U.S. Department of the Interior

U.S. Geological Survey

In cooperation with the 

Idaho Division of Environmental Quality and 

Lower Boise River Water Quality Plan, Inc.

Water-Quality Conditions of 

the Lower Boise River, Ada and 

Canyon Counties, Idaho, May 

1994 Through February 1997

Water-Resources Investigations Report 98–4111
Water-Quality Conditions of 

the Lower Boise River, Ada and 

Canyon Counties, Idaho, May 

1994 Through February 1997

By William H. Mullins

Water-Resources Investigations Report 98–4111

In cooperation with the

Idaho Division of Environmental Quality and 

Lower Boise River Water Quality Plan, Inc.

Boise, Idaho

1998
U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Thomas J. Casadevall, Acting Director

Any use of firm, trade, and brand names in this report is for

identification purposes only and does not constitute 

endorsement by the U.S. Government.

Additional information can be obtained from: Copies of this report can be purchased from

District Chief U.S. Geological Survey

U.S. Geological Survey Information Services

230 Collins Road Box 25286

Boise, ID 83702-4520 Federal Center

http://idaho.usgs.gov Denver, CO 80225

e-mail: infoservices@usgs.gov
CONTENTS

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Study background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Description of the lower Boise River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Geographic setting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Geologic setting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Land use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Surface water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Ground water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Previous investigations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Methods of data collection and analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Water-quality conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Nitrogen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Phosphorus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Nitrogen-to-phosphorus ratios. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Suspended sediment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Nitrogen and phosphorus loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Selected water-quality constituents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Dissolved oxygen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

pH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Specific conductance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Water temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Fecal coliform bacteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

References cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

FIGURES

1. Location of lower Boise River Basin and sampling sites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

2. Schematic diagram of diversions, drains, and tributaries along the Boise River from Lucky Peak Lake

to Snake River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

3. Graphs showing annual mean discharge and mean monthly discharge in the Boise River near Parma, 

water years 1975–96 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

4. Graphs showing discharges at which water-quality samples were collected at Boise River sites, May 1994

through February 1997. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

5. Boxplots showing instantaneous concentrations and daily loads of total nitrogen in samples from 19 sites 

in the lower Boise River Basin, May 1994 through February 1997 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

6. Boxplots showing instantaneous concentrations and daily loads of dissolved inorganic nitrogen in samples 

from 19 sites in the lower Boise River Basin, May 1994 through February 1997 . . . . . . . . . . . . . . . . . . . . . . . 

7. Graphs showing time series and trend line of concentrations of total nitrogen and dissolved inorganic 

nitrogen in samples from the Boise River near Parma, June 1974 through February 1997 . . . . . . . . . . . . . . . . 

8. Boxplots showing instantaneous concentrations and daily loads of total phosphorus in samples from 19 sites

in the lower Boise River Basin, May 1994 through February 1997 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

9. Boxplots showing instantaneous concentrations and daily loads of dissolved orthophosphorus in samples 

from 19 sites in the lower Boise River Basin, May 1994 through February 1997 . . . . . . . . . . . . . . . . . . . . . . . 

10. Graphs showing time series and trend line of concentrations of total phosphorus and dissolved orthophosphorus in samples from the Boise River near Parma, June 1974 through February 1997 . . . . . . . . . . . . . . . . . 

11. Boxplots showing mass ratios of dissolved inorganic nitrogen to dissolved orthophosphorus, grouped by

Boise River sites, May 1994 through February 1997 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Co
12. Boxplots showing instantaneous concentrations and daily loads of suspended sediment in samples from

19 sites in the lower Boise River Basin, May 1994 through February 1997 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

13. Graphs showing time series and trend line of concentrations of suspended sediment in samples from the

Boise River near Parma, June 1974 through February 1997 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

14. Graphs showing discharge and nutrient loads entering the Boise River from wastewater treatment facilities 

and tributary/drains during four synoptic sampling rounds, November 1994 through May 1996 . . . . . . . . . . . 

15. Boxplots showing concentrations of selected water-quality constituents in samples from 16 sites in the

lower Boise River Basin, May 1994 through February 1997 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

16. Graph showing daily mean water temperatures at five Boise River sites between July 18 and 

September 5, 1996 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

TABLES

1. Means and ranges for selected water-quality constituents reported by the Bureau of Reclamation in 1977 

for sites in the lower Boise River Basin that correspond with sites measured by the U.S. Geological

Survey from May 1994 through February 1997 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

2. Water-quality constituents analyzed in samples from sites in the lower Boise River Basin, May 1994

through February 1997. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

3. Locations of sampling sites, types of samples collected, and collection frequency, lower Boise River Basin,

May 1994 through February 1997 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

4. Statistical summary of total nitrogen concentrations and instantaneous loads in samples from sites in the

lower Boise River Basin, May 1994 through February 1997 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

5. Statistical summary of total phosphorus concentrations and instantaneous loads in samples from sites in the

lower Boise River Basin, May 1994 through February 1997 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

6. Statistical summary of suspended sediment concentrations and instantaneous loads in samples from sites 

in the lower Boise River Basin, May 1994 through February 1997 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATED WATER-QUALITY UNITS

To convert °C (degrees Celsius) to °F (degrees Fahrenheit), use the following equation:

°F = (1.8°C) + 32

Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929—a geodetic datum derived from a gen

adjustment of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929.

