the western margin of the basin.

The dominant land cover in the basin upstream from 

site P is rangeland; about 59 percent of the drainage area 

land cover is herbaceous grassland and another 29 percent is 

shrubland (table 1). Important land uses of these rangelands 

include grazing by livestock and wildlife, oil and gas development, and surface coal mining. Land cover adjacent to streams 

in the basin upstream from site P also is dominated by rangeland. About 71 percent of the land cover on alluvial deposits 

in the basin is herbaceous grasslands and shrublands. About 

12 percent of the alluvial deposits in the basin have agricultural uses on them.

The hydrology of site P is characteristic of large streams 

with headwaters in the mountainous areas of the YELL 

that flow across the basins and plains. Annual streamflow 

characteristics are a combination of the annual streamflow 

characteristics of mountain streams and basin and plains 

streams. Annual streamflows at site P consist of a plains 

(lowland) snowmelt peak during late winter through early 

spring followed by a peak from the mountain snowmelt during 

late spring through early summer (fig. 11). Several short to 

moderate duration rainstorm peaks are superimposed on the 

snowmelt peak and throughout the remainder of the summer. 

Annual mean streamflow at site P is only about 5 percent of 

the annual mean streamflow at site YS near the mouth of the 

Yellowstone River; drainage area at site P accounts for about 

19 percent of the drainage area at site YS.

The Powder River downstream at site P is classified by 

the State of Montana as Class B waters (Montana Department of Environmental Quality, 2002a). The Powder River 

in this reach was not assessed by the State of Montana for 

impairments (Montana Department of Environmental Quality, 

2002b).

20 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
Figure 12. Annual hydrograph (1967-2001) and photograph for the 

Yellowstone River near Sidney, Montana (site YS).

Photograph from U.S. Geological Survey files

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Yellowstone River near Sidney, Montana (YS)

The Yellowstone River flows east from site YF then 

northeast through the plains of southeastern Montana and into 

western North Dakota to its confluence with the Missouri 

River. The Tongue and Powder Rivers are major tributaries 

to the Yellowstone River in this part of the YELL. Site YS 

(fig. 2) is located near Sidney, Montana, about 29 river miles 

upstream from the confluence with the Missouri River (Shields 

and others, 2001). About 55 percent of the basin is located 

within the Northwestern Great Plains ecoregion (table 1). 

Mean basin elevation is about 5,000 feet above NAVD 88, 

with elevations ranging from more than 13,800 feet above 

NAVD 88 in the Wind River Range to about 1,900 feet above 

NAVD 88 near site YS. Mean annual precipitation for the 

basin is about 17 inches, which is substantially less than the 

mean annual precipitation at the mainstem sites (site YCS and 

site YB) in the upper basin. The geologic groups for the basin 

at site YS reflect the diverse geology of the sub-basins and 

ranges from Precambrian-era rocks and Tertiary-period volcanic rocks in the high mountains to predominantly Tertiaryperiod sedimentary rocks (48 percent) in the eastern part of the 

basin near Sidney, Montana. Cretaceous-period sedimentary 

rocks that generally are exposed along the flanks of uplifted 

areas compose 26 percent of the drainage area for the basin.

The dominant land cover in the basin upstream from 

site YS is rangeland. About 47 percent of the drainage area 

land cover is herbaceous grassland and 27 percent is shrubland 

(table 1). The shift in land cover characteristics downstream 

along the Yellowstone River from forested land to rangeland 

continues between sites YF and YS. Land cover adjacent to 

streams in the basin upstream from site YS also is dominated 

by rangeland. About 58 percent of the land cover on alluvial 

deposits in the basin is herbaceous grasslands and shrublands. 

About 20 percent of the alluvial deposits in the basin have 

agricultural uses on them.

The hydrology of site YS is characteristic of large 

streams with headwaters in the mountainous areas of the 

YELL that flow across the basins and plains. Annual streamflow characteristics are a combination of the annual streamflow characteristics of mountain streams and basin and plains 

streams. Annual streamflow statistics at site YS (water years 

1967-2001) consist of a plains (lowland) snowmelt peak 

during late winter through early spring followed by a peak 

from the mountain snowmelt during late spring through early 

summer (fig. 12). The larger drainage area at site YS results in 

lower variability in streamflow.

The Yellowstone River at site YS is classified by the State 

of Montana as Class B waters (Montana Department of Environmental Quality, 2002a). The river upstream from Sidney, 

Montana is listed as only partially supporting warm-water 

fishery probably because of habitat alterations from stream 

modification and dam construction (Montana Department of 

Environmental Quality, 2002b).

Environmental Settings of Fixed Sites 21
Table 4. Summary of data collected by constituent grouping and calendar year for fixed sites in the Yellowstone River 

Basin, 1999-2001.

[X; at least one sample collected during calendar year]

Site 

report 

identifier 

(fig. 2)

Field measurements, 

major ions, nutrients, 

iron, manganese, and 

suspended sediment Bacteria

Trace elements (other 

than iron and manganese) Pesticides

1999 2000 2001 1999 2000 2001 1999 2000 2001 1999 2000 2001

SB X X X X X X X X

YCS X X X X X X

CF X X X X X X X

YB X X X X X X X

B X X X X X X X

YF X X X X X X X X X X X

T X X X X X X

LP X X X X X X X X

P X X X X X X X X

YS X X X X X X X X X X X

Data Collection and Analysis

Stream-water quality of the YELL was assessed through 

the collection of samples generally on a monthly basis from 

January 1999 to September 2001. A summary of the data set 

used during analysis of the fixed sites by constituent grouping and calendar year is presented in table 4. In addition to the 

collection of environmental samples, quality-control samples 

were collected to estimate the bias and variability that result 

from sample collection, processing, and analysis. Sampling 

methods, data-analysis methods, and quality-control data are 

described in this section of the report.

Sampling Methods

One of the design components of the NAWQA Program 

is the use of nationally consistent methods for sample collection, field measurements, sample processing, and laboratory 

analyses. Samples were collected in accordance with established USGS methods and NAWQA protocols (Edwards and 

Glysson, 1988; Ward and Harr, 1990; Horowitz and others, 

1994; Shelton, 1994, 1997; U.S. Geological Survey, 1997-

2004). During normal streamflow conditions, samples generally were collected using depth-integrated samplers, using the 

equal-width-integrated method that is described in Edwards 

and Glysson (1988) and Ward and Harr (1990). When samples 

were collected from streams during extreme conditions, such 

as hazardous ice conditions and very low flows, traditional 

depth- and width-integrating techniques may not have been 

used. During these conditions, multiple-vertical or dip-sampling techniques were used. Dissolved organic carbon (DOC) 

and microbiological samples were collected separately from 

the primary sample with dip-sampling techniques. When 

a wading sample could not be collected, a weighted bottle 

sampler was used to obtain the DOC sample from the centroid 

of flow.

Field measurements of streams made at the time of 

sampling included instantaneous streamflow, water temperature, specific conductance, pH, dissolved oxygen, and alkalinity. Air temperature also was measured. All of the fixed sites 

were located at streamflow-gaging stations, so generally gage 

heights were measured and the instantaneous streamflow was 

determined using the most current streamflow rating curve. 

Stream temperature and dissolved oxygen were measured 

in-stream using a multi-parameter water-quality probe. A 

composite sample taken from the cone splitter was analyzed 

for specific conductance, pH, and alkalinity.

Water samples to be analyzed for inorganic and organic 

constituents were processed onsite using standard methods and 

equipment described by Horowitz and others (1994), Shelton 

(1994, 1997), and the U.S. Geological Survey (1997-2004). 

22 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
Samples that were analyzed for dissolved-inorganic constituents were filtered with a 0.45 micrometer (μm) disposable filter. Samples that were analyzed for dissolved-organic 

constituents were filtered with a 0.70 μm glass filter. Samples 

that were analyzed for total-constituent concentrations, which 

include dissolved and particulate forms, were unfiltered. 

Samples for fecal coliform and Escherichia coli (E. coli) were 

processed onsite using sterile techniques and membrane-filtration methods. Subsamples over a range of volumes were 

filtered in order to obtain countable plates within the ideal 

ranges of 20 to 60 colonies per 100 milliliters (col/100 mL) 

for fecal coliform and 20 to 80 col/100 mL for E. coli. Filters 

were plated, processed, and enumerated according to Myers 

and Wilde (1997).

Water samples were sent to the USGS National Water 

Quality Laboratory in Lakewood, Colorado, for analysis using 

standard USGS analytical methods (Fishman and Friedman, 

1989; Faires, 1993; Fishman, 1993; McLain, 1993; Zaugg and 

others, 1995; Jones and Garbarino, 1999; Patton and Truit, 

2000). Sediment samples were sent to the USGS sediment 

laboratory in Helena, Montana, and were analyzed for concentration in accordance with methods described in Guy (1969) 

and Lambing and Dodge (1993).

Data-Analysis Methods

Data in this report are summarized using parametric and 

nonparametric statistics. Descriptive summary statistics were 

computed using standard methods. Some constituent concentrations were less than laboratory reporting levels (censored 

data). Statistics of constituent concentrations that included 

censored data were estimated using robust methods (Helsel 

and Cohn, 1988; Helsel and Hirsch, 1992). Robust methods 

use distributions fit to data that are greater than the reporting 

level(s) to estimate summary statistics. In this report, summary statistics for most data sets with censored values were 

estimated using log-probability regression. In some cases, 

data were censored to a consistent reporting level in order to 

compare data through time or across constituents. Summary 

statistics are shown using boxplots for some constituents. For 

boxplots, the lower and upper edges of the box indicate the 

25th and 75th percentiles, respectively. The median is a line 

within the box, and whiskers extend to the 10th and 90th percentiles. For some boxplots, values outside the 10th and 90th 

percentiles are shown as individual points. Laboratory reporting levels are indicated on the boxplots that were produced 

from data sets with censored values.

Parametric statistical techniques (Pearson’s r) were used 

to test for correlations between data sets when data were normally distributed. Transformation of a data set may have been 

used to achieve a normal distribution. Nonparametric statistical techniques were used to test for correlations between data 

sets when the data distributions were unknown. For data sets 

where the sample size was less than 20, Kendall’s tau was used 

to measure the strength and direction of the relation between 

variables. Spearman’s correlation coefficient (Spearman’s rho) 

was used to measure the strength and direction of the relation between variables of larger data sets (Helsel and Hirsch, 

1992). Kendall’s tau and Spearman’s Rho use rank-based 

procedures rather than actual data values and are resistant 

to the effects of outliers. The nonparametric Kruskal-Wallis 

test was used to compare whether concentrations for selected 

constituents varied seasonally or annually. The Kruskal-Wallis 

test uses data ranks rather than actual data values to reduce the 

effect of outliers. In the most general form, the Kruskal-Wallis test determines whether three or more groups of ranked 

data have similar distributions or at least one group differs in 

its distribution (Helsel and Hirsch, 1992). Data are presented 

with p-values for correlations and statistical tests. The p-value 

for correlations indicates the probability of determining the 

correlation strength by chance alone. Statistical significance 

for tests was determined using a 95 percent confidence level 

(p-values <0.05).

Water quality is discussed in terms of constituent concentrations, loads, and yields. Constituent concentrations define 

the water-quality conditions at a point in time and generally 

are used for assessing the suitability of the water for aquatic 

life and other uses. For selected constituents, statistics of flowweighted mean concentrations and estimated loads and yields 

also are summarized. Flow-weighted mean concentrations 

were computed from the sum of estimates of daily concentrations divided by the sum of daily streamflows. Estimates of 

daily concentrations were computed using the rating-curve 

method (Cohn and others, 1989) and the computer program 

LOADEST (Crawford, 1991). The LOADEST program uses 

robust estimation methods for data that are censored. Because 

streamflow data are typically skewed, statistics of sample concentrations collected at equal intervals (for example, monthly) 

can be skewed depending on the relation of the constituent 

concentration with streamflow. A flow-weighted concentration is influenced less by this skew because it is representative 

of the concentration of the total mass discharge (load) of the 

constituent. Similarly, flow-weighted concentrations allow for 

comparisons between sites with differing sampling frequencies. Estimates of daily concentrations using this method 

are subject to large errors; as such, only annual and seasonal 

statistics are used in this report. Estimated constituent loads 

and yields (load divided by drainage area) also were computed 

using the rating-curve method (Cohn and others, 1989) and the 

computer program LOADEST (Crawford, 1991).

Quality Control

The data-quality objectives of the NAWQA Program 

include the collection of field quality-control samples for inorganic and organic constituents as part of the fixed-site sampling. Quality-control samples, including equipment blanks, 

replicates, and matrix spikes, are used to estimate the extent 

to which contamination, measurement variability, and matrix 

interference affect the interpretation of the environmental data 

Data Collection and Analysis 23
(Mueller and others, 1997). Equipment blank samples were 

prepared in the field at each of the fixed sites by processing 

inorganic-grade or pesticide-grade deionized water through the 

sampling equipment immediately before collecting the environmental sample. Replicate samples were prepared at each 

of the fixed sites by splitting the environmental sample into 

duplicate samples. Matrix spikes were prepared by injecting 

a laboratory-prepared spike solution of pesticide compounds 

into replicate environmental samples at sites where samples 

for pesticides were collected. In addition to field quality-control samples for pesticides, surrogate solutions were added 

to all of the pesticide samples at the laboratory before solidphase extraction of pesticides and were used to measure the 

extraction efficiency of each individual sample.

Summary statistics of the concentrations of major ions, 

nutrients, dissolved organic carbon, and selected trace elements for field equipment blank samples collected at all 10 

of the fixed sites are presented in table 5. Concentrations of 

constituents in equipment blank samples were smaller than the 

reporting level for the 90th percentile for all the constituents in 

table 5, except silica. The detectable concentrations of silica in 

blank samples were an order of magnitude smaller than silica 

concentrations in environmental samples. The results of the 

blank samples indicate that sampling collection, processing, 

and analysis methods and equipment were not routinely introducing contaminants that would cause a substantial positive 

bias in the environmental samples and affect the interpretation 

of the environmental data.

Field equipment blanks for pesticide samples were 

processed at site CF, site YF, and site YS. None of the 47 

pesticides that were analyzed were detected at concentrations 

larger than the reporting level in any of the 9 equipment blank 

samples. An estimated concentration of 0.001 microgram per 

liter (μg/L) of one pesticide, tebuthiuron, was detected in one 

of the equipment blank samples. Tebuthiuron is a broad spectrum herbicide used to control weeds in noncropland areas, 

rangelands, rights-of-way, and industrial sites (Meister Publishing Company, 2001). Because the environmental sample 

collected with this blank sample at site YS also contained an 

estimated concentration of tebuthiuron, the environmental 

sample analysis of tebuthiuron was not included in the pesticide summary in this report because the sample potentially 

could have been contaminated with a low-level concentration 

of tebuthiuron.

Measurement variability was determined for constituents 

using environmental and replicate samples from the 10 fixed 

sites by calculating a relative percent difference (RPD) when 

concentrations of the constituent were detected in both the 

environmental sample (sample 1) and the replicate sample 

(sample 2) or the constituent was censored at a common level 

in both samples. The RPD was calculated using the equation:

Summary statistics of the RPD for major ions, nutrients, and 

selected trace elements indicate that variability was minimal 

for most constituents (table 6). The median RPD in replicate 

samples was less than 5 percent for 20 of the 24 major-ion, 

nutrient, and trace-element constituents. A few constituents 

had an occasional large value for the RPD for some replicate 

samples, but this generally occurred when concentrations were 

small and near the reporting level. For example, the RPD for 

total ammonia plus organic nitrogen was 39.4 percent when 

the environmental sample had a concentration of 0.218 milligrams per liter (mg/L) and the replicate had a concentration 

of 0.325 mg/L.

Replicate samples also were collected to measure 

variability of pesticide compounds. Out of 47 pesticide 

compounds, 35 compounds were reported as less than the 

reporting level in both the environmental and replicate sample 

in all eight of the replicate sample sets. Four compounds 

were detected in one of the samples but concentrations were 

less than the reporting levels in the replicate, so the RPDs 

could not be determined. The RPD was determined for eight 

compounds that had a measurable concentration in both the 

environmental sample and the replicate sample (table 6). 

Atrazine, the most commonly detected pesticide in the replicate samples, had a median RPD of 5.21 percent. The larger 

median RPD for pesticide compounds compared to the other 

constituents is probably because concentrations were small 

and near reporting levels.

Field matrix-spike samples were collected to determine 

the effects of matrix interference or analyte degradation on 

concentrations of pesticides in environmental samples. During method development, average mean recovery was about 

83 percent in laboratory spike samples for all pesticides 

combined at low-level concentrations (Zaugg and others, 

1995). The average median recovery for the field matrix spikes 

was 98 percent (fig. 13) and the average mean recovery was 

101 percent for all pesticide compounds in the YELL matrixspike samples. Deethylatrazine demonstrated a small recovery 

(9 to 19 percent) during method development (Zaugg and 

others, 1995), but had a mean recovery of 57 percent in field 

matrix spikes; however, environmental concentrations from 

this breakdown product may still be biased low. Carbaryl, carbofuran, methyl azinphos, and terbacil were identified during 

method development as having variable performance (Zaugg 

and others, 1995). The range in percent recovery for spiked 

samples from the YELL was variable for these compounds, 

particularly for carbaryl, carbofuran, and methyl azinphos, 

which had percent recoveries larger than 200 percent for 

some samples. These compounds with variable performance, 

however, were detected infrequently in the environmental 

samples. The laboratory reported all concentrations for carbaryl, carbofuran, and deethylatrazine as estimated concentrations in spiked and environmental samples because of their 

variable performance during method development (Zaugg and 

others, 1995). The low mean recoveries for p’p-DDE in field 

matrix spikes were consistent with low mean recoveries during 

method development. The poor recovery of atrazine in two 

24 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites

RPD = sample1-sample2

sample1 sample2 +

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x 100
Table 5. Statistical summary for concentrations of selected constituents in field equipment blank samples for fixed sites in the Yellowstone River Basin, 1999-2001.

