Water Quality

in the Yakima River Basin 

Washington, 1999–2000

U.S. Department of the Interior

U.S. Geological Survey

Circular 1237
Points of Contact and Additional Information

The companion Web site for NAWQA summary reports:

http://water.usgs.gov/nawqa/nawqa_sumr.html

Other NAWQA summary reports

River Basin Assessments

Acadian-Pontchartrain Drainages (Circular 1232)

Albemarle-Pamlico Drainage Basin (Circular 1157)

Allegheny and Monongahela River Basins (Circular 1202)

Apalachicola-Chattahoochee-Flint River Basin (Circular 1164)

Central Arizona Basins (Circular 1213)

Central Columbia Plateau (Circular 1144)

Central Nebraska Basins (Circular 1163)

Connecticut, Housatonic and Thames River Basins (Circular 1155)

Cook Inlet Basin (Circular 1240)

Delaware River Basin (Circular 1227)

Delmarva Peninsula (Circular 1228)

Eastern Iowa Basins (Circular 1210)

Georgia-Florida Coastal Plain (Circular 1151)

Great and Little Miami River Basins (Circular 1229) 

Great Salt Lake Basins (Circular 1236)

Hudson River Basin (Circular 1165)

Island of Oahu (Circular 1239)

Kanawha - New River Basins (Circular 1204)

Lake Erie - Lake Saint Clair Drainages (Circular 1203)

Long Island - New Jersey Coastal Drainages (Circular 1201)

Lower Illinois River Basin (Circular 1209)

Lower Susquehanna River Basin (Circular 1168)

Lower Tennessee River Basin (Circular 1233)

Las Vegas Valley Area and the Carson and Truckee River Basins (Circular 1170)

Mississippi Embayment (Circular 1208)

Mobile River Basin (Circular 1231)

New England Coastal Basins (Circular 1226)

Northern Rockies Intermontane Basins (Circular 1235)

Ozark Plateaus (Circular 1158)

Potomac River Basin (Circular 1166)

Puget Sound Basin (Circular 1216)

Red River of the North Basin (Circular 1169)

Rio Grande Valley (Circular 1162)

Sacramento River Basin (Circular 1215)

San Joaquin-Tulare Basins (Circular 1159)

Santa Ana Basin (Circular 1238)

Santee River Basin and Coastal Drainages (Circular 1206)

South-Central Texas (Circular 1212)

South Platte River Basin (Circular 1167)

Southern Florida (Circular 1207)

Trinity River Basin (Circular 1171)

Upper Colorado River Basin (Circular 1214)

Upper Illinois River Basin (Circular 1230)

Upper Mississippi River Basin (Circular 1211)

Upper Snake River Basin (Circular 1160)

Upper Tennessee River Basin (Circular 1205)

Western Lake Michigan Drainages (Circular 1156)

White River Basin (Circular 1150)

Willamette Basin (Circular 1161)

Yellowstone River Basin (Circular 1234)

National Assessments

The Quality of Our Nation‘s Waters—Nutrients and Pesticides (Circular 1225)

The Quality In the Nation’s Streams and Aquifers—Overview of Selected 

Findings, 1991-2001 (Circular 1265)

Yakima River Basin contact and Web site:

USGS State Representative

U.S. Geological Survey

Water Resources Discipline

10615 S.E. Cherry Blossom Drive

Portland, OR 97216–3159

e-mail: info-or@usgs.gov

http://oregon.usgs.gov/yakima/

National NAWQA Program:

Chief, NAWQA Program

U.S. Geological Survey

Water Resources Discipline

12201 Sunrise Valley Drive, M.S. 413

Reston, VA 20192

http://water.usgs.gov/nawqa/

Front cover: Wapato Irrigation Canal Diversion (right) from the Yakima River (photograph by Henry Ngan). 

Back cover: Left to right, grapes, pears, apples (photographs by Yakima NAWQA Staff). 
U.S. Department of the Interior

U.S. Geological Survey

Water Quality in the Yakima River Basin, 

Washington, 1999–2000

By Gregory J. Fuhrer, Jennifer L. Morace, Henry M. Johnson, Joseph F. Rinella, 

James C. Ebbert, Sandra S. Embrey, Ian R. Waite, Kurt D. Carpenter, 

Daniel R. Wise, and Curt A. Hughes

Circular 1237
Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Fuhrer, G.J., Morace, J.L., Johnson, H.M., Rinella, J.F., Ebbert, J.C., Embrey, S.S., Waite, I.R., Carpenter, K.D., 

Wise, D.R., and Hughes, C.A., 2004, Water Quality in the Yakima River Basin, Washington, 1999–2000: 

U.S. Geological Survey Circular 1237, 34 p.

U.S. Geological Survey, Reston, Virginia: 2004

U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

World Wide Web: http://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government
Contents

National Water-Quality Assessment Program ......................................................... iv 

Summary of Major Findings .............................................................................. 1

Introduction to the Yakima River Basin ............................................................... 3

Major Findings ............................................................................................. 8

High concentrations of nutrients result from agricultural activities ........................ 8

NATIONAL PERSPECTIVE—Small agricultural watersheds had large 

percentages of elevated concentrations of nutrients ........................... 8

NATIONAL PERSPECTIVE—Ground-water discharges are a major source of 

surface-water nitrate in irrigated areas of the Western United States ...... 10

Bacteria indicate the presence of fecal contamination ....................................... 12

Arsenic, a known human carcinogen, was detected at levels of concern .................. 13

Historically used pesticides are still present in the Yakima River Basin ..................... 14

Currently used pesticides were routinely detected ............................................. 17

Aquatic communities are affected by poor water-quality and habitat conditions 

in intensely agricultural areas ......................................................... 23

Study-Unit Design ....................................................................................... 27

References Cited .......................................................................................... 30

Glossary ................................................................................................... 32

Appendix—Water Quality Data from the Yakima River Basin in a National Context ............ 33
iv

National Water-Quality Assessment Program

In 1991, the U.S. Congress began to appropriate funds to the USGS to conduct the National 

Water-Quality Assessment (NAWQA) Program. Since that time, NAWQA has evaluated the 

quality of streams, ground water, and aquatic ecosystems in more than 50 major river basins 

and aquifer systems across the Nation, referred to as “Study Units.” As indicated on the map, 

timing of the assessments varies within the program’s rotational design: about one-third of all 

Study Units are intensively investigated for 3 to 4 years, which is followed by 6 to 7 years of 

low-level monitoring.

In 2001, the NAWQA Program entered its second decade of investigations and an intensive reassessment of water conditions was begun to determine trends, based on 10 years of 

comparable monitoring data collected at selected streams and ground-water sites. The next 10 

years of study also will fill critical gaps in characterizing water-quality conditions, and increase 

understanding of processes that control water-quality conditions, which will better establish 

critical links among sources of contaminants, their transport through the hydrologic system, and 

the potential effects of contaminants on ecological health and on the quality of drinking water.

The Yakima River Basin assessment is one of two special studies activated in 1999 for the 

purpose of piloting study techniques for use in NAWQA’s second decade of investigations. Specifically, the Yakima River Basin assessment piloted techniques to (1) monitor trends in surface 

water, (2) evaluate transport of agricultural chemicals to streams, and (3) assess the possible 

effects of agricultural chemicals from irrigated farmland on stream ecosystems. The Yakima 

River Basin assessment builds upon monitoring data that the NAWQA Program collected 

previously in the basin from 1987 through 1991 as part of pilot studies conducted before full 

program implementation in 1991. These data provided a baseline characterization of pesticides, 

nutrients, trace elements, suspended solids, and aquatic life in streams.

1991–95

1994–98

1997–2001

Not yet scheduled

HighPlains Regional

GroundWaterStudy,

1999–2004

NAWQA Study Units—

Assessment schedule

Yakima River Basin

1999–2001
What kind of water-quality information does the NAWQA 

Program provide?

The NAWQA Program assesses the quality of the Nation’s water resources, which is integrally 

linked to the long-term availability of water that is clean and safe for drinking and recreation 

and also suitable for industry, irrigation, and habitat for fish and wildlife. Assessments in the 

major river basins and aquifer systems include water resources available to more than 60 percent of the population and cover about one-half of the land area of the conterminous United 

States. Scientists in the NAWQA Program work with partners in government, research, and 

public-interest groups to assess the spatial extent of water-quality conditions, the way water 

quality changes with time, and the effects of human activities and natural factors on water 

quality. This information is useful for guiding water-management and protection strategies, 

research, and monitoring in different hydrologic and land-use settings across the Nation.

Water-quality assessments by a single program cannot possibly address all of the Nation’s 

water-resources needs and issues. Therefore, it is necessary to define the most pertinent context 

for NAWQA information. 

• Total resource assessment—NAWQA assessments are long-term and interdisciplinary, 

and include information on water chemistry, hydrology, land use, stream habitat, and 

aquatic life. Assessments are not limited to a specific geographic area or water-resource 

problem at a specific time. Therefore, the findings describe the general health of the total 

water resource, as well as emerging water issues, thereby helping managers and decision 

makers to set priorities.

• Source-water characterization—Assessments focus on the quality of the available, 

untreated resource and thereby complement (rather than duplicate) Federal, State, and 

local programs that monitor drinking water. Findings are compared to drinking-water 

standards and health advisories, if available, as a way to characterize the resource. 

• Compounds studied—Assessments focus on chemical compounds that have well-established methods of investigation. It is not financially or technically feasible to assess all 

the contaminants in our Nation’s waters. In general, the NAWQA Program investigates 

those pesticides, nutrients, volatile organic compounds, and metals that have been or are 

currently used commonly in agricultural and urban areas across the Nation. A complete 

list of compounds studied is on the NAWQA web site at http://water.usgs.gov/nawqa.

• Detection relative to risk—Compounds are measured at very low concentrations, often 

10 to 100 times lower than Federal or State standards and health advisories. Detection of 

compounds, therefore, does not necessarily translate to risks to human health or aquatic 

life. However, these analyses are useful for identifying and evaluating emerging issues, 

such as the presence of new contaminants or the occurrence of mixtures, as well as for 

tracking contaminant levels over time.

• Consistent approach—Assessments are guided by a nationally consistent study design 

and uniform methods of sampling and analysis. Findings thereby pertain not only to 

water quality of a particular stream or aquifer, but also contribute to the larger picture 

of how and why water quality varies regionally and nationally. This consistent approach 

helps to determine if a water-quality issue is isolated or pervasive. It also allows direct 

comparisons of how human activities and natural processes affect water quality in the 

Nation’s diverse environmental settings. 

v
vi

This report contains the major findings of a 1999–2000 assessment of water quality in streams 

and drains in the Yakima River Basin. It is one of a series of reports by the NAWQA Program 

that present major findings on water resources in 51 major river basins and aquifer systems 

across the Nation. 

In these reports, water quality is assessed at many scales—from large rivers that drain 

lands having many uses to small agricultural watersheds—and is discussed in terms of local, 

State, and regional issues. Conditions in the Yakima River Basin are compared to those found 

elsewhere and to selected national benchmarks, such as those for drinking-water quality and the 

protection of aquatic organisms. 

This report is intended for individuals working with water-resource issues in Federal, 

Tribal, State, or local agencies; universities; public interest groups; or the private sector. The 

information will be useful in addressing a number of current issues, such as source-water 

protection, pesticide registration, human health, drinking water, hypoxia and excessive growth 

of algae and plants, the effects of agricultural land use on water quality, and monitoring and 

sampling strategies. This report is also for individuals who wish to know more about the quality 

of water resources in areas near where they live, and how that water quality compares to the 

quality of water in other areas across the Nation.

Other products describing water-quality conditions in the Yakima River Basin are available. Detailed technical information, data and analyses, methodology, and maps that support the 

findings presented in this report can be accessed from http://or.water.usgs.gov/yakima. Other 

reports in this series and data collected from other basins can be accessed from the national 

NAWQA Web site (http://water.usgs.gov/nawqa). 

“The USGS provides local, 

State, and Federal agencies 

with top quality data and 

accurate reporting that both 

the farming community and 

the environmental community 

can trust. NAWQA’s ability to look at water quality 

over the long term helps to 

evaluate the effectiveness of 

water-management decisions, 

conservation activities, and 

certain farming practices that 

are used to reduce sediment 

and runoff of agricultural 

nutrients and chemicals from 

fields, such as related to 

conservation tillage, buffer 

strips along streams, manure 

management systems, and 

improved irrigation systems. 

High quality and consistent 

monitoring of our natural 

resource is even more critical 

now as we begin to implement 

the 2002 Farm Bill, which 

authorizes over $39 billion 

for conservation—the highest 

level of funding in history for 

conservation programs that 

reduce soil erosion, preserve 

and restore wetlands, clean 

the air and water, and enhance 

wildlife habitat.”

Jeff Loser, 

National Leader for 

Clean Water Programs, 

USDA Natural Resources 

Conservation Service

Water-quality sampling in Granger Drain

Introduction to this Report
Summary of Major Findings 1

Summary of Major Findings

1

The following list highlights the major 

findings from this study of surface-water quality in 

the Yakima River Basin. A wide variety of waterquality topics are addressed—including an update on 

historically used pesticides like DDT and lead arsenate, documentation of the widespread occurrence of 

azinphos-methyl in streams and drains, the potential 

implications of elevated concentrations of arsenic 

and phosphorus on the shallow ground-water system, 

and the positive influence of best management 

practices on some measures of water quality. 

• The extensive irrigation-water delivery and drainage system in the Yakima River Basin greatly controls water-quality conditions and aquatic health 

in agricultural streams, drains, and the Yakima 

River (p. 6). 

• Nitrate and orthophosphate were the dominant 

forms of nitrogen and phosphorus found in the 

Yakima River and its agricultural tributaries. 

These forms of nitrogen and phosphorus are 

highly water soluble, and concentrations in some 

agricultural drains were high enough to support 

nuisance-level growths of algae (p. 8). 

• Concentrations of total phosphorus have begun to 

decrease in the major agricultural tributaries in 

the Lower Valley, but concentrations frequently 

exceeded the U.S. Environmental Protection 

Agency (USEPA) desired goal to prevent nuisance 

growths of aquatic plants in streams (p. 10). 

• The combination of best management practices (BMPs) 

and improvements resulting from total maximum daily load 

(TMDL) assessments have reduced concentrations of sediment and sediment-sorbed contaminants (p. 11). 

• The majority of the agricultural streams and drains sampled 

exceeded the Washington State fecal-coliform bacteria standard for multiple water uses. No samples from the Yakima 

River exceeded the standard (p. 12). 

• Concentrations of fecal-coliform bacteria in the Yakima 

River and the mouths of major tributaries increased with 

increasing suspended sediment, turbidity, nutrients, and 

specific conductivity. Such relations are not as evident in 

smaller agricultural streams and drains (p. 12). 

• Arsenic, a known human carcinogen, was detected in 

agricultural drains at elevated concentrations during the 

nonirrigation season when ground water is the primary 

source of streamflow. Elevated concentrations of arsenic 

during the nonirrigation season are a cause for concern 

since many rural-area residents rely on wells less than 

100 feet deep for their drinking water (p. 13).

The Yakima River flows 214 miles from its headwaters in the forested Cascade 

Foothills to its confluence with the Columbia River near Richland. Inflows 

from streams and drains in the highly productive agricultural areas result in 

degraded water quality in the river. 

• Historically used organochlorine insecticides were 

frequently detected in agricultural streams and drains in 

the Yakima River Basin. DDT, DDE, DDD, dieldrin, and 

heptachlor epoxide exceeded the USEPA chronic waterquality criteria for the protection of aquatic life (p. 14). 

• Concentrations of total DDT in water have decreased since 

1991. The reductions were associated, in large part, with 

decreases in concentrations of suspended sediment and 

sorbed DDT that resulted from the agricultural community’s 

implementation of erosion-controlling BMPs (p. 16).

• Recent data show that the total DDT criterion could be met 

when concentrations of suspended sediment are well above 

7 mg/L, which suggests that the TMDL target for suspended 

sediment could be increased (p. 16).

• Concentrations of azinphos-methyl, an insecticide heavily used on orchards in the Yakima River Basin, routinely 

exceeded the USEPA freshwater chronic-toxicity criterion 

for the protection of aquatic life. The insecticides carbaryl, 

diazinon, and malathion and the herbicide metribuzin infrequently exceeded aquatic-life guidelines (p. 18). 

YAKIMA

Naches

RIVER

River

Moxee Drain

Granger

Drain

EXPLANATION

Streams and drains

Canals

25 Miles

Yakima River

47°30'

46°00'

121°00'

119°30'

Cascade

Range

Columbia Plateau Yakama

Indian

Nation

Yakima

Kiona

Ellensburg

Cle Elum

Toppenish Sunnyside Richland

WASHINGTON

Yakima River Basin

0
2 Water Quality in the Yakima River Basin

No samples collected

No samples collectedNo samples collected

Small Streams

Agricultural

Selected Indicators of Stream-Water Quality

Major Rivers

Mixed

Land Uses

Proportion of samples with detected concentrations greater than or equal

to health-related national guidelines for drinking water, protection of aquatic

life, or the desired goal for preventing nuisance aquatic plant growth

Proportion of samples with detected concentrations less than healthrelated national guidelines for drinking water, protection of aquatic life, or

below the desired goal for preventing nuisance aquatic plant growth

Proportion of samples with no detections

Herbicides and

breakdown products1

Insecticides1

Historically used

pesticides2

Nitrate as nitrogen1

Total

phosphorus2

Arsenic1

Fecal-coliform bacteria2

Special Studies

Agricultural

Drains

Irrigation

Supplies

1 In filtered water. 2 In unfiltered water.

Dormant orchards near Zillah

• Azinphos-methyl was not detected during the nonirrigation 

season and is likely not present in the ground-water system 

(p. 19). 