Multiply By To obtain

acre 4,047 square meter

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

cubic foot per second (ft3

/s) 0.02832 cubic meter per second

foot (ft) 0.3048 meter

foot per mile (ft/mi) 0.1894 meter per kilometer

inch (in.) 2.54 centimeter

mile (mi) 1.609 kilometer

pound (lb) 0.4536 kilogram 

pound per day (lb/d) 0.4536 kilogram per day 

square mile (mi2

) 2.590 square kilometer 

ton per day (ton/d) 907.2 kilogram per day

iv Water-Quality Conditions of the Lower Boise River, Idaho
Outlier—75th percentile value plus

 data values less than or equal to 3

 and more than 1.5 times the IQR

75th percentile value plus data values

 less than or equal to 1.5 times the IQR

75th percentile value

Median value

25th percentile value

25th percentile value minus data values

 less than or equal to 1.5 times the IQR

Outlier—25th percentile value minus

 data values less than or equal to 3 and

 more than 1.5 times the IQR

Outlier—25th percentile value minus

 data values more than 3 times the IQR

Interquartile range

(IQR)

EXPLANATION OF BOXPLOTS

(Figures 5, 6, 8, 9, 11, 12, 15)

Abbreviated water-quality units:

μg/L micrograms per liter

μm micrometer

μS/cm microsiemens per centimeter at 25°C

mg/L milligrams per liter

mL milliliter

Co
Ab

WATER-QUALITY CONDITIONS OF THE 

LOWER BOISE RIVER, ADA AND CANYON 

COUNTIES, IDAHO, MAY 1994 THROUGH 

FEBRUARY 1997

By William H. Mullins

Abstract 

Agricultural land and water use, wastewater 

treatment facility discharges, land development, 

road construction, urban runoff, confined-animal 

feeding operations, reservoir operations, and river 

channelization affect the water quality and biotic 

integrity of the lower Boise River between Lucky 

Peak Dam and the river’s mouth at Parma, Idaho. 

During May 1994 through February 1997, 4 sites 

on the Boise River, 12 tributary/drain sites, and 

3 wastewater treatment facilities were sampled at 

various intervals during the irrigation (high-flow) 

and post-irrigation (low-flow) seasons to determine 

sources, concentrations, and relative loads of nutrients and suspended sediment. Discharge entering 

the Boise River from the 12 tributary/drain sites 

and 3 wastewater treatment facilities was measured 

to determine the nutrient loads being contributed 

from each source.

Total nitrogen, total phosphorus, and suspended 

sediment concentrations and loads tended to increase in a downstream direction along the Boise 

River. Among the 15 sources of discharge to the 

Boise River, 3 southside tributary/drains and the 

West Boise wastewater treatment facility contributed the largest loads of total nitrogen; the median 

daily load was more than 2,000 pounds per day. 

The West Boise wastewater treatment facility contributed the largest median daily load of total phosphorus (810 pounds per day); Dixie Drain contributed the largest median daily load of suspe

sediment (26.4 tons per day).

Nitrogen-to-phosphorus ratios at the fou

River sites indicated that phosphorus could 

iting algal growth at the Diversion Dam site

as nitrogen could be limiting algal growth a

Glenwood and Middleton sites during som

of the year. Algal growth in the Boise Rive

Parma did not appear to be nutrient limited

Because of the complexity of the plumb

tem in the lower Boise River (numerous div

and inflow points), accurate comparisons b

discharge and nutrient loads entering the ri

measured sites during high-flow sampling p

were difficult. During low-flow sampling p

southside tributary/drains contributed most 

discharge and total nitrogen load, and wast

treatment facilities contributed most of the 

phosphorus load to the Boise River.

During the 50-day period July 18 throu

tember 5, 1996, the Idaho State standard fo

mum daily average temperature for coldwat

was exceeded by 34 percent at Middleton, 

cent at Caldwell, and 80 percent near Parm

lations of State standards for primary and s

ary contact recreation were observed at all 

tary/drains and in the Boise River near Parm

dian instantaneous concentrations of fecal c

bacteria exceeded State standards for prima

tact recreation at five tributary/drains and ex

Abstract
2 Water-Quality Conditions of the Lower Boise River, Idaho

standards for secondary contact recreation at one 

tributary/drain (Dixie Drain).

INTRODUCTION

 Agricultural land and water uses, wastewater treatment facility (WTF) discharges, land development, road 

construction, urban runoff, and confined-animal feeding 

operations (CAFOs), coupled with reservoir operations 

and river channelization, affect water quality and biotic 

integrity of the lower Boise River. The Boise River between Lucky Peak Dam at river mile (RM) 64 and Eagle 

Island at RM 42 (fig. 1) is affected primarily by effluent 

from surrounding urban communities. The river between 

Eagle Island and the confluence with the Snake River is 

affected primarily by irrigation diversions and return 

flows, CAFOs, and other small municipal effluent discharges and urban runoff. These land- and water-use 

activities affect streamflow in the river, increase nutrient 

and sediment concentrations and loads, bacteria levels, 

and water temperatures.