[<, less than]

Constituent

Number of 

samples 10th percentile

50th percentile

(median) 90th percentile

Major ions and dissolved solids, in milligrams per liter

Calcium, dissolved 17 <0.02 <0.02 <0.02

Magnesium, dissolved 17 <.014 <.014 <.014

Potassium, dissolved 16 <.24 <.24 <.24

Sodium, dissolved 17 <.09 <.09 <.09

Chloride, dissolved 16 <.29 <.29 <.29

Flouride, dissolved 16 <.2 <.2 <.2

Silica, dissolved 17 <.09 <.09 .40

Sulfate, dissolved 16 <.3 <.3 <.3

Solids, dissolved, residue on evaporation 16 <10 <10 <10

Nutrients, in milligrams per liter

Ammonia plus organic nitrogen, dissolved as nitrogen 18 <0.1 <0.1 <0.1

Ammonia plus organic nitrogen, total as nitrogen 18 <.1 <.1 <.1

Ammonia, dissolved as nitrogen 19 <.04 <.04 <.04

Nitrite, dissolved as nitrogen 19 <.01 <.01 <.01

Nitrite plus nitrate, dissolved as nitrogen 19 <.05 <.05 <.05

Orthophosphate, dissolved as phosphorus 19 <.02 <.02 <.02

Phosphorus, dissolved as phosphorus 18 <.006 <.006 <.006

Phosphorus, total as phosphorus 18 <.05 <.05 <.05

Organic carbon, dissolved 19 <.3 <.3 <.3

Trace elements, in micrograms per liter

Arsenic, dissolved 12 <2 <2 <2

Copper, dissolved 12 <1 <1 <1

Iron, dissolved 17 <10 <10 <10

Manganese, dissolved 21 <3 <3 <3

Selenium, dissolved 11 <1 <1 <1

Zinc, dissolved 12 <2 <2 <2

Data Collection and Analysis 25
Table 6. Statistical summary of the relative percent difference determined for selected constituents in replicate 

samples for fixed sites in the Yellowstone River Basin, 1999-2001.

[--, not applicable]

Constituent

Number of 

samples

Relative percent difference

10th percentile

50th 

percentile 

(median)

90th percentile

Major ions and dissolved solids

Calcium, dissolved 20 0.26 0.94 2.36

Magnesium, dissolved 20 .20 .89 2.46

Potassium, dissolved 20 .31 1.14 4.00

Sodium, dissolved 20 .15 1.35 3.03

Chloride, dissolved 20 .05 1.35 4.18

Flouride, dissolved 20 .0 .74 3.19

Silica, dissolved 20 .09 .29 1.69

Sulfate, dissolved 20 .11 .40 1.66

Solids, dissolved, residue on evaporation 20 .0 .51 1.22

Nutrients

Ammonia plus organic nitrogen, dissolved as nitrogen 20 1.15 4.13 23.9

Ammonia plus organic nitrogen, total as nitrogen 21 1.23 8.60 39.4

Ammonia, dissolved as nitrogen 21 .0 .0 2.96

Nitrite, dissolved as nitrogen 21 .0 .0 10.5

Nitrite plus nitrate, dissolved as nitrogen 20 .0 .69 3.36

Orthophosphate, dissolved as phosphorus 20 .0 .0 19.5

Phosphorus, dissolved as phosphorus 21 .0 5.53 28.6

Phosphorus, total as phosphorus 21 .0 3.17 12.9

Organic carbon, dissolved 20 .0 2.14 5.68

Trace elements

Arsenic, dissolved 12 .097 4.46 12.0

Copper, dissolved 9 -- 7.18 --

Iron, dissolved 19 .0 .0 16.8

Manganese, dissolved 23 .0 1.22 18.2

Selenium, dissolved 10 .0 .0 25.8

Zinc, dissolved 5 -- 32.6 --

Pesticides

Atrazine, dissolved 7 -- 5.21 --

Cyanazine, dissolved 2 -- 16.84 --

Deethylatrazine, dissolved 3 -- .98 --

Malathion, dissolved 1 -- 211.3 --

Metolachlor, dissolved 2 -- 11.15 --

Prometon, dissolved 2 -- 114.5 --

Triallate, dissolved 3 -- 12.2 --

Trifluralin, dissolved 1 -- 27.87 --

1

Average of two relative percent differences

2

Relative percent difference for one sample

26 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
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Figure 13. Recovery of pesticide compounds in field matrix spikes for fixed sites in the Yellowstone River Basin, 1999-2001.

Data Collection and Analysis 27
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Figure 14. Recovery of surrogate compounds in pesticide 

samples for fixed sites in the Yellowstone River Basin, 1999-2001.

of the field matrix-spike samples was in a spike set where the 

concentration in the environmental sample was larger than the 

associated spike samples.

In addition to the field matrix-spike samples, surrogate 

compounds are added to environmental samples at the laboratory and are used for assessing pesticide recoveries. Surrogate 

compounds are compounds that are not expected to be in the 

environmental sample, but are expected to behave like pesticide compounds that may be found in environmental samples. 

The gas chromatography-mass spectrometry (GCMS) method 

of pesticide analysis for data in this report uses diazinon-d10 

and alpha-HCH-d6 as surrogates. The median recoveries for 

the surrogate compounds in the fixed-site samples were about 

105 percent for diazinon-d10 and about 99 percent for alphaHCH-d6, indicating good extraction efficiency of the environmental samples (fig. 14).

Fixed-Site Water Quality, 1999-2001

The hydrologic conditions during sampling events and 

results for field measurements and analyses for fecal-indicator 

bacteria, major ions, dissolved solids, nutrients, trace elements, pesticides, and suspended sediment for the samples 

collected at the 10 fixed sites in the YELL during 1999-2001 

are summarized in this section of the report. Results for 

400 samples are included in the data analysis for this report. 

The number of results for individual constituents may be 

slightly different because field equipment malfunctioned or 

only partial laboratory results were received for a few samples. 

The discrete data values are presented in Swanson and 

others (2000, 2001, 2002). In addition, data are available 

online at URL http://nwis.waterdata.usgs.gov/nwis.

Hydrology

Streamflows at the fixed sites during the study period 

generally ranged from slightly greater than average during 

water year 1999 to much less than average during the drought 

conditions of water years 2000 and 2001. Streamflow records 

indicate that water year 2001 was one of the driest years in 

the last century for the YELL. For some of the fixed sites, 

annual mean streamflows for water year 2001 were the lowest 

on record (site CF, 63 years; site YB, 73 years; site YF, 24 

years; site T, 70 years). For the period following regulation by 

major reservoirs, annual mean streamflows in water year 2001 

were the third lowest at site B (50 years) and the lowest at 

site YS (35 years). For other fixed sites, annual mean streamflows for water year 2001 were the third (site YCS, 95 years; 

site P, 63 years) or fourth (site LP, 29 years) lowest on record. 

Streamflow records at site SB were only available for the 

sampling period (1999-2001). Water-quality samples collected 

at the fixed sites during the study period generally covered 

the range of streamflows that have been recorded at the sites 

(fig. 15) and were representative of historical streamflow conditions in spite of the drought conditions of water years 2000 

and 2001.

Field Measurements

Field measurements of streams made at the time of sampling included water temperature, specific conductance, pH, 

dissolved oxygen and alkalinity. All of these measurements 

were collected onsite and provide a general picture of the 

water-quality conditions at the fixed sites. Boxplots of water 

temperature, specific conductance, pH, and dissolved-oxygen 

concentrations are shown in figure 16. Alkalinity is discussed 

in the “Major Ions and Dissolved Solids” section of this report.

Water temperature is an important field measurement 

because it has a direct influence on the physical, chemical, 

and biological processes that occur in streams. Some of the 

physical properties that are affected by temperature include 

28 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
100 microsiemens per centimeter at 25°C (μS/cm) for site T 

would have a corresponding dissolved-solids concentration 

of about 57 mg/L, and a sample with a specific conductance 

of 1,000 μS/cm for site LP would have a corresponding dissolved-solids concentration of about 810 mg/L. Conversion 

factors tend to be larger for streams that have large sulfate 

concentrations, like site LP. Water-quality criteria for specific 

conductance have not been established for most streams by the 

States of Montana and Wyoming (Wyoming Department of 

Environmental Quality, 2001b, Montana Department of Environmental Quality, 2002a). A numeric standard for a single 

sample of 2,500 μS/cm has been established for the Powder 

River and Little Powder River in Montana (Montana Department of Environmental Quality, 2002a).

Median specific conductance values varied substantially 

at fixed sites, ranging from 202 μS/cm at site SB to 

3,400 μS/cm at site LP (fig. 16). Maximum specific-conductance values for sites near mountainous areas (site SB, 

site YCS, and site T) were lower than median specific-conductance values for streams that flow primarily through the basins 

and plains (site CF, site YB, site B, site YF, site LP, site P, 

and site YS), owing to higher precipitation and more resistant 

rock types in mountainous areas. Specific-conductance values 

had the largest range at the rangeland indicator site, site LP 

(358 μS/cm to 4,460 μS/cm), where Tertiary-period sedimentary rocks are the predominant rock type in the basin. Specific 

conductance was larger than the numeric standard of 

2,500 μS/cm in more than 75 percent of the samples from 

site LP and about 18 percent of the samples at site P.

Hydrogen-ion activity is a measure of the acidic or alkaline character of the stream and is expressed in terms of pH, 

which is the negative base-10 log of the hydrogen-ion activity. 

A pH value of 7 is considered neutral, whereas a pH value 

greater than 7 is considered alkaline and a pH value less than 

7 is considered acidic. Water-quality criteria for pH are not 

a single number. In the State of Montana, criteria for pH for 

Class B waters are based on levels of induced variation in pH 

of less than 0.5 pH units, within the range of 6.5 to 8.5 or 9.0 

(Montana Department of Environmental Quality, 2002a). In 

the State of Wyoming, chronic values of pH in the range of 6.5 

to 9.0 are allowed (Wyoming Department of Environmental 

Quality, 2001b). Values for pH that are outside of these ranges 

are considered harmful to aquatic life.

All stream measurements of pH at fixed sites in the 

YELL were alkaline, indicating that the soils and rocks 

naturally buffer the atmospheric waters, which typically have 

a pH of 5.65 (Hem, 1985). The median pH values at the fixed 

sites ranged from 7.8 at site T to 8.4 at site YS (fig. 16). The 

minimum pH value that was measured was 7.2 at site YCS 

and site T, and the maximum pH value that was measured was 

8.9 at site YF. All values for pH were within the water-quality 

criteria established by the States of Montana and Wyoming.

Dissolved-oxygen analysis is the measure of gaseous 

oxygen dissolved in an aqueous solution. Oxygen, although 

soluble in water, is considered poorly soluble because it does 

not react chemically with water (Stednick, 1991). Concentradensity, surface tension, gas solubility, and diffusibility. The 

gain and loss of dissolved gases, such as dissolved oxygen 

and dissolved nitrogen, are in part controlled by these physical 

properties. The rates at which chemical reactions proceed are 

influenced by temperature, with higher temperatures generally 

increasing chemical reaction rates (Stevens and others, 1975). 

Biological processes that are affected by water temperature 

include the metabolism of aquatic organisms and their ability 

to survive and reproduce. Water temperatures in streams are 

affected by solar radiation, precipitation, air and ground temperature, and the temperature of tributary and ground-water 

inflows.

Median stream temperatures varied among sites in the 

YELL, ranging from 2.5 degrees Celsius (°C) at site SB 

to 15°C at site YS (fig. 16). The low median temperatures 

at site SB, site YCS, and site T result from cooler air temperatures at the higher elevations and less solar radiation 

reaching streams in forested areas in comparison to conditions at other sites in the YELL. The maximum temperature 

at site YCS (22°C) was higher compared to the maximum 

temperatures at site SB (12°C) and site T (17.5°C), which 

probably reflects inputs from the thermal springs upstream 

from site YCS. Median stream temperatures in the Yellowstone River increased as it flowed from the forested area onto 

the plains. The median temperature more than doubled from 

site YCS (7.0°C) to site YS (15°C). These changes in the 

stream temperature are likely due to combinations of natural 

causes, such as increased solar radiation as a result of fewer 

trees, increased air temperatures at lower elevations, and 

human causes, including irrigation return flows. Site B had the 

most variability in stream temperature, ranging from 0°C to 

27.5°C, probably mostly due to the wide range of air temperatures that are characteristic of the Bighorn River Basin, which 

ranged from –10°C to 35°C during sampling events. Irrigation 

return flows also are common in the Bighorn River. Stream 

temperatures are not compared to water-quality criteria for 

temperature in this report because water-quality criteria for 

stream temperatures in Montana and Wyoming primarily are 

not a single value, but rather are related to allowable increases 

to stream temperatures resulting from anthropogenic inputs, 

such as waste effluent (Wyoming Department of Environmental Quality, 2001b; Montana Department of Environmental 

Quality, 2002a).

Specific conductance is a measure of a substance’s ability 

to conduct an electrical current at a specific temperature. Pure 

water has a very low electrical conductance; as concentrations 

of dissolved solids that carry an ionic charge increase in a 

stream, the specific conductance increases. Therefore, specific 

conductance can be used as an indication of the concentration 

of dissolved solids in a stream. The conversion factor from 

specific conductance to dissolved-solids concentrations for 

natural waters is about 0.54 to about 0.96 (Hem, 1985). The 

median conversion factor between specific conductance and 

dissolved-solids concentrations varied for sites in the YELL 

and ranged from about 0.57 for site T to about 0.81 for site LP. 

For example, a sample with a specific conductance of 

Fixed-Site Water Quality, 1999-2001 29
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Figure 15. Distribution of samples relative to daily mean streamflow duration for fixed sites in the Yellowstone River 

Basin, 1999-2001.

30 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
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Figure 15. Continued.

Fixed-Site Water Quality, 1999-2001 31
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Figure 16. Statistical summary of water temperature, specific conductance, pH, and dissolved-oxygen concentrations for fixed 

sites in the Yellowstone River Basin, 1999-2001.

32 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
tions of dissolved oxygen primarily are affected by atmospheric pressure and temperature. Atmospheric pressure and 

dissolved oxygen are directly proportional to each other, 

whereas temperature and dissolved oxygen are inversely proportional; so, as pressure increases and temperature decreases, 

oxygen becomes more soluble in a stream. Concentrations of 

dissolved oxygen in streams are depleted through respiratory 

uptake by organisms and by the decaying of organic matter 

in streams. Oxygen is replenished from the atmosphere and 

by photosynthesis of aquatic plants. Water-quality criteria for 

dissolved oxygen that have been determined for the States of 

Montana and Wyoming are not a single number and depend on 

aquatic life stages present in a stream (Wyoming Department 

of Environmental Quality, 2001b, Montana Department of 

Environmental Quality, 2002a) and, as such, are not used for 

comparison in this report, except in general terms.

Median dissolved-oxygen concentrations varied slightly 

among sites and ranged from 9.3 mg/L at site YS to 11.2 mg/L 

at site SB (fig. 16), which are acceptable concentrations when 

compared to State criteria for minimum concentrations for 

all life forms. The median dissolved-oxygen concentrations 

tended to be larger at sites that are closer to mountainous 

areas, where stream temperatures also were the lowest; thus, 

making oxygen more soluble, despite lower atmospheric pressure with elevation. The median dissolved-oxygen concentrations tended to be lower at sites in the basin and plains, like 

site LP, where stream temperatures generally are warmer, 

although atmospheric pressure tends to be higher. Dissolvedoxygen conditions for all sites generally were near saturation 

(100 percent); median values ranged from 94.6 percent of 

saturation at site LP to 109 percent of saturation at site YCS.

Fecal-Indicator Bacteria

Analyses for fecal-indicator bacteria of fecal coliform 

and E. coli were added to the fixed-site sampling during 2000 

and 2001 to assess the sanitary quality at the fixed sites in the 

YELL, because the presence of these bacteria can be an indication that contamination from fecal material has occurred. 

Fecal coliform was identified as the primary cause of impairment for streams in Wyoming in the 2002 305(b) report, 

including several reaches in the Bighorn River and Tongue 

River Basins (Wyoming Department of Environmental Quality, 2002). Antiquated facilities and shifting ground resulted in 

nine sewage spills in Yellowstone National Park during 1999-

2001 (Associated Press, 2001a, 2001b; Wyoming Department 

of Environmental Quality, 2002). Stream reaches in Montana 

that were identified with fecal-coliform impairments by the 

Montana Department of Environmental Quality were outside 

of the YELL (Montana Department of Environmental Quality, 

2002b). Although fecal-indicator bacteria do not necessarily 

cause illness themselves, large levels of fecal-indicator bacteria can indicate the possible presence of other pathogens that 

cause such waterborne diseases as gastroenteritis and bacillary 

dysentery, typhoid fever, and cholera (Myers and Sylvester, 

1997).