• Shallow ground water underlying agricultural areas contributes soluble pesticides (mostly herbicides, such as atrazine) 

and nutrients (such as nitrate) to streams all year (p. 9, 19).

• The types of pesticides in streams reflects the types of crops 

grown in the areas they drain. The median number of pesticide detections from the Lower Valley, which has a large 

diversity of crop types, was twice that in the Kittitas Valley, 

which is dominated by hay and pasture land (p. 20).

• Transport of a pesticide to streams depends, in large part, 

on its tendency to dissolve in water or adhere to soil (as 

reflected by the organic-carbon partitioning coefficient, or 

Koc). Pesticides that strongly adhere to soil (high Koc value) 

were detected at a lower frequency than expected for their 

application amounts, while pesticides that weakly adhere 

to soil (low Koc value) were detected at a higher frequency 

than expected for their application amounts (p. 21). 

• The yield of high-Koc (more sorptive) pesticides increased 

in proportion to the amount of rill-irrigated farmland, 

whereas the yield of low-Koc (less sorptive) pesticides was 

relatively constant. Generally, yields of low-Koc pesticides 

were higher than yields of high-Koc pesticides (p. 22).

• As overall stream conditions decline, benthic-invertebrate 

assemblages are less diverse and increasingly composed 

of pollution-tolerant species, and algal assemblages are 

increasingly dominated by species indicative of high concentrations of nutrients (p. 23).

• Algal biomass at most agricultural streams and drains was 

most likely limited by light from high turbidity, by sedimentation that smothers suitable substrate where algae may 

attach, or by herbicides that interfere with algal photosynthesis (p. 24). 

• The dominant types of algae found in agricultural streams 

and drains were those that prefer or require high concentrations of nutrients and alkaline conditions (p. 25). Bing cherries ripening in the Lower Valley
Introduction 3

Introduction to the Yakima River Basin

3

The Yakima River drains 

6,155 square miles of forest, rangeland, 

and agricultural land in south-central 

Washington (fig. 1). The river originates in the Cascade Range and flows 

214 river miles southeastward to the 

Columbia River. The western part of 

the basin contains high peaks and deep 

valleys, and the central and eastern parts 

feature broad valleys and basalt ridges of 

the Columbia Plateau. The western part 

of the basin is predominantly forested, 

whereas the eastern uplands are dominated by sagebrush and grasses. The 

lowlands in the central and eastern basin 

support the agricultural community. The 

Yakama Indian Nation lands, located in 

the southwestern portion of the basin, 

occupy about 15 percent of the basin.

The basin lies in the rain shadow of 

the snow-covered Cascade Range, and 

mean annual precipitation in the basin 

ranges from 140 inches in the mountains 

to less than 10 inches in the eastern 

lowlands. The Yakima River and its largest tributary, the Naches River, are both 

perennial streams with peak runoff during snowmelt, usually in April and May. 

The livelihood for many of the 

basin’s 293,700 residents is based in 

some way on agriculture. The Kittitas 

Valley produces predominantly hay, 

cereal crops, and irrigated pasture, 

whereas the Mid and Lower Valleys 

produce fruits, vegetables, grapes, and 

other specialty crops, such as hops and 

mint. A rapid expansion in the dairy and 

beef industries has occurred in the past 

decade, and Yakima County currently 

ranks first in the State for milk production (Laurie Crowe, South Yakima 

Conservation District, oral commun., 

2003). Yakima County also ranks first 

nationally in the production of apples, 

mint, and hops and ranks fifth in total 

agricultural production. Timber harvesting and recreation are the major uses 

in the forested areas, and cattle grazing 

occurs primarily in the rangeland. Most 

people reside in the Mid and Lower Valleys with about half in rural areas [1, 2]. 

Yakima

Richland

Kittitas

Valley

Mid Valley

Lower Valley

Forest (33%)

Generalized land cover

EXPLANATION

Range (36%)

Cities and towns (2%)

Agriculture (28%)

Water (1%)

Streams and drains

Canals

Yakima River

Boundary of agricultural area

Lakes and reservoirs

Dry wheat

Hops

Irrigated hay

Mixed row crops

Orchards

Orchards and grapes

25 Miles

47°30'

46°00'

121°00'

119°30'

0

Figure 1. The Yakima River integrates many landscapes and ultimately yields most of its flow to canals that supply water for irrigation.

Hops in Mid Valley

Apples Corn Hops

Headwaters of the Yakima River

Roza Canal Diversion

Grapes Dairy Cows

Sunnyside Canal in Lower Valley
4 Water Quality in the Yakima River Basin

Water is the life blood of the 

Yakima River Basin

The Yakima River Basin is one 

of the most intensively irrigated areas 

in the United States. The Bureau of 

Reclamation’s Yakima Project has 

six irrigation districts and one storage division and provides water to 

irrigate almost one-half million acres. 

Its facilities include 6 storage reservoirs, 416 miles of canals, 145 miles 

of drains, 30 pumping plants, and 

2 small hydroelectric plants [3]. 

Surface-water diversions are equivalent to about 60 percent of the mean 

annual streamflow from the basin. 

During the summer, return flows 

downstream from the city of Yakima 

range from 50 to 70 percent of the 

flow in the lower Yakima River. 

The extensive irrigation system, 

coupled with a ready supply of commercial fertilizers and pesticides, has 

made the Yakima River Basin one 

of the most agriculturally productive 

areas in the Nation. In addition to the 

productivity and economic challenges inherent in agriculture, today’s 

farmers face a myriad of environmental concerns related to waterquantity and water-quality issues. 

Runoff from irrigated fields can carry 

sediment, pesticides, nutrients, and 

pathogenic bacteria to waterways, 

which has resulted in degraded water 

quality and violations of water-quality standards. In addition, infiltration 

of irrigation water transports soluble 

agricultural chemicals into the 

ground water. 

Water managers and 

farmers work to balance 

environmental concerns 

and agricultural production

When a waterway fails to 

meet drinking-water standards or 

aquatic-life criteria, the Clean 

Water Act directs the State environmental regulatory agency, in 

this case the Washington Department of Ecology, to perform a 

total maximum daily load (TMDL) 

assessment to develop a cleanup 

plan. Four TMDL assessments 

have been completed for water 

bodies within the Yakima River 

Basin [4]. These assessments focus 

on improving water temperatures 

and reducing concentrations of 

suspended sediment, organochlorine pesticides (including DDT), 

and fecal-coliform bacteria in 

several areas in the basin. 

The Endangered Species Act 

(ESA) also has played a large role 

in shaping policy in the Yakima 

River Basin. Bull trout and summer steelhead are currently listed 

as threatened under the ESA. The 

agricultural community and water 

managers have worked diligently 

to improve the health of the 

Yakima River while maintaining 

a delicate balance with agricultural production. Improvements 

include enhancements to irrigation 

systems, screens to keep fish from 

entering irrigation canals, and 

improvements in fish and riparian

habitat.

The Previous Yakima NAWQA Study during 1987–91

 A great deal was learned about water quality and its effects on aquatic life in the Yakima River Basin during the previous NAWQA study more than a decade ago [5]. The scope of the earlier study was broad and covered surface-waterquality and ecological conditions associated with forested, range, and agricultural land uses. Based on the broad array 

of chemical and ecological measures employed in the previous study, the most affected areas were those associated with 

agriculture, and the measures of concern were pesticides, nutrients, arsenic, and fecal-indicator bacteria. Historically 

used pesticides, like DDT and its metabolites, were common in the surface water, streambed sediment, and aquatic biota. 

Another area of concern was habitat degradation, which resulted in impacts to aquatic insects, fish, and algae. More than 

20 reports and journal articles were produced by the USGS detailing results from the previous sampling period [see http:

//oregon.usgs.gov/yakima/pubs.html for a complete listing]. To build on this previous work, the current assessment focuses 

exclusively on agricultural impacts to surface-water quality, aquatic insects, and algae.

Water-quality 

issues in the 

Yakima River 

Basin are 

affected 

by both 

agricultural 

production and 

environmental 

concerns.

Drain water entering the 

Yakima River

Harvesting alfalfa

Fishing near Cle Elum
Introduction 5

Streamflow can have a large 

effect on water quality

Streamflows in the Yakima River 

Basin can be highly variable from year 

to year and must be considered when 

evaluating the results of water-quality 

assessment studies from one year to 

the next. Depending on the winter 

snowfall in the Cascade Range, summertime flows in the Yakima River 

can be either plentiful or inadequate 

to meet all of the competing water 

demands. Onni Perala, retired chief 

engineer for the Roza Irrigation District, states, “When the water supply 

is plentiful, there is more operational 

spill and more return flow.” The 

normal operation of an open-channel 

irrigation canal results in the return of 

unused water to the Yakima River at 

certain points along the system. This 

water is termed operational spill and 

is usually of higher quality than that 

in the agricultural drains. Operational 

spill has an effect on the water quality 

of the drains and the Yakima River by 

diluting the concentrations of sediment and chemicals that have been 

washed off the fields and into the 

MONTH

Oct Nov Dec Jan Feb Mar Apr May June July Aug Sept

S

T

REA

MFLO

W, IN

C

UBIC FEET PER

SEC

O

N

D

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

Low streamflow

Med year (1977) ian streamflow

year (1980)

Previous

sampling period

(1987–1991)

Current

sampling period

(1999–2000)

MEAN MONTHLY STREAMFLOW

*WATER YEAR is

October through September

WATER YEAR*

197719801991199019871988198919992000

S

T

REA

MFLO

W,

IN

C

UBIC FEET PER

SEC

O

N

D

0

1,000

2,000

3,000

4,000

5,000

ANNUAL MEAN STREAMFLOW

Figure 2. The amount of water measured near the mouth of the Yakima River can vary greatly from year to year. In early spring, the 

streamflow reflects the quantity of water stored in the High Cascades snowpack, while during the dry summer months it reflects the 

quantity of water released from the basin’s storage reservoirs. 

SURFACE WATER

Irrigation

Public Industrial

Ground water

WATER SOURCES

Surface water

GROUND WATER

Irrigation

Public

Industrial

Domestic

waterways. Therefore, water availability 

and potential dilution effects must be 

considered when comparing water quality between years and when examining 

findings from a particular year. Both 

annual mean streamflows and mean 

monthly streamflows during the current 

sampling period were generally higher 

than those of the previous sampling 

period (1987–91), implying that more 

land may have been irrigated during 

the current period, and thus more water 

may have been available to dilute the 

sediment and chemicals washed from 

agricultural fields (fig. 2). 

Surface water supplies most 

water needs in the Yakima 

River Basin

Water withdrawals in the 

Yakima River Basin are primarily 

from surface-water sources, with 

95 percent of surface-water withdrawals used for irrigation (fig. 3). Surface 

water also provides drinking water 

for cities like Yakima and towns such 

as Cle Elum, but most of the drinking water comes from wells. Consequently, the movement of agricultural 

chemicals from the land surface 

into the ground-water system has 

important human-health implications, 

especially for rural residents. Figure 3. Nearly all the water withdrawals in 

the Yakima River Basin are from surface-water 

sources. The primary irrigation season generally 

spans the period March 15 to October 15. 
6 Water Quality in the Yakima River Basin

Basin farmers employ diverse 

irrigation and agricultural 

practices

Water Delivery and Drainage 

Systems

To meet the water demands of 

crops during the hot, dry summer, an 

extensive irrigation network has been 

constructed over the last 100 years. 

Water delivery and water drainage are 

integral components of the irrigation 

network. The water delivery system 

consists of four parts: (1) reservoirs that 

collect winter rain and snowmelt from 

the Cascade Range, (2) the Yakima 

River, which delivers water released 

from the reservoirs to the canal diversions, (3) irrigation canals that convey 

water from the Yakima River to the agricultural lands, and (4) delivery laterals 

that move water from the canals to the 

fields. The water drainage system consists of natural and constructed channels, 

which transport tailwater from farms 

and operational spill from the irrigation 

network back to the Yakima River.

Irrigation Methods

Irrigation in the Yakima River 

Basin is accomplished using one of 

three methods: rill, sprinkler, or drip. 

Rill irrigation is the oldest and simplest 

form in use (fig. 4). In its simplest form, 

an open channel (head ditch) delivers 

water to the high point of a field. Water 

is siphoned out of the head ditch and 

into small furrows cut into the field 

between each crop row. Water exits the 

furrows at the low point of the field, and 

is collected in a second open channel 

(tail ditch). The tailwater in the tail ditch 

is routed to a drain that feeds into the 

regional drainage network. On many rillirrigated fields, the open head ditch has 

been replaced with PVC pipe. Instead of 

siphon tubes, manually operated spigots 

or sliding gates direct irrigation water 

into the furrows.

A variety of sprinkler systems 

are used throughout the Yakima River 

Basin, and each system varies in its 

efficiency of delivering water. Portable 

solid set, wheel lines, and big guns are 

examples of simple systems to operate, 

but typically do not provide a uniform 

coverage of water to a field. They also 

require manual labor to move from place 

to place in a field. Fixed solid set, center 

pivots, and linears are more expensive to 

install and more complex to operate, but 

they provide a more even coverage and 

give the farmer greater control over the 

irrigation process. These systems can be 

fully automated, enabling the farmer to 

irrigate a large area with less labor. The 

most sophisticated systems use feedback 

from soil-moisture probes to cycle the 

irrigation system off and on.

Drip irrigation employs plastic 

lines with small openings to deliver 

water directly to the base of the plant. 

The drip lines may be installed above 

or below the soil. A properly operating 

drip-irrigation system enables a farmer 

to make maximum use of his allotment 

of water—very little water is lost to 

evaporation, no tailwater is generated, 

and virtually no water is lost to the 

ground-water system. Drip systems also 

enable the farmer to deliver nutrients 

and some pesticides through the lines, 

significantly reducing the amount of 

chemicals used on the field and reducing 

the potential for the chemical to leave 

the field.

Figure 4. Rill irrigation uses gravity to deliver water to crops and removes the unused 

portion by way of ditches and drains.

Agricultural drain

Head ditch

Irrigation water 

delivery from canal

Tail ditch

Furrows

Tailwater 

returned to 

agricultural 

drain

Sunnyside Canal diversion (left) from the 

Yakima River (right)

Wheel line sprinkler

Sand filters and chemical-storage tanks 

for a drip-irrigation system
Introduction 7

Most basin farmers use 

best management practices

The earliest modern best management practices (BMPs) in the Yakima 

River Basin were not implemented for 

the purpose of maintaining instream 

flows or water-quality concerns, but 

because they were in the best interest of 

the farmer. For example, the drought of 

1977 resulted in significantly reduced 

water deliveries to the holders of junior 

water rights. Farmers in the Roza Irrigation District were among the most heavily affected. This drought prompted many 

farmers to reevaluate the type of crops 

they were growing and how they were 

irrigating their crops. In the years following the drought, thousands of acres of 

rill-irrigated row crops in the Roza Irrigation District were converted to sprinklerirrigated orchards. Additionally, most 

irrigation systems in existing orchards 

were converted to sprinkler systems. 

Today, most farmers employ multiple BMPs to reduce water use and to 

minimize soil erosion from their fields. 

For example, irrigation districts throughout the Yakima River Basin are required 

by State and Federal regulatory agencies 

to reduce contamination in agricultural 

return flow that enters the Yakima 

River. As a result, farmers in the Roza 

and Sunnyside Valley Irrigation Districts 

who are consistently in violation of 

district water-quality standards face cuts 

in their water allotments. It is, therefore, 

in the interest of the farmer to implement 

BMPs.

Commonly Used BMPs

Irrigation-Method Conversion

Converting from rill irrigation to 

sprinkler or drip irrigation or upgrading an older sprinkler system to a more 

efficient one provides many benefits to 

the farmer, including water conservation, 

reduced erosion, and decreased runoff. It 

is an expensive undertaking and is not an 

operationally viable option for all crops. 

Conversion costs range from $300 to 

$1,600 per acre.

Polyacrylamide (PAM)

The use of PAM is an effective, 

low-cost method to improve the quality of tailwater from rill-irrigated fields. 

PAM is a chemical added to the irrigation water that causes soil particles in 

the furrows to adhere to one another. 

PAM has been used very effectively to 

reduce erosion from rill-irrigated fields. 

It also enhances water infiltration into 

the soil, thereby leading to a more uniform irrigation of the crops along a row.

Piping Irrigation Laterals and Head 

Ditches

Many irrigation districts are 

upgrading their open, earthen or concrete delivery laterals to PVC pipe. The 

PVC pipe virtually eliminates water 

losses to the ground water and atmosphere. The irrigation water arrives at 

the farms cleaner, and, in some cases, 

with enough pressure to operate the irrigation system without a pump. On many 

rill-irrigated fields, the open, earthen 

head ditch has been replaced with PVC 

pipe with the same benefits.