Studies conducted by the Idaho Department of 

Health and Welfare (1989, p. 54) documented that the 

lower Boise River only partially supported the designated beneficial uses of coldwater biota, salmonid 

spawning, and primary and secondary contact recreation. Later studies documented continued declines in 

water quality (Idaho Department of Health and Welfare, 

1992, p. 7). In October 1994, the lower Boise River was 

listed as water-quality limited in accordance with paragraph 303(d) of the Clean Water Act (U.S. Environmental Protection Agency, 1994, p. 6). This listing required 

the State of Idaho to develop total maximum daily loads 

(TMDLs) for the lower Boise River. The reaches from 

the Snake River to Star (RMs 0 to 34) were assigned a 

high-priority ranking, whereas the reaches from Star to 

Lucky Peak Lake (RMs 34 to 64) were assigned a lowpriority ranking. Constituents of concern in these reaches 

that must be addressed in a TMDL include nutrients, 

suspended sediment, bacteria, elevated water temperature, low dissolved-oxygen concentrations, oil and 

grease, and flow modification. The TMDL is being 

developed and is scheduled for completion in 1998.

Study Background

The Lower Boise River Water Quality Plan, Inc. 

(LBRWQP), composed of public and private agencies, 

groups, and individuals, identified a need to ass

rent water-quality conditions of the lower Boise 

The LBRWQP was established in 1992 to (1) id

areas in the basin that contribute high nutrient a

pended sediment concentrations and loads, (2) i

voluntary water-quality management practices, 

(3) monitor the long-term effectiveness of these 

tices on the water quality and biotic integrity of 

lower Boise River.

To assess the existing water quality and biot

rity of the Boise River and to provide a baseline 

which to assess future trends, the U.S. Geologic

vey (USGS) began an 8-year comprehensive asse

of the river in 1994. The study is cooperatively 

by the Idaho Division of Environmental Quality (

LBRWQP, and USGS.

The three primary objectives of this investig

are to (1) describe chemical and biological condi

the river and its tributaries and drains, (2) asses

otic integrity of the river, and (3) monitor the lon

water-quality trends and biotic integrity of the r

The study is being implemented in three ph

Phase 1 consisted of synoptic sampling (sample

lected at 4 main-stem river sites and 12 tributar

cultural drain sites) to assess the quality and qua

irrigation return flows during the irrigation seas

the ground-water seepage after the irrigation se

The phase 1 data were used to determine the m

sources, concentrations, and relative loads of nu

and suspended sediment and to select long-term 

toring sites and sampling frequency. Phase 1 sy

sampling was conducted during the first two stud

(April 1994 through March 1996), in May (irrig

season) and November (post-irrigation season).

Phase 2 consisted of long-term water-qualit

toring and aquatic biological assessment activit

overlapped the second year of phase 1. Phase 2 

ties included 2 years of intensive interval water-

sampling, continuation of the two annual synop

pling rounds, and initiation of semiquantitative 

biological and habitat assessment. Interval samp

consisted of measuring the quantity and quality o

at four main-stem river sites and eight tributary

every other month, and one extra round of samp

during spring runoff, at the beginning of the irri

season.

Annual synoptic and interval water-quality 

pling and semiquantitative aquatic biological an

tat assessment will continue in the 5-year phase 

study, beginning in April 1997. Phase 3 interval 

Introduction
Base from U.S. Geological Survey

digital data, 1:100,000, 1980

Albers Equal-Area projection

Standard parallels 43° 30', 47° 30',

and -114° 00', 41° 45'

No false easting or false northing

0

0 10

10

20 KILOMETERS

20 MILES

Figure 1. Location of lower Boise River Basin and sampling sites.

117° 00'

116° 30'

116° 15'

116° 00'

43° 45'

43° 30'

43° 15'

Lake

Lowell

Lucky

Peak

Lake

Boise

Parma

Notus

Caldwell

Middleton

Nampa

Kuna

Meridian

Star Eagle

Garden

Boise

City

2

1

4

6

7

10 9 8 12

11

13

14 15

16

18

19 20

22 21

River

Boise

River

Dixie

Drain

Conway

Gulch

West

Hartley

Gulch

East

Hartley Gulch

Willow

Creek

Mill

Slough

Mason

Slough Fivemile Creek

Tenmile

Creek

Thurman

Drain

Eagle

Drain

Mason

Creek

New

York Canal

New

York

Canal

Indian

Creek

20

26

44

I84

PAYETTE GEM

BOISE

ELMORE

ADA

CANYON

I84

I84

3

5 17 Boise Fifteenmile River

Creek

Snake

River

BOISE MOUNTAINS

Diversion

Dam

Lucky

Peak

Dam

4

EXPLANATION

Sampling site and reference

 number—(see table 3)

Hydrologic Unit Code (HUC)

 17050114 boundary

IDAHO

Western Snake

River Plain

Sudy Area

Snake

River

Wilson

Drain
4 Water-Quality Conditions of the Lower Boise River, Idaho

pling will be conducted at the same frequency as in 

phase 2, but only at the four main-stem sites. 

This report summarizes chemical data collected 

during phases 1 and 2 of the study and describes the 

water-quality conditions of the river and its tributaries 

and drains. 

Acknowledgments

The author wishes to express appreciation to the 

following staff of the USGS Idaho District Office and 

Boise Field Office for assistance in field work, data management, and advice: Michael Beckwith, Gregory Clark, 

Amber Erickson, Steve Garcia, David George, Walton 

Low, Terry Maret, Susan Moore, Sabrina Nicholls, 

Ivalou O’Dell, Doug Ott, Tomas Puga, Alvin Sablan, 

Jim Schaefer, and Paul Woods. Special thanks go to 

Greg Clark, who drafted the sections of this report on 

nitrogen-to-phosphorus ratios and synoptic estimates of 

loads and prepared most of the figures.