The occurrence of fecal coliform in recreational waters 

is not positive confirmation that fecal contamination has 

occurred because at least one member of the fecal-coliform 

group, Klebsiella, has non-fecal sources, including pulp and 

paper mill effluents, textile processing plant effluents, cotton 

mill wastewaters, and sugar beet wastes (U.S. Environmental 

Protection Agency, 1986a). The presence of E. coli, another 

member of the fecal-coliform group, is direct evidence that 

fecal contamination has occurred because the only sources 

are humans or other warm-blooded animals (Cabelli, 1977; 

Dufour, 1977). E. coli was determined to have a stronger relation to swimming-associated gastrointestinal illness than fecal 

coliform and, as such, was determined to be a better fecalindicator bacteria for monitoring recreational waters (Dufour, 

1984; U.S. Environmental Protection Agency, 1986a). However, because both the States of Montana and Wyoming were 

using fecal coliform in their water-quality criteria at the time 

of this study (Wyoming Department of Environmental Quality, 2001b, Montana Department of Environmental Quality, 

2002a), it was important to monitor for both of the fecal-indicator bacteria.

The water-quality criteria for fecal coliform for the States 

of Montana and Wyoming are not a single number and are 

based on multiple samples in a 30-day period, the class of 

water, time of year, or location relative to sewage treatment 

outfalls (Wyoming Department of Environmental Quality, 2001b, Montana Department of Environmental Quality, 

2002a). Because multiple samples were not collected during 

a 30-day period in most cases, recommended limits for single 

samples that were proposed by the U.S. Environmental Protection Agency (USEPA) are used in this report for assessing the 

magnitude of fecal-indicator-bacteria concentrations.

Concentrations

The medians and ranges of fecal-indicator-bacteria 

concentrations varied among the fixed sites (fig. 17). For all 

sites, the largest median concentrations for fecal coliform of 

135 col/100 mL and E. coli of 156 col/100 mL were at site LP, 

which is the rangeland indicator site. The largest concentration 

in a single sample from all 156 samples of fecal coliform 

was 1,400 col/100 mL at site P. For all 145 samples of 

E. coli, the largest concentration in a single sample was 

1,500 col/100 mL at site LP. The Little Powder River and 

Powder River Basins are both dominated by grasslands that 

are grazed by cattle; however, small towns, rural domestic 

homes with septic systems, and agricultural return flows also 

may contribute to bacteria in these basins. For all sites, the 

smallest median concentrations were 3 col/100 mL of fecal 

coliform and 3 col/100 mL for E. coli at site YCS, which 

drains a predominantly forested basin of Yellowstone National 

Park. Concentrations of fecal-indicator bacteria for the mineral 

resource area (site SB) and the forested (site T) indicator sites, 

which both drain predominantly forested areas, were small as 

Fixed-Site Water Quality, 1999-2001 33
Figure 17. Statistical summary of fecal-indicator-bacteria concentrations for fixed sites in the Yellowstone River Basin, 

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well; median concentrations were 14 col/100 mL or less for 

fecal coliform and E. coli at both sites. Fecal-indicatorbacteria concentrations at site SB, site YCS, and site T may be 

good indicators of wildlife contributions in forested drainage 

basins in the YELL.

The largest median concentrations of fecal coliform 

(55 col/100 mL) and E. coli (22 col/100 mL) on the mainstem 

of the Yellowstone River were at site YB, which is downstream from parts of the Billings, Montana urban area. The 

median fecal-indicator-bacteria concentrations at site YB were 

smaller than median concentrations of fecal coliform 

(540 col/100 mL) and E. coli (420 col/100 mL) for sites with 

urban land use during a NAWQA synoptic study of fecalindicator bacteria in Wyoming (Clark and Gamper, 2003); 

however, the streams sampled as part of the synoptic study had 

substantially smaller streamflow than the Yellowstone River.

Comparison to Recommended Limits

Historically, USEPA studies determined that statistically significant swimming-associated gastrointestinal illness 

may occur when concentrations of fecal coliform for a single 

sample are larger than 400 col/100 mL (U.S. Environmental 

Protection Agency, 1976). The USEPA recommends four 

different limits for E. coli concentrations for a single sample, 

depending on the degree of exposure with the source waters. 

The recommended limit for E. coli for a single sample defined 

in the USEPA study are: 235 col/100 mL for designated beach 

areas, 298 col/100 mL for moderate use, full-body contact 

recreation, 406 col/100 mL for light use, full-body contact 

recreation, and 576 col/100 mL for infrequent use, full-body 

contact recreation (U.S. Environmental Protection Agency, 

1986a). The recommended limit of 235 col/100 mL was not 

used for comparison in this report because none of the fixed 

sites were at designated beaches. Values that exceed recommended limits do not necessarily indicate violations of water34 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
Table 7. Fecal-indicator bacteria exceeding U.S. Environmental Protection Agency’s recommended limits for a single sample for recreational contact with water for fixed sites in the Yellowstone River Basin, 2000-2001.

[col/100 mL, colonies per 100 milliliters; >, greater than]

Site report 

idenfifier 

(fig. 2)

Number of 

fecal-coliform 

samples 

Percent of 

samples where 

fecal coliform 

concentration 

>400 col/100 mL

Number of 

Escherichia coli

concentration 

samples

Percent of 

samples where 

Escherichia coli

concentration 

>298 col/100 mL

(moderate use, 

full-body contact)

Percent of 

samples where 

Escherichia coli

concentration 

>406 col/100 mL

(light use, fullbody contact)

Percent of 

samples where 

Escherichia coli

concentration 

>576 col/100 mL

(infrequent 

use, full-body 

contact)

SB 15 0.0 15 0.0 0.0 0.0

YCS 14 .0 14 .0 .0 .0

CF 16 .0 14 14.3 7.1 7.1

YB 16 .0 14 .0 .0 .0

B 18 5.6 18 11.1 11.1 5.6

YF 16 .0 12 .0 .0 .0

T 17 .0 17 .0 .0 .0

LP 19 10.5 18 27.8 27.8 11.1

P 13 7.7 12 16.7 16.7 16.7

YS 12 .0 11 .0 .0 .0

All sites 156 2.6 145 7.6 6.9 4.1

quality criteria for the State of Montana or Wyoming, but are 

used for comparative purposes.

Concentrations of fecal-indicator bacteria in some 

samples exceeded recommended criteria. The USEPA recommended single-sample limit for fecal coliform was exceeded 

in 2.6 percent of the 156 samples for fecal coliform, and the 

recommended single-sample limit for moderate use, full-body 

contact recreation for E. coli was exceeded in 7.6 percent 

of 145 samples (table 7). No concentrations exceeded the 

recommended limits for fecal coliform and E. coli in samples 

collected from the Yellowstone River (sites YCS, YB, YF and 

YS). No concentrations exceeded the recommended limits 

for fecal coliform and E. coli in samples collected from the 

mineral resource area (site SB) and the forested (site T) indicator sites. At least one sample from the three major tributary 

sites (site CF, site B, and site P) had a fecal-indicator-bacteria 

concentration that exceeded one of the recommended limits. 

Site LP, the rangeland indicator site, had the largest percentage of samples (10.5 percent) where fecal coliform exceeded 

the recommended single-sample limit of 400 col/100 mL. 

E. coli concentrations at site LP exceeded the recommended 

limits for moderate and light use, full-body contact recreation 

in 27.8 percent of the samples. Stream reaches in the Bighorn 

River upstream from Kane, Wyoming and the Little Powder 

were assessed as being impaired by fecal coliform for contact 

recreational use in the Wyoming 305(b) water-quality assessFixed-Site Water Quality, 1999-2001 35

ment for 2002 (Wyoming Department of Environmental Quality, 2002).

The Spearman’s Rho correlation coefficient between 

fecal coliform and E. coli was 0.820 (p-value <0.001) for 

samples collected from the fixed sites (fig. 18). Fecal coliform 

and E. coli data from the NAWQA synoptic study in Wyoming 

also were correlated (Spearman’s Rho=0.976, p-value <0.001) 

(Clark and Gamper, 2003). These results indicate that E. coli

is an important contributor to fecal-coliform concentrations at 

YELL fixed sites. Because of this relation, historical fecalcoliform data generally will be a useful indicator of E. coli

presence in these streams as the States of Montana and Wyoming transition to using E. coli for recreational water-quality 

criteria as recommended by USEPA (U.S. Environmental 

Protection Agency, 2002c).

Temporal Variability

Fecal-coliform (p-value <0.001) and E. coli concentrations (p-value <0.001) significantly varied by sampling period. 

Median concentrations of fecal coliform and E. coli have the 

same general seasonal pattern, where the smallest median 

concentrations were during January–March and the largest median concentrations were during April–June (fig. 19). 

Elevated concentrations of fecal-indicator bacteria during 

the April–June sampling period are probably the result of 
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Figure 19. Seasonal variations in fecal-indicator-bacteria concentrations for fixed sites in the Yellowstone River Basin, 2000-2001. ����������������� �������������������������������

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Figure 18. Fecal-coliform and Escherichia coli relation for fixed 

sites in the Yellowstone River Basin, 2000-2001.

36 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
increased streamflow associated with lowland thunderstorms 

or snowmelt runoff and increased land-use activity. Streamflow has been demonstrated to have a positive relation with 

bacteria because of overland flow that can carry bacteria-laden 

sediment to streams or turbulent flows that can resuspend bacteria-laden sediment from the stream bottom (Stephenson and 

Street, 1978; Elder, 1987; Hunter and others, 1992; Barbe ́ and 

Francis, 1995). Concentrations that exceeded USEPA recommended limits for single samples were observed in samples 

during the October–December, April–June, and July–September sampling periods. Examination of the sampling event dates 

indicates that the individual samples that exceeded limits were 

collected during the months of May to October. Human health 

risk to exposure is highest during summer months because 

recreational contact with waters is most likely occurring at that 

time. The water-quality criteria for recreational contact generally apply to the period from May to September.

Major Ions and Dissolved Solids

The general quality of stream waters often is described 

on the basis of the major-ion composition and dissolved-solids 

concentrations. The major-ion composition includes those 

inorganic ionic constituents commonly present in concentrations exceeding 1.0 mg/L (Hem, 1985). The relative proportions of the major cations (generally calcium, magnesium, 

potassium, and sodium) and the major anions (generally 

bicarbonate plus carbonate, chloride, fluoride, sulfate, and 

nitrate) are used to describe the water type. Although nitrate 

is used in characterizing water type, general discussion of 

nitrate is included in the “Nutrients” section of this report. 

Dissolved-solids concentrations represent the combined sum 

of all the dissolved constituents in a water sample with the 

primary contributors being the major cations, major anions, 

and nonionic silicon that is reported in terms of the equivalent 

concentration of silica. Dissolved-solids concentrations were 

determined in the laboratory using a residue-on-evaporation 

method at 180°C (Fishman and Friedman, 1989). Dissolved 

solids in stream waters primarily result from the weathering of 

minerals in rocks and soils near the land surface, but also can 

result from human activities, such as irrigation and oil and gas 

development.

Water Type

Variations in water composition at the fixed sites are 

reflective of the diverse geologic terrain in the YELL. A trilinear diagram, which illustrates the relative percentage of the 

major cations and anions on two trilinear plots and a diamondshaped plot that combines the cation and anion information 

(Piper, 1944), indicates that water composition in the YELL 

varied among sites, ranging from dilute calcium-bicarbonate 

type at site SB and site T to concentrated sodium-sulfate type 

at site LP (fig. 20). Stiff diagrams (Stiff, 1951), which detail 

the magnitude of concentrations of the major ions in milliequivalents per liter, illustrate how water type changes through 

the basin (fig. 21). A sample with typical (near the median) 

dissolved-solids concentration was selected to represent the 

major-ion composition for the Piper and Stiff diagrams for 

each site. Concentrations of the dominant ions (calcium, 

sodium, bicarbonate, and sulfate) varied at the fixed sites 

(fig. 22).

On the mainstem of the Yellowstone River, the water type 

changes from a mixed-cation bicarbonate type upstream at 

site YCS to a mixed-cation sulfate type downstream at site YF 

and site YS. The water type at site YCS is a dilute sodiumcalcium-magnesium bicarbonate type, and is reflective of the 

Cretaceous-, Tertiary-, and Quaternary-period volcanic rocks 

that are the dominant rock types in the YELL basin upstream 

from site YCS. Waters draining areas underlain by igneous 

rocks typically have small concentrations of dissolved solids 

with sodium and calcium as the major cations and bicarbonate 

as the major anion (Drever, 1997). Reaches of the Yellowstone 

River that drain YNP upstream from site YCS receive inputs 

of geothermal waters (Knapton and Bahls, 1993), which are 

highly mineralized and typically contribute sodium, chloride, 

fluoride, and silica to major-ion chemistry of the area stream 

waters (Cox, 1973). Concentrations of silica also generally 

were larger at site YCS compared to the other fixed sites 

(Swanson and others, 2000, 2001, 2002). Downstream on the 

Yellowstone River at site YB, in addition to the volcanic rocks, 

Cretaceous-period sedimentary rocks also underlie a large 

part of the basin, which results in calcium and magnesium 

comprising a larger percentage of the cation composition. The 

major-ion median concentrations in the Yellowstone River are 

higher at site YF and site YS compared to sites YCS and YB, 

as the proportion of the area underlain by fine-grained Cretaceous- and Tertiary-period sedimentary rocks increases in the 

downstream basins. The water type of the Yellowstone River 

at site YS is a calcium-sodium-magnesium sulfate type.

Different geology in the Clarks Fork Yellowstone River, 

Bighorn River, and Powder River Basins produces different 

water types for the major tributaries. Geology of the Clarks 

Fork Yellowstone River Basin is diverse and includes Precambrian-era crystalline rocks, Paleozoic- and Mesozoicera sedimentary rocks, and Cretaceous- and Tertiary-period 

volcanic and sedimentary rocks. The median water type at site 

CF plots as calcium bicarbonate type (fig. 20). The dominant 

anion in samples at site CF varied between bicarbonate and 

sulfate depending on the time of year. Bicarbonate dominates 

in late spring and early summer when dissolved atmospheric 

gases in the snow are contributed during snowmelt runoff 

(Colby and others, 1956). In contrast, sulfate dominates during 

winter when sulfate-rich ground water that has been in contact 

with basin materials for a long time is a larger proportion of 

the stream’s base flow. A study of the lithologic controls of 

calcium concentrations in the upper reaches of the Clarks Fork 

Yellowstone River upstream from site CF found the Paleozoicera sedimentary rocks to be a larger contributor of calcium 

than the volcanic or crystalline rocks (Horton and others, 

1999). The water types at site B and site P are mixed-cation 

Fixed-Site Water Quality, 1999-2001 37
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Figure 20. Trilinear diagram showing major-ion composition and dissolved-solids concentrations for fixed sites in the 

Yellowstone River Basin, 1999-2001.

38 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
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Figure 21. Stiff diagrams showing major-ion composition for fixed sites in the Yellowstone River Basin, 1999-2001.

Fixed-Site Water Quality, 1999-2001 39
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Figure 22. Statistical summary of concentrations of dissolved calcium, sodium, bicarbonate, and sulfate for fixed sites in the 

Yellowstone River Basin, 1999-2001.

40 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
sulfate types owing to weathering of larger percentages of 

Cretaceous- and Tertiary-period sedimentary rocks underlying the basins compared to the Clarks Fork Yellowstone River 

Basin. The water type at site B is calcium-sodium-magnesium 

sulfate compared to site P, which is a sodium-calcium-magnesium sulfate. The predominance of sodium-based salts, which 

result from evaporation, in the Powder River Basin results in 

larger sodium adsorption ratios (ranging from 3 to 9) at site P 

compared to other integrator sites (Swanson and others, 2000, 

2001, 2002).

In comparison to the major tributary integrator sites, the 

drainage areas of the minor tributary indicator sites are small 

with more homogenous geology underlying the basins. The 

water types at the indicator sites are dominated by a single 

cation and single anion as compared to the mixed water types 

at the integrator sites. The water type for site SB and site T is 

dilute calcium bicarbonate. Igneous rocks and Paleozoic- and 

Mesozoic-era sedimentary rocks underlie over 97 percent of 

the basins upstream from site SB and site T. The water type 

for site LP is a concentrated sodium sulfate. Tertiary-period 

sedimentary rocks underlie nearly 100 percent of the Little 

Powder Basin. Median concentrations of calcium, sodium, 

bicarbonate, and sulfate were the largest at site LP for all sites 

in the YELL (fig. 22). In addition, larger sodium adsorption 

ratios (ranging from 2 to 9) were measured at site LP compared to the other indicator sites (Swanson and others, 2000, 

2001, 2002).

Dissolved Solids

In addition to geology, variations in precipitation, evaporation, and contact times affect ranges of dissolved-solids concentrations in samples from the fixed sites in the YELL (fig. 

23). Median dissolved-solids concentrations ranged from 118 

mg/L in samples from site SB to 2,840 mg/L in samples from 

site LP. Dissolved-solids concentrations generally were smallest at site YCS, site SB, and site T, where annual precipitation 

is high and rock types are resistant to weathering. Site YCS 

and site SB are near YNP, which can receive annual precipitation in excess of 59 inches and mean annual evaporation is 

low in the cool highlands of the Park (Zelt and others, 1999). 