Sediment-Retention Ponds

Sediment-retention ponds are 

located at low point of a rill-irrigated 

field. The ponds reduce the velocity of 

the irrigation tailwater, which allows 

some of the sediment to settle out before 

the water is returned to the agricultural drain system. Some farmers have 

installed pumps that enable them to 

reuse water from these ponds rather than 

allowing it leave their farm. To be effective, sediment-retention ponds must be 

properly sized for the amount of inflow 

and they must be cleaned periodically.

Riparian Fencing

Controlling livestock access to 

waterways can reduce concentrations 

of nutrients, suspended sediment, and 

fecal coliform bacteria in streams. The 

reduced traffic encourages the growth of 

vegetation in and along the waterway. 

Riparian vegetation removes nutrients 

from the water, provides habitat for 

insects (both beneficial and problematic), and is important for stream shading.

New or Experimental BMPs

Constructed Wetlands

Routing irrigation-return flow 

through a constructed managed wetland 

can reduce concentrations of nutrients 

and suspended sediment. Increased 

populations of pest insects and increased 

concentrations of fecal-coliform bacteria 

from birds and mammals attracted to the 

wetlands must be addressed before this 

promising BMP can be widely implemented. 

Soil-Moisture Probes

Electronic sensors installed at 

multiple depths in the soil enable farmers to monitor the downward movement 

of irrigation water on their fields. With 

experience and experimentation, the data 

from the moisture probes can be used 

to fine-tune irrigation systems, so the 

plants get the water they need without 

flushing water and dissolved minerals, 

nutrients, and pesticides into the ground 

water.

Riparian fencing along a drain

Sediment-retention pond at the bottom 

of a corn field
8 Water Quality in the Yakima River Basin

High concentrations of nutrients 

result from agricultural activities 

During the irrigation season, most of the 

water in the lower Yakima River is agricultural 

return flow. Concentrations of nutrients (nitrogen 

and phosphorus) in the river reflect the influx of 

agricultural chemicals. In August 1999, concentrations of total phosphorus in the Yakima River 

increased from 0.01 mg/L in the headwaters near 

Cle Elum to 0.14 mg/L near the mouth at Kiona 

(fig. 5). Although high, the concentrations of nutrients in the Yakima River at Kiona were similar to 

those in other large rivers nationally (see Appendix, p. 34).

Concentrations of phosphorus were higher in 

the agricultural tributaries than in the Yakima River 

(fig. 5). At two frequently sampled sites, Moxee 

Drain and Granger Drain (see p. 27), concentrations of total phosphorus were higher than those 

in most other agricultural streams nationwide (see 

Appendix, p. 34).

Nitrate and orthophosphate were the dominant 

forms of nitrogen and phosphorus found in the 

Yakima River and its agricultural tributaries. These 

forms of nitrogen and phosphorus are highly watersoluble, and are transported to streams and drains 

in irrigation runoff. After the irrigation season, 

they continue to enter streams and drains through 

ground-water discharges (fig. 6). Concentrations 

of nutrients in some agricultural drains were high 

enough to support nuisance-level growths of algae (see p. 24). Although 

not assessed in this study, heavy growths of algae and rooted aquatic plants 

have been observed in the lower Yakima River. Large diurnal fluctuations 

in pH and dissolved oxygen due to excessive algal and plant growth can 

Figure 5. Concentrations of total phosphorus increase downstream in the 

Yakima River, particularly in the Lower Valley, where most of the water is 

from agricultural return flow.

Yakima River

Tributaries

AGRICULTURAL TRIBUTARIES IN DOWNSTREAM ORDER

Wilson CreekCherry Creek

Naches River

U

mtanum

Creek

Moxee Drain

Wide Hollow

Creek

Ahtanum

Creek

East Toppenish Drain

Sub 35 Drain

Granger Drain

Marion Drain

Toppenish Creek

Satus Creek

South Drain

Sulphur Cr Wasteway

Spring Creek

Snipes Creek

0

0.1

0.2

0.3

0.4

0.5

T

O

T

A

L

P

H

O

S

P

H

O

R

U

S,

IN

MIL

LIG

R

A

M

S

P

E

R

LIT

E

R

Kittitas Valley Mid Valley Lower Valley

TOTAL PHOSPHORUS

PERCENTAGE OF CONCENTRATIONS

Less than or equal to 0.1 mg/L

Greater than 0.1 mg/L

Yakima Small Agricultural Watersheds

Arid Western Agricultural Basins

All NAWQA Basins

DISSOLVED NITRATE

Less than or equal to 2 mg/L

Between 2 and 10 mg/L

Greater than 10 mg/L

0 20 40 60 80 100

Irrigation Season

Yakima Small Agricultural Watersheds

Nonirrigation Season

Irrigation Season

Yakima Small Agricultural Watersheds

Arid Western Agricultural Basins

All NAWQA Basins

Irrigation Season

Yakima Small Agricultural Watersheds

Nonirrigation Season

Irrigation Season

0 20 40 60 80 100

PERCENTAGE OF CONCENTRATIONS

In a special study of small agricultural watersheds in the Yakima River 

Basin, concentrations of phosphorus in 

71 percent of the irrigation-season samples and 80 percent of the nonirrigationseason samples exceeded the USEPA 

desired goal of 0.1 mg/L to prevent 

nuisance growth of plants in streams 

[6]. In the same study, 13 percent of 

the nonirrigation-season concentrations of nitrate exceeded 10 mg/L—the 

USEPA drinking-water standard [7]. 

These percentages are high compared to 

other NAWQA studies in the West and 

throughout the Nation (see figure). 

Major Findings

The data from the Yakima small agricultural watersheds are not shown in the Appendix on p. 34.

Small agricultural watersheds had large percentages

of elevated concentrations of nutrients
Major Findings 9

produce conditions that are unhealthy 

for fish and other aquatic life. Furthermore, when die-offs of aquatic vegetation occur, drifting algal or plant material may become an aesthetic nuisance 

along stream banks and can foul water 

intakes, canals, and fish screens. 

Seasonal differences between 

nitrogen and phosphorus 

reflect source differences

Concentrations of total phosphorus in Granger Drain were as much as 

five times higher during the irrigation 

season than during the nonirrigation 

season (fig. 6). The high concentrations 

were commonly associated with high 

concentrations of suspended sediment, 

suggesting most of the phosphorus is 

bound to soil particles. The consistent 

elevated concentrations observed during 

the nonirrigation season most likely 

reflect a large reservoir of dissolved 

orthophosphate in the shallow ground 

water that will challenge water managers 

trying to meet lower nutrient standards. 

In contrast to total phosphorus, 

concentrations of nitrate were lowest during the irrigation season and 

increased in the fall, when ground-water 

discharge becomes the dominant source 

of streamflow. Nitrate is highly watersoluble and readily leaches into ground 

water, where it is transported to streams 

and drains. During the irrigation season, 

unused irrigation water and overland 

runoff provide dilution water that lowers 

concentrations of nitrate. Once irrigation ends, streamflows subside and 

concentrations of nitrate increase. In 

Granger Drain, 

for example, 

concentrations of 

nitrate increased 

to more than 

6 mg/L once the 

irrigation season 

ended (fig. 6 

and table 1). 

Thirteen percent 

of the concentrations from 

small-watershed 

sites (see p. 27) 

sampled during 

the nonirrigation 

season exceeded 

the USEPA 

drinking-water 

standard for 

nitrate of 10 mg/L, indicating a potential 

health risk to nearby residents with shallow wells.

Concentrations of nutrients in 

agricultural streams and drains 

exceeded criteria 

The USEPA has suggested regional 

nutrient criteria for concentrations of 

total phosphorus and total nitrogen in 

streams of the Xeric West (Nutrient 

Ecoregion III) to protect against the 

adverse effects of nutrient enrichment 

[8]. These guidelines provide an upper 

limit that is protective of aquatic life, 

and is to be used as a starting point for 

States and Tribes in the development 

of their own criteria. The Yakima River 

Basin is part of the Columbia Plateau 

Ecoregion 10, where the suggested 

reference conditions for total nitrogen 

and total phosphorus are 0.36 mg/L and 

0.03 mg/L, respectively. 

Concentrations of total nitrogen at 

four reference sites in the Yakima River 

Basin ranged from 0.30 to 0.34 mg/L, 

which is slightly below the reference 

condition. All other streams and drains 

had much higher concentrations of total 

nitrogen, some exceeding 10 mg/L. 

Concentrations of total phosphorus at 

the reference sites ranged from 0.034 

to 0.10 mg/L, with the highest concentration occurring in Umtanum Creek. 

MAYJUNEJULY AUG SEPT OCT NOV DEC JAN

T

O

T

AL PH

O

SPH

O

R

U

S,

IN

MILLIG

R

A

M

S PER LITER

0

0.2

0.4

0.6

0.8

1.0

1.2

DIS

S

OLVED

NIT

R

A

TE,

IN

MILLIG

R

A

M

S PER LITER

0

1

2

3

4

5

6

7

Total phosphorus

Dissolved nitrate

IRRIGATION SEASON

NONIRRIGATION

SEASON

1999 2000

Figure 6. Concentrations of dissolved nitrate were highest during 

the nonirrigation season when ground water is the primary source 

of water to Granger Drain. Concentrations of total phosphorus, 

however, were highest during the irrigation season, when overland 

runoff delivers phosphorus-rich sediment to the drain. 

Table 1. Concentrations of nutrients sometimes exceeded USEPA guidelines for 

controlling nuisance plants and algae in streams

Site name Site type

Range of 

concentrations 

(milligrams 

per liter)

Percentage of samples 

exceeding desired goal

Yakima 

NAWQA site

Western 

NAWQA sites

Total phosphorus (Desired goal = 0.1 milligrams per liter) [8]

Yakima R at Kiona Yakima River 0.08–0.27 44 55

Moxee Drain Agricultural tributary 0.16–0.37 100 55

Granger Drain Agricultural tributary 0.17–1.1 100 55

Dissolved nitrate (Desired goal = 0.072 milligrams per liter) [8]

Yakima R at Kiona Yakima River 0.3–1.2 100 97

Moxee Drain Agricultural tributary 0.8–5.9 100 97

Granger Drain Agricultural tributary 1.9–6.2 100 97

Reporting Conventions

Concentrations of nutrients are 

reported as elemental nitrogen and 

phosphorus. References to dissolved nitrate refer to an analysis 

of dissolved nitrate plus nitrite. 

Because nitrite was rarely detected 

or was detected at very low concentrations, it is more convenient 

to simply refer to these as dissolved nitrate. 
10 Water Quality in the Yakima River Basin

Although the concentrations of total phosphorus in all reference streams exceeded 

the suggested reference condition, none 

exceeded 0.10 mg/L, the USEPA desired 

goal to prevent nuisance growths of aquatic 

plants in streams. In contrast, concentrations 

of total phosphorus in all drains and streams 

affected by agriculture exceeded 0.10 mg/L, 

sometimes by as much as a factor of nearly 

five. In 1999, all of the concentrations of 

total phosphorus measured in both Moxee 

and Granger Drains [9] exceeded this goal 

(table 1).

Irrigation method and landscape 

differences affect nutrient contributions to streams

The tailwater from a rill-irrigated field 

provides a direct path for nutrients, pesticides, and suspended sediment to enter 

agricultural drains. Through the use of PAM 

and other BMP implementations, great 

progress has been made in the Yakima River 

Basin in reducing the amount of suspended 

sediment in rill tailwater and decreasing 

the amount of runoff. Data from the small 

agricultural watersheds (see p. 27), however, 

clearly show that rill irrigation still results in 

a larger per acre loss of sediment and nutrients than sprinkler or drip irrigation (Hank 

less than 3 percent—typically found 

near the valley floor. These relatively flat 

areas are where streams and drains commonly flow year-round in response to 

continuous upwelling of shallow ground 

water. The proximity to flowing water 

and shallow ground-water upwelling 

mean that the chemicals lost from rillirrigated fields are more likely to reach 

agricultural tributaries. Also, crops that 

tend to be rill irrigated, such as corn, 

generally require a higher per acre appliJohnson and Dan Wise, U.S. Geological Survey, unpub. data, 2004). 

High rill-irrigation watersheds lost 

four times more total phosphorus 

and dissolved nitrate and five times 

more suspended sediment than low 

rill-irrigation watersheds (fig. 7). 

The landscape characteristics of 

the areas also factor into these differences in nutrient contribution. In the 

Yakima River Basin, rill irrigation 

tends to be used on land with slopes 

Total phosphorus

0 0.5 1.0 1.5 2.0 2.5

Dissolved nitrate

0 3 6 9 12 15

Suspended

sediment

0 50 100 150 200 250

MEDIAN YIELD,

IN GRAMS PER DAY PER ACRE

MEDIAN YIELD,

IN GRAMS PER DAY PER ACRE

More than 32% rill

Less than 32% rill

Median for all

watersheds

EXPLANATION

Figure 7. Small agricultural watersheds with large amounts of rill-irrigated farmland lost more total phosphorus, dissolved nitrate, and suspended sediment per 

acre than those with more sprinkler- or drip-irrigated land. 

0

10

20

30

40

5

15

25

35

DISSOLVED NIT

R

ATE, IN MILLIG

R

A

MS PER LITER

YAKIMA RIVER

BASIN

CENTRAL COLUMBIA

PLATEAU

No data

Irrigation season

Nonirrigation season

Shallow ground water

Maximum concentration

Median concentration

Discharge of agriculturally affected ground water to the Snake River 

from springs accounts for about 70 to 80 percent of the nitrate leaving 

the upper Snake River Basin in Idaho [10]. Nitrate contributions from 

subsurface agricultural drains to the San Joaquin River in California has 

increased steadily since the 1950s [11]. In the Central Columbia Plateau in 

Washington, the similarities between concentrations of nitrate in shallow 

ground water and concentrations in agricultural drains and wasteways 

sampled during the nonirrigation season were used to infer trends in 

concentrations of nitrate in shallow ground water over time [12]. Maximum concentrations of nitrate in agricultural drains and wasteways in the 

Central Columbia Plateau were higher than those in the Yakima River 

Basin, but median values and seasonal patterns were similar. This strongly 

suggests that shallow ground water underlying some agricultural areas in 

the Yakima River Basin also has elevated concentrations of nitrate. These 

findings raise concerns that some shallow domestic wells in agricultural 

areas have concentrations of nitrate that are above the drinking-water 

standard of 10 mg/L. 

Ground-water discharges are a major source of surfacewater nitrate in irrigated areas of the Western United States
Major Findings 11

cation of fertilizer than those that are usually drip or sprinkler 

irrigated, such as grapes. Consequently, these factors also 

contribute to increased nutrient loss from rill-irrigated areas. 

Agricultural BMPs have decreased

concentrations of sediment and phosphorus

During the past several years, the implementation of 

BMPs, such as the use of PAM and conversion from rillirrigation to sprinkler- and drip-irrigation methods, have 

diminished the amount of agricultural runoff entering Yakima 

River Basin streams and drains. Concentrations of suspended 

sediment and total phosphorus in Granger Drain (fig. 8) and 

Sulphur Creek Wasteway, for example, have decreased—

especially during 1999 and 2000 [7]. These improvements in 

water quality support the continued implementation of BMPs. 

Similar improvements in water quality were not, however, 

noted in the Yakima River during 1997–2000 [7]. Because of 

its larger size, it may take longer to improve than the smaller 

drains and tributaries. Alternatively, annual differences in 

flow in the Yakima River may mask improvements in water 

quality. Although it may be somewhat early to see the full 

extent of improvements in water quality from the BMPs 

implemented thus far, the 1999–2000 suspended sediment 

and total phosphorus data are encouraging (fig. 8).

BMPs are needed to reduce nitrate 

contamination in ground water 

Concentrations of nitrate in the agricultural drains and 

streams were high, especially after the irrigation season, 

when ground-water discharges dominate flow in the drains. 

Concentrations of dissolved nitrate in Granger Drain have 

increased over the period 1991–2000 [7]. Most BMPs are 

designed to control erosion and therefore aim to reduce the 

transport of sediment and pollutants associated with sediment 

such as phosphorus and DDT. Such BMPs are less effective 

in controlling the movement of water-soluble agricultural 

pollutants such as nitrate and dissolved pesticides, which 

leach into ground water during the irrigation season. As a 

result, despite the implementation of BMPs, reductions in 

concentrations of nitrate have not yet occurred (fig. 9). Some 

farmers are now using soil-moisture monitors to prevent overirrigation, a practice that should help reduce nitrate leaching. 

Nutrient data collected in 2001 by the Roza-Sunnyside Board 

of Joint Control suggest that concentrations of nitrate in the 

agricultural drains may be leveling off [7]. Because aquifers 

flush slowly, however, it may 

take years or decades to flush 

clean such agricultural pollutants, even without additional 

contamination. 

Figure 8. Concentrations of suspended sediment and total phosphorus in Granger Drain show slight decreases since 1997 that 

may correspond with the increased use of agricultural BMPs in 

the Granger Basin. Data provided by the Roza-Sunnyside Board 

of Joint Control (RSBOJC).

0

20

40

60

80

100

0

20

40

60

80

100

STREAMFLO

W, IN CUBIC FEET PER SECOND

1997 1998 1999

YEAR

2000 2001

0

0.5

1.0

1.5

2.0

0

200

400

600

800

1,000

CONCENTRATION, IN MILLIGRAMS PER LITER

Suspended solids

Total phosphorus

Streamflow

Figure 9. Dissolved nitrate, the principal component of the total 

nitrogen found in Granger Drain, is not associated with sediments and therefore has not decreased in response to BMP 

implementation. Data provided by the RSBOJC.