DESCRIPTION OF THE LOWER BOISE 

RIVER BASIN

Geographic Setting

The 1,290-mi2 lower Boise River Basin is located in 

Ada and Canyon Counties in southwestern Idaho between Lucky Peak Lake (RM 64) and the confluence of 

the Boise and Snake Rivers (fig. 1). The basin contains 

the most industrialized and urbanized areas in Idaho. 

The 1990 population of 296,000 in Ada and Canyon 

Counties constitutes about 29 percent of Idaho's total 

population.

The lower Boise River Basin is in the northern part 

of the western Snake River Plain. The southern boundary of the lower basin is a low ridge south of Indian 

Creek. Other basin boundaries are formed by a low ridge 

above the Snake River to the west, the Boise Mountains 

to the northeast, and a low ridge of foothills to the north. 

The upper basin upstream from Lucky Peak Lake is 

mountainous and sparsely populated. In addition to the 

Boise River, the study area is drained by several tributaries interconnected with a complex irrigation system 

of canals, laterals, and drains.

Geologic Setting

The lower Boise River lies in a broad, alluv

filled basin with several steplike terraces, or ben

which are more pronounced and continuous on 

south side of the river. Downstream from Lucky 

Lake, the basin floor slopes northwestward at a g

of about 10 ft/mi. The altitude of the basin near 

Peak Lake is about 2,800 ft above sea level; the 

near the river mouth is about 2,200 ft (Thomas 

Dion, 1974, p. 7).

The flood plain of the Boise River and som

larger tributaries consists of unconsolidated allu

(silt, sand, and coarse, well-sorted gravel) as mu

about 50 ft thick. This layer is covered with a m

soil as much as 20 ft thick. River terraces north 

south of the Boise River are composed of uncon

dated clay, silt, sand, and well-sorted gravel con

gravel and cobbles from the Idaho batholith and 

River Group. These deposits are as much as 100 

Flows of vesicular olivine basalt as much as 300 

belonging to the Snake River Group crop out so

of Boise and north of Caldwell (Thomas and Dion

p. 12), forming cliffs above the river between Di

and Lucky Peak Dams and north of Caldwell.

Older terrace gravel, consisting of unconso

silt, sand, and well-sorted gravel beds about 150 

and rocks of the Glenns Ferry Formation, comp

mainly of unconsolidated deposits of clay, silt, 

and fine gravel about 2,000 ft thick, underlie mo

lower Boise River Basin. The basement rock pr

consists of granitic rocks of the Idaho batholith

formed a deep trough in which younger rocks w

deposited (Thomas and Dion, 1974, p. 11–12).

Climate

Climate in the lower Boise River Basin is ch

ized as semiarid; winters are cool and wet, and su

are warm and dry. Area climate is controlled pr

by the general atmospheric circulation over the n

Pacific Ocean. In the summer, subtropical air fr

Pacific Ocean and Gulf of Mexico circulates nor

resulting in high temperatures and generally dry 

tions, although sporadic thunderstorms cause sm

amounts of precipitation. During the fall and wi

movements shift to a westerly flow from the Pa

Ocean, and most precipitation develops from fr

systems passing through the area. During the re

wet spring months (March-May), a combination 

Description of the Lower Boise River Basin
Description of the Lower Boise River 

thunderstorms and frontal systems produces nearly onethird of the annual precipitation. Mean annual precipitation as measured by the National Weather Service at the 

Boise airport during 1951–93 was about 11.9 in.

Land Use

Land use in the lower Boise River Basin consists 

primarily of irrigated and nonirrigated agriculture and 

related uses and urban activities. Land use in the upper 

Boise River Basin consists primarily of logging and recreation. Historically, parts of the upper basin have been 

heavily mined for gold by using shaft- and placer-mining methods.

Land use in the lower Boise River Basin has undergone major shifts in recent decades. Significant population growth has resulted in the conversion of large tracts 

of farmland to residential subdivisions and commercial 

facilities, and many residential areas within and adjacent to cities have been replaced with businesses, shopping centers, and parking lots, resulting in an increase in 

stormwater runoff into the Boise River and its tributaries (Kjelstrom, 1995, p. 1).

Surface Water

Flow in the Boise River between Lucky Peak Dam 

and the mouth is controlled primarily by reservoir regulation, irrigation withdrawals, irrigation return flows, 

and seepage of shallow ground water (Thomas and Dion, 

1974, p. 4). Lucky Peak Lake (fig. 1) and Arrowrock 

and Anderson Ranch Reservoirs (about 7 mi east, and 

about 30 mi southeast, respectively, of Lucky Peak 

Lake) in the upper Boise River Basin are managed primarily for irrigation and flood control and secondarily 

for recreation and power generation. These reservoirs 

and lake have a combined storage capacity of about 1.06 

million acre-ft and supply irrigation water to about 

350,000 acres in the lower Boise River Basin. Lake 

Lowell (fig. 1) stores water diverted from the Boise 

River at Diversion Dam east of Boise. Thirty diversions 

divert water from the Boise River and Payette River for 

irrigation, and 12 major irrigation tributary/drains discharge to the Boise River between Lucky Peak Lake and 

the mouth (fig. 2). Water diverted from the Payette River 

at Black Canyon Dam through the Black Canyon, CLine, and D-Line Canal complex is used to irrigate 

lands on the north side of the Boise River and ultimately 

flows into the Boise River through several northside 

tributary/drains (Naylor and others, 1976, p. 4–

ham, 1993, p. 2). (The Payette River parallels th

River about 10 mi to the north. Black Canyon D

the Payette River is located about 15 mi north of 

Water pumped from the Black Canyon Canal en

lower Boise River Basin through the C-Line and 

Canal complex about 13 mi north of Caldwell.)