Along with the high annual precipitation, the steep gradients in 

mountain streams produce fast stream velocities, resulting in 

short contact time between stream waters and basin materials 

(Colby and others, 1956). In contrast, the largest median dissolved-solids concentrations were at site LP and site P; parts 

of the plains region, which includes site LP and site P, receive 

mean annual precipitation of about 14 inches. Annual evaporation also is substantially higher in the plains than in the mountainous areas and may exceed annual precipitation, resulting in 

the accumulation of soluble salts in or near the surface. Slower 

stream velocities in flatter areas than in mountainous areas are 

more favorable for the dissolution of salts (Colby and others, 

1956). Median dissolved-solids concentrations for samples 

from site CF, site B, and the sites downstream from site YCS 

on the mainstem of the Yellowstone River (site YB, site YF, 

and site YS) are in between those of the mountains and plains 

fixed sites (fig. 23). Although these sites are in areas that 

may receive low annual precipitation, their dissolved-solids 

concentrations are diluted from basin tributaries that partially 

drain mountainous areas.

Although the natural factors are important controls on 

dissolved solids, land-use activities from humans also may 

contribute dissolved solids to streams. Increased dissolved 

solids in streams in the YELL have been attributed to irrigation (Knapton and Bahls, 1993; Peterson, 1993; Lindner-Lunsford and others, 1992). Irrigation contributes dissolved solids 

to streams because as crops consume applied irrigation water, 

they leave behind salts that can later be transported to streams 

(Colby and others, 1956). Land use along the Clarks Fork 

Yellowstone, Bighorn, Little Powder, Powder, and Yellowstone Rivers includes agricultural covers, such as row crops, 

small grains, and hay that are irrigated and may contribute to 

increased dissolved solids. The Bighorn, Little Powder, and 

Powder Rivers also receive inputs of discharge water associated with coal, oil, or gas development that may be high in 

dissolved solids (Lindner-Lunsford and others, 1992; Peterson, 

1993; Clark and others, 2001).

Comparison to Water-Quality Criteria

National Secondary Drinking Water Regulations or 

Secondary Maximum Contaminant Levels (SMCLs), which 

are non-enforceable guidelines that regulate contaminants that 

may cause cosmetic or aesthetic effects in drinking water, are 

established for chloride, fluoride, sulfate, and dissolved solids 

(U.S. Environmental Protection Agency, 2002d). SMCLs are 

useful for assessing the relative magnitude of concentrations 

of these constituents in samples from the YELL. The SMCLs 

of 250 mg/L for chloride and 2.0 mg/L for fluoride were not 

exceeded in any samples from the fixed sites in the YELL. The 

SMCLs of 250 mg/L for sulfate and 500 mg/L for dissolved 

solids were exceeded in some samples from fixed sites (table 

8). Concentrations of sulfate and dissolved solids exceeded 

SMCLs in 100 percent of the samples collected at site P and 

in 95.2 percent of the samples collected at site LP. Concentrations exceeding the sulfate and dissolved-solids SMCLs also 

were frequent in samples collected at site B.

Temporal Variability

Concentrations of dissolved solids significantly varied by 

sampling period (fig. 24) for site SB, site YCS, site CF, site 

YB, site YF, site T, and site YS (p-values <0.05). For these 

sites, median dissolved-solids concentrations were smallest during the April-June sampling period, when the more 

concentrated base flow is diluted by snowmelt runoff. Because 

dissolved solids generally are inversely related to streamflow 

and much of the variation in streamflow is seasonal, variation 

in dissolved-solids concentrations also can be seasonal. The 

variance is low and medians are larger for dissolved-solids 

Fixed-Site Water Quality, 1999-2001 41
Table 8. Sulfate and dissolved-solids concentrations exceeding U.S. Environmental Protection Agency’s Secondary 

Maximum Contaminant Levels for fixed sites in the Yellowstone River Basin, 1999-2001

[mg/L, milligrams per liter; >, greater than]

Site report 

identifier 

(fig. 2)

Number of sulfate 

samples

Percent of samples 

where sulfate concentration >250 mg/LNumber of dissolvedsolids samples

Percent of samples where 

dissolved-solids concentration >500 mg/L

SB 36 0.0 36 0.0

YCS 36 .0 36 .0

CF 40 5.0 40 12.5

YB 38 .0 37 .0

B 45 53.3 43 65.1

YF 42 .0 42 4.8

T 38 .0 37 .0

LP 42 95.2 42 95.2

P 38 100 38 100

YS 45 8.9 44 29.5

All sites 400 27.0 395 31.9

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Figure 23. Statistical summary of dissolved-solids concentrations for fixed sites in the Yellowstone River 

Basin, 1999-2001.

42 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
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Figure 24. Seasonal variations in dissolved-solids concentrations for fixed sites in the Yellowstone River Basin, 1999-2001.

Fixed-Site Water Quality, 1999-2001 43
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Figure 25. Annual variations in dissolved-solids concentrations for fixed sites in Yellowstone River Basin, 1999-2001.

44 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
concentrations at these sites during the October–December 

and January–March sampling periods when base flow dominates the stream chemistry. A significant difference in concentrations was not determined at site B (p-value=0.135), where 

the smallest median concentration was during the July-September sampling period. A large reservoir, Boysen Reservoir, 

that captures snowmelt runoff regulates the streamflow on the 

Bighorn River upstream from site B and releases can dilute 

flows during the irrigation season. The seasonal pattern of dissolved-solids concentrations at site LP and site P are different 

from the other fixed sites. Dissolved-solids concentrations are 

variable throughout most of the year, with the largest median 

concentrations occurring during the July–September sampling period. Irrigation return flows and decreased streamflow 

because of low precipitation and high evaporation may contribute dissolved solids during the July–September sampling 

period.

In addition to seasonal variations in streamflow, annual 

variations in streamflow affected dissolved-solids concentrations on a longer time scale (fig. 25). Significant differences 

in annual dissolved-solids concentrations were determined 

for site CF, site YB, site B, and site P (p-values <0.05) during 

the 3-year study period. The variations in median concentrations are attributed to decreased streamflows associated with 

drought conditions that occurred during water years 2000 and 

2001. In particular, streamflows in the Bighorn River (site B) 

and Powder River (site P) were substantially smaller in water 

years 2000 and 2001 compared to water year 1999. The 

minimum dissolved-solids concentrations at these sites during 

water year 2001 exceeded the median concentrations of water 

year 1999, which was a normal to moderately wet year.

Nutrients

Nutrients analyzed as part of the YELL fixed-site sampling include dissolved and total phases of nitrogen, phosphorus, and organic carbon. Nitrogen and phosphorus are essential 

nutrients for healthy plant and animal populations (Fuhrer 

and others, 1999). Solutes of organic carbon are nutrients 

for microbes, which are factors in some chemical processes 

(Hem, 1985). Excessive nutrient concentrations, however, can 

degrade or facilitate degradation of water quality. Nutrients are 

the third leading pollutant in impaired rivers and streams in the 

United States (U.S. Environmental Protection Agency, 2000a).

Nitrogen analyses during the fixed-site sampling included 

dissolved ammonia plus organic nitrogen as nitrogen, total 

ammonia plus organic nitrogen as nitrogen, dissolved ammonia as nitrogen, dissolved nitrite as nitrogen, and dissolved 

nitrite plus nitrate as nitrogen (referred to as dissolved nitrate 

in this report). Nitrate, the oxidized form of nitrogen, typically 

is the most common form of dissolved nitrogen in streams 

(U.S. Environmental Protection Agency, 1986b). Total nitrogen in this report is the sum of the total ammonia plus organic 

nitrogen and dissolved nitrate. If the concentration of one form 

of nitrogen was censored, the total-nitrogen concentration was 

equal to the concentration of the uncensored form. If concentrations for both forms were censored, the total-nitrogen 

concentration was censored at the largest reporting level.

Pathways of nitrogen to streams include atmospheric 

deposition, overland runoff, ground-water discharge, and point 

discharges. Sources of nitrogen in streams include natural 

biological and chemical reactions, plant material, as well as 

anthropogenic activities such as fertilizer application and 

sewage disposal. Concerns for nitrogen in streams include 

dissolved-nitrate concentrations larger than ambient conditions resulting in human health issues for drinking water, and 

eutrophication and subsequent hypoxic conditions (dissolvedoxygen concentrations smaller than 2.0 mg/L) for streams 

and other receiving waters (Fuhrer and others, 1999). Median 

flow-weighted mean concentrations for streams in relatively 

undeveloped basins of the United States (background concentrations) are about 0.020 mg/L for dissolved ammonia, 

0.087 mg/L for dissolved nitrate, and 0.26 mg/L for total 

nitrogen (Clark and others, 2000).

Phosphorus analyses during the fixed-site sampling 

included dissolved orthophosphate as phosphorus, dissolved 

phosphorus, and total phosphorus. Dissolved phosphorus 

primarily is in the form of orthophosphate. Phosphates sorb 

strongly to soil and sediment particles. For some soils, large 

soil phosphorus levels result in more phosphorus available in 

the dissolved form (Fuhrer and others, 1999). Total phosphorus primarily includes phosphates and particulate forms.

Pathways of phosphorus to streams include overland 

runoff and point discharges. Natural sources of phosphorus 

in streams in the Western United States include soils and 

sediments derived from marine sedimentary rocks. Because 

phosphorus is essential in metabolism, anthropogenic sources 

of phosphorus include animal and human waste (Hem, 1985). 

Phosphorus also is a necessary plant nutrient and is sometimes 

added as a fertilizer. Eutrophication is the primary concern for 

phosphorus in streams (Fuhrer and others, 1999). Background 

concentrations are about 0.010 mg/L for orthophosphate and 

0.022 mg/L for total phosphorus (Clark and others, 2000).

Organic carbon analyses during the fixed-site sampling 

included DOC and total organic carbon. Because concentrations of DOC approximated concentrations of total organic 

carbon in solution for samples in the YELL, only DOC is 

discussed in this report. Organic solutes are important in 

weathering processes, diagenesis, photosynthesis, photochemical reactions, and transport of metals (Drever, 1997, p. 107). 

Complexation of metals by DOC can result in high concentrations of metals in solution (Drever, 1997, p. 35 and p. 188); 

however, several metals are less toxic to aquatic organisms 

when complexed with organic solutes (Drever, 1997, p. 179). 

When water is treated for drinking, organic compounds react 

with chlorine to form potentially carcinogenic disinfection byproducts (U.S. Geological Survey, 1997). Concentrations of 

DOC in streams of temperate and arid/semiarid zones generally are about 3 mg/L (Hem, 1985).

Fixed-Site Water Quality, 1999-2001 45
Concentrations

Concentrations of nitrogen species, phosphorus species, 

and organic carbon in samples were examined for the fixed 

sites. In addition, flow-weighted concentrations were determined for dissolved nitrate, total nitrogen, and total phosphorus.

Nitrogen

Dissolved-ammonia concentrations in most samples 

from the fixed sites were less than laboratory reporting levels 

(fig. 26). Concentrations generally were largest in samples 

collected at site YCS (median concentration 0.04 mg/L; 

maximum concentration 0.23 mg/L) downstream from YNP in 

comparison with concentrations for other fixed sites. Ammonia occurs naturally in many geothermal waters of YNP; 

concentrations larger than 600 mg/L (as nitrogen) have been 

measured in some springs in YNP (Ball and others, 1998, 

p. 23). A probable source of the relatively large ammonia 

concentrations is leaching of organic-rich sedimentary rocks at 

depth by the high-temperature geothermal waters and subsequent surface discharge of those waters (D. Kirk Nordstrom, 

USGS, written commun., 2000; Love and Good, 1970). Sorey 

and others (1991) reported a total discharge of about 2.2 cubic 

feet per second (ft3/sec) from La Duke Hot Spring upstream 

from site YCS. Because of the chemical properties of ammonia and the physical characteristics of these surface waters, a 

substantial fraction of the ammonia in the geothermal waters 

upstream from site YCS probably becomes oxidized, contributing to nitrate concentrations at that site.

Median dissolved-nitrate concentrations in samples 

from the fixed sites ranged from 0.04 mg/L to 0.54 mg/L 

(fig. 26). Dissolved-nitrate concentrations were smallest for 

the indicator sites SB, T, and LP; concentrations were less than 

laboratory reporting levels in 67 percent of the samples from 

site LP. Dissolved-nitrate concentrations were largest for the 

integrator sites CF and B. On the mainstem Yellowstone River, 

dissolved-nitrate concentrations increased downstream in the 

upper part of the basin from site YCS to site YF; however, 

dissolved-nitrate concentrations were similar at site YF and 

site YS in the lower part of the basin.

In general, flow-weighted mean dissolved-nitrate concentrations at YELL fixed sites were related to drainage area 

and land-cover characteristics on alluvial deposits, where 

anthropogenic sources of nitrate would most commonly be 

applied. Flow-weighted mean dissolved-nitrate concentrations 

increased with increasing drainage area (fig. 27A; Kendall’s 

tau (τ) = 0.56; p-value = 0.025). Correlations between flowweighted mean dissolved-nitrate concentrations and drainage 

area for the tributary and mainstem fixed sites were similar; 

however, an apparent negative shift was observed from the 

tributary relation to the mainstem relation, probably due in 

part to flow dilution on the mainstem. In comparing flowweighted mean dissolved-nitrate concentrations between sites 

with similar size drainage areas, annual mean streamflows 

were about 3 to 12 times greater at the mainstem sites than at 

the tributary sites.

Flow-weighted mean dissolved-nitrate concentrations 

were most strongly correlated with increasing agricultural land 

use on alluvial deposits upstream from the sites (fig. 27D; τ = 

0.62; p-value = 0.012). For all tributary sites, the largest flowweighted mean dissolved-nitrate concentrations were determined for sites CF and B, where the percent of agricultural 

lands on alluvial deposits also were largest. Flow-weighted 

mean dissolved-nitrate concentrations were smaller at sites 

with more forested land (fig. 27B; τ = -0.56; p-value = 0.025) 

compared to sites with more rangeland (fig. 27C; τ = 0.56; 

p-value = 0.025) on alluvial deposits. The positive correlation of concentrations with rangeland area and the negative 

correlation of concentrations with forested land area are 

characteristics consistent with results from other investigations. Nolan and Hitt (2003, p. 10) reported that background 

dissolved-nitrate concentrations in samples from shallow aquifers beneath rangelands were significantly (p-value < 0.001) 

larger than ground-water concentrations beneath forested lands 

and attributed the larger concentrations to natural sources and 

processes.

Flow-weighted mean dissolved-nitrate concentrations for 

the YELL fixed sites in relatively undeveloped basins (site SB, 

site YCS, site T, and site LP) generally were smaller than or 

similar to concentrations for streams in relatively undeveloped 

basins in the United States (background concentrations). For 

site SB, site YCS, and site T, flow-weighted mean dissolvednitrate concentrations generally were smaller than or similar to 

the computed median background concentrations for dissolved 

nitrate of 0.087 mg/L (Clark and others, 2000). The exception 

was site LP, where the flow-weighted mean dissolved-nitrate 

concentration (0.18 mg/L) was larger than the median and 

smaller than the 75th-percentile (0.21 mg/L) of background 

concentrations; however, the estimated flow-weighted mean 

concentration has a large degree of uncertainty because a large 

percentage of the dissolved-nitrate concentrations in samples 

from site LP were reported as less than laboratory reporting 

levels.

Median total-nitrogen concentrations in samples from 

the fixed sites ranged from 0.13 mg/L to 0.95 mg/L (fig. 26). 

Concentrations were smaller for the mineral resource area (site 

SB) and forested (site T) indicator sites compared to the integrator sites on the major tributaries (site CF, site B, and site P). 

Median total-nitrogen concentrations for mainstem sites (site 

YCS, site YB, site YF, and site YS) increased downstream. 

Organic nitrogen composed proportionally more of the total 

nitrogen in samples for site LP and site P when compared to 

all other fixed sites.

The flow-weighted mean total-nitrogen concentrations 

were correlated with land-cover characteristics on alluvial 

deposits (fig. 28). In general, flow-weighted mean totalnitrogen concentrations were most strongly correlated with 

increasing rangeland (τ = 0.87; p-value < 0.001) and decreasing forested land (τ = -0.87; p-value < 0.001) on alluvial 

deposits upstream from the sites. In contrast to comparisons 

46 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
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Fixed-Site Water Quality, 1999-2001 47
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Figure 27. Flow-weighted mean dissolved-nitrate concentrations related to A, drainage area; B, forested lands;

C, rangeland; and D, agricultural lands on alluvial deposits for fixed sites in the Yellowstone River Basin, 1999-2001.

48 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
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Figure 28. Flow-weighted mean total-nitrogen concentrations related to A, drainage area; B, forested lands;

C, rangeland; and D, agricultural lands on alluvial deposits for fixed sites in the Yellowstone River Basin, 1999-2001.

Fixed-Site Water Quality, 1999-2001 49
of flow-weighted mean dissolved-nitrate concentrations with 

land-cover characteristics, flow-weighted mean total-nitrogen 

concentrations were not correlated with agricultural lands on 

alluvial deposits (τ = 0.31; p-value = 0.209).

Flow-weighted mean total-nitrogen concentrations in 

samples from fixed sites in relatively undeveloped basins (site 

SB, site YCS, site T, and site LP), generally were smaller than 

or similar to concentrations for streams in relatively undeveloped basins in the United States (background concentrations). 