0

2

4

6

8

10

0

20

40

60

80

100

1997 1998 1999 2000 2001

0

2

4

6

8

10

0

20

40

60

80

100

CONCENTRATION, IN MILLIGRAMS PER LITER

STREAMFLO

W, IN CUBIC FEET PER SECOND

YEAR

Total nitrogen

Dissolved nitrate Streamflow

Detailed information on nutrients and suspended sediment in surface water in the 

Yakima River Basin can be found in the following report:

Concentrations and loads of suspended sediment and nutrients in surface water 

of the Yakima River Basin, Washington, 1999–2000—With an analysis of trends in 

concentrations, by J.C. Ebbert and others: U.S. Geological Survey Water-Resources 

Investigations Report 03–4026 at http://pubs.water.usgs.gov/wri034026/
12 Water Quality in the Yakima River Basin

Bacteria indicate the presence 

of fecal contamination

Water from streams with poor 

sanitary quality can transmit diseases 

such as cholera, typhoid fever, and 

bacillary and amoebic dysentery. Fecalcoliform bacteria are indicators of fecal 

contamination that have been correlated 

with the incidence of gastrointestinal 

disease resulting from bodily contact 

with certain freshwater sources. Wastes 

from warm-blooded animals, including 

humans, are sources of fecal contamination. In 1998, the Washington Department of Ecology, under the guidelines 

of the Clean Water Act, listed 18 river 

reaches in the Yakima River Basin as 

impaired or threatened water bodies, 

based on concentrations of bacteria.

During the summer, concentrations 

of fecal-coliform bacteria in streams 

and drains in the Yakima River Basin 

commonly exceed the Washington State 

water-quality standard (200 colonies per 

100 milliliters) for multiple water uses 

[13]. During two irrigation-season samplings in August 1999 and July 2000, 

concentrations of fecal-coliform bacteria 

at 56 and 65 percent of the sites sampled, respectively, exceeded the standard 

(fig. 10). None of these exceedances, 

however, were observed in the mainstem Yakima River. Instead, the highest 

concentrations were measured in tributaries draining predominantly agricultural and(or) urban areas. 

During the 

fall nonirrigationseason sampling, 

only 19 percent 

of the sites 

sampled exceeded 

the standard 

(fig. 10). Four 

of the six sites 

that exceeded the 

standard in the 

fall are agricultural drains 

located in the 

Granger Drain 

and Sulphur 

Creek Wasteway subbasins in the Lower 

Valley. These two subbasins have the 

highest livestock densities in the basin 

and, therefore, also have more manure 

applications to agricultural fields for 

fertilization. Several other tributaries 

with high concentrations of bacteria, 

however, could not be explained by 

livestock density or manure application. The issue is much more complex, 

with potential sources including, but not 

limited to, humans (for example, failing 

septic systems), pets, livestock, birds, 

and wildlife. 

In an effort to better understand 

some of these high concentrations, the 

bacteria data were tested for relations 

with other physical and chemical variables [14]. The concentrations of bacteria measured in the Yakima River and 

the mouths of major streams and drains 

increased significantly 

with increasing suspended sediment, turbidity, nutrients, and 

specific conductance. 

For example, the three 

major tributaries with 

the highest concentrations of fecal-coliform bacteria, including Moxee Drain, Granger Drain, and 

Sulphur Creek Wasteway, also had some 

of the highest concentrations of suspended sediment.

In contrast, the concentrations of 

bacteria measured in streams and drains 

in small agricultural watersheds were 

not as strongly associated with these factors, except selected nutrients and water 

temperature. These differences illustrate 

how important it is to consider the scale 

of sampling (large subbasin compared to 

small watershed) and the complexity of 

potential sources when analyzing fecalcoliform bacteria data. 

Looking forward to future monitoring goals, research needs, and BMP 

development, subjects that need further 

investigation were identified [14]. These 

include (a) the transport mechanisms of 

fecal-coliform bacteria from land surfaces to streams through overland runoff, 

(b) the specific role played by suspended 

sediment in the occurrence and transport 

of bacteria, and (c) the quantification 

of the relations between fecal-coliform 

contamination in streams and wildlife, 

livestock, and people in the basin. 

75

50

25

AUGUST 1999

25 SITES

JULY 2000

51 SITES

OCT/NOV 2000

31 SITES

100

0

IRRIGATION SEASON

NONIRRIGATION

SEASON

P

E

R

C

E

N

TA

G

E

O

F

SIT

E

S

Less than 200 colonies/100 mL

Greater than 200 colonies/100 mL

Figure 10. Fecal-coliform bacteria concentrations commonly 

exceed the Washington State water-quality standard of 

200 colonies per 100 milliliters, particularly during the 

irrigation season. 

Detailed information on fecal contamination in surface water in 

the Yakima River Basin can be found in the following report:

Fecal-indicator bacteria in the Yakima River Basin, Washington—An examination of 1999 and 2000 

synoptic-sampling data and their relation to 

historical data, by J.L. Morace and S.W. 

McKenzie: U.S. Geological Survey WaterResources Investigations Report 02–4054 at 

http://pubs.water.usgs.gov/wri024054/

Summer is a time of 

increased recreation in 

the Yakima River
Major Findings 13

Arsenic, a known human 

carcinogen, was detected at 

levels of concern

Although nearly all trace elements 

in the aquatic environment are from 

natural sources, some are enriched by 

human activities. In general, concentrations of trace elements in the Yakima 

River Basin were small and of no known 

concern to human or aquatic health. Of 

the 23 trace elements for which samples were analyzed [14], only arsenic 

exceeded the Maximum Contaminant 

Level (see box below).

Arsenic enters the environment 

from applications of pesticides and fertilizers, the release of volcanic gases and 

geothermal water, and the weathering of 

arsenic minerals [15]. Lead arsenate has 

been used in the past to control codling moths in apple orchards in eastern 

Washington. Currently, commercial 

fertilizers containing phosphate are 

also a potential source of arsenic [14]. 

Fuhrer and others [16] reported natural 

sources of arsenic in the 

headwaters of the Yakima 

River Basin and agricultural sources of arsenic 

in the Sulphur Creek 

subbasin in the Yakima 

Valley agricultural area.

In 1999, concentrations of arsenic in 

the Yakima River near 

the mouth were at their 

highest level in August 

(fig. 11); only two samples, however, exceeded 

the Risk-Specific Dose 

(RSD4) value of 2 micrograms per liter (μg/L) 

that corresponds to a 

cancer risk of 1 in 10,000. 

At the end of the irrigation season, concentrations slowly declined and returned to a 

nondetectable level by January. In contrast, concentrations of arsenic in two 

agricultural drains (Granger Drain and 

Moxee Drain) were highest during the 

nonirrigation season. All samples from 

Granger Drain exceeded 2 μg/L, and two 

samples exceeded the existing MCL of 

10 μg/L. Most irrigation-season samples 

from Moxee Drain were near or below 

2 μg/L, while all nonirrigation-season 

samples exceeded 2 μg/L and three were 

near 10 μg/L.

Elevated concentrations of arsenic 

during the nonirrigation season were 

again observed in Moxee Drain and 

Granger Drain in 2000. An additional 

30 agricultural streams and drains from 

throughout the Yakima River Basin 

were sampled for arsenic in October and 

November of 2000. Of the 32 sites, 18 

had concentrations of arsenic exceeding the RSD4 value of 2 μg/L and 5 had 

concentrations exceeding the MCL of 

10 μg/L. Concentrations in agricultural 

drains in the Moxee, Granger, and Sulphur Creek Subbasins were higher than 

concentrations from Ahtanum Creek, 

Spring Creek, Snipes Creek, and most 

drains in the Kittitas Valley.

During the irrigation season, 

agricultural drains in the Yakima River 

Basin contain a mixture of ground water 

and agricultural return flow. During the 

nonirrigation season, most of the water 

in the drains is discharge from the shallow ground-water system. The increase 

in the concentration of arsenic in the 

drains during the nonirrigation season is 

highly suggestive of elevated concentrations in the shallow ground-water system. Because many rural-area residents 

rely on wells less than 100 feet deep 

for their drinking water, nonirrigationseason concentrations of arsenic in the 

drains near the MCL are a cause for concern. Subsequent samplings of Lower 

Valley wells have shown that concentrations of arsenic in more than half of the 

74 wells sampled exceeded 2 μg/L [17].

Standards and Guidelines

for Arsenic in Water

Arsenic has been classified 

as a human carcinogen by the 

USEPA; therefore, the unenforceable Maximum Contaminant 

Level Goal (MCLG) is zero. The 

enforceable Maximum Contaminant Level (MCL) is “set as close 

to the MCLG as feasible using 

the best available analytical and 

treatment technologies and taking 

cost into consideration [18].” In 

January 2001, USEPA lowered the 

MCL for arsenic from 50 μg/L to 

10 μg/L. 

The USEPA has also established 

Risk-Specific Dose (RSD) values, 

which represent the concentrations 

of a chemical in drinking water 

that corresponds to defined levels 

of increased lifetime cancer risk. 

For arsenic, the RSD4 value corresponding to a cancer risk of 1 in 

10,000 is 2 μg/L [19]. 

0

2

4

6

8

10

12

M J

1999 2000

A

J A S O N D J

R

SENIC, IN

MIC

R

O

G

R

A

M

S PER LITER

Moxee Drain

Granger Drain

Yakima River at Kiona

NONIRRIGATION

SEASON

IRRIGATION SEASON

Figure 11. Concentrations of arsenic in two agricultural 

drains were highest during the nonirrigation season, when 

ground water is the primary source of water, whereas 

concentrations in the Yakima River were highest during 

the irrigation season, when irrigation return flow influences water quality. 

Detailed information on trace 

elements in surface water in the 

Yakima River Basin can be found in 

the following report:

Occurrence and distribution of 

dissolved trace elements in the 

surface waters of the Yakima River 

Basin, Washington, 1999–2000, by 

C.A. Hughes: U.S. 

Geological Survey 

Water-Resources 

Investigations Report 

02–4177 at http:

//pubs.water.usgs.gov/

wri024177/
14 Water Quality in the Yakima River Basin

Historically used pesticides 

are still present in the Yakima 

River Basin

In the mid-1900s, DDT and other 

organochlorine insecticides were used 

to control a wide variety of pests in the 

Yakima River Basin and throughout 

the Nation. After several decades of 

use, however, the adverse impacts on 

ecosystems were found to outweigh the 

benefits. These insecticides are relatively 

insoluble in water and tend to adhere to 

soil particles and stream sediment. They 

are persistent in the environment and 

are easily transported to streams during 

irrigation or precipitation-induced erosion. In the 1970s and 1980s, uses of 

most of the organochlorine insecticides 

were cancelled because they are carcinogenic, accumulate in the food chain, 

and are hazardous to wildlife [20]. Since 

1968, organochlorine insecticides that 

have been detected most frequently in 

the Yakima River Basin are total DDT 

(DDT and its breakdown products, DDE 

and DDD) and dieldrin [21]. 

Concentrations of DDT

in fish and surface water 

are decreasing 

From 1988 to 1991, USGS sampling determined that DDT and several 

other organochlorine insecticides were 

distributed widely in agricultural soils, 

stream water, suspended sediment, and 

resident fish [22]. Concentrations of 

total DDT in bottom fish in the lower 

Yakima River in the late 1980s were 

among the highest in the Nation. Based 

on these findings, the Washington 

Department of Health issued a warning 

in 1993 stating, “people who frequently 

eat bottom fish caught in the Yakima 

River may suffer adverse health effects,” 

and recommended that people limit 

their consumption of bottom fish from 

the lower Yakima River to one meal per 

week [22]. More recent data collected 

on largescale sucker, smallmouth bass, 

and carp from the Yakima River at 

Granger and Prosser in 1996–98 showed 

that concentrations of total DDT had 

decreased to about one-half of 

those in 1989–90 [23, 24] but 

still exceeded the guidelines 

for the protection of fish-eating 

wildlife (200 micrograms of total 

DDT per kilogram of whole fish, 

wet weight) [25].

Twelve of 23 organochlorine compounds analyzed in 

unfiltered-water samples in 

August 1999 were detected in 

agricultural areas throughout 

the basin [26], with DDT, DDE, 

DDD, dieldrin, and heptachlor 

epoxide exceeding the USEPA 

chronic water-quality criteria 

for the protection of freshwater 

aquatic life. Many of the compounds detected in August 1999 

also were detected in June 1989; 

however, the number of sites 

with detections in 1999 generally 

decreased by more than 50 percent.

DDT, DDE, and DDD were the 

most frequently detected organochlorine compounds in both June 1989 and 

August 1999. Most of the detections 

in August 1999 occurred in drains and 

tributaries that received agricultural runoff downstream from the city of Yakima 

(fig. 12). In 1989, concentrations of 

total DDT in the lower Yakima River 

commonly exceeded the USEPA chronic 

water-quality criterion of 1 nanogram 

per liter (ng/L) for the protection of 

freshwater aquatic life. In August 1999, 

however, total DDT was not detected at 

the 1-ng/L level (fig. 13). In the drains 

and tributaries that received agricultural runoff, concentrations generally 

Wilson CreekCherry Creek

U

mtanum

Creek

Naches River

Moxee Drain

Wide Hollow

Creek

Ahtanum

Creek

East Toppenish Drain

Sub 35 Drain

Granger Drain

Marion Drain

Toppenish Creek

Satus Creek

South Drain

Sulphur Cr Wasteway

Spring Creek

Snipes Creek

D

D

T+D

DE+D

D

D,

IN

N

A

N

O

G

R

A

M

S PER LITER

0

30

60

90

June 1989

August 1999

Not detected

in 1999

City of Yakima

City of Ellensburg

City of Grandview

AGRICULTURAL TRIBUTARIES IN DOWNSTREAM ORDER

Kittitas Valley Mid Valley Lower Valley

YAKIMA RIVER SITES (RIVER MILE)

Cle Elum

(R

M 182)

U

mtanum

(R

M 140)

Union Gap

(R

M 107)

near Satus

(R

M 72)

Grandview

(R

M 55)

Kiona

(R

M 30)

D

D

T+D

DE+D

D

D,

IN

N

A

N

O

G

R

A

M

S PER LITER

0

4

8

12

16

Detected—June 1989

Not detected—August 1999

USEPA chronic

water-quality

criterion = 1 ng/L

City of Ellensburg

City of Yakima

City of Grandview

No data No data

Figure 12. Concentrations of total DDT in water samples from major tributaries to the 

Yakima River decreased sharply between 1989 and 1999.

Figure 13. Although total DDT was ubiquitous in 

the Yakima River in 1989, it was not detected in 

water samples in the Yakima River in 1999.
Major Findings 15

were five or more times lower in 1999 

than those measured in 1989, although 

some concentrations still exceeded the 

aquatic-life criterion. In August 1999, 

concentrations of DDT, DDE, or DDD 

in unfiltered water from several of the 

drains and tributaries also were well 

above the USEPA human-health criteria 

for consumption of fish. In tributaries 

where DDT was detected in water at 

1 ng/L or more, the increase in cancer risk is estimated to be at least 1 in 

1,000,000 for people who consume 

one fillet (4 ounces of resident fish) per 

month from that stream [18].

In Granger and Moxee Drains, 

which were previously identified as 

major sources of DDT in 1989 [21], concentrations of total DDT and suspended 

sediment in 1999 continued to peak 

during periods of increased irrigationinduced erosion in the June–July period. 

Although the concentrations of total 

DDT in water samples in 1999–2000 

were still above the USEPA chronic 

aquatic-life criterion, they were four or 

more times lower than those measured in 

1988–89 (fig. 14). In the Yakima River 

at Kiona, concentrations of total DDT in 

water have decreased almost two orders 

of magnitude since the cancellation of 

DDT products in 1972 (fig. 15). Detections observed after 1985 were made 

possible by achieving a lower reporting 

level for the analysis of these compounds in unfiltered water. From May 

1999 through January 2000, concentrations of total DDT in the Yakima River 

at Kiona were at or below the USEPA 

chronic aquatic-life criterion.

Best management practices 

reduce erosion and concentrations of DDT—an agricultural 

community works together to 

improve water quality

In the 1990s, stakeholders in the 

basin, including Federal, Tribal, State, 

and local agencies, farmers, irrigation 

districts, and conservation districts, 

began working together to control the 

amount of total DDT entering the river 

system from agricultural fields. Because 

DDT primarily is attached to soil 

particles and enters the streams during episodes of erosion, farmers began 

implementing BMPs to control irrigation-induced erosion. Widely implemented BMPs included less erosive 

irrigation practices (for example, drip 

and sprinkler systems), cover crops and 

ground cover, sediment-retention basins, 

and the use of PAM.

0

40

80

120

1988–89 Moxee Drain

Granger Drain

USEPA chronic waterquality criterion is 1 ng/L

MAY JUNE JULY AUG SEPTOCT NOV DEC JAN

1988 1989

FEB MAR

1999–2000

MAY JUNE JULY AUG SEPT OCT NOV DEC JAN

1999 2000

D

D

T

+

D

D

E

+

D

D

D, IN

N

A

N

O

G

R

A

M

S

P

E

R LIT

E

R

0

40

80

120

Figure 14. Concentrations of total DDT in water samples from Moxee 

and Granger Drains decreased sharply from 1988 to 1999 during the 

irrigation season, when concentrations typically are highest.