Flood-control releases from Lucky Peak Lak

spring result in high streamflows (fig. 3) that pe

the way to the Snake River. However, in years o

and (or) consecutive drought, such as those in t

1980’s to early 1990’s, late-winter and spring fl

main low except for short periods of time. In we

such as those in the early 1980’s and during 199

high flows can last from December or January t

June. Irrigation releases typically begin in mid-A

following flood releases) and continue through 

October. Although relatively high streamflows a

leased from Lucky Peak Lake, streamflow progre

diminishes downstream to a low point in the St

dleton reach as many irrigation diversions extrac

from the river. Downstream from Middleton, st

flow again increases as a result of irrigation retur

and seepage of shallow ground water. During the 

minimum flows of about 150 ft3

/s usually are re

from Lucky Peak Lake to maintain fish habitat 

lute effluent from WTFs. Flows in the river incr

steadily downstream as a result of ground-wate

age and tributary inflow. Thomas and Dion (1974

estimated that surface drains contributed about 

cent of the total inflow to the Boise River down

from Lucky Peak Dam, and that about 60 percen

inflow entered the river in the 20-mi reach betwe

(RM 44) and Notus (RM 14.)

Mean annual flow during 1955–96 was 2,28

(2,014,000 acre-ft/yr) at the gaging station on th

River downstream from Lucky Peak Lake (Bren

others, 1997). Mean annual flow during 1982–9

1,198 ft3/s (868,100 acre-ft/yr) at the gaging sta

the Boise River at Glenwood Bridge, downstrea

several major diversions (Brennan and others, 1

Mean annual discharge during 1971–96 was 1,6

(1,179,000 acre-ft/yr) at the gaging station near 

near the mouth of the Boise River. Annual mean 

charge and mean monthly discharge during 1975

the gaging station on the Boise River near Parm

shown in figure 3.
6 Water-Quality Conditions of the Lower Boise River, Idaho

Lucky Peak Lake

Boise Project Main (NewYork) Canal

Barber Dam

Ridenbaugh Canal

Bubb, Meeves, #1 & #2, Rossi Mill

Settlers Canal

Drainage District #3

Davis Ditch

Thurman Mill Canal

EAGLE ISLAND

9 Eagle

Island

Canals Thurman Drain

Eureka #1 and Phyllis

Canals

Caldwell Highline Canal

Fifteenmile Creek

Mason Slough; Mason Creek

Riverside and Pioneer Dixie Canals

Caldwell Bridge

61.2

50.4

38.0

32.9

58.8

58.3

52.0

51.0

32.4

27.7

26.3

24.7

23.2

22.6

22.4

21.9

21.1

17.9

17.6

McManus and Teater Canals

Eureka #2 Canal

Upper Center Point Canal

Bowman and Swisher Canal

Penitentiary Canal

Boise City Canal

Farners Union and Boise Valley Canals

Lander Street WTF

New Dry Creek and New Union Canals

Ballentine Canal

Eagle Drain

Middleton Canal

Little Pioneer Canal

Canyon Canal

Mill Slough below Grade Ditch

Willow Creek

Hartley Drain and Gulch

Sebree, Campbell, and Siebenburg Canals

Lower Center Point Canal

Dixie Drain

Haas Canal

Island Highland Canal

McConnel Island Canal

Conway Gulch

Baxter and Boone Canals

Andrews Ditch

Mammon Pumps

Parma Canal

00.0

16.0

03.8 Boise River near Parma

13.8 Boise River at Notus

29.1 Boise River near Middleton

47.5 Boise River at Glenwood Bridge

Boise River below Diversion Dam

63.6 Boise River near Boise

Snake River

Figure 2. Schematic diagram of diversions, drains, and tributaries along the Boise River from Lucky Peak Lake to 

Snake River. (Modified from Warnick and Brockway, 1974; underlined sites are those sampled during this study)

West Boise WTF

River mile

19.7 Indian Creek

Caldwell WTF
Description of the Lower Boise River 

4,000

3,500

3,000

2,500

2,000

1,500

1,000

500

0

Annual mean discharge

Mean annual discharge for

period of record (1971–96)

DISCHARGE, IN CUBIC FEET PER SECOND

1975 1980 1985 1990 1

WATER YEAR

4,000

3,500

3,000

2,500

2,000

1,500

1,000

500

0

Mean monthly discharge

Mean annual discharge

for period of record (1971–96)

Oct. Jan.

MONTH

Nov. Dec. Feb. May Mar. Apr. June July Aug.

Figure 3. Annual mean discharge and mean monthly discharge in the Boise River near Parma, water years 1975–96.

(Site 21, figure 1)

Ground Water

Aquifers underlying the lower Boise River Basin 

are classified as deep or shallow. The widespread application of irrigation water, which began in 1863, has significantly altered the shallow ground-water system in 

the basin. Ground-water levels were reported to have 

risen as much as 140 ft in some areas in the early 1900’s 

(Nace and others, 1957, p. 10). Most of the recharge to 

the shallow aquifers results from the downward percolation of precipitation and irrigation water. Other sources 

of recharge include leakage from irrigation canals, laterals, and septic tank systems (Thomas and Dion

p. 13). The general direction of ground-water flo

lower Boise River Basin is toward the river.