For site SB, site YCS, and site T, flow-weighted mean totalnitrogen concentrations generally were smaller than or similar 

to the computed median background concentrations for total 

nitrogen of 0.26 mg/L (Clark and others, 2000). The flowweighted mean total-nitrogen concentration at site LP 

(1.9 mg/L) was larger than the 75th-percentile (0.50 mg/L) 

background concentration. Physical and hydrologic characteristics of the sites used in the analyses by Clark and others 

(2000, fig. 3) are very different from those for site LP. The 

drainage area for site LP is much larger than the drainage 

areas for most of the background sites used by Clark and others (2000), whereas the mean streamflow and annual runoff 

are much smaller for site LP in comparison to most of the 

background sites. Additionally, most of the background sites 

used in the analyses by Clark and others (2000) were in basins 

that were not characterized as mostly rangeland. Sources and 

cycling of nitrogen in rangelands can differ substantially from 

sources and cycling of nitrogen in other land covers.

Phosphorus

Median dissolved-phosphorus concentrations in samples 

ranged from less than reporting levels at site T to 0.026 mg/L 

at site SB (fig. 26). The smallest concentrations were measured at the forested indicator site T; more than 50 percent of 

the samples analyzed from this site had concentrations less 

than the maximum reporting level. The largest dissolvedphosphorus concentrations generally were measured at the 

mineral resource area indicator site SB, where concentrations 

ranged from 0.012 mg/L to 0.039 mg/L. Potential sources 

for dissolved phosphorus upstream from site SB probably 

are both natural and anthropogenic. Phosphorus is a common constituent in marine sedimentary rocks (Hem, 1985); 

outcrops of formations with these lithologies are upstream 

from site SB (Elliott, 1979). In addition to the simple dissolution of particulate phosphorus from these outcrops, past 

mining activities resulting in increased weathering of phosphorus-containing minerals could contribute to dissolved 

phosphorus concentrations at moderate to high streamflows. 

In a previous investigation of the hydrogeology of the Soda 

Butte Creek Basin, Metesh and others (1999, p. 22) noted an 

increase in dissolved-nitrate concentrations in the downstream 

direction during March 1997. Considering the observation by 

Metesh and others (1999) and because phosphorus is found in 

human and animal waste (Hem, 1985), shallow ground-water 

discharge from unsewered development along the creek could 

contribute to dissolved-phosphorus concentrations at site SB at 

low streamflows.

Median total-phosphorus concentrations in samples from 

the fixed sites ranged from 0.007 mg/L to 0.18 mg/L (fig. 26). 

Concentrations were smallest in samples collected from the 

forested indicator site T and largest in samples collected from 

site P. Median total-phosphorus concentrations at mainstem 

sites (site YCS, site YB, site YF, and site YS) increased downstream.

Concentrations of total phosphorus typically increase 

with increasing suspended-sediment concentrations (fig. 29) 

because of physical and chemical properties. Because of the 

erosive nature of the soils in much of the basins and plains 

areas of the YELL, suspended-sediment concentrations in 

streams can be large. Thus, total-phosphorus concentrations 

can be large (for example, site P) and generally increase 

downstream with increasing suspended-sediment concentrations (for example, site YCS, site YB, site YF, and site YS). 

Ordinary least squares and robust linear-regression relations (Helsel and Hirsch, 1992; Insightful Corp., 2002) were 

developed for each site using base-10 logarithms of total-phosphorus and suspended-sediment concentrations. Correlation 

coefficients (Pearson’s r) ranged from 0.68 (site T) and 0.79 

(site YB) to 0.97 (site YS) and 0.98 (site YCS and site YF). 

When compared to concentrations measured at other YELL 

fixed sites, dissolved phosphorus at site SB composed a larger 

fraction of the total phosphorus at lower suspended-sediment 

concentrations and streamflows, probably because of natural 

and anthropogenic sources in the basin (see previous discussion in this section).

Potential sources of phosphorus in samples from YELL 

fixed sites most likely are natural. Anthropogenic inputs of 

phosphorus in the YELL are low relative to other parts of the 

United States (David Mueller, U.S. Geological Survey, written 

commun., 2002). Natural sources of particulate phosphorus in 

the YELL, however, are more common relative to sources in 

other parts of the Nation. Outcrops of Permian-period marine 

phosphorites occur throughout western Wyoming and southwestern Montana (McKelvey and others, 1953). Soil phosphorus content in the upper Missouri River Basin is relatively high 

compared to other parts of the United States (Parker, 1953). 

Shacklette and Boerngen (1984) noted that mean phosphorus 

concentrations in soils and other surficial materials generally 

are naturally larger in the western United States (320 micrograms per gram (μg/g)) than in the eastern United States 

(200 μg/g). Phosphorus concentrations in bed sediments also 

are naturally larger in western U.S. streams than eastern U.S. 

streams (Jeffrey Grossman, U.S. Geological Survey, written 

commun., 2003).

Flow-weighted mean total-phosphorus concentrations 

ranged from 0.04 mg/L to 2.1 mg/L. As with sample median 

concentrations, flow-weighted concentrations in samples 

from the fixed sites were smallest at site T, largest at site P, 

and increased downstream at mainstem sites (sites YCS, 

YB, YF, and YS). Flow-weighted mean total-phosphorus 

concentrations at sites in relatively undeveloped basins in 

50 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
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Figure 29. Relations of total-phosphorus and suspended-sediment concentrations for fixed sites in the Yellowstone 

River Basin, 1999-2001.

the YELL (site SB, site YCS, site T, and site LP) were larger 

than the computed 75th-percentile background concentration of 0.022 mg/L by Clark and others (2000, table 1). The 

flow-weighted mean total-phosphorus concentration at site LP 

(0.46 mg/L) was larger than the maximum background concentration reported by Clark and others (2000). The relatively 

large total phosphorus-concentrations at YELL fixed sites 

probably result from natural sources. Additionally, physical 

and hydrologic characteristics of the sites used in the analyses 

by Clark and others (2000) are very different from those for 

site LP.

Organic Carbon

Median DOC concentrations in samples from the fixed 

sites ranged from 0.89 mg/L to 9.3 mg/L (fig. 26). Concentrations generally were smaller than 3 mg/L, which is typical for 

streams of temperate and arid/semiarid zones (Hem, 1985). 

The largest DOC concentrations were measured at the rangeFixed-Site Water Quality, 1999-2001 51

land indicator site, site LP, where DOC concentrations ranged 

from 5.2 mg/L to 38 mg/L. Carbon fractionation analyses were 

completed for a single sample collected at site LP. Fractionation results indicated a relatively large component of aliphatic 

(straight or branched chain) carbon (George Aiken, USGS, 

written commun., 2000). These results might be expected 

if the DOC concentrations at site LP were derived from a 

relatively large source of weathered carbon. Ground-water discharge from coal aquifers probably is not the source of DOC 

at site LP, because DOC concentrations in samples at site LP 

do not have a negative correlation with streamflow and DOC 

concentrations in samples from coal aquifers in the region 

generally are small. However, possible sources of weathered 

carbon upstream from site LP are washoff from coal outcrops 

and (or) springs and seeps that discharge in response to rainfall 

or snowmelt from clinker in the basin, where waters in contact 

with residuum from the burned coal over adequate residence 

times could contribute to larger DOC concentrations at larger 

streamflows.
Nitrogen

Median dissolved-nitrate concentrations generally were 

larger during October–December and January–March for the 

mainstem fixed sites (fig. 30). Sources of nitrate (for example, 

oxidation of ammonia in geothermal waters or discharge from 

alluvial aquifers) are less dilute during winter months when 

streamflows are lower than during other months. Uptake of 

nitrate by algae—an important process that reduces concentrations in streams during summer—also is minimal during 

winter months when solar inputs are smaller than during 

other months and stream temperatures are near freezing. For 

samples from the mainstem sites, the largest differences in 

seasonal nitrate concentrations were at site YS where concentrations during January–March were much larger than those 

during July–September. At site YS, the larger nitrate concentrations during January–March probably are a result of discharges from shallow ground-water sources. During July–September, the smaller nitrate concentrations probably are caused 

in part by increased uptake during July and August when algae 

are most active (Peterson and others, 2004).

Dissolved-nitrate concentrations varied by sampling 

period for samples from major tributary integrator sites and 

minor tributary indicator sites (fig. 30). Because concentrations generally increase when flows decrease, ground water 

that is discharged from alluvial deposits is a probable source 

of nitrate in stream samples at the tributary sites. For site SB, 

median dissolved-nitrate concentrations were largest during January–March when biological uptake is diminished 

and dilution by streamflow is lowest. For site CF, median 

dissolved-nitrate concentrations were largest during October–December. Dissolved-nitrate concentrations, however, 

also were large during July–September for site CF as well as 

for site B. The large dissolved-nitrate concentrations during 

July–September when algal uptake is greatest probably are the 

result of nitrogen-enriched irrigation return flows and shallow 

ground-water discharge.

Total-nitrogen concentrations in samples from YELL 

fixed sites varied by sampling period (fig. 31). For samples 

from the mainstem sites, the largest concentrations shifted 

from January–March at site YCS to April–June at site YS. 

From upstream to downstream at the mainstem sites, relatively 

less of the total nitrogen present is composed of dissolvedinorganic nitrogen (for example, ammonia and nitrate), which 

is present in larger concentrations during January–March and 

relatively more is composed of organic nitrogen, which is 

present in larger concentrations during April–June. For site B, 

site T, site LP, and site P, median total-nitrogen concentrations 

were largest during April–June. Because streamflows are largest during April–June and result in large suspended-sediment 

concentrations, the large total-nitrogen concentrations likely 

are related to suspended particulate organic matter. For site 

SB, median total-nitrogen concentrations were largest during 

January–March, similar to dissolved-nitrate concentrations. 

For site CF, median total-nitrogen concentrations were similar 

during all seasons.

Comparison to Water-Quality Criteria

Nutrient concentrations in samples from YELL fixed sites 

generally were smaller than water-quality criteria. Dissolvednitrate concentrations in all samples from YELL fixed sites 

were smaller than the Maximum Contaminant Level (MCL) 

of 10 mg/L for human health (U.S. Environmental Protection 

Agency, 2002d). Aquatic-life criteria pertaining to ammonia 

concentrations are water temperature- and pH-dependent 

and further classified by fish life stage (U.S. Environmental 

Protection Agency, 1999). Ammonia concentrations in all 

samples from fixed sites did not exceed any of the aquatic-life 

criteria. Total-phosphorus concentrations in some samples 

from some YELL fixed sites were larger than the desired goal 

of 0.10 mg/L for preventing nuisance plant growth in streams 

(U.S. Environmental Protection Agency, 1986b). Median totalphosphorus concentrations exceeded the recommended goal 

in samples from site B, site P, and site YS. Total-phosphorus 

concentrations in samples from these sites likely are naturally 

occurring.

Total-nutrient concentrations for YELL fixed sites 

were larger than concentrations for USEPA nutrient ecoregion reference conditions. For preventing adverse effects of 

excess human-caused nutrient inputs in the Middle Rockies, 

Wyoming Basin, and Northwestern Great Plains Ecoregions, 

USEPA developed unique nutrient criteria from monitoring data for each ecoregion (U.S. Environmental Protection 

Agency, 2000b, 2000c, 2001). Because data for reference sites 

are few, the criteria were based on the lower quartile of sample 

concentrations from all monitoring data. The ecoregion criteria 

for total nitrogen (0.090 mg/L, Middle Rockies; 0.25 mg/L, 

Wyoming Basin; 0.38 mg/L, Northwestern Great Plains) were 

exceeded by the sample 10th-percentile concentrations for 

all fixed sites except site SB. For site SB, the sample median 

concentration exceeded the ecoregion criterion. The ecoregion 

criteria for total phosphorus (0.015 mg/L, Middle Rockies; 

0.022 mg/L, Wyoming Basin; 0.029 mg/L, Northwestern 

Great Plains) were exceeded by the sample 25th-percentile 

concentrations for most fixed sites. The exceptions were site 

SB and site YCS (10th-percentile exceeded criterion), site 

LP (median exceeded criterion), and site T (75th-percentile 

exceeded criterion).

Temporal Variability

Nutrients for YELL fixed sites were evaluated by season 

to assess temporal variations in concentrations as related 

to environmental factors. Daily concentrations of dissolved 

nitrate, total nitrogen, and total phosphorus were estimated 

using the rating-curve method (Cohn and others, 1989) and 

the computer program LOADEST (Crawford, 1991). Daily 

concentrations estimated using this method are subject to large 

errors. To minimize the effects of potential errors, statistical 

summaries of the estimated values for October–December, 

January–March, April–June, and July–September are used to 

assess seasonal variations.

52 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
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Figure 30. Seasonal statistical summary of LOADEST estimated daily dissolved-nitrate concentrations for fixed 

sites in the Yellowstone River Basin, 1999-2001.

Fixed-Site Water Quality, 1999-2001 53
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Figure 31. Seasonal statistical summary of LOADEST estimated daily total-nitrogen concentrations for fixed sites in the 

Yellowstone River Basin, 1999-2001.

54 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
Phosphorus

Total-phosphorus concentrations in samples from 

mainstem and tributary YELL fixed sites were largest during 

April–June (fig. 32). Streamflows at all fixed sites generally 

are largest during this period as a result of runoff from snowmelt events and rainfall events. Because suspended-sediment 

concentrations are largest when streamflows are largest and 

because phosphorus sorbs to sediment particles, the large totalphosphorus concentrations during April–June are expected.

Trace Elements

The dissolved trace elements of iron and manganese routinely were analyzed as part of the YELL fixed-site sampling 

and are discussed in this section of the report. In addition, 

targeted sampling of selected trace elements was added to 

address regional issues. Specifically:

• Selected dissolved trace elements were analyzed for 

sites in the Powder River Basin (site LP and site P) and 

on the lower mainstem Yellowstone River (site YF and 

site YS) to augment baseline water-quality data for the 

lower Yellowstone River Basin;

• Dissolved arsenic was analyzed for sites on the mainstem Yellowstone River (site YCS, site YB, site YF, 

and site YS) to document the flux of arsenic from 

YNP; and

• A comprehensive schedule of trace elements was 

analyzed for site SB where mineralized rocks and past 

mining activities characterize about one-third of the 

drainage area upstream from the site.

Concentrations of arsenic, copper, selenium, and zinc are 

discussed in this report because of their importance to regulatory interests and/or regional issues. Results of trace-element 

analyses are summarized using descriptive statistics of sample 

concentrations. Some trace-element concentrations were less 

than laboratory reporting levels, so statistics of sample concentrations were estimated using robust methods (see “Data-Analysis Methods” section of this report).

Iron and Manganese

Median concentrations of dissolved iron varied among 

sites (fig. 33). Concentrations of dissolved iron generally were 

small for the tributary sites, including site SB, site CF, site B, 

and site T. A large number of samples from site LP and site 

P were diluted during analysis owing to large dissolved-solids concentrations and, as a result, iron concentrations were 

reported at a higher reporting level than for samples from the 

other fixed sites. Median dissolved-iron concentrations generally were low for samples from site YB, site YF, and site YS 

on the mainstem. For all fixed sites, the median dissolved-iron 

concentration was largest for samples collected at site YCS 

(median concentration of 35.4 μg/L, fig. 33). One probable 

source for the dissolved iron is geothermal water. Ball and 

others (1998, p. 23) reported concentrations of dissolved iron 

(Fe(II)) as large as 65,000 μg/L from acidic thermal springs 

in the basin. Concentrations of dissolved iron in samples from 

site YCS generally were largest during the months of January–March when streamflows were small and the influence 

of geothermal waters on stream-water quality would be most 

substantial. Concentrations of dissolved iron of about 40 μg/L, 

however, occurred in samples from site YCS collected over 

a range of streamflows, including the largest streamflows 

(greater than 15,000 ft3/sec). Other factors probably contribute 

to these observed concentrations. For example, at least some 

of the iron in many of these samples probably is in a colloidal 

form. Dissolved constituents are defined operationally by the 

nominal pore size of the filter of 0.45 μm. Some iron colloids 

are small enough to pass through the filter and be analyzed 

as part of the dissolved fraction. Also, the bed-sediment iron 

concentration of a sieved (62 μm) composite sample from site 

YCS was the largest of the fixed sites sampled during 1998 

(Peterson and Boughton, 2000). Large streamflows can suspend bed sediments including colloids, thereby contributing to 

increased dissolved concentrations.

Concentrations of dissolved manganese range from 

less than 1 to 350 μg/L for all samples from the fixed sites 

(fig. 33). The median concentration of dissolved manganese 

was substantially larger at site LP than at the other fixed sites. 

Dissolved manganese in samples from site LP tended to be 

large when streamflows were small, indicating that ground 

water probably is the source of the manganese. Other streams 

in northeastern Wyoming have elevated concentrations of dissolved manganese (Swanson and others, 2002), and manganese has been cited as a cause of stream impairment for the 

area (Wyoming Department of Environmental Quality, 2002). 

Samples from site CF had the largest median concentration of 

dissolved manganese of samples from the integrator sites. For 

samples from the mainstem sites, the median concentration of 

dissolved manganese, like iron, was largest at site YCS.

Arsenic

The sampling frequency for dissolved arsenic was 

variable at the fixed sites. Dissolved-arsenic concentrations 

in stream samples were as large as 41.6 μg/L at site YCS 

(fig. 33). Median concentrations in samples from the Yellowstone River were 21.0 μg/L at site YCS and 10.5 μg/L at 

site YB. Although few in number, samples from tributary fixed 

sites (sites SB, LP, and P) indicate that arsenic concentrations 

were small or less than reporting levels.