1968 1972 1976 1980 1984 1988 1992 1996 2000

D

D

T

+

D

D

E

+

D

D

D,

IN

N

A

N

O

G

R

A

M

S

P

E

R

LIT

E

R

0.1

1

10

100

Sale of DDT

cancelled in 1972

Detected

Not detected

Minimum reporting level

USEPA chronic

water-quality criterion = 1 ng/L

Figure 15. Concentrations of total DDT in water samples from the Yakima River 

at Kiona have decreased almost two orders of magnitude since the cancellation 

of DDT in 1972.
16 Water Quality in the Yakima River Basin

quality criterion of 1 ng/L [27]. The 1999 data, however, 

show that the total DDT criterion could be met when 

concentrations of suspended sediment are well above 

7 mg/L. This finding suggests that the TMDL target for 

suspended sediment could be increased if the higher 

concentrations of suspended sediment are not a concern.

The reduction in concentrations of total DDT detected in the 

Yakima River Basin in 1999 was associated, in large part, with 

decreases in concentrations of suspended sediment and sorbed DDT 

that resulted from the agricultural community’s implementation of 

erosion-controlling BMPs. For example, in Moxee Drain, maximum concentrations of suspended sediment decreased sharply from 

more than 600 mg/L in 1988–89 to about 200 mg/L in 1999–2000 

(fig. 16). This decrease in suspended sediment is a consequence of 

the conversion of rill irrigation to less erosive drip irrigation over the 

last decade (fig. 17). 

In Granger Drain, the amount of total DDT associated with the 

eroded soil particles (suspended sediment) has decreased notably 

over time, possibly due to (1) degradation of total DDT in soils and 

in bed sediment over the last decade, (2) dilution of suspended sediment with uncontaminated eroded soils, or (3) use of PAM in the 

flocculation and sedimentation of fine-grained, organically enriched 

soil particles that tend to sorb total DDT. For example, the total 

DDT concentration for a given concentration of suspended sediment 

in Granger Drain has decreased by a factor of three or more from 

1988–89 to 1999–2000 (fig. 16). 

The decrease in concentrations of total DDT and suspended 

sediment in surface water in the Lower Valley has implications for 

targets established by the Washington Department of Ecology for 

TMDLs. According to the TMDL, the target concentration of 7 mg/L 

of suspended sediment was established to meet the total DDT waterD

D

T+D

DE+D

D

D, IN

N

A

N

O

G

R

A

M

S PER LITER

0

20

40

60

80

Moxee Drain

SUSPENDED SEDIMENT, IN MILLIGRAMS PER LITER

0 100 200 300 400 500 600 700

0

40

80

120

Granger Drain

1999–2000

1988–1989

1999–2000

1988–1989

Figure 16. Since 1988–89, the relation between total DDT 

and suspended sediment has changed in Moxee and 

Granger Drains. The suspended sediment is now less 

contaminated with total DDT.

YEAR

1988 1990 1992 1994 1996 1998 2000

T

H

O

U

S

A

N

D

S

OF A

C

RES

0

2

4

6

8

Drip-irrigated hops

Rill-irrigated hops

Figure 17. Conversion of rill irrigation to less-erosive 

drip irrigation has probably resulted, in large part, in the 

sharp decrease in concentrations of suspended sediment and total DDT in Moxee Drain (see figure 16).

Low levels of steroids and 

other organic wastewater 

contaminants have been 

detected in the Yakima River

In the first round of sampling for pharmaceuticals, hormones, 

steroids, personal care products, and other wastewater contaminants in U.S. streams, 8 chemicals were detected in the Yakima 

River downstream from intense agricultural activities [28].

Chemical Use

Cholesterol Plant/animal steroid

Coprostanol Fecal steroid

N,N-diethyl toluamide Insect repellent

Triclosan Antimicrobial disinfectant

Tri(2-chloroethyl) phosphate Fire retardant

Tri(dichloroisopropyl) phosphate Fire retardant

Carbaryl Insecticide

Naphthalene Polyaromatic hydrocarbon

Concentrations of all these compounds were low and were 

comparable to national data. The first five chemicals listed 

above were among the most frequently detected in the Nation. 

Except for carbaryl and naphthalene, which did not exceed 

drinking-water health advisories, aquatic-life guidelines or 

drinking-water standards have not been established for the 

chemicals listed above . 
Major Findings 17

Currently used pesticides were 

routinely detected 

Pesticides were detected in 

98 percent or more of the samples from 

streams and drains in the Yakima River 

Basin. Seventy-six pesticide compounds 

were detected—38 herbicides, 17 insecticides, 15 breakdown products, and 

6 others. The compounds selected for 

analysis represent the 176 most heavily applied compounds nationally. 

Compounds detected in the Yakima 

River Basin represent 43 percent of this 

national list. Agricultural crops receive 

the largest application of pesticides in 

the Yakima River Basin, but several 

compounds detected also are used for 

weed and pest control in urban areas and 

along roadsides, fences, and canals.

Insecticides were detected 

frequently but at low 

concentrations 

Insecticides were detected more 

frequently in agricultural drains and 

streams in the Yakima River Basin than 

in other agricultural areas across the 

Nation (table 2). For example, insecticides were detected more than twice as 

often in Moxee and Granger Drains than 

in other agricultural streams sampled 

nationally, and about one-third more 

often in the Yakima River at Kiona than 

in other major rivers. The high frequency of detection of insecticides in the 

Yakima River Basin is due, in large part, 

to the heavy use of insecticides, such as 

azinphos-methyl, in apple, pear, cherry, 

and other fruit orchards.

Although the frequency of detection of insecticides in the Yakima 

River Basin differed from that found in 

streams sampled nationally, the concentrations of insecticides in the agricultural streams and drains of the basin 

(as reflected by a summed cumulative 

concentration of all compounds) are 

not notably different than those in other 

parts of the Nation. For example, a 

cumulative concentration of insecticides 

greater than 100 ng/L was reported in 

only 12 percent of the samples collected 

in Moxee and Granger Drains, which is 

slightly higher than in other agricultural 

streams sampled nationally (table 2). No 

concentrations exceeded 100 ng/L in the 

Yakima River at Kiona, which is slightly 

lower than other major rivers sampled 

nationally (7 percent).

In contrast to insecticides, the 

frequency of detection of herbicides in 

streams and drains draining agricultural 

areas in the Yakima River Basin is no 

greater than that in other agricultural 

areas sampled nationally. Data collected 

within the basin and across the Nation 

indicate that herbicides were detected 

in more than 90 percent of the samples. 

Differences are noted, however, in the 

concentrations of herbicides. Specifically, cumulative concentrations of herbicides are lower in agricultural streams 

of the Yakima River Basin than in those 

sampled nationally; only 12 percent of 

the concentrations exceeded 100 ng/L 

in Moxee and Granger Drains and in the 

Yakima River at Kiona, whereas concentrations in 70 percent of samples collected nationally from other agricultural 

streams and in 52 percent of the samples 

collected from major rivers exceeded 

100 ng/L.

2,4-D, terbacil, and azinphosmethyl were the most 

frequently detected pesticides

Pesticides were detected more 

frequently, and generally at higher concentrations, in the agricultural tributaries than in the Yakima River (fig. 18). 

Screened detection frequencies (see 

above) in the tributaries decreased in the 

order: 2,4-D, terbacil, azinphos-methyl, 

atrazine, carbaryl, and deethylatrazine. 

In contrast, many fewer compounds 

were detected above the common 

screening level in the Yakima River. The 

two most frequently detected pesticides 

in the tributaries also were the most 

frequently detected pesticides in the 

Yakima River.

17

Table 2. Insecticides were detected more frequently in the Yakima River Basin than in other agricultural areas in the Nation, but at 

comparably lower concentrations. [1,000 nanograms per liter (ng/L) = 1 microgram per liter (μg/L); %, percent]

Insecticides Herbicides

Agricultural streams Mixed land-use streams Agricultural streams Mixed land-use streams

Moxee and 

Granger Drains

National 

average

Yakima River 

at Kiona

National 

average

Moxee and 

Granger Drains

National 

average

Yakima River

at Kiona

National 

average

Frequency of detection 80% 37% 71% 53% 91% 96% 90% 96%

Frequency of 

cumulative 

concentrations 

exceeding:

10 ng/L 59 25 54 38 86 93 90 90

100 ng/L 12 7 0 7 12 70 12 52

1,000 ng/L 1 1 0 1 0 20 0 9

Common Screening Level

Because laboratory reporting 

limits can vary among pesticides, 

a common screening level of 

21 ng/L was adopted. This 

common level allows meaningful 

comparisons among pesticides 

with varying reporting limits. 

Without screening, pesticides with 

lower reporting limits could have 

higher detection frequencies than 

those with higher reporting limits.

Azinphos-methyl (Guthion)

An organophosphate insecticide 

used extensively on fruit orchards 

in the Yakima River Basin. It is 

highly toxic to fish and benthic 

invertebrates. 
18 Water Quality in the Yakima River Basin

Pesticides were detected 

year-round

Pesticides generally were detected 

more frequently and at higher concentrations during the irrigation season 

than during the nonirrigation season 

(figs. 19 and 20). This is because (1) 

most pesticides are applied during the 

irrigation season and (2) water is available to transport the chemicals from 

the fields and into streams, drains, 

and the shallow ground water. Insecticides were rarely detected during the 

nonirrigation season, whereas some 

herbicides were detected year-round, 

although concentrations were lower 

during the nonirrigation season. Many 

herbicides are relatively water soluble 

to facilitate their uptake by the target 

weeds. This solubility, however, also 

enhances their movement in the shallow ground-water system, which is the 

primary source of water in most agricultural drains during the nonirrigation 

season. For Moxee and Granger Drains 

(fig. 20) and the Yakima River at 

Kiona, the herbicide atrazine and its 

breakdown product, deethylatrazine, 

were the most commonly detected 

pesticide compounds during the 

nonirrigation season [29].

Concentrations of 

azinphos-methyl 

frequently 

exceeded the 

aquatic-life 

guideline

Concentrations 

of azinphos-methyl in 

Moxee and Granger 

Drains (fig. 20) and the 

Yakima River at Kiona 

routinely exceeded 

the USEPA freshwater 

chronic-toxicity criterion for the protection 

of aquatic life [18]. 

Likewise, most samples 

collected from the small 

agricultural watersheds 

during the 2000 irrigation season (see p. 27) 

exceeded the azinphosmethyl criterion. In 

Granger Drain, the 

insecticides carbaryl and 

diazinon exceeded their 

aquatic-life chronictoxicity guidelines only 

infrequently [30, 31]. 

In the summer of 2000, 

however, concentra-

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Figure 18. Herbicides were detected frequently in agricultural tributaries while oftentimes undetected in the Yakima River, when 

based on a common screening level of 21 nanograms per liter. 

1999 2000

0

4

8

12

16

20

24

N

U

M

B

E

R

O

F

D

E

T

E

C

TIO

N

S

IRRIGATION

SEASON

NONIRRIGATION

SEASON

M J J A S O N D J

0

4

8

12

16

20

24

N

U

M

B

E

R

O

F

D

E

T

E

C

TIO

N

S

HERBICIDES

Yakima River at Kiona

Moxee and Granger Drains

INSECTICIDES

Yakima River at Kiona

Moxee and Granger Drains

IRRIGATION

SEASON

NONIRRIGATION

SEASON

Figure 19. Insecticides were most commonly detected during 

the irrigation season, whereas herbicides were detected 

year-round in the Yakima River at Kiona and Moxee and 

Granger Drains. 
Major Findings 19

tions of carbaryl in three small agricultural watersheds in the Granger subbasin 

exceeded the aquatic-life criterion, and 

one detection of the insecticide malathion 

exceeded its criterion [18]. One detection 

of the insecticide disulfoton exceeded a 

nonenforceable human-health advisory for 

drinking water [7].

None of the herbicide detections 

in Moxee and Granger Drains or in the 

Yakima River at Kiona exceeded aquaticlife chronic-toxicity criteria. One detection of the herbicide metribuzin, however, 

exceeded its guideline [30] in the small 

agricultural watersheds. Even these occasional exceedances may affect the aquatic 

biota. In addition, most human-health and 

aquatic-life guidelines are based on single 

chemical toxicities, while chemicals in 

surface water often occur in mixtures. The 

potentially adverse effects of exposure 

to mixtures of pesticides on humans and 

aquatic biota is not fully understood and 

may be underestimated (see box below).

Mixtures of pesticides and pesticide breakdown products occurred at most sites

Ninety-one percent of the samples collected from the small agricultural watersheds contained at least two pesticides or 

pesticide breakdown products. The median number of chemicals in a mixture was 8, and the maximum was 26. The herbicide 2,4-D occurred most often in the mixtures. This was due to its widespread use not only on agricultural land, but also 

along roads, irrigation canals, and agricultural drains to 

control weeds. Azinphos-methyl, the most heavily applied 

pesticide, and atrazine, one of the most mobile in water, 

also occurred often in the mixtures.

Research to understand the effect of mixtures of pesticides 

on human health and aquatic life is in its early stages [32, 

33]. For some pesticide mixtures, laboratory studies have 

shown that test organisms respond to each compound in 

the mix as if it were exposed to a solution containing just 

that compound (additive). For other mixtures, test organisms respond as if they were exposed to lower concentrations of both compounds; that is, the mixture is less toxic 

than the individual compounds (antagonistic or protective). The opposite effect also has been observed—mixtures of some pesticides are more toxic than their individual components (synergistic) [34].

The USEPA has taken the initial steps to regulate mixtures of pesticides by conducting exposure and risk assessments for 

groups of chemicals having a common mode of toxicity. The first of these assessments has been completed for the organophosphate insecticides, which includes azinphos-methyl and diazinon [35]. These initial cumulative risk assessments only 

address human exposure in foods. Acute and chronic aquatic-life guidelines are still based on a single chemical exposure.

2,4-D + Atrazine + Terbacil

2,4-D + Atrazine + Bentazon

2,4-D + Atrazine + Diuron

2,4-D + Atrazine + 2,4-D methyl ester

2,4-D + Atrazine + Deethylatrazine

2,4-D + Deethylatrazine

2,4-D + Diuron

2,4-D + 2,4-D methyl ester

2,4-D + Atrazine

2,4-D + Azinphos methyl

PERCENTAGE OF SAMPLES

WITH THE INDICATED MIXTURE

0 25 50

The most frequently occurring mixtures of pesticides at sites 

sampled in July 2000 at concentrations greater than at the 

21 ng/L screening level.

1

10

100

1,000

100

20

40

60

80

C

O

N

C

E

N

T

R

ATIO

N, IN

N

A

N

O

G

R

A

M

S

P

E

R LIT

E

R

S

T

R

E

A

MFLO

W, IN

C

U

BIC FE

E

T

P

E

R

S

E

C

O

N

D

USEPA freshwater chronic-toxicity criterion=1,800 ng/L

1

10

100

J F M A M J J A S O N D J

1999 2000

100

20

40

60

80

ATRAZINE

AZINPHOS-METHYL

IRRIGATION SEASON

USEPA freshwater chronic-toxicity criterion=10 ng/L

500

Streamflow

Not detected

Pesticide detection

Figure 20. Because soluble pesticides like atrazine can percolate to the ground 

water, they are detected not only during the irrigation season when they are applied, 

but also during the nonirrigation season when ground water discharges to Granger 

Drain. In contrast, azinphos-methyl is detected only during the irrigation season, but 

almost always at levels exceeding the aquatic-life criterion. 
20 Water Quality in the Yakima River Basin

Cropping patterns and river management affect pesticide detections

Regional differences in cropping patterns 

in the Yakima River Basin are reflected in the 

occurrence of pesticides in water samples. An 

August 1999 sampling along the Yakima River 

and its tributary mouths showed more pesticide detections in the Lower Valley than in the 

Kittitas or Mid Valleys (fig. 21). The same pattern was evident in data collected in July 2000 

from the small agricultural watersheds. These 

differences reflect regional cropping patterns. 

As an example, in the Kittitas Valley, 89 percent 

of the irrigated agricultural land draining to 

the sampled sites was hay or pasture. Samples 

collected from these sites in July 2000 contained 19 unique pesticides or pesticide breakdown products, with a median of 8 compounds 

detected per site (fig. 22). In comparison, at 

sites near Sunnyside in the Lower Valley, six 

different crops made up 90 percent of the irrigated agricultural land. Samples collected from 

these sites contained 56 pesticide or pesticide 

breakdown products, with a median of 16 detections per site.

In addition to differences in crop types 

among the Kittitas, Mid, and Lower Valleys, 

there are differences in water volume in the 

Yakima River. For example, there is less water 

in the Yakima River in the Lower Valley. Three 

large irrigation canals divert water from the 

Yakima River downstream from the Kittitas 

Valley; however, there is only one significant 

natural inflow to the river along this reach (the 

Naches River). Less water in the river equates 

to less water available to dilute contaminants in 

agricultural return flow to the river. In August 

1999, the flow of the Yakima River where it left 

the Kittitas Valley was 2,700 cubic feet per 

second (ft3/s), of which approximately 300–

350 ft3/s was from agricultural drains and 

streams. Just downstream from where the river 

leaves the Mid Valley, the flow in the Yakima 

River was about 700 ft3/s. At Kiona, the flow in 

the Yakima had increased to about 2,000 ft3/s. 