The shallow aquifer discharges fairly uniform 

to the Boise River, directly as seepage and indire

through tributary streams and drains, primarily F

mile Creek, Mason Creek, Indian Creek, and Dixi

(Thomas and Dion, 1974, p. 17). During most w

nearly all the discharge to the Boise River be-twe

Lucky Peak Lake and the mouth is from ground-

seepage. The post-irrigation season contribution 
8 Water-Quality Conditions of the Lower Boise River, Idaho

ground-water seepage is about 300,000 acre-ft, roughly 

equivalent to the usable storage in Lucky Peak Lake or 

Arrowrock Reservoir (Thomas and Dion, 1974, p. 14).

PREVIOUS INVESTIGATIONS

Water quality was monitored in the lower Boise 

River and several of its tributaries during several past 

Federal and State monitoring programs. The most recent comprehensive monitoring of the lower Boise 

River and most of its major tributaries was in the early 

1970’s (Bureau of Reclamation, 1977). From July 1971 

through October 1975, 1,616 water samples were collected from 56 sample locations as part of the monitoring study. Selected water-quality constituents, including 

nutrients, suspended sediment, and indicator bacteria 

from the Bureau of Reclamation study (1977) are summarized in table 1. The Bureau of Reclamation concluded that the Boise River entered the city of Boise 

with generally high-quality water. As the river passed 

through the city, water quality significantly deteriorated 

as a result of municipal and industrial wastewater discharges and stormwater runoff. Downstream to the 

mouth of the Boise River, the water quality further deteriorated, primarily from irrigation return flows and 

diversions, as well as from wastewater discharges from 

Meridian, Nampa, Caldwell, and individual industrial 

sites.

The Bureau of Reclamation study identified the primary constituents of concern in the Boise River as nutrients (nitrogen associated with irrigation return flows 

and phosphorus associated primarily with municipal 

discharges), fecal bacteria from municipal and agricultural sources, suspended solids in the river from irrigation return flows downstream from Star, and low dissolved oxygen in the lower reaches (Bureau of Reclamation, 1977). Water in tributary/drains in the basin varied widely in quality but generally declined in quality 

downstream. Factors contributing to degraded water 

quality in tributary/drains included shallow groundwater seepage, drain length and intensity of farming, 

quality of water applied to lands within the basin, and 

municipal and industrial effluents.

Several tributary/drains that discharge to the lower 

Boise River were monitored in the past. Of these, Conway Gulch was monitored for more than 20 years. Naylor and others (1976) reported that nitrate-nitrogen concentrations increased downstream in Conway Gulch 

and peaked in July. However, no trends were identified 

in nitrate-nitrogen concentrations in Wilson Dra

only other drain sampled in that study, and the a

advised caution when attempting to extrapolate 

mation from one drain to another.

In 1983, the IDEQ (formerly the Idaho Depa

of Health and Welfare, Division of Environment) 

reported the results of a water-quality monitorin

gram that was established for the irrigation drai

system in the lower Boise River Basin (Clark and 

1983). Two of the drains evaluated, Dixie Drain 

Conway Gulch, empty into the Boise River and 

of the lower Boise River water-quality assessme

Among the conclusions drawn from the 1983 st

were that all the evaluated drains transported larg

of nutrients (ni-trogen and phosphorus), sedimen

bacteria (primarily from livestock), and the orga

rine pesticides DDT and toxaphene.

During 1988–89, the IDEQ conducted addi

monitoring of Conway Gulch to measure the ef

ness of Best Management Practices (BMPs) im

mented in 1983 under the Conway Gulch Water 

Project, a cooperative effort among the IDEQ, t

yon Soil Conservation District, and cooperating 

owners (Ingham, 1993). The goal of this project 

reduce point and nonpoint source agricultural ef

water quality through the implementation of BM

Monitoring results indicated that even with abo

percent of the critical area under some form of 

ment, Conway Gulch remained a major source 

ment, nutrients, trace elements, and bacteria to 

lower Boise River. There were no significant cha

suspended or bedload sediment concentrations. 

ent (nitrate and total phosphorus) concentration

ceeded criteria for the prevention of eutrophic c

tions, and fecal bacteria concentrations continu

exceed State water-quality standards. Recomme

tions made in the IDEQ study included further 

tions of erosion to reduce suspended sediment a

phosphorus loadings by in-corporating irrigatio

management (a more conservative application o

tion water) into existing treatments. Other poten

BMPs identified included better fertilizer manag

use of instream retention ponds (artificial wetla

establishment of vegetation filter strips along C

Gulch, and further evaluation of CAFOs and lan

within the project area that directly affected Co

Gulch (Ingham, 1993, p. 27).

In 1989, the IDEQ reported that water qualit

lower Boise River steadily deteriorated from Lu

Peak Lake to the mouth as a result of frequent irr

Previous Investigations
Table 1. Means and ranges for selected water-quality constituents reported by the Bureau of Reclamation in 1977 for sites in the lower Boise River Basin that 

correspond with sites measured by the U.S. Geological Survey from May 1994 through February 1997

[Mean values are listed on the top line for each site; ranges are listed in parentheses; values and ranges are from laboratory analyses unless identified as a field analysis; μS/cm; microsiemens per centimeter; mg/L, milligrams per liter; Dis., dissolved; col/100 mL, colonies per 100 milliliters; —, no data]

Field specific Dis. nitrite Total Dis. ortho- Suspended Total Fecal

Field pH conductance plus nitrate phosphorus phosphorus sediment coliform coliform