Concentrations of trace elements in natural waters not 

affected by anthropogenic activities generally are very small 

(Drever, 1997); however, elevated concentrations of arsenic 

are common in many geothermal waters (Hem, 1985). In YNP, 

there are over 10,000 thermal features including more than 

300 geysers (Yellowstone National Park, 2001). Concentrations of dissolved arsenic in samples collected at selected sites 

in the YELL Study Unit indicate that the geothermal waters 

Fixed-Site Water Quality, 1999-2001 55
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Figure 32. Seasonal statistical summary of LOADEST estimated daily total-phosphorus concentrations for fixed sites 

in the Yellowstone River Basin, 1999-2001.

56 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
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Figure 33. Statistical summary of selected trace-element concentrations for fixed sites in the Yellowstone River Basin, 1999-2001.

Fixed-Site Water Quality, 1999-2001 57
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Figure 34. Relation of dissolved-arsenic concentrations and streamflow for fixed sites on 

the Yellowstone River in the Yellowstone River Basin, 1999-2001.

of YNP are a substantial source of arsenic in the Yellowstone River (fig. 34, site YCS). The largest dissolved-arsenic 

concentrations in samples from site YCS were observed 

during low streamflows; small concentrations are the result of 

dilution from large streamflows. In the oxidizing environment 

of streams in and around YNP, arsenic—as arsenate—has 

been shown to be relatively conservative (Stauffer and others, 

1980; Nimick and others, 1998). Analyses of arsenic in fine 

sediments (less than 62 μm) of bed materials for the mainstem 

indicated a decrease in arsenic concentrations from site YCS 

to site YS (Peterson and Boughton, 2000, table 8) similar to 

the decrease observed in stream samples (fig. 33; fig. 34). 

Because concentrations of arsenic in samples from tributary 

fixed sites were small or less than reporting levels, downstream decreases in arsenic concentration for the mainstem 

Yellowstone River probably are a result of dilution from tributary inflows downstream from site YCS.

Copper

Sampling frequency for dissolved copper was variable at 

the fixed sites. Concentrations of dissolved copper generally 

were small for samples collected at fixed sites in the YELL 

(fig. 33). The median concentration of dissolved copper was 

largest at site LP, the rangeland indicator site. Copper, however, is the most strongly complexed transition element and 

is often complexed by organic solutes (Drever, 1997, p. 189). 

Complexation of copper by organic solutes can increase the 

dissolved concentrations in solution. Large concentrations of 

DOC at site LP may contribute to dissolved-copper concentrations at that site. Large dissolved-solids and DOC concentrations in samples from site LP indicate that part of the dissolved 

copper at site LP probably is complexed, which decreases the 

toxicity of copper to aquatic life.

Elevated concentrations of copper commonly are associated with acid mine drainage (Hem, 1985, p. 141). Mineralized rocks and past mining activities characterize one-third 

of the drainage area upstream from site SB, and mine tailings 

were disposed of in-channel upstream from site SB. Earlier 

studies in and near the Soda Butte Creek drainage basin 

reported some trace elements, including copper, at concentrations of concern in bed sediment, tissue, and stream samples 

(Nimmo and Willox, 1996; Peterson and Boughton, 2000; 

Boughton, 2001). However, large concentrations of dissolved 

copper were not observed during the fixed-site sampling at 

site SB. The large concentrations described by some previous 

investigators were from samples collected at or near obvious 

sources of trace elements, such as seeps from mine tailings. 

Copper concentrations in bed sediment and tissue were largest 

at site SB when compared to concentrations measured at the 

other nine fixed sites (Peterson and Boughton, 2000).

Selenium

Sampling frequency for dissolved selenium was variable at the fixed sites. Concentrations of dissolved selenium 

in samples from these sites ranged from less than laboratory 

reporting levels to 4.6 μg/L (fig. 33). Comparison of discrete 

concentrations between sites is complicated by multiple laboratory reporting levels. Concentrations of dissolved selenium 

58 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
generally were largest in samples collected at site P, ranging 

from 0.48 μg/L to 4.6 μg/L. Elevated selenium concentrations are associated with areas underlain by Cretaceousperiod rocks, such as parts of the Powder River Basin (U.S. 

Department of Interior, 1998). Selenium naturally occurs in 

Cretaceous-period sedimentary rocks of marine origin and the 

sediment, soils, and other geologic units derived from those 

rocks. Previous investigations have shown selenium to be 

very mobile in alkaline soils in the arid regions of the Western United States, and dissolved concentrations may become 

concentrated in streams draining irrigated lands with those 

characteristics (U.S. Department of Interior, 1998).

Zinc

Sampling frequency for dissolved zinc was variable at the 

fixed sites. The median concentration of dissolved zinc was 

largest in samples collected at site LP. Large DOC concentrations are an important factor in the complexation of zinc by 

organic solutes (Drever, 1997, p. 110, 188-189). Large concentrations of DOC at site LP may contribute to the dissolvedzinc concentrations at that site. Elevated concentrations of 

zinc commonly are associated with acid mine drainage (Hem, 

1985, pg. 142). Historical mining in the Soda Butte Creek 

Basin, resulted in exposed mine tailings upstream from the 

mineral resource area indicator site, site SB; however, large 

concentrations of dissolved zinc were not observed during the 

fixed-site sampling at site SB.

Comparison to Water-Quality Criteria

To assess the magnitude of trace-element concentrations 

for the fixed sites in the YELL, concentrations of iron, manganese, arsenic, copper, selenium, and zinc were compared to 

water-quality criteria. SMCLs are established for dissolved 

iron and manganese (U.S. Environmental Protection Agency, 

2002d). All of the dissolved-iron concentrations analyzed in 

samples from the fixed sites were smaller than the SMCL of 

300 μg/L, except for one sample from site YS. Concentrations 

of dissolved manganese in samples from all of the sites, except 

site LP, were smaller than the SMCL of 50 μg/L. Dissolvedmanganese concentrations exceeded the SMCL in about 

76 percent of the samples from site LP; however, the Little 

Powder River is not used for domestic drinking water. The 

USEPA MCL for dissolved arsenic is 10 μg/L (U.S. Environmental Protection Agency, 2002b). Ingestion of arsenic in 

water can cause damage to the skin and circulatory systems 

and may result in increased risk of bladder and lung cancer. 

Concentrations of arsenic from the Yellowstone River were 

larger than the MCL in about 75 percent of the samples at site 

YCS and in more than 50 percent of the samples from site YB. 

The Yellowstone River is used as a municipal drinking-water 

supply in this reach, including by the city of Billings, Montana.

Aquatic-life criteria for some trace elements, including 

copper and zinc, often are expressed as a function of hardness, 

which is a measure of the amount of calcium and magnesium in water, and are not a single number. Hardness is used 

as a surrogate for several water-quality characteristics that 

affect the toxicity of those metals; toxicity of certain metals 

decreases with increasing hardness (U.S. Environmental Protection Agency, 2002a). Dissolved copper and zinc concentrations in all samples collected at fixed sites were smaller than 

the chronic aquatic-life criteria. Dissolved-selenium concentrations in all of the samples were smaller than the chronic 

aquatic-life criterion of 5 μg/L (U.S. Environmental Protection 

Agency, 2002a); however, concentrations were larger than 

2 μg/L in about 31 percent of the samples at site P. Concentrations of total selenium greater than 2 μg/L in water appear 

to produce adverse effects on some fish and wildlife species 

(U.S. Department of Interior, 1998, table 32).

Pesticides

Pesticides are used on a regular basis in a variety of agricultural and non-agricultural areas to control nuisance plants 

and organisms. National pesticide use has increased substantially during the last several decades and, with their increased 

use, an increase in crop production and control of public health 

hazards has occurred (Larson and others, 1997). Correspondingly, because of their widespread use, pesticides commonly 

are detected in streams, raising concerns about the potential 

adverse effects on human health and aquatic life (Larson and 

others, 1999). The NAWQA Program has collected thousands 

of samples to describe the distribution, trends, and governing 

factors of pesticide occurrence in streams in the United States.

To assess the occurrence of pesticides in the YELL, water 

samples were collected and analyzed for selected pesticides 

at five of the fixed sites (site CF, site YB, site B, site YF, and 

site YS) that have mixed land use. Pesticide samples were 

collected from January to December 1999 at site CF, site YB, 

and site B. Samples at site YF and site YS were collected from 

January 1999 to September 2001. For all sites, at least one 

sample was collected during each month of the year to address 

temporal variation in pesticide occurrence.

A GCMS method (Zaugg and others, 1995) was used to 

analyze for 47 commonly used pesticides, including 26 herbicides, 17 insecticides, and 4 breakdown products, in samples 

collected from the YELL (table 9). A second analytical 

method was used to detect additional pesticides in streams but 

only results for the samples analyzed using the GCMS method 

are presented in this report because the other analytical method 

was still under development during the collection of most of 

the samples. The GCMS method measures pesticides at very 

small concentrations, often 10 to 1,000 times smaller than the 

USEPA drinking-water standards and method reporting levels 

commonly used at other analytical laboratories. The low-level 

methods are used to detect and evaluate emerging issues, as 

well as to track contaminant concentrations over time. 

Fixed-Site Water Quality, 1999-2001 59
Table 9. Trade names, type, reporting levels, drinking-water criteria, and aquatic-life criteria for pesticide compounds analyzed by gas 

chromatography/mass spectrometry method.

[NWIS, National Water Information System; μg/L, micrograms per liter; --, not available]

NWIS

parameter

code

Pesticide 

compound Trade name Type

Method 

reporting 

level, in μg/L

Other reporting levels 

used, in μg/L

Drinkingwater criteria, 

in μg/L

Aquatic-life 

criteria, in 

μg/L

82660 2,6-Diethylanaline -- Breakdown 

product

 0.002 0.003 -- --

49260 Acetochlor Guardian, 

Relay

Herbicide .002 .004 -- --

46342 Alachlor Alanex, Lasso Herbicide .002 .004 12 --

34253 alpha-HCH -- Breakdown 

product

 .002 .005 20.06 --

39632 Atrazine AAtrex Herbicide .001 .003, 

 .005,

 .006

1

3 41.8

82673 Benfluralin Balan, Benefin Herbicide .002 .01 -- --

04028 Butylate Sutan+, 

Genate Plus

Herbicide .002 3400 --

82680 Carbaryl Carbatox, 

Sevin

Insecticide .003 .041 3700 40.20

82674 Carbofuran Furadan Insecticide .003 .01,

 .013,

 .02,

 .03

1

40 41.8

38933 Chlorpyrifos Dursban, 

Lorsban

Insecticide .004 .005 320 5.041

04041 Cyanazine Bladex Herbicide .004 .018 31 42.0

(interim)

82682 DCPA Dacthal Herbicide .002 .003,

 .004

3

70 --

04040 Deethylatrazine-- Breakdown 

product

 .002 .004,

 .007

 -- --

39572 Diazinon Basudin, 

Spectracide

Insecticide .002 .005 3.6 6.08

39381 Dieldrin Panoram D31, OctaloxInsecticide .001 .005 7.02 5.056

82677 Disulfoton Di-Syston Insecticide .017 .021 3.3 --

82668 EPTC Eptam, EradicaneHerbicide .002 .005, 

 .007,

 .008

 -- --

82663 Ethalfluralin Sonalan Herbicide .004 .009 -- --

82672 Ethoprop Mocap, ProphosInsecticide .003 .005 -- --

04095 Fonofos Dyfonate Insecticide .003 -- 310 --

60 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
Table 9. Trade names, type, reporting levels, drinking-water criteria, and aquatic-life criteria for pesticide compounds analyzed by gas 

chromatography/mass spectrometry method.—Continued.

NWIS

parameter

code

Pesticide 

compound Trade name Type

Method 

reporting 

level, in μg/L

Other reporting levels 

used, in μg/L

Drinkingwater criteria, 

in μg/L

Aquatic-life 

criteria, in 

μg/L

39341 gamma-HCH Lindane, 

Isotox

Insecticide .004 1.2 4.01

82666 Linuron Linurex, 

Lorox

Herbicide .002 .035 -- 47.0

(interim)

39532 Malathion Cythion, 

Malaspray

Insecticide .005 .027 3100 5.1

82686 Methyl 

azinphos

Guthion Insecticide .001 .050 -- 5.01

82667 Methyl parathion

Penncap-M Insecticide .006 .030,

 .050

3

2 --

39415 Metolachlor Bicep, Dual Herbicide .002 .004, 

 .005,

 .013

3

100 47.8

82630 Metribuzin Lexone, 

Sencor

Herbicide .004 .006 3200 41.0

(interim)

82671 Molinate Hydram, 

Ordram

Herbicide 0.002 0.004 -- --

82684 Napropamide Devrinol Herbicide .003 .007,

 .020

 -- --

34653 p,p’-DDE -- Breakdown 

product

 .003 .006 71 50.001 

(total DDT)

39542 Parathion Alkron, 

Bladan

Insecticide .004 .007 -- 5.013

82669 Pebulate Tillam Herbicide .002 .004,

 .030

 -- --

82683 Pendimethalin Prowl, Stomp Herbicide .004 .010 -- --

82687 cis-Permethrin Ambush Insecticide .005 .006 -- --

82664 Phorate Thimet, RampartInsecticide .002 .011 -- --

04037 Prometon Pramitol, 

Gesafram

Herbicide .02 3100 --

82676 Pronamide Kerb Herbicide .003 .004 350 --

04024 Propachlor Bexton, RamrodHerbicide .007 .010 390 --

82679 Propanil Stampede Herbicide .004 .011 -- --

82685 Propargite Comite, Omite Insecticide .013 .023,

 .030

 -- --

04035 Simazine Aquazine, 

Princep

Herbicide .005 .011 14 410

Fixed-Site Water Quality, 1999-2001 61
Table 9. Trade names, type, reporting levels, drinking-water criteria, and aquatic-life criteria for pesticide compounds analyzed by gas 

chromatography/mass spectrometry method.—Continued.

NWIS

parameter

code

Pesticide 

compound Trade name Type

Method 

reporting 

level, in μg/L

Other reporting levels 

used, in μg/L

Drinkingwater criteria, 

in μg/L

Aquatic-life 

criteria, in 

μg/L

82670 Tebuthiuron Graslan, Spike Herbicide .01 .02,

 .08

3

500 41.6

(interim)

82665 Terbacil Sinbar, Herbicide 732Herbicide .007 .034 390 --

82675 Terbufos Counter, ContravenInsecticide .01 .02 3.9 --

82681 Thiobencarb Bolero, Saturn Herbicide .002 .005 -- --

82678 Triallate Far-Go, Avadex BWHerbicide .001 .002, 

 .003,

 .005 

 -- 4.24

(interim)

82661 Trifluralin Treflan, Trim Herbicide .002 .009 35 4.20

1

Maximum Contaminant Level, U.S. Environmental Protection Agency (2002d)

2

Risk-specific dose at 10-5 cancer risk, U.S. Environmental Protection Agency (2002f)

3

Health Advisory level, U.S. Environmental Protection Agency (2002d)

4

Canadian Council of Ministers of the Environment, 2002

5

Continuous chronic criteria, U.S. Environmental Protection Agency (2002a)

6

International Joint Commission United States and Canada (1978)

7

Risk-specific dose at 10-4 cancer risk, U.S. Environmental Protection Agency (2002f)

The method reporting level for each pesticide is included in 

table 9. For some samples, other reporting levels were used for 

the analysis because of matrix effects in the sample, instrument performance, or changes in the method reporting level 

through time. The USEPA MCLs, health advisory levels, risk 

specific dose at 10-4 cancer risk (RSD4) and risk specific dose 

at 10-5 cancer risk (RSD5) for human health, and guidelines 

for the protection of aquatic life issued by USEPA, Canadian 

water-quality guidelines, and the International Joint Commission of Canada and the United States, were compiled for the 

pesticides. These criteria values are presented for assessing the 

magnitude of a sample concentration for a pesticide but do not 

necessarily correspond to the water-quality criteria that would 

be applicable at a site (table 9).

Pesticide Use

The occurrence of pesticides in streams are dependent 

on many factors, such as the land use and land cover, timing 

of the application, amount of the pesticide that is applied, soil 

properties, and the physical and chemical characteristics of 

each pesticide—such as, the water solubility, persistence, and 

sorption properties (Larson and others, 1997). The agricultural 

land covers (including row crops, small grains, pasture or hay, 

and fallow) and urban land covers (including urban grasses, 

residential areas, and transportation) combined composed less 

than 10 percent of the basins of the five fixed sites that were 

sampled for pesticides in the YELL. However, these agricultural and urban land covers frequently are adjacent to stream 

corridors in the basins and compose a large percentage of the 

area on alluvial deposits. Crop types typically grown in the 

YELL include hay, alfalfa, wheat, oats, barley, sugar beets, 

beans, and corn (National Agricultural Statistics Service, 

2003). The amount of active ingredient applied in the entire 

YELL for 20 of the 47 pesticides analyzed by the GCMS 

method used for samples collected in this study (fig. 35) was 

compiled from crop acreage data from the 1992 Census of 

Agriculture (U.S. Department of Commerce, 1995).