Of the 1,300 ft3/s that the river gained between 

the Mid Valley and Kiona, inputs from agricultural streams and drains can account for 

approximately 900 ft3/s [7]. The reduced flow, 

combined with an increase in the agricultural 

return flows, resulted in an increase in the number of pesticides detected in the Yakima River. 

For example, the few detections in the sample 

collected from the Yakima River between 

Toppenish and Satus Creeks contrasts sharply 

Kittitas sites Sunnyside sites

N

U

M

B

E

R

O

F

U

NIQ

U

E

P

E

S

TICID

E

S

D

E

T

E

C

T

E

D

0

20

40

60

Herbicides

Insecticides

Other

PESTICIDES DETECTED

CROP TYPES

Other

Pasture

Orchard

Hops

Hay

Grapes

Corn

Figure 22. Many more pesticides were detected in the Lower Valley near 

Sunnyside than in the Kittitas Valley. This difference can be explained by the 

high diversity of crops grown in the Lower Valley compared with the Kittitas 

Valley, which is dominated by hay and pasture. 

N

U

M

B

E

R

O

F

D

E

T

E

C

TIO

N

S

0

5

10

15

20

25

AGRICULTURAL TRIBUTARIES IN DOWNSTREAM ORDER

Height of bar represents the total

number of pesticide detections

Insecticide detections

Herbicide detections

Yakima River pesticide detections

Wilson CreekCherry Creek

Naches River

U

mtanum

Creek

Moxee Drain

Wide Hollow

Creek

Ahtanum

Creek

East Toppenish Drain

Sub 35 Drain

Granger Drain

Marion Drain

Toppenish Creek

Satus Creek

South Drain

Sulphur Cr Wasteway

Spring Creek

Snipes Creek

Kittitas Valley Mid Valley Lower Valley

Figure 21. The number of pesticides detected in the Yakima River and its major 

agricultural tributaries increased from the Kittitas Valley to the Lower Valley 

due to an increase in the crop diversity and a decrease in the volume of water 

in the Yakima River.
Major Findings 21

with the large number of detections in 

the two samples collected downstream 

from Sulphur Creek Wasteway (fig. 21).

Pesticide loading to the 

Yakima River was highest 

in the Lower Valley

To evaluate relative contributions of 

pesticides to the Yakima River, the load

or mass of pesticide issuing from each 

tributary was calculated (fig. 23). Loads 

were used in the calculations because 

small tributaries with low flows and high 

concentrations can contribute as much 

pesticide mass as large tributaries with 

high flows and small concentrations. 

Pesticide loads were relatively small in 

the upper reaches of the Yakima River 

and throughout the Kittitas Valley [29], 

where hay, alfalfa, and cattle dominate 

the agricultural landscape. In the Lower 

Valley, however, where agricultural 

return flows from orchards, vineyards, 

and fields of corn, hops, grains, and 

other crops influence water quality, the 

loads of atrazine, terbacil, azinphosmethyl, and carbaryl from agricultural 

tributaries were notable (fig. 23). The 

chemical signature of each tributary 

contribution varied. For example, East 

Toppenish Drain contributed a significant portion of the 

terbacil load to the 

reach below the city 

of Yakima, whereas 

Toppenish Creek was 

a significant contributor of carbaryl.

Pesticide 

mobility is highly 

dependent on 

its tendency to 

adhere to soil 

particles

Many factors 

affect the mobility 

of pesticides in the 

environment, including the manner, amount, frequency, 

and timing of application; the method 

of irrigation; and the chemical properties of the pesticide. Other important 

factors are associated with landscape 

characteristics, such as soil properties, 

slope, and the proximity to flowing 

water. Two key factors help to explain 

pesticide occurrence in small agricultural watersheds in the Yakima River 

Basin: (1) the tendency of the pesticide to adhere to soil (as reflected by 

the organic-carbon partitioning coefficient, 

or Koc; see box on page 22) and (2) the 

method of irrigation (Hank Johnson and 

Dan Wise, U.S. Geological Survey, unpub. 

data, 2004).

For many pesticides, there was little 

correlation between the amount applied 

and the frequency of detection in streams 

and drains (fig. 24). For example, the two 

most frequently detected pesticides, 2,4-D 

and azinphos-methyl, differed markedly 

in the amount of active ingredient applied 

annually. Approximately nine times more 

azinphos-methyl was applied than 2,4-D, 

and yet it was detected about half as 

often. Similarly, the herbicides bentazon, 

dicamba, and terbacil ranked 35th, 33d, 

and 28th in use, respectively, but were the 

7th, 8th, and 9th most frequently detected 

pesticides. The insecticides chlorpyrifos 

and endosulfan were the 2d and 7th most 

heavily applied pesticides but were rarely 

detected. A general pattern emerges when 

the Koc values of these pesticides are compared (fig. 24): specifically, pesticides that 

strongly adhere to soil (high Koc value) 

were detected at a lower frequency than 

expected for their application amounts, 

while pesticides that weakly adhere to soil 

(low Koc value) were detected at a higher 

frequency than expected for their application amounts.

The method of irrigation affects the 

movement of high-Koc pesticides more 

than low-Koc pesticides. For example, 

in watersheds with a large percentage of 

Frequency of detection

100 80 60 40 20 0

Mass of chemical applied

35,000 70,000

Included with 2,4-D

Degradation product of atrazine

Pesticide

Deethylatrazine

Endosulfan 4,000

Disulfoton 600

Chlorpyrifos 6,070

Propargite 4,000

Norflurazon 600

EPTC 200

Carbaryl 300

Myclobutanil 500

Terbacil 55

Bentazon 34

Dicamba 2

Diuron 480

2,4-D methyl ester 100

Atrazine 100

Azinphos-methyl 1,000

2,4-D 20

PERCENT POUNDS OF ACTIVE INGREDIENT

Koc

0

--

Figure 24. Pesticides in irrigation runoff were not always detected in proportion to the 

quantity applied to agricultural land. Other factors, including the degree to which certain pesticides adhere to soil, affected how often pesticides were detected in agricultural runoff (see explanation of Koc in box on page 22).

East

Toppenish

Drain

Sub 35

Drain

Granger

Drain

Marion

Drain

Toppenish

Creek

0

5

10

15

20

25

30

35

40

P

E

S

TICID

E LO

A

D, IN

G

R

A

M

S

P

E

R

D

A

Y

*

*

* * *

HERBICIDES

Atrazine

Terbacil

Concentration exceeds aquatic-life guideline

INSECTICIDES

Azinphos-methyl

Carbaryl

*

Figure 23. The composition of pesticide loads discharged from 

agricultural tributaries in the Lower Valley varied greatly.
22 Water Quality in the Yakima River Basin

rill-irrigated fields, the yield (see box 

below) of high-Koc pesticides was larger 

than in watersheds with a small percentage of rill-irrigated fields (fig. 25). 

Pesticides with high Koc values tend to 

remain bound to the soil when irrigation 

water is applied. Downward migration 

through the soil is slow and provides the 

opportunity for a variety of processes to 

break down the pesticide. Therefore, the 

primary mechanism for the movement of 

these pesticides off the field is through 

the movement of the soil itself. In contrast, the yield of low-Koc pesticides was 

similar for all watersheds, regardless of 

irrigation method. Low-Koc pesticides 

do not strongly partition 

into the soil. They are 

easily transported off 

the field, either dissolved in rill tailwater or 

downward through the 

soil and into the shallow 

ground-water system 

where they enter the 

streams and drains as 

base flow.

Reducing soil 

erosion and irrigation 

runoff are two effective 

means of minimizing 

the transport of high-Koc

pesticides. Many BMPs 

designed to control 

erosion and runoff are 

commonly used in the 

Yakima River Basin, 

including irrigation-system conversions, settling ponds at the bottom of rill-irrigated fields, and the use of 

PAM in rill furrows and tail ditches. Continued implementation and proper operation 

of these and similar BMPs should continue to minimize the movement of high-Koc

compounds, including many of the most toxic insecticides such as azinphos-methyl, 

chlorpyrifos, and diazinon. Additional considerations are needed to control the transport of low-Koc pesticides. For these compounds, it is necessary to minimize both 

the surface and subsurface movement of water from the field. The use of soil-moisture sensors in conjunction with sprinkler or drip irrigation may help to reduce the 

transport of low-Koc pesticides to drains and streams.

Pesticide Yield

The yield of a pesticide describes 

how much of an applied pesticide 

reaches a sampled water body. The 

yield value is useful as a descriptive term to compare the relative 

mobility of one pesticide with 

another; however, it should not 

be used as a measurement of the 

actual amount of pesticide lost 

from an applied area. The yield is 

defined as the mass of a pesticide 

detected in the drain or stream 

water sample divided by the mass 

of the pesticide that was applied in 

that basin. Yields were calculated 

for each pesticide detected during 

the 2000 growing season (Hank 

Johnson and Dan Wise, U.S. Geological Survey, unpub. data, 2004).

Organic-carbon partitioning coefficient, Koc

When a pesticide is first applied, most of it attaches to soil or plant surfaces. When irrigation or rainwater reaches a treated field, a portion of the pesticide will dissolve into the water. The separation 

of a pesticide into two phases—dissolved in the water and bound to soil 

and plant material—is called partitioning. The amount of pesticide that 

dissolves in the water is controlled by a property of the pesticide called 

its organic-carbon partitioning coefficient, or Koc. A pesticide with a 

large Koc value will remain largely bound to the soil or plant material 

and only a small amount will dissolve in the water (see figure at right). 

Conversely, a pesticide with a small Koc value will more readily 

detach from the soil or plant material and dissolve in the water. 

Koc values for currently used pesticides range from less than 10 

(dicamba, clopyralid) to more than 100,000 (bifenthrin, oxyfluorfen).

Irrigation water entering

soil with a sorbed pesticide

Fate of low

Koc pesticide

Fate of high

Koc pesticide

�������������������������������

�����������������������������������

�����������������������

�������������������������������

�������

������

�����

����

���

�������������������������������

��� ���� ����� ������

��������������������������������

Figure 25. The yield of high-Koc (more sorptive) pesticides 

increased in proportion to the amount of rill-irrigated farmland, whereas the yield of low-Koc (less sorptive) pesticides 

was relatively constant. Generally, yields of low-Koc pesticides were higher than yields of high-Koc pesticides.

Detailed information on pesticides and breakdown products in surface 

water in the Yakima River Basin can be found in the following report:

Pesticides in surface water of the Yakima River Basin, Washington 

1999–2000—Their occurrence and an assessment of factors affecting 

concentrations and loads, by J.C. Ebbert and S.S. Embrey: U.S. Geological Survey Water-Resources Investigations Report 01–4211 at http:

//pubs.water.usgs.gov/wri014211/ 
Major Findings 23

Aquatic communities are affected by poor 

water-quality and habitat conditions in 

intensely agricultural areas

The composition of algae and benthic invertebrates

in streams and drains in the Yakima River Basin reflects 

the water-quality and habitat conditions in which they are 

found. In an effort to characterize the overall conditions 

at a site and allow comparisons among sites, a stream 

condition index (SCI) was developed based on water-quality and habitat conditions at each site. In general, streams 

and drains with higher SCI scores (good-condition sites) 

support more diverse and complex aquatic communities 

with fewer pollution-tolerant species. In the Yakima River 

Basin, the good-condition sites are associated with little or 

no agriculture. At sites with lower SCI scores (poor-condition sites), however, benthic-invertebrate assemblages 

are less diverse and increasingly composed of pollutiontolerant species, and algal assemblages are increasingly 

dominated by species indicative of high concentrations of 

nutrients. The poor-condition sites in the Yakima River 

Basin are associated with intensive agriculture. 

Agricultural activities affect streamwater quality and habitat

Agricultural activities in the Yakima River Basin have 

the potential to degrade water quality through the inputs of 

sediment, nutrients, and pesticides to streams. Additionally, 

habitat conditions in streams draining agricultural land 

may not be of sufficient quality to support diverse aquatic 

communities. Features such as woody debris, boulders, 

and side channels provide important habitats for aquatic 

life and help sustain productive aquatic ecosystems. These 

features commonly are lacking in constructed agricultural 

drains and stream channels modified to receive agricultural 

return flow. The low-quality habitat in modified channels 

does not provide adequate conditions for diverse aquatic 

assemblages to exist and is one of the major factors affecting aquatic communities in streams [36]. 

Natural-channel streams in the Yakima River Basin 

usually provide a mix of habitat types, such as riffles and 

pools that are critical for aquatic life. In contrast, instream 

habitat in agricultural drains and modified streams often 

lacks complexity and is often dominated by relatively deep 

and slow-moving runs. Agriculturally affected streams and 

drains also exhibit a high degree of substrate embeddedness (indicative of the degree of streambed siltation) and 

are sheltered by little riparian vegetation. Stream shading 

provided by riparian vegetation helps maintain lower water 

temperatures and also helps to stabilize stream banks. 

Riparian buffer zones can intercept sediment and other 

agricultural pollutants before they reach streams. When 

buffers are not present, erosion may result in stream sedimentation and negative effects to aquatic communities.

Stream Condition Index (SCI)

A stream condition 

index (SCI) was 

developed to characterize the overall 

water-quality and 

habitat conditions 

at a site. The SCI 

provides an overall 

measure of stream 

quality by using 

variables important 

for the health of 

aquatic organisms. 

The SCI includes 

four measures of 

water quality—

turbidity and the 

concentrations of 

total nitrogen, total 

phosphorus, and 

total pesticides—

and four measures 

of habitat quality—

substrate size,

habitat complexity, 

stream shading, 

and the percentage 

of run habitat (see 

p. 28 for details 

about calculating SCI scores). 

Though the five 

streams with poor 

stream condition 

are associated with 

intensive agriculture, there is no 

distinct geographic 

pattern—two sites 

are in the Kittitas 

Valley and three are 

in the Sulphur and 

Granger subbasins. 

All sites with good 

stream condition, 

however, are associated with little 

or no agriculture 

and are located on 

the west side of the 

basin.

N

I

K

O

G

X

W

J

V

H

S

U

A

T

L

E

D

P

M

Total phosphorusSubstrate sizeTurbidityTotal nitrogenPercent run habitatStream shadingHabitat complexity

Water-quality

variables

Habitat

variables

F

C

B

R

Q

Total pesticides

Sites

Stream

Condition Index 38

36

36

36

36

34

32

30

24

24

24

24

24

24

20

20

20

18

16

14

10

8

14

14

Poor condition Intermediate Good condition

B

E

A C

D F

G

I J

K

H

L M N O

P

Q

R

S

T U

V

W

X

EXPLANATION

Higher

Intermediate

Lower

See page 27 for full site names.

Good

Intermediate

Poor

Water/Habitat Quality

Stream Condition
24 Water Quality in the Yakima River Basin

Algal assemblages reflect 

nutrient availability in streams 

and drains

Algal biomass (as indicated by 

the amount of chlorophyll a in algae 

attached to stream rocks) in the Yakima 

River Basin was not especially high, 

with most sites having values less than 

25 milligrams per square meter (mg/m2). 

Nevertheless, there was a notable difference in biomass—good-condition sites 

had biomass values five times lower than 

those in intermediate- or poor-condition sites. The expected low biomass 

in the forested streams is due to the 

relatively low availability of nutrients 

and(or) light. In contrast, algal biomass 

in the agriculturally affected streams and 

drains was lower than expected. Here, 

biomass may be limited by light from 

high turbidity, by sedimentation that 

smothers suitable substrate where algae 

may attach, or by herbicides that interfere with algal photosynthesis. In the 

Yakima River Basin, only Moxee and 

Granger Drains had biomass values (180 

and 210 mg/m2, respectively) exceeding 

nuisance conditions (100–150 mg/m2

[37, 38]). High algal biomass at these 

sites may be due to the greater availability of nutrients and(or) sunlight (from 

poor stream shading). Another possibility is that insecticides may be reducing the density of benthic-invertebrate 

scrapers that would normally eat the 

algae. Although insecticide concentrations in Moxee and Granger Drains were 

relatively high and may have reduced 

the insect grazer population, variable 

streamflows or poor habitat also may 

have negatively affected benthic invertebrates in these drains, thereby indirectly 

increasing algal biomass.

Good Habitat Conditions

• Diversity of habitat types—

riffles, runs, and pools

• Good stream shading 

(dense riparian canopy)

• Variety of substrate sizes with 

minimal fine sediment Ahtanum Creek below Bachelor Creek

JD 27.5 at VanBelle Road

Mayflies are 

intolerant of 

poor stream 

conditions

Poor Habitat Conditions

• Low habitat complexity—

dominated by runs

• No stream shading 

(lack of riparian canopy)

• No coarse substrates—

mostly silt-sized sediments

Midges are 

tolerant of poor 

stream conditions

Photograph by Howell Daly, North American Benthological Society

Photograph by Dave Penrose, North American Benthological Society
Major Findings 25

Algal species composition in Yakima River 

Basin streams and drains was determined in part 

by the availability of nutrients, especially nitrogen. 