Sampling site name (standard units) (μS/cm) (mg/L) (mg/L) (mg/L) (mg/L) (col/100 mL) (col/100 mL)

Boise River below Lucky Peak Dam1 . . . . . . . . . . . . . . . . . . 27.2 77 0.15 0.04 0.01 20 151 1

(6.57–7.61) (50–100) (0.06–2.6) (0.02–0.16) (0–0.04) (4–108) (0–1,030) (0–10)

Boise River at Glenwood Bridge near Boise . . . . . . . . . . . . 27.48 106 0.23 0.22 0.16 15 4,787 886

(7.06–7.92) (63–174) (0.1–0.54) (0.04–0.86) (0.01–0.78) (2–64) (28–40,000) (0–16,000)

Eagle Drain at Eagle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 .55 281 1.03 0.18 0.12 23 4,106 570

(7.20–7.96) (220–360) (0.47–1.75) (0.09–0.26) (0.05–0.17) (4–74) (600–22,000) (0–1,940)

Thurman Drain near Eagle. . . . . . . . . . . . . . . . . . . . . . . . . . . 27.89 493 2.27 0.15 0.11 297 2,203 153

(7.57–8.38) (380–600) (1.12–3.47) (0.09–0.20) (0.07–0.14) (180–368) (80–22,200) (0–1,200)

Boise River near Middleton. . . . . . . . . . . . . . . . . . . . . . . . . . 7.1 96 0.31 0.09 0.04 — 3,150 495

(6.9–7.4) (90–102) (0.26–0.37) (0.08–0.10) (0.03–0.05) — (400–5,900) (270–720)

Fifteenmile Creek at mouth near Middleton3 . . . . . . . . . . . . 7.7 429 1.86 0.39 0.27 64 10,914 1,829

(7.0–8.6) (185–705) (0.71–3.28) (0.13–0.81) (0.09–0.45) (2–208) (1,000–46,000) (0–18,800)

Mill Slough below Grade Ditch near Middleton4 . . . . . . . . . 7.63 372 1.62 0.27 0.15 44 6,448 1,068

(6.96–8.02) (180–610) (0.53–2.91) (0.16–0.8) (0.02–0.25) (6–180) (340–45,000) (100–8,200)

Willow Creek at Highway 44 at Middleton . . . . . . . . . . . . . . 7.5 265 0.85 0.41 0.22 165 120 15

(7.4–7.7) (100–730) (0.15–2.42) (0.20–0.84) (0.05–0.3335) (2–1,493) (120–49,000) (15–9,000)

Mason Slough at mouth near Caldwell5 . . . . . . . . . . . . . . . . 27.87 536 1.21 0.35 0.26 33 7,403 1,142

(7.42–8.5) (360–740 (0.53–2.12) (0.10–1.21) (0.05–1.00) (2–128) (100–50,000) (2–18,400)

Mason Creek at mouth near Caldwell6 . . . . . . . . . . . . . . . . . 8.2 567 2.92 0.41 0.22 82 14,818 3,181

(8.1–8.4) (240–860) (1.47–4.83) (0.14–1.67) (0.08–0.99) (8–264) (400–123,000) (30–75,200)

West Hartley Drain (Gulch) near Caldwell . . . . . . . . . . . . . . 7.5 454 1.95 0.49 0.35 55 14,958 2,968

(6.8–8.1) (220–710) (0.49–4.13) (0.09–1.3) (0.04–0.7) (6–160) (200–62,000) (0–24,000)

East Hartley Drain (Gulch) near Caldwell. . . . . . . . . . . . . . . 27.87 668 2.01 0.38 0.24 82 15,978 5,148

(7.24–8.78) (345–1,000) (0.89–3.51) (0.26–0.75) (0.16–0.36) (15–268) (1,600–100,000) (0–48,400)

Indian Creek at mouth near Caldwell . . . . . . . . . . . . . . . . . . 7.8 600 2.42 0.42 0.28 66 30,328 2,921

(7.2–8.2) (240–840) (0.73–3.93) (0.25–0.75) (0.08–0.50) (4–338) (300–730,000) (50–60,000)

Conway Gulch at Notus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27.9 787 2.86 0.49 0.22 173 12,318 740

(7.5–8.3) (395–1,145) (1.62–4.05) (0.17–2.42) (0.15–1.1) (6–926) (100–164,000) (10–3,300)

Dixie Drain near Wilder. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 649 1.90 0.43 0.23 70 134,224 4,180

(8.0–8.4) (330–900) (0.75–3.55) 0.17–1.46) (0.08–0.65) (13–214) (1,000–1,200,000) (50 – 70,000)

1 Closest upstream site to Boise River below Diversion Dam.

2 Lab pH values; no or insufficient field pH values were reported.

3 Identified as Tenmile Creek in Bureau of Reclamation report (1977).

4 Combined North and South Middleton Drain in Bureau of Reclamation report (1977).

5 Combined Mason Creek North Channel and Mason Creek South Channel in Bureau of Reclamation report (1977).

6 Mason Drain in Bureau of Reclamation report (1977).
10 Water-Quality Conditions of the Lower Boise River, Idaho

withdrawals and returns, as well as municipal wastewater discharges. Water quality near Parma was classified 

as poor, due to “excessive bacteria, nutrients, sediment, 

and metals, as well as elevated temperatures” (Idaho 

Department of Health and Welfare, 1989, p. 46).