Frequency of Detections

At least one pesticide was detected in 87 percent of the 

136 samples that were collected. The frequency of pesticide 

detections in samples varied among the sites—about 54 percent of the samples from site YB had a pesticide detection 

compared to about 95 percent of the samples at site YS. Of the 

pesticides that were analyzed with the GCMS method, 14 of 

the 26 herbicides were detected; 5 of the 17 insecticides were 

detected; and 1 of the 4 breakdown products was detected in 

the samples (table 10). The number of different pesticides 

62 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
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Figure 35. Pesticide use in the Yellowstone River Basin during 1992 (U.S. Department of Commerce, 1995).

detected in samples varied among sites—site YB had the least 

with 7 different pesticide compounds identified, compared to 

site B and site YS that had 16 different pesticide compounds 

detected. Site YS had the highest number of different herbicides detected (11), and site B had the highest number of 

different insecticides detected (5).

Herbicides frequently were detected in stream samples 

in the YELL (fig. 36). Atrazine, a selective herbicide generally used in agricultural settings, was the most frequently 

detected herbicide at each of the fixed sites and was present in 

74.8 percent of all samples. Although atrazine was not one of 

the most frequently applied pesticides in the YELL, it has high 

potential to move in the hydrologic system because of moderate to high mobility in soils and lengthy half-life (more than 

90 days) (Larson and others, 1997). Atrazine also has been 

determined to move long distances through atmospheric transport processes (Goolsby and others, 1995). The second most 

frequently detected herbicide was a breakdown product of 

atrazine, deethylatrazine, which was present in 39.7 percent of 

all samples. Metolachlor (38.2 percent) and triallate (37.5 percent), which are selective herbicides generally used in agricultural settings (Meister Publishing Company, 2001), also were 

frequently detected. Like atrazine, metolachlor is commonly 

detected in streams owing to its large runoff potential (Larson 

and others, 1997). In contrast, triallate is not readily dissolved 

in water; however, it is persistent in soil and may become 

desorbed and leach into water under certain environmental 

conditions (Cornell University, 2002). The frequent detection 

of triallate probably is a result of its frequent use in the YELL 

(fig. 35). Prometon, a nonselective herbicide, was detected in 

23.5 percent of the samples (table 10) and is commonly used 

and detected in urban settings (Barbash and Resek, 1996).

Insecticides were less frequently detected than herbicides 

in pesticide samples from the five sites in the YELL (fig. 36). 

Chlorpyrifos was the most commonly detected insecticide 

and was detected in 5.1 percent of all samples (table 10). The 

most frequently detected insecticide in samples varied among 

sites and included carbaryl (6.2 percent) at site CF, carbofuran 

(7.7 percent) at site YB, malathion (24 percent) at site B, carbofuran (2.4 percent) and chlorpyrifos (2.4 percent) at site YF, 

and chlorpyrifos (6.8 percent) at site YS (table 10). The occurrences of carbaryl, chlorpyrifos, and malathion in streams have 

been associated with their use in urban areas (Larson and others, 1999). The frequency of detection of malathion at site B 

is higher than might be expected from its chemical properties 

because malathion is known to degrade quickly in soil thereby 

having a small runoff potential (Larson and others, 1997). The 

most frequently applied insecticide, terbufos, was detected in 

less than 1 percent of all samples. The low detection frequency 

of terbufos is probably due to several factors, including its 

rapid conversion to its metabolites, low water solubility (CorFixed-Site Water Quality, 1999-2001 63
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Figure 36. Frequency of pesticide detections for fixed sites in the Yellowstone River Basin, 1999-2001.

than the detection frequency of about 26 percent for atrazine 

in stream samples from undeveloped sites in the United States 

compiled for NAWQA with the adjusted reporting level of 

0.01 μg/L (U.S. Geological Survey, 2003a). Carbofuran and 

malathion were the most commonly detected insecticides, 

with a frequency of detection of about 2.9 percent using the 

adjusted reporting level. Many of the pesticides that were 

detected using the lower reporting levels had concentrations 

less than the adjusted reporting level of 0.01 μg/L, including 

alachlor, benfluralin, carbaryl, chlorpyrifos, DCPA, ethalfluralin, and trifluralin.

Comparison to Water-Quality Criteria

Drinking-water criteria and aquatic-life criteria are 

toxicologically derived values that are useful for assessing the 

magnitude and risk associated with pesticide concentrations 

in streams. Drinking-water criteria have been established by 

the USEPA for 27 of the 47 pesticides analyzed by the GCMS 

method. Concentrations of pesticides were substantially 

(generally an order of magnitude or more) smaller than drinking-water criteria for human health in all samples collected at 

fixed sites in the YELL. Aquatic-life criteria, including interim 

criteria that have been developed by the USEPA, Canada, and 

the International Joint Commission exist for 19 of the 47 pesticides. Concentrations of pesticides were smaller than aquaticlife criteria in all 136 samples.

Possible risks to humans and aquatic life implied by the 

NAWQA findings for the 47 pesticides in the YELL remain 

nell University, 2002), and a relatively high method reporting 

level (0.01 μg/L) compared to the other pesticides.

Mixtures of two or more pesticides were detected in 

75 percent of the samples. The frequency of occurrence of 

mixtures of two or more pesticides in samples varied by site. 

About 38 percent of the samples at site CF had two or more 

pesticides compared to site YS where over 86 percent of 

the samples had two or more pesticides detected. Samples 

containing mixtures of four or more pesticides accounted for 

about 33 percent of all the samples, including 50 percent of the 

samples collected at site YS, which integrates all the waters 

in the basin. One sample from site B contained a mixture of 

10 different pesticides, including 8 herbicides, 1 insecticide, 

and 1 breakdown product.

Although pesticide detections were frequent in stream 

samples from the YELL, the concentrations of pesticides 

generally were small. Method reporting levels varied among 

pesticides, and previous studies have indicated an inverse 

relation between the method reporting level and pesticide 

detection frequencies (Barbash and Resek, 1996; Larson 

and others, 1997). The frequency of detections substantially 

decreased when an adjusted reporting level of 0.01 μg/L was 

used (fig. 36, table 10). The reporting level of 0.01 μg/L was 

selected because this is a reporting level commonly used by 

other laboratories and other studies for pesticide analyses 

(Larson and others, 1997). Atrazine was still the most commonly detected herbicide; however, the frequency of detection 

decreased from 74.8 percent to about 9.6 percent using the 

adjusted reporting level of 0.01 μg/L. The detection frequency 

of 9.6 percent for atrazine in samples in the YELL was less 

64 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
Site CF

Atrazine 15 40.0(6) 6.7(1) E0.002 E0.003 0.159

Carbaryl 16 6.2(1) -- -- -- E.008

DCPA 16 6.2(1) -- -- -- E.001

Deethylatrazine 16 12.5(2) 6.2(1) E.005 -- E.019

Ethalfluralin 16 6.2(1) -- -- -- E.003

Simazine 16 6.2(1) 6.2(1) -- -- .014

Tebuthiuron 16 6.2(1) -- -- -- E.01

Triallate 16 25.0(4) -- E.002 E.003 .004

Trifluralin 16 25.0(4) -- E.001 E.002 .005

Site YB

Atrazine 13 38.5(5) -- E.003 E.003 .008

Carbofuran 13 7.7(1) 7.7(1) -- -- E.013

Deethylatrazine 13 23.1(3) -- E.003 E.003 E.004

Metolachlor 13 7.7(1) -- -- -- E.004

Prometon 13 7.7(1) -- -- -- M

Simazine 13 7.7(1) -- -- -- E.003

Triallate 13 23.1(3) -- E.002 .004 .004

Site B

Atrazine 21 81.0(17) -- E.002 .005 .009

Carbaryl 21 4.8(1) -- -- -- E.004

Carbofuran 21 4.8(1) 4.8(1) -- -- E.020

Chlorpyrifos 21 14.0(3) -- E.001 E.003 E.004

Cyanazine 21 19.0(4) 9.5(2) .006 .009 .14

DCPA 21 9.5(2) -- E.002 -- E.002

Deethylatrazine 21 43.0(9) -- E.003 E.004 E.006

EPTC 21 14.0(3) 4.8(1) E.001 .006 .021

Ethalfluralin 21 4.8(1) -- -- -- E.002

Table 10. Statistical summary of detections and concentrations of pesticides for fixed sites in the Yellowstone River Basin, 1999-2001. 

[Herbicides are in plain text, insecticides are in bold text, and breakdown products are in italicized text. μg/L, micrograms per liter; --, not applicable; E, estmated; M, compound was identified, but not quantified

Pesticide

Compound

Number of 

samples

Percent of 

samples, 

compound 

identified

(number of 

detections)

Percent of 

samples, 

concentration

greater than or 

equal to 0.01 μg/L

(number of 

detections)

Statistical summary of detections

Minimum, 

in μg/L

Median, 

in μg/L

Maximum, in 

μg/L

Fixed-Site Water Quality, 1999-2001 65
Site B—Continued

Malathion 21 24.0(5) 19.0(4) .006 .012 .025

Metolachlor 21 38.0(8) 4.8(1) E.002 .004 .019

Prometon 21 29.0(6) -- M M E.01

Tebuthiuron 21 24.0(5) -- M E.01 E.01

Terbufos 21 4.8(1) 4.8(1) -- -- .03

Triallate 21 33.0(7) -- .001 E.003 .007

Trifluralin 21 4.8(1) -- -- -- E.002

Site YF

Atrazine 42 85.7(36) 11.9(5) E.003 .006 .328

Benfluralin 42 2.4(1) -- -- -- E.003

Carbofuran 42 2.4(1) 2.4(1) -- -- E.034

Chlorpyrifos 42 2.4(1) -- -- -- E.002

Cyanazine 42 23.8(10) 7.1(3) E.003 E.008 .018

Deethylatrazine 42 40.5(17) -- M E0.004 E0.005

EPTC 42 14.3(6) 2.4(1) E0.001 E.002 .016

Metolachlor 42 40.5(17) -- E.002 E.004 E.009

Prometon 42 28.6(12) -- M M E.01

Simazine 42 2.4(1) -- -- -- E.003

Tebuthiuron 42 4.8(2) -- M -- E.01

Triallate 42 47.6(20) 2.4(1) E.001 E.003 .010

Trifluralin 42 2.4(1) -- -- -- E.002

Site YS

Acetochlor 44 4.5(2) 4.5(2) .015 -- .016

Alachlor 44 2.3(1) -- -- -- E.003

Atrazine 44 84.1(37) 15.9(7) E.002 .006 .055

Carbaryl 44 2.3(1) -- -- -- E.005

Carbofuran 44 2.3(1) 2.3(1) -- -- E.021

Chlorpyrifos 44 6.8(3) -- E.002 E.002 E.002

Cyanazine 44 22.7(10) 4.5(2) E.003 E.006 .021

Table 10. Statistical summary of detections and concentrations of pesticides for fixed sites in the Yellowstone River Basin, 

1999-2001.—Continued.

Pesticide

Compound

Number of 

samples

Percent of 

samples, 

compound 

identified

(number of 

detections)

Percent of 

samples, 

concentration

greater than or 

equal to 0.01 μg/L

(number of 

detections)

Statistical summary of detections

Minimum, 

in μg/L

Median, 

in μg/L

Maximum, in 

μg/L

66 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
Site YS—Continued

DCPA 44 4.5(2) -- E.001 -- E.002

Deethylatrazine 44 52.3(23) -- E.001 E.004 E.006

EPTC 44 13.6(6) 2.3(1) E.001 E.004 .010

Malathion 44 2.3(1) -- -- -- .006

Metolachlor 44 59.1(26) 4.5(2) M .005 .017

Prometon 44 29.5(13) 2.3(1) M E.01 E.01

Simazine 44 4.5(2) 4.5(2) .013 -- .014

Tebuthiuron 43 9.3(4) 2.3(1) M E.01 .02

Triallate 44 38.6(17) -- E.001 E.002 .008

All samples

Acetochlor 136 1.5(2) 1.5(2) .015 -- .016

Alachlor 136 0.7(1) -- -- -- E.003

Atrazine 135 74.8(101) 9.6(13) E.002 E.006 .328

Benfluralin 136 .7(1) -- -- -- E.003

Carbaryl 136 2.2(3) -- E.004 E.005 E.008

Carbofuran 136 2.9(4) 2.9(4) E.013 E.020 E.034

Chlorpyrifos 136 5.1(7) -- E.001 E.002 E.004

Cyanazine 136 17.6(24) 5.1(7) E.003 E.007 .021

DCPA 136 3.7(5) -- E.001 E.002 E.002

Deethylatrazine 136 39.7(54) 0.7(1) M E.004 E.019

EPTC 136 11.0(15) 2.2(3) E.001 E.003 .021

Ethalfluralin 136 1.5(2) -- E.002 -- E.003

Malathion 136 4.4(6) 2.9(4) .006 .011 .025

Metolachlor 136 38.2(52) 2.2(3) M E.004 .019

Prometon 136 23.5(32) .7(1) E.001 E.004 E.011

Simazine 136 3.7(5) 2.2(3) E.003 .013 .014

Tebuthiuron 135 8.9(12) .7(1) M E.01 .02

Terbufos 136 .7(1) .7(1) -- -- .031

Triallate 136 37.5(51) .7(1) E.001 E.003 .01

Trifluralin 136 4.4(6) -- E.001 E.002 .005

Table 10. Statistical summary of detections and concentrations of pesticides for fixed sites in the Yellowstone River Basin, 

1999-2001.—Continued.

Pesticide

Compound

Number of 

samples

Percent of 

samples, 

compound 

identified

(number of 

detections)

Percent of 

samples, 

concentration

greater than or 

equal to 0.01 μg/L

(number of 

detections)

Statistical summary of detections

Minimum, 

in μg/L

Median, 

in μg/L

Maximum, in 

μg/L

Fixed-Site Water Quality, 1999-2001 67
unclear, however, because criteria have limitations in their use 

in evaluating potential risks of pesticides in streams. Criteria 

have not been established for 20 of the pesticides and breakdown products analyzed for this study, including 5 pesticides 

(acetochlor, benfluralin, deethylatrazine, EPTC, ethalfluralin) 

that were detected in stream samples in the YELL. In addition, 

human-health and aquatic-life criteria generally are established based on toxicity tests conducted for a single compound; however, most of the YELL samples contained two or 

more compounds. In addition, the aquatic-life criteria do not 

account for the potential combined effects of pesticides and 

other stressors, such as temperature fluctuations (Larson and 

others, 1999).

Temporal Variability

The occurrence of pesticides in streams is related to the 

time of pesticide application and precipitation or irrigation 

events. Most pesticides, particularly herbicides, are applied 

during short seasonal periods; for example, preemergent herbicides are applied just before planting or an insecticide may be 

applied during a certain period to control a specific pest. The 

seasonal application of pesticides, followed by the first runoff 

event from rain or irrigation, is the primary source for pesticide transport to streams (Larson and others, 1997).

The temporal variations of pesticide concentrations 

were examined using atrazine, the most commonly detected 

pesticide, in relation to streamflow for site YF and site YS, 

which were the sites with the most continuous sampling 

for pesticides (fig. 37). Atrazine generally is applied for 

early, preplant surface treatments because of operational use 

limitations for Wyoming and Montana. Atrazine also may be 

applied to stubble ground after wheat harvest in wheat-cornfallow crop rotations in the Wyoming part of the basins (U.S. 

Environmental Protection Agency, 2002e). The largest atrazine 

concentration (0.328 μg/L) in a single sample occurred during 

April 1999 at site YF, which may reflect runoff after preplant 

treatment. Small concentrations during late spring at both sites 

during 1999 and 2000 probably are caused by dilution during 

snowmelt runoff. Samples with concentrations larger than 

0.01 μg/L generally occurred during April to August, which 

typically coincides with the growing season. The low-level, 

but persistent, presence of atrazine during fall and winter 

months indicates that ground water probably is contributing 

to concentrations in streams because irrigation has ceased and 

rainfall runoff events are infrequent. The presence of atrazine 

in ground water has been reported for the YELL (Eddy-Miller, 

1998; Eddy-Miller and Norris, 2001; Peterson and others, 

2004).

Suspended Sediment

Suspended-sediment concentrations in streams were 

analyzed as part of the YELL fixed-site network. Sediments 

in streams are part of the natural fluvial processes of erosion, transport, and deposition (siltation). As with chemical 

constituents in streams, however, excessive concentrations of 

sediment can be cause for concern. These concerns include 

degradation of water quality and aquatic habitat, and reduction of reservoir capacity. For example, siltation is the leading 

pollutant in impaired rivers and streams in the United States 

(U.S. Environmental Protection Agency, 2000a). In addition 

to siltation, sediment in streams can facilitate the transport 

of other water-quality degradates, including nutrients, trace 

elements, and pesticides. Conversely, decreased sediment 

delivery also can affect aquatic habitat. Diminished sediment 

transport—either through removal of the sediment source or 

through reduction of the streamflows transporting the sediment—can result in channel changes including increased 

aggradation or degradation and changes in particle-size 

distribution. Decreased suspended sediment can be detrimental 

to endemic fish; for example, turbid water is believed to be 

essential habitat for the endangered pallid sturgeon, a species 

endemic to the YELL (Duffy and others, 1995).

Results of suspended-sediment analyses are summarized 

in this report using descriptive statistics of sample concentrations. Flow-weighted mean concentrations and estimated total 

annual loads and yields also are summarized. Yield is the load 

per unit drainage area upstream from a site. Large reservoirs 

are sediment sinks where decreased velocities result in settling 

of particulates and removal of nearly all suspended sediment 

(Meade and others, 1990, p. 267). Thus, after construction 

of a large reservoir, that part of the basin upstream from the 

reservoir does not contribute to the suspended-sediment flux 

at a site downstream. In this report, yields for the fixed sites 

were computed using only that part of the basin drainage areas 

downstream from large reservoirs and reported as reservoiradjusted yields.