During this and the previous NAWQA study [39], the 

dominant types of algae found were those that prefer 

or require high concentrations of nutrients and alkaline conditions (pH greater than 7). In contrast, algae 

indicative of low or moderate nitrogen concentrations 

were mostly restricted to sites with high SCI scores 

(fig. 26), where the lowest nitrogen concentrations 

occurred. Here, the primary algal types were bluegreen algae, including Nostoc, and diatoms in the 

family Epithemiaceae, which are able to fix their own 

nitrogen. Nitrogen-fixing algae were notably absent, 

however, in nearly all of the agriculturally affected 

streams and drains. At these sites, higher concentrations of nitrogen create conditions favorable for other 

types of algae, especially eutrophic (high nutrient 

indicating) diatoms and high-biomass forms, such as 

Cladophora, a filamentous green algae. 

Benthic-invertebrate assemblages 

respond negatively to poor stream 

conditions in agricultural areas

Benthic invertebrates are good indicators of 

overall stream conditions, both water-quality and 

habitat conditions, due to the large number of organisms with widely diverse environmental requirements 

[40]. Sensitive or intolerant benthic invertebrates, 

such as EPT insects (see box below), generally live in 

streams with cool, clean water and diverse habitats. 

These organisms are usually found at sites with 

higher SCI scores. In the Yakima River Basin, average total benthic invertebrates were more abundant at 

sites with high SCI scores than at sites with low SCI 

scores (fig. 27). 

When just EPT insects are considered, the average abundance was 12 times higher at the sites with 

high SCI scores than at the sites with low SCI scores 

(fig. 27). EPT insects, calculated as a percentage of 

each site total, also showed a general increase as the 

SCI scores increased (fig. 28). Most sites with SCI 

scores above 28 had twice the percent EPT abundance (greater than 70 percent) of sites with SCI 

scores below 18 (less than 35 percent). 

8 12 16 20 24 28 32 36 40

STREAM CONDITION INDEX (SCI) SCORE

Better stream quality

RELA

TIVE PER

CEN

T

ABU

N

D

A

N

CE

OF EPT IN

SEC

T

S

0

20

40

60

80

100

0

2,000

4,000

6,000

8,000

10,000

12,000

Intermediate

SCI sites

Low SCI sites

(poor condition)

High SCI sites

(good condition)

14,000

A

VER

A

GE ABU

N

D

A

N

CE,

IN

N

U

MBER PER

S

Q

U

A

RE METER

Total benthic invertebrates

EPT insects

Figure 26. As the Stream Condition Index (SCI) scores increased, lownitrogen algal indicators also increased, while high-nitrogen algal indicators decreased.

Figure 28. Relative abundance of EPT insects increased as SCI scores 

increased.

Figure 27. As the Stream Condition Index (SCI) scores increased, the 

average abundance of benthic invertebrates and EPT insects increased.

EPT Insects

Insects in the Orders Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera 

(caddisflies)—EPT insects—are generally 

considered intolerant of poor habitat or waterquality conditions.

Intermediate

SCI sites

0

20

40

60

80

100

0

5

10

15

20

25

30

35

A

VER

A

GE PER

CEN

T

RELA

TIVE DEN

SIT

Y

FO

R

HIG

H-NIT

R

O

GEN

ALG

AL IN

DIC

A

T

O

R

S

A

VER

A

GE PER

CEN

T

RELA

TIVE DEN

SIT

Y

FO

R LO

W-NIT

R

O

GEN

ALG

AL IN

DIC

A

T

O

R

S

Low SCI sites

(poor condition)

High SCI sites

(good condition)

Low-nitrogen algal indicators

High-nitrogen algal indicators
26 Water Quality in the Yakima River Basin

In contrast to the mostly intolerant EPT insects, 

tolerant organisms can thrive in streams with varying combinations of high water temperatures; high 

amounts of sediment, nutrients, and pesticides; and 

simplified or poor habitat conditions. These tolerant 

benthic invertebrates, such as Dipterans (flies), oligochaetes (worms), and amphipods (scuds), are usually 

found in higher numbers at poor-condition sites (low 

SCI scores). This was indicated by a general decrease 

in the score of tolerant benthic invertebrates (based 

upon the USEPA tolerance value weighted by taxon 

abundance) as the SCI scores increased (fig. 29). 

The proportion of noninsects (primarily oligochaetes 

and amphipods) also decreased as the SCI scores 

increased (fig. 30). 

Benthic invertebrates can be classified into functional feeding groups based on how they obtain their 

food. A stream with good biological integrity generally has a diverse assemblage of feeding groups, not 

dominated by a few types. Scrapers are a functional 

feeding group of insects that graze algae and other 

microorganisms from rocks and plant surfaces. They 

are a vital link between the primary producers (algae) 

and higher trophic levels (fish) in stream food webs. 

The average scraper abundance among sites with 

high SCI scores (good water quality and habitat) was 

about 2,500 organisms/m2, while the average scraper 

abundance among sites with a low SCI was less than 

600 organisms/m2.

As previously discussed, benthic-invertebrate 

assemblages are affected by both water-quality and 

habitat conditions in streams, and it is difficult to isolate the effects of multiple factors. One of the factors 

that may affect aquatic life in streams is pesticides. 

Pesticides were commonly detected in streams and 

drains throughout the basin, often at concentrations 

exceeding the chronic aquatic-life criteria for one or 

more pesticides. To assess the relative toxicity of the 

waters in each stream or drain sampled, a pesticide 

toxicity index (PTI) was applied [41]. Although the 

PTI does not verify whether water in a sample is 

toxic, its values can be used to rank or compare the 

relative toxicity of samples. In general, sites where 

insecticides were found had higher PTI scores compared to sites where only herbicides were detected 

because insecticides are more toxic to benthic invertebrates than herbicides. Furthermore, as the PTI scores 

increased, the number of tolerant taxa increased 

(fig. 31). The higher number of tolerant taxa at these 

sites, however, may also be related to other factors, 

such as poor habitat quality.

2

3

4

5

6

7

8 12 16 20 24 28 32 36 40

BENTHIC INVERTEBR

ATE

TOLER

ANCE SC

O

RE

STREAM CONDITION INDEX (SCI) SCORE

Better stream quality

STREAM CONDITION INDEX (SCI) SCORE

Better stream quality

8 12 16 20 24 28 32 36 40

0

0.5

1.0

1.5

2.0

LO

G PER

CENT NONINSECTS

Figure 29. Tolerant benthic invertebrates decreased as SCI scores 

increased.

Figure 30. Proportion of noninsects was highest at sites with low SCI 

scores.

0

5

10

15

20

25

Sites with pesticides detected

Sites with no pesticides detected

0 5 10 15 20 25

PESTICIDE TOXICITY INDEX (RANK)

FOR BENTHIC INVERTEBRATES

N

U

MBER

OF T

OLER

A

N

T

BEN

T

HIC-IN

VER

TEBR

A

TE T

A

X

A (R

A

N

K)

Increasing pesticide concentration

Figure 31. The number of tolerant taxa increased as the Pesticide Toxicity 

Index (PTI) scores increased. A high PTI rank does not necessarily mean 

the water was toxic to the benthic invertebrates.
Study Unit Design 27

Water Quality in the Yakima River 

and Major Agricultural Tributaries*

 1. Yakima River at Cle Elum 13. Granger Drain

 2. Wilson Creek 14. Marion Drain

 3. Cherry Creek 15. Toppenish Creek

 4. Umtanum Creek 16. Yakima R at river mile 72

 5. Yakima River at Umtanum 17. Satus Creek

 6. Naches River 18. South Drain

 7. Moxee Drain 19. Sulphur Creek Wasteway

 8. Wide Hollow Creek 20. Yakima River at Grandview

 9. Yakima River at Union Gap 21. Spring Creek

10. Ahtanum Creek 22. Snipes Creek

11. East Toppenish Creek 23. Yakima River at Kiona

12. Sub 35 Drain

*Umtanum Creek (site 4) was sampled to assess natural background conditions and does not receive agricultural return flow.

Aquatic Ecological Conditions of 

Streams and Drains

A. Caribou Creek M. Granger Drain

B-C. Park Creek N. Toppenish Creek

 B. at Park Creek Road O. Satus Creek

 C. at South Ferguson Rd P. JD 34.2 at Woodin Road

D. Johnson Drain Q. JD 51.4 at Yakima River

E. Badger Creek R. JD 52.8 Wamba Road

F. Cherry Creek S. JD 55.1 at Bettinson Road

G. Umtanum Creek T-V. Spring Creek 

H. Moxee Drain T. at Hanks Road

I-K. Ahtanum Creek U. at McCreadie Road

 I. below Bachelor Creek V. at mouth at Whitstran

 J. at 62d Avenue W-X. Snipes Creek

 K. at Union Gap W. at McCreadie Road

L. JD 27.5 at VanBelle Road X. at mouth at Whitstran

Water Quality in Small Agricultural Watersheds

Small agricultural watersheds were studied to understand 

how sediment and agricultural chemicals move from fields into 

waterways in the Yakima River Basin. Sampling sites for water 

chemistry and suspended sediment were located at the outflows 

of 44 agricultural watersheds and 2 nonagricultural reference 

watersheds. Nine irrigation-water delivery canals also were 

sampled. Sites were sampled two times during the 2000 irrigation season and once immediately after the canals were shut 

down for the winter. Detailed information on soil properties, 

crops grown, irrigation methods used, nutrients and pesticides 

used, slope of the land surface, and elevation were gathered for 

each watershed. Environmentally relevant physical and chemical 

properties were obtained for each chemical known to have been 

applied in the watersheds.

Study-Unit Design

Yakima

Richland

Forest

Land cover

EXPLANATION

Range

Cities and towns

Agriculture

Streams and drains

Yakima River

Canals

25 Miles

47°30'

46°00'

121°00'

119°30'

Sampling site

1

2 3

4

4 Site number

Frequently sampled site

5

7

10 9

8

6

11 13

14

12

15 17 19

20 18

16 21 22

23

0

Yakima

Richland

Forest

Land cover

EXPLANATION

Range

Cities and towns

Agriculture

Streams and drains

Canals

Yakima River

25 Miles

47°30'

46°00'

121°00'

119°30'

Sampling site

0

Yakima

Richland

Forest

Land cover

EXPLANATION

Range

Cities and towns

Agriculture

Streams and drains

Canals

Yakima River

25 Miles

47°30'

46°00'

121°00'

119°30'

Sampling site

Trend site

0

B

E

C A

D F

G

I J K H

L

N M

O

P

Q

R S

T U

V

W

X
28 Water Quality in the Yakima River Basin

The Yakima NAWQA Study during 1999–2000

Study

component

What data were collected

and why Types of sites sampled Number of sites sampled Sampling frequency and period

Stream Chemistry

Intensive 

fixed sites

Streamflow, field parameters,1

102 currently used2 and 23 historically used pesticides and their 

breakdown products,3 23 trace 

elements, nutrients, major ions, 

and suspended sediment to 

describe concentrations.

Yakima River at Kiona 

(12510500) near the mouth 

of the basin and two agricultural drains—Moxee Drain at 

Birchfield Road (12500420) 

and Granger Drain at Granger 

(12505450)

3 Biweekly at Kiona and weekly 

at Moxee and Granger Drains 

during the irrigation season 

(May–September 1999) and 

monthly during the nonirrigation 

season (October 1999–

January 2000)

Synoptic 

sampling—

general 

water quality

The same constituents as above to 

examine occurrence, distribution, 

and transport.

6 Yakima River sites, 

mouths of 17 major tributaries, 

3 reference sites, and 

8 wastewater-treatment plants

34 August 2–6, 1999

Aquatic Ecology

Aquatic 

biology—

single-reach 

assessment

Aquatic insects, algae, chlorophyll 

a, stream habitat, 176 pesticides 

and breakdown products,3 and 

nutrients to assess the response 

of the ecological community to 

agricultural influences.

Mouths of 7 major tributaries 

(these trend sites were sampled 

in 1990 also), 17 streams and 

drains in medium-sized 

agricultural watersheds

24 September–October 2000 

 (habitat, algae, aquatic insects)

July–September 2000 

 (water quality)

Special Studies

Synoptic 

samplings—

agricultural 

chemicals

Streamflow, field parameters,1

176 currently used pesticides 

and breakdown products,3 and 

nutrients to examine how agricultural practices and landscape 

characteristics affect runoff.

Streams and drains in small 

agricultural watersheds

51

57

45

June 12–22, 2000

July 10–20, 2000

October 30–November 2, 2000

Synoptic 

samplings—

fecal-indicator 

bacteria

Fecal coliform bacteria, 

Escherichia coli, and 

enterococci to examine 

occurrence and distribution.

Streams and drains included in 

the general water-quality and 

agricultural chemical synoptic 

samplings listed above

25

57

43

August 2–6, 1999

July 10–20, 2000

October 30–November 2, 2000

Synoptic

samplings—

emerging 

contaminants

28 antibiotic compounds, 21 human prescription and nonprescription drugs, 46 organic wastewater 

contaminants, and 14 steroid 

compounds as part of a nationwide 

reconnaissance.

Yakima River at Kiona 

(12510500) near the mouth 

of the basin and a well in an 

animal feeding operation in 

the Lower Valley

2 July 19, 2000 (Kiona)

August 28, 2000 (well)

1

Field parameters are turbidity, dissolved oxygen, pH, specific conductance, and water temperature.

2

Between March 1999 and March 2000, the method [42] used for analyzing some of these pesticide compounds was not yet approved and analysis protocols 

were not always met; therefore, the data were qualified [43]. 3

The listing of current pesticides analyzed was derived from a national listing based on pesticide use and was not designed to be exhaustive.

Calculation of the Stream Condition Index (SCI)

Individual scores for each water-quality and habitat measure at a site were assigned a categorical value based on percentile distributions 

(5=0–25th, 3=25–75th, and 1=75–100th). For substrate size, habitat complexity, and stream shading, scoring was reversed so that a categorical value of 5 always represents the highest quality condition. The SCI score is the sum of all eight categorical values for all of the 

water-quality and habitat measures combined, with scores ranging from 8 (poor condition) to 40 (good condition). 

For example, concentrations of total phosphorus ranged from 0.03 to 0.48 mg/L. The 25th percentile was 0.08 mg/L and the 75th percentile was 0.21 mg/L. Sites with concentrations of total phosphorus less than or equal to 0.08 mg/L received a score of 5, while sites with 

concentrations between 0.08 and 0.21 mg/L received a score of 3. Likewise, sites with concentrations greater than 0.21 mg/L received a 

score of 1. A similar analysis was performed for each site on all eight measures used in the SCI.
Study Unit Design 29

The Yakima NAWQA Study during 1987–91

Study

component

What data were collected

and why Types of sites sampled Number of sites sampled Sampling frequency and period

Stream Chemistry

Intensive fixed 

sites—general 

water quality

Streamflow, field parameters,1

nutrients, major ions, suspended 

sediment, and trace elements 

(both in water and on suspended 

sediment) to describe concentrations and determine occurrence.

Yakima R at Cle Elum (12479500), 

Umtanum (12484500), Union 

Gap (12500450), Grandview 

(12509050), Kiona (12510500); 

Naches River (12499000); 

Sulphur Creek Wasteway 

(12508850)

7 Monthly (April 1987–90)

and several storm events

Intensive fixed 

sites—

pesticides

Streamflow, field parameters,1

organic compounds,2 and suspended sediment to describe concentrations and examine seasonal 

variability.

Seven major tributaries and the 

Yakima River at Kiona (12510500)

8 May, June, July, August, 

November 1988; March 1989

Synoptic 

samplings—

pesticides

Streamflow, field parameters,1

organic compounds,2 and 

suspended sediment to determine 

spatial distribution and to 

examine transport characteristics.

Yakima River sites, major and 

minor tributaries, and agricultural 

streams and drains

18 (unfiltered)

~30 

(filtered and 

suspended)

July 1988 (unfiltered water)

June 1989; May–July, 

September 1991 

(filtered and suspended phases)

Synoptic 

samplings—

nutrients and 

trace elements

Streamflow, field parameters,1

trace elements, and nutrients to 

examine occurrence, distribution, 

and seasonal variability.

Yakima River sites, major and 

minor tributaries, and agricultural 

streams and drains

~100 (nutrients)

~30 

(trace elements)

August 1986; 

July, November 1987; 

March, July 1988 (nutrients)

July, November 1987; 

May 1989; March 1990 

(trace elements)

Contaminants 

in streambed 

sediment

Organic and semivolatile organic 

compounds, organic carbon, and 

trace elements to determine 

occurrence, distribution, and 

associations with crops.

Yakima River sites, major and 

minor tributaries, and agricultural 

streams and drains

~30 (organics)

~460 

(trace elements)

Varied 1987–90 (organics)

Varied 1987–91 (trace elements)

Contaminants 

in tissues of 

aquatic 

organisms

Historically used pesticides, 

polycyclic aromatic hydrocarbons (PAHs), and trace elements 

in fish, insects, clams, and plants 

to describe concentrations.

Yakima River sites, major and 

minor tributaries, and agricultural 

streams and drains

~50 (organics)

~30 

(trace elements)

May, October, November 1989; 

October, November 1990 

(organics)

May, November 1989; 

November 1990; October 1991 

(trace elements)

Aquatic Ecology

Aquatic 

biology

Aquatic insects, algae, fish community structure, stream habitat, 

and more than 140 variables to 

assess linkages between biological characteristics and land use.