68 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
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Figure 37. Relation between atrazine concentrations and streamflow for site YF and site YS in the 

Yellowstone River Basin, 1999-2001.

Fixed-Site Water Quality, 1999-2001 69
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Figure 38. Statistical summary of suspended-sediment concentrations for fixed sites in the Yellowstone River Basin, 

1999-2001.

Concentrations

Median suspended-sediment concentrations in samples 

from the fixed sites ranged from 2.0 mg/L to 421 mg/L 

(fig. 38). Suspended-sediment concentrations generally were 

smallest for the indicator sites in mountainous areas with 

resistant geology, site SB and site T, and largest for the major 

tributary integrator site P. On the mainstem Yellowstone River, 

suspended-sediment concentrations generally increased downstream from site YCS to site YS. The range of suspended-sediment concentrations varied substantially among the fixed sites. 

The interquartile range (IQR) of concentrations varied from 

4 mg/L for site T to 1,490 mg/L for site P.

Flow-weighted mean suspended-sediment concentrations at YELL fixed sites generally increased with increasing 

drainage area. Base-10 logarithms of flow-weighted mean 

concentrations and reservoir-adjusted drainage areas (in mi2) 

were well correlated (Pearson’s r = 0.88, p-value = 0.022) 

for the tributary sites (fig. 39A). Different relations between 

flow-weighted mean suspended-sediment concentrations and 

drainage area were observed for the tributary and mainstem 

sites. Flow-weighted mean suspended-sediment concentrations 

also increased downstream from site YCS to site YS.

Flow-weighted mean suspended-sediment concentrations were correlated with geologic and soil characteristics. 

Base-10 logarithms of flow-weighted mean concentrations and 

the adjusted area of Tertiary-period sedimentary rocks (in mi2) 

were well correlated (Pearson’s r = 0.94, p-value = 0.0048) for 

the tributary sites (fig. 39B). For the mainstem sites, flowweighted mean suspended-sediment concentrations generally 

increased with increasing area of Tertiary-period sedimentary 

rocks.

Suspended-sediment concentrations also were correlated to soil characteristics. Specifically, soil erodibility is the 

susceptibility of soil particles to detachment and movement 

by water. The soil erodibility factor K is used in empirical 

relations to calculate soil loss by water (U.S. Department of 

Agriculture, 2000). Basin soil erodibility was determined for 

the fixed sites using data compiled by Schwarz and Alexander 

(1995). Base-10 logarithms of flow-weighted mean suspended-sediment concentrations were correlated (all sites: τ = 

0.61, p-value = 0.02; tributary sites: τ = 0.80, p-value = 0.05) 

with reservoir-adjusted area-weighted mean soil erodibility 

factor (in percent) (fig. 39C).

Flow-weighted mean suspended-sediment concentrations 

also were correlated to land-cover characteristics. In general, base-10 logarithms of flow-weighted mean suspendedsediment concentrations were most strongly correlated with 

increasing reservoir-adjusted rangeland (in percent) (fig. 39D; 

Pearson’s r = 0.88, p-value = 0.0008). Geologic characteristics 

probably are a factor in the positive correlation of suspendedsediment concentrations and rangeland area. Base-10 logarithms of reservoir-adjusted, Tertiary-period sedimentary rocks 

(in percent) were strongly correlated with reservoir-adjusted 

rangeland (in percent) (Pearson’s r = 0.92, p-value = 0.0004).

70 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
Table 11. Estimated water year and average total annual suspended-sediment loads and reservoir-adjusted yields for 

fixed sites in the Yellowstone River Basin, 1999-2001.

[--, insufficient data.]

Site 

report 

identifier 

(fig. 2)

Estimated total annual load (tons)

Estimated total annual yield

(tons per square mile)

1999 2000 2001 Average 1999 2000 2001 Average

SB -- 3,600 1,500 12,600 -- 130 52 290

YCS 600,000 220,000 62,000 290,000 230 85 24 110

CF 1,400,000 780,000 390,000 840,000 670 380 190 420

YB 1,700,000 870,000 350,000 990,000 150 74 30 84

B 6,500,000 500,000 220,000 2,400,000 810 63 28 300

YF 2,900,000 1,100,000 510,000 1,500,000 140 54 25 73

T 5,500 3,400 470 3,100 27 17 2 15

LP 47,000 2,000 13,000 21,000 38 2 10 17

P 9,100,000 670,000 730,000 3,500,000 690 51 55 270

YS 7,600,000 3,500,000 2,000,000 4,400,000 150 71 40 88

1

Load is average of water years 2000 and 2001 only.

2

Yield is average of water years 2000 and 2001 only.

Temporal Variability

Estimated daily suspended-sediment concentrations 

using LOADEST were evaluated by season to assess temporal variations in concentrations for YELL fixed sites. Suspended-sediment concentrations generally were largest during 

April–June for all fixed sites (fig. 40). Suspended-sediment 

concentrations were correlated with streamflow. Correlation 

coefficients (Pearson’s r) for base-10 logarithms ranged from 

0.62 (site LP) to 0.90 (site YCS) (p-value < 0.0001 all correlations). On average, the largest streamflows of the year occur 

during April–June, resulting from mountain snowmelt runoff. 

Similarly, suspended-sediment concentrations were smallest 

during October–December and January–March when streamflows and sediment inputs are small. During the winter, some 

of the streams are ice covered, fewer rainstorms result in less 

overland runoff, and surface irrigation return flows are small 

to nonexistent. For fixed sites with substantial portions of their 

drainage area in the plains or basins of the YELL, rainstorms 

during July–September can result in large streamflows with 

large suspended-sediment concentrations. During 2000 and 

2001, however, precipitation was much lower than normal, 

resulting in much lower than normal streamflows and possibly 

lower suspended-sediment concentrations during July–September.

Estimated Loads and Yields

Estimated suspended-sediment loads and yields at YELL 

fixed sites were computed to describe the sediment flux for 

streams in the YELL (table 11). Because suspended-sediment 

load is a function of streamflow and differences in streamflows 

between the fixed sites are large, differences in suspendedsediment loads between the same fixed sites also are large. For 

example, average annual suspended-sediment loads for minor 

tributary indicator sites (site SB, site T, and site LP) are at least 

an order of magnitude smaller than average annual suspendedsediment loads for major tributary integrator sites (site CF, 

site B, and site P) and the mainstem integrator sites (site YCS, 

site YB, site YF, and site YS). Average annual streamflows at 

site SB, site T, and site LP also are proportionally smaller than 

streamflows at the other fixed sites. Similarly, on the mainstem 

Yellowstone River, average annual loads increased downstream with increasing streamflows from site YCS to site YS. 

For the tributary integrator sites, average annual suspendedsediment loads were similar to the mainstem sites; however, 

mean annual streamflows were smaller when compared as a 

group with the mainstem sites (table 2).

Estimated mean annual suspended-sediment yields 

(table 11) generally decreased with increasing drainage area 

(table 1) within site groups for the indicator sites and major 

Fixed-Site Water Quality, 1999-2001 71
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Figure 39. Flow-weighted mean suspended-sediment concentration relation to reservoir-adjusted A, drainage area; B, Tertiaryperiod sedimentary rocks; C, soil-erodibility factor; and D, rangeland for fixed sites in the Yellowstone River Basin, 1999-2001.

tributary integrator sites. Reservoir-adjusted mean annual 

suspended-sediment yields were largest for site CF, site B, and 

site P on major tributaries, which have large drainage areas 

with mixed geology that includes Tertiary-period sedimentary 

rocks. Langbein and Schumm (1958) developed an empirical relation between suspended-sediment yield and mean 

annual precipitation. The result was a relation where sediment 

yield is a maximum for basins where annual precipitation is 

between about 10 and 14 inches. For basins receiving less 

than about 10 inches of precipitation a year, sediment yield is 

less because of a deficiency of streamflow runoff. For basins 

receiving more than about 14 inches per year, increased vegetation density limits sediment availability. Estimated mean 

annual suspended-sediment yields for the YELL fixed sites 

for the period 1999-2001 were less than would be estimated 

by the Langbein-Schumm relation (fig. 41A); only site CF 

was within about one standard deviation (reported as about 30 

percent, Langbein and Schumm, 1958, p. 1077) of the relation. 

Streamflows during water years 2000 and 2001 were smaller 

than average; thus, estimated annual mean suspended-sediment yields for the period 1999-2001 probably are smaller 

than average. A comparison of sediment yields for water year 

1999 indicated good correlation for site CF, site B, and site P 

with the Langbein-Schumm relation (fig. 41B).

72 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
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Figure 40. Seasonal statistical summary of LOADEST estimated daily suspended-sediment concentrations for fixed 

sites in the Yellowstone River Basin, 1999-2001.

Fixed-Site Water Quality, 1999-2001 73
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Figure 41. Suspended-sediment yield related to mean annual 

precipitation for A, 1999-2001; and B, 1999 for fixed sites in 

theYellowstone River Basin.

Summary

The National Water-Quality Assessment Program of the 

U.S. Geological Survey initiated an assessment in 1997 of the 

quality of water resources in the Yellowstone River Basin. The 

Yellowstone River Basin has a drainage area of 70,100 square 

miles and extends from central Wyoming north to include 

most of southeastern Montana and a small part of western 

North Dakota. The basin is largely undeveloped; rangelands, 

which consist of herbaceous grasslands and shrublands, compose about 74 percent of the basin and forested land compose 

about 14 percent. Agricultural and urban areas compose less 

than 10 percent of the basin.

Water-quality samples regularly were collected during 

1999-2001 at 10 fixed sites on streams representing the major 

environmental settings of the basin. Integrator sites, which 

are heterogeneous in land use and geology, were established 

on the mainstem of the Yellowstone River from Corwin 

Springs, Montana to Sidney, Montana (4 sites) and on three 

major tributaries—Clarks Fork Yellowstone River (1 site), the 

Bighorn River (1 site), and the Powder River (1 site). Indicator 

sites, which are more homogeneous in land use and geology 

than the integrator sites, were located on minor tributaries 

with important environmental settings—Soda Butte Creek in 

a mineral resource area (1 site), the Tongue River in a forested 

area (1 site), and the Little Powder River in a rangeland area 

(1 site). Water-quality sampling frequency generally was at 

least monthly and sampling included field measurements and 

laboratory analyses of fecal-indicator bacteria, major ions, 

dissolved solids, nutrients, trace elements, pesticides, and 

suspended sediment.

Annual streamflows at all of the sites, except the Little 

Powder River, are dominated by a snowmelt peak or peaks 

during late spring through early summer with generally low 

variability throughout the rest of the year. Streamflows for the 

Little Powder River are more variable in response to precipitation events. The hydrologic conditions varied during the study 

period from above average streamflow during water year 1999 

to substantially less than average streamflow in response to 

drought conditions during water years 2000 and 2001.

Median concentrations of fecal coliform and Escherichia 

coli were largest for basins that were predominantly rangeland and smallest for basins that were predominantly forested. 

Fecal-coliform concentrations exceeded the U.S. Environmental Protection Agency recommended limit for a single 

sample of 400 colonies per 100 milliliters in 2.6 percent of all 

samples. Escherichia coli concentrations exceeded the 

U.S. Environmental Protection Agency recommended limit 

for a single sample of 298 colonies per 100 milliliters for 

moderate use, full-body contact recreation in 7.6 percent of 

all samples. Escherichia coli concentrations for the rangeland indicator site on the Little Powder River exceeded the 

U.S. Environmental Protection Agency recommended limit of 

298 colonies per 100 milliliters in 27.8 percent of the samples. 

Concentrations of fecal coliform and Escherichia coli signifi74 Water-Quality Assessment of the Yellowstone River Basin, Montana and Wyoming—Water Quality of Fixed Sites
cantly varied by season (p-value <0.001); the smallest median 

concentrations were during January–March and the largest 

median concentrations were during April–June.

Variations in water type in the basin are reflective of the 

diverse geologic terrain in the Yellowstone River Basin. Water 

type of the Yellowstone River changed from a mixed-cation 

bicarbonate type upstream to a mixed-cation sulfate type 

downstream, where proportionally more of the geology is Tertiary-period sedimentary rocks. The water type of Soda Butte 

Creek and the Tongue River was calcium bicarbonate. These 

two sites are in forested and mountainous areas where igneous 

rocks and Paleozoic-era and Mesozoic-era sedimentary rocks 

are the dominant geologic groups. The water type of the Little 

Powder River was sodium sulfate. The Little Powder River 

originates in the plains and geology of the basin is nearly 

homogenous with Tertiary-period sedimentary rocks.

Dissolved-solids concentrations ranged from fairly dilute 

in Soda Butte Creek, which had a median concentration of 

118 milligrams per liter, to concentrated in the Little Powder 

River, which had a median concentration of 2,840 milligrams 

per liter. Dissolved-solids concentrations at some sites varied 

by sampling period and annually in response to variations in 

streamflow. Significant differences in dissolved-solids concentrations by sampling period were determined for sites on Soda 

Butte Creek, the Yellowstone River (four sites), the Clarks 

Fork Yellowstone River, and the Tongue River (p-values 

<0.05) as a result of snowmelt runoff. Significant differences 

in annual dissolved-solids concentrations were determined for 

sites on the Clarks Fork Yellowstone River; Yellowstone River 

at Billings, Montana; Bighorn River; and the Powder River (pvalues <0.05) as a result of annual variations in streamflow.

Nutrient concentrations generally were small and reflect 

the relatively undeveloped conditions in the basin. Ammonia 

concentrations generally were largest in samples collected 

from the Yellowstone River at Corwin Springs, Montana, 

which is downstream from Yellowstone National Park and 

receives discharge from geothermal waters that are high in 

ammonia. Some correlations were made with anthropogenic 

factors. Median dissolved-nitrate concentrations in all samples 

from the fixed sites ranged from 0.04 milligram per liter to 

0.54 milligram per liter. Flow-weighted mean dissolved-nitrate 

concentrations were positively correlated with increasing agricultural land use and rangeland on alluvial deposits upstream 

from the sites and negatively correlated with increasing 

forested land. Median total-phosphorus concentrations ranged 

from 0.007 to 0.18 milligram per liter. Median total-phosphorus concentrations exceeded the U.S. Environmental Protection Agency’s recommended goal of 0.10 milligram per liter 

for preventing nuisance plant growth for samples collected 

from the Bighorn River, Powder River, and Yellowstone River. 

Total-phosphorus concentrations were positively correlated 

with sediment concentrations. Sediment derived from sedimentary rocks that are of marine origin probably is the source 

of the phosphorus.

Seasonal variations were observed in nutrient concentrations. Dissolved-nitrate concentrations generally were largest 

during October to March when plant uptake of nitrate is lowest. In contrast, total-phosphorus concentrations were largest during April–June when sediment concentrations, which 

contribute to the total-phosphorus concentrations, are largest.

Concentrations of trace elements generally were small in 

samples for sites in the Yellowstone River Basin. Soda Butte 

Creek, which is in a mineral resource area with historical mining in the basin upstream from the sampling site, did not have 

elevated concentrations of trace elements compared to other 

sites. On the Yellowstone River, median concentrations of dissolved arsenic of 21 micrograms per liter at Corwin Springs, 

Montana, and 10.5 micrograms per liter at Billings, Montana, 

exceeded the drinking-water Maximum Contaminant Level of 

10 micrograms per liter. Geothermal waters from Yellowstone 

National Park are a significant source of arsenic in the Yellowstone River; dissolved-arsenic concentrations decreased in the 

downstream direction. Concentrations of dissolved selenium 

were largest in the Powder River, ranging from 0.48 microgram per liter to 4.6 micrograms per liter. Concentrations were 

smaller than the chronic aquatic-life criterion of 5 micrograms 

per liter; however, other studies have shown that concentrations of total selenium larger than 2 micrograms per liter may 

produce adverse effects on some fish and wildlife species.

Pesticide concentrations generally were small for three 

sites on the Yellowstone River, one site on the Clarks Fork 

Yellowstone River, and one site on the Bighorn River. Herbicides were more frequently detected than insecticides. 

Atrazine was the most commonly detected herbicide and 

was detected in 74.8 percent of all samples. The second most 

frequently detected herbicide was a breakdown product of 

atrazine, deethylatrazine, which was present in 39.7 percent 

of all samples. Chlorpyrifos was the most commonly detected 

insecticide and was detected in 5.1 percent of all samples. 

Concentrations of all compounds generally were smaller 

than 0.01 microgram per liter and substantially smaller than 

aquatic-life or human-health criteria. Mixtures of two or more 

pesticides were detected in 75 percent of the samples.

Suspended-sediment concentrations were seasonally 

variable and were largest during April–June during snowmelt 

runoff. Suspended-sediment concentrations were smallest 

for the fixed sites on Soda Butte Creek and the Tongue River 

because of the resistant geology in the mountainous settings. 

Reservoir-adjusted yields were largest for the Clarks Fork Yellowstone River, Bighorn River, and the Powder River, which 

have large drainage areas with mixed geology that includes 

Tertiary-period sedimentary rocks. On the Yellowstone River, 

suspended-sediment loads increased in the downstream direction.

Summary 75
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