Large-river sites and sites from 

each of the three ecoregions—

Cascades, Eastern Cascades, and 

Columbia Basin

25 October–November 1990

Special Studies

Synoptic 

samplings—

radionuclides

Gross alpha and beta activities 

in filtered water and suspended 

sediment to assess conditions.

The general water-quality intensive 

fixed sites shown above

7 April, May, August, 

November 1987; 

December 1989; January 1990

Synoptic 

sampling—

fecal-indicator 

bacteria 

Fecal coliform bacteria, 

Escherichia coli, turbidity, and 

suspended sediment to examine 

occurrence and distribution.

Yakima River sites, major and 

minor tributaries, and agricultural 

streams and drains

58 July 1988

1

Field parameters are turbidity, dissolved oxygen, pH, specific conductance, and water temperature. 

2

Carbamates, chlorophenoxy-acid herbicides, organophosphorus compounds, and triazine herbicides.
30 Water Quality in the Yakima River Basin

References Cited

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January 29, 2001.

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programs/wq/tmdl/watershed/yakima_wq/intro.html, 

accessed February 4, 2004.

3. Bonneville Power Administration, 1985, Issue Alert—

Yakima Basin passage improvement—July 1985: 

Report 1A–4–18, 8 p.

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cleanup plans (TMDLs) in the Yakima River Basin: http://

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the Yakima River Basin in Washington: Overview of 

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water quality criteria recommendations—Rivers and 

streams in Nutrient Ecoregion III: EPA 822–B–00–016, 

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nutrients in surface water of the Yakima River Basin, 

Washington, 1999–2000—With an analysis of trends in 

concentrations: U.S. Geological Survey Water-Resources 

Investigations Report 03–4026, 100 p. [also available at 

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Low, W.H., Ott, D.S., 1998, Water quality in the Upper 

Snake River Basin, Idaho and Wyoming, 1992–95: 

U.S. Geological Survey Circular 1160, 35 p.

11. Dubrovsky, N.M., Kratzer, C.R., Brown, L.R., Gronberg, 

J.M., and Burow, K.R., 1998, Water-quality in San JoaquinTulare Basins, California, 1992–95: U.S. Geological Survey 

Circular 1159, 38 p.

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Ebbert, J.C., and Vanderpool, A.M., 1997, Water quality

in the Central Columbia Plateau, Washington and Idaho, 

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An examination of 1999 and 2000 synoptic-sampling data 

and their relation to historical data: U.S. Geological Survey 

Water-Resources Investigations Report 02–4054, 32 p. [also 

available at http://pubs.water.usgs.gov/wri024054/]

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15. Fetter, C.W., 1993, Contaminant hydrogeology: New York, 

Macmillan Publishing Company, 458 p.

16. Fuhrer, G.J., Cain, D.J., McKenzie, S.W., Rinella, J.F., 

Crawford, J.K., Skach, K.A., and Hornberger, M.I., 1999, 

Surface-water-quality assessment of the Yakima River Basin 

in Washington—Spatial and temporal distribution of trace 

elements in water, sediment, and aquatic biota, 1987–91: 

U.S. Geological Survey Water-Supply Paper 2354–A, 186 p.

17. Sell, Ron, and Knutson, L., 2002, Quality of ground water 

in private wells in the lower Yakima Valley, 2001–02: 

Yakima, Washington, Valley Institute for Research and 

Education, 71 p.

18. U.S. Environmental Protection Agency, 2002, National 

recommended water quality criteria, 2002: EPA-822-R02-047, accessed February 4, 2004, at http://www.epa.gov/

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risk information system (IRIS)—Arsenic, inorganic 

(CASRN 7440-38-2): http://www.epa.gov/iris/subst/

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chemicals in special review: EPA–738–R–00–001, 

accessed February 4, 2004, at http://www.epa.gov/oppsrrd1/

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21. Rinella, J.F., McKenzie, S.W., Crawford, J.K., Foreman, 

W.T., Fuhrer, G.J., and Morace, J.L., 1999, Surface-waterquality assessment of the Yakima River Basin, Washington—Distribution of pesticides and other organic compounds in water, sediment, and aquatic biota, 1987–91: 

U.S. Geological Survey Water-Supply Paper 2354–B, 180 p. 
References Cited 31

22. Washington Department of Health, 1993, DDT in bottom 

fish from the Yakima River: Washington Department of 

Health, Office of Toxic Substances [pamphlet].

23. U.S. Geological Survey, Biomonitoring of Environmental 

Status and Trends Large Rivers Program—BEST Database 

Query Tool: http://www.cerc.usgs.gov/data/best/search/, 

accessed February 12, 2004. 

24. U.S. Environmental Protection Agency, 2002, Columbia 

River Basin Fish Contaminant Survey, 1996–98: EPA 910/

R–02–006, 246 p.

25. Newell, A.J., Johnson, D.W., and Allen, L.K., 1987, Niagara River Biota Contamination Project—Fish flesh criteria 

for piscivorous wildlife: New York State Department of 

Environmental Conservation, Division of Fish and Wildlife, 

Bureau of Environmental Protection, Technical Report 87-3. 

26. U.S. Geological Survey, 2001, Water quality in the Yakima 

River Basin—Data: http://or.water.usgs.gov/yakima/

data.html, accessed February 4, 2004. 

27. Joy, Joe, and Patterson, Barbara, 1997, A suspended sediment and DDT total maximum daily load evaluation report 

for the Yakima River: Olympia, Washington State Department of Ecology, Publication no. 97–321, 110 p.

28. Kolpin, D.W., Furlong, E.T., Meyer, M.T., Thurman, E.M., 

Zaugg, S.D., Barber, L.B., and Buxton, H.T., 2002, 

Pharmaceuticals, hormones, and other wastewater 

contaminants in U.S. streams, 1999–2000—A national 

reconnaissance: Environmental Science and Technology, 

v. 36, p. 1202–1211. 

29. Ebbert, J.C., and Embrey, S.S., 2002, Pesticides in surface 

water of the Yakima River Basin, Washington 1999–2000—

Their occurrence and an assessment of factors affecting 

concentrations and loads: U.S. Geological Survey WaterResources Investigations Report 01–4211, 49 p. [also 

available at http://pubs.water.usgs.gov/wri014211/]

30. Canadian Council of Ministers of the Environment, 2002, 

Canadian Environmental Quality Guidelines, Summary 

Table, 2002: Canadian Council of Ministers of the 

Environment, accessed February 4, 2004, at http://

www.ccme.ca/assets/pdf/e1_06.pdf.

31. International Joint Commission United States and Canada, 1989, Great Lakes water quality agreement of 1978, 

as amended by protocol signed November 18, 1987—

Annex 1, Specific objectives: http://www.ijc.org/rel/agree/

quality.html, accessed February 4, 2004.

32. Mileson, B.E., 1999/2000, Common mechanism of toxicity—Evaluation of carbamate pesticides: Reviews in 

Toxicology, v. 3, 1999/2000, p. 127–138.

33. Richardson, J.R., Chambers, H.W., and Chambers, J.E., 

2001, Analysis of the additivity of in vitro inhibition of 

cholinesterase by mixtures of chlorpyrifos-oxon and 

azinphosmethyl-oxon: Toxicology and Applied 

Pharmacology, v. 172, p. 128–139.

34. Danish Veterinary and Food Administration, 2003, 

Combined actions and interactions of chemicals in mixtures—The toxicological effects of exposure to mixtures of 

industrial and environmental chemicals: Fodevare Rapport 

2003, v. 12, 158 p.

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Organophosphate pesticides—Revised OP cumulative risk 

assessment: http://www.epa.gov/pesticides/cumulative/

rra-op/, accessed February 4, 2004.

36. Waters, T.F., 1995, Sediment in streams—Sources, 

biological effects and control: Bethesda, Maryland, 

American Fisheries Society, Monograph 7, 251 p.

37. Welch, E.B., Jacoby, J.M., Horner, R.R., and Seeley, 

M.R., 1988, Nuisance biomass levels of periphytic algae in 

streams: Hydrobiologia, v. 157, p. 161–168.

38. Welch, E.B., Horner, R.R., and Patmont, C.R., 1989, 

Prediction of nuisance periphytic biomass—A management 

approach: Water Resources, v. 23, no. 4, p. 401–405.

39. Cuffney, T.F., Meador, M.R., Porter, S.D., and Gurtz, M.E., 

1997, Distribution of fish, benthic invertebrate, and algal 

communities in relation to physical and chemical conditions, 

Yakima River Basin, Washington, 1990: U.S. Geological 

Survey Water-Resources Investigations Report 96–4280, 

94 p.

40. Rosenberg, D.M., and Resh, V.H., 1993, Freshwater 

biomonitoring and benthic macroinvertebrates: New York, 

Chapman and Hall, p. 488.

41. Munn, M.D., and Gilliom, R.J., 2001, Pesticide toxicity 

index for freshwater aquatic organisms: U.S. Geological 

Survey Water-Resources Investigations Report 01–4077, 

55 p.

42. Furlong. E.T., Anderson, B.D., Werner, S.L., Soliven, 

P.P., Coffey, L.J., and Burkhardt, M.R., 2001, Methods of 

analysis by the U.S. Geological Survey National Water 

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by graphitized carbon-based solid-phase extraction and 

high-performance liquid chromatography/mass spectrometry: U.S. Geological Survey Water-Resources Investigations 

Report 01–4134, 73 p. 

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Data-reporting conventions and implications for interpreting 

results from custom method 9060 for samples collected from 

March 1, 1999, to December 31, 1999: National Water Quality Laboratory Technical Memo 03.01, February 28, 2003. 
32 Water Quality in the Yakima River Basin

Glossary

Agricultural return flow—The water in an aquifer or surfacewater body that comes from delivered but unused irrigation 

water, operational discharges from canals, and the portion 

of irrigation water applied to a field that is not consumed by 

evapotranspiration or uptake by plants.

Algae—Chlorophyll-bearing nonvascular, primarily aquatic 

species that have no true roots, stems, or leaves; most algae 

are microscopic, but some species can be as large as vascular 

plants.

Aquifer—A water-bearing layer of soil, sand, gravel, or rock 

that will yield usable quantities of water to a well. 

Assemblage—A grouping of species from the same general 

category of living organisms such as fish, aquatic insects, hard 

wood trees, or riparian vegetation. 

Benthic invertebrates—Insects, mollusks, crustaceans, 

worms, and other organisms without a backbone that live in, 

on, or near the bottom of lakes, streams, or oceans. 

Best management practice (BMP)—An agricultural practice 

that has been determined to be an effective, practical means of 

preventing or reducing nonpoint-source pollution.

Biomass—The amount of living matter, in the form of organisms, present in a particular habitat, usually expressed as 

weight per unit area. 

Breakdown product—A compound derived by chemical, biological, or physical action upon a pesticide. The breakdown is 

a natural process that may result in a more toxic or a less toxic 

compound that is either more persistent or less persistent than 

the parent compound. 

Community—In ecology, the species that interact in a common 

area. 

Criterion—A standard rule or test on which a judgment or 

decision can be based.

DDT—Dichloro-diphenyl-trichloroethane. An organochlorine 

insecticide no longer registered for use in the United States.

Diversion—A turning aside or alteration of the natural course 

of a flow of water, normally considered physically to leave the 

natural channel. In some States, this can be a consumptive use 

direct from another stream, such as by livestock watering. In 

other States, a diversion must consist of such actions as taking 

water through a canal, pipe, or conduit. 

Drip irrigation—An irrigation system in which water is applied 

directly to the root zone of plants by means of applicators (orifices, emitters, porous tubing, perforated pipe, and so forth) 

operated under low pressure. The applicators can be placed on 

or below the surface of the ground or can be suspended from 

supports. 

Habitat—The part of the physical environment where plants 

and animals live.

Intolerant organisms—Organisms that are not adaptable to 

human alterations to the environment and thus decline in numbers where human alterations occur. See also Tolerant species. 

Load—General term that refers to a material or constituent in 

solution, in suspension, or in transport; usually expressed in 

terms of mass or volume. 

Micrograms per liter (μg/L)—A unit expressing the concentration of constituents in solution as weight (micrograms) of 

solute per unit volume (liter) of water; equivalent to one part 

per billion (ppb) in most stream water and ground water. One 

thousand micrograms per liter equals 1 milligram per liter.

Nanograms per liter (ng/L)—A unit expressing the concentration of constituents in solution as weight (nanograms) of solute per unit volume (liter) of water; equivalent to one part per 

trillion in most stream water and ground water. One thousand 

nanograms per liter equals 1 μg/L.

Riffle—A shallow part of the stream where water flows swiftly 

over completely or partially submerged obstructions to produce surface agitation. 

Rill irrigation—A type of surface irrigation in which water is 

applied at the upper end of a field and flows in furrows to the 

lower end. 

Riparian—Areas adjacent to rivers and streams with a high 

density, diversity, and productivity of plant and animal species 

relative to nearby uplands.

Run—A relatively shallow part of a stream with moderate 

velocity and little or no surface turbulence.

Streamflow—A type of channel flow, applied to that part 

of surface runoff in a stream whether or not it is affected by 

diversion or regulation. 

Suspended sediment—Particles of rock, sand, soil, and 

organic detritus carried in suspension in the water column, in 

contrast to sediment that moves on or near the streambed.

Taxon (plural taxa)—Any identifiable group of taxonomically 

related organisms. 

Tolerant species—Those species that are adaptable to 

(tolerant of) human alterations to the environment and often 

increase in number when human alterations occur. 

Turbidity—Reduced clarity of surface water because of suspended particles, usually sediment. 

Unfiltered water—Water that has not been filtered or centrifuged, or altered in any way from the original matrix.

Withdrawal—The act or process of removing; such as removing water from a stream for irrigation or public water supply. 

Yield—The mass of material or constituent transported by a 

river in a specified period of time divided by the drainage area 

of the river basin. 
Appendix 33

Appendix—Water-Quality Data from the Yakima River Basin 

in a National Context

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Coordination with agencies and organizations in the Yakima River Basin was integral to the success 

of this water-quality assessment. We thank those who served as members of our liaison committee. 

Federal Agencies

U.S. Environmental Protection Agency

Bureau of Reclamation

USDA–Forest Service

U.S. Fish and Wildlife Service

U.S. Bureau of Indian Affairs

Natural Resources Conservation 

 Service

Indian Nations

Yakama Indian Nation

State Agencies

Washington Department of Agriculture

Washington Department of Ecology

Washington Department of Fisheries

Washington Department of Health

Washington Department of Wildlife

Universities

Washington State University

Local Agencies

Benton Conservation District

Kittitas County Conservation District

North Yakima Conservation District

South Yakima Conservation District

Kittitas Reclamation District

Yakima County

Roza Irrigation District

Sunnyside Valley Irrigation District

Wapato Irrigation District

Roza–Sunnyside Board of Joint Control

We thank the following individuals for contributing to this effort. 

Sampling

Dewey Copeland

Joseph Gilbert

Ellen Harris

Jennifer Key

 (Central Washington University)

C.G. Laird

Stuart McKenzie 

 (retired, U.S. Geological Survey)

Jeanette O’Neil

Paivikki “Vicky” Pihl 

 (Tampere University, Finland)

Stephen Rodgers

Michael Sarantou

Johnna Sheehy

Wastewater Treatment Plant Operators

 in Cle Elum, Ellensburg, Granger,

 Prosser, Selah, Sunnyside, Yakima,

 and Zillah

Sampling Support

Amy Brooks

Brent Morace (volunteer)

Bacteria Sampling Coordination

 and Analysis Funding

Chris Coffin and 

Ryan Anderson 

 (Washington Department of Ecology)

Sample Analysis

Staff at USGS National Water Quality

 Laboratory in Denver, Colorado

Staff at Washington Dept. of Ecology 

 Laboratory in Manchester, Washington

Ann Rice 

 (Roza–Sunnyside Board of Joint Control)

William Rice 

 (Roza–Sunnyside Board of Joint Control)

Collaborating Agencies

Stephen Fanciullo 

 (Bureau of Reclamation)

Anna Lael 

 (Kittitas County Conservation District)

Scott Manley

 (Benton Conservation District)

William Rice 

 (Roza–Sunnyside Board of Joint Control)

Roger Satnik 

 (Kittitas Reclamation District)

Moses Squeochs

 (Yakama Indian Nation)

Robert Stevens

 (Washington State University, 

 Prosser Irrigated Agriculture Research 

 and Extension Center)

James Thomas

 (Yakama Indian Nation)

Marie Zuroske 

 (South Yakima Conservation District)

Information

Laurie Crowe 

 (South Yakima Conservation District)

Stuart McKenzie

 (retired, U.S. Geological Survey)

Onni Perala 

 (Roza Irrigation District)

Michael Tobin 

 (North Yakima Conservation District)

Marie Zuroske 

 (South Yakima Conservation District)

Technical Reviews

Stephen Anthony

 (U.S. Geological Survey)

Onni Perala 

 (Roza Irrigation District)

Marie Zuroske 

 (South Yakima Conservation District)
Fuhrer and others— Water Quality in the Yakima River Basin 

U.S. Geological Survey Circular 1237

National Water-Quality Assessment (NAWQA) Program

Yakima River Basin

NAWQA

COLUMBIA RIVER

COLUMBIA RIVER

Richland

Yakima River Yakima

Ellensburg

WASHINGTON

OREGON