Water from five major storm-sewer outfalls that 

empty into the Boise River in Boise and Garden City 

was sampled by the USGS during 1993–94 (Kjelstrom, 

1995) to assess the suitability of regional and adjusted 

regional models to estimate runoff volume and loads 

from storm-sewer outfalls. Samples were analyzed for 

nutrients, dissolved and suspended solids, trace elements, organic compounds, major ions, specific conductance, pH, alkalinity, water temperature, oxygen 

demand, and indicator bacteria. Mean annual runoff 

volumes and loads were estimated by computing runoff 

volume and loads for 904 storms during 1976 through 

1993.

The City of Boise recently reported that storm runoff within Boise contributes relatively minor pollutant 

loads to the Boise River for four reasons: (1) About 

61 percent of the urban runoff from Boise is diverted 

into other waterways before entering the Boise 

and is reused as irrigation water, (2) about 10 p

of the urban impact area retains stormwater ons

(3) only 42 percent of the average annual precip

creates runoff because of small storm size and e

tion, and (4) Boise is not heavily industrialized a

ports primarily clean industries (Joan Meitl, Bo

Stormwater Coordinator, written commun., 199

METHODS OF DATA COLLECTION A

ANALYSIS 

Water-quality analyses included field analy

kalinity, dissolved oxygen, pH, specific conduc

and water temperature), nutrients (nitrogen and 

phorus), suspended sediment, and total and feca

form bacteria (table 2). Sampling site locations 

listed in table 3.

Depth- and width-integrated water samples 

collected and processed according to the metho

scribed by Edwards and Glysson (1988) and Sh

(1994). Water samples were composited in a chu

ter from which subsamples were obtained. Unfi

water in the churn was mixed thoroughly to acc

represent water collected in each cross section. 

samples to be analyzed for dissolved constituen

filtered through a 0.45-μm-pore-size capsule fil

Samples were preserved at 4°C until analysis. N

were analyzed by the USGS National Water-Qu

Laboratory according to methods described by F

(1993) and quality-assurance/quality-control pr

as described by Pritt and Raese (1995). Approx

10 percent of the nutrient samples were submitt

duplicates or blanks for quality-assurance purpo

described by Friedman and Erdmann (1982). 

Suspended sediment was analyzed by the U

Cascades Volcano Observatory Sediment Labor

according to methods described by Guy (1969)

Alkalinity, pH, and specific conductance we

sured in depth- and width-integrated samples by 

electrometric meters that were calibrated at the 

ning of each sampling day. Alkalinity, bicarbona

carbonate were measured using the fixed end-p

method (Shelton, 1994).

Dissolved oxygen and water temperature we

sured at the stream centroid by using an electro

meter. The dissolved oxygen meter was calibrate

beginning of each sampling day and frequently 

brated during the day. Ambient air temperature a

Table 2. Water-quality constituents analyzed in samples from 

sites in the lower Boise River Basin, May 1994 through 

February 1997

[WATSTORE, WATer data STOrage and REtrieval system; —, not applicable; ft3

/s, cubic feet per second; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; dis., dissolved; N, nitrogen; tot., total; P, phosphorus; ortho, orthophosphorus; mL, milliliter]

 WATSTORE 

parameter Reporting

Constituent code level

Field analyses

Instantaneous discharge (ft3/s) . . . . . . . . . . . . . . . . . . . 00061 —

Alkalinity (mg/L as CaCO3) . . . . . . . . . . . . . . . . . . . . 00418 —

Dissolved oxygen (mg/L). . . . . . . . . . . . . . . . . . . . . . . 00300 —

Dissolved oxygen saturation (percent). . . . . . . . . . . . . 00301 —

pH (standard units). . . . . . . . . . . . . . . . . . . . . . . . . . . . 00400 —

Specific conductance (μS/cm) . . . . . . . . . . . . . . . . . . . 00095 —

Water temperature (degrees Celsius) . . . . . . . . . . . . . . 00010 —

Air temperature (degrees Celsius) . . . . . . . . . . . . . . . . 00200 —

Nutrients

Nitrogen, dis., ammonia (mg/L as N) . . . . . . . . . . . . . 00608 0.015

Nitrogen, dis., ammonia + organic (mg/L as N) . . . . . 00623 .2

Nitrogen, tot., ammonia + organic (mg/L as N). . . . . . 00625 .2

Nitrogen, dis., nitrite + nitrate (mg/L as N) . . . . . . . . . 00631 .1

Phosphorus, tot. (mg/L as P) . . . . . . . . . . . . . . . . . . . . 00665 .01

Phosphorus, dis. (mg/L as P) . . . . . . . . . . . . . . . . . . . . 00666 .01

Phosphorus, dis., ortho (mg/L as P). . . . . . . . . . . . . . . 00671 .01

Sediment

Suspended sediment (mg/L). . . . . . . . . . . . . . . . . . . . . 80154 —

Bacteria

Total coliform (colonies/100 mL) . . . . . . . . . . . . . . . . 31501 —

Fecal coliform (colonies/100 mL) . . . . . . . . . . . . . . . . 31625 —

Methods of Data Collection and Analysis
Table 3. Locations of sampling sites, types of samples collected, and collection frequency, lower Boise River Basin, May 1994 through February 1997

[Sampling site locations are shown by reference number on figure 1. Sampling site name abbreviation prefix: R, river; W, wastewater treatment facility; N, northside tributary/drain; S, southside tributary/drain. Sample collection frequency: S, synoptic; I, interval; B, biological site sampled once annually]

Sampling

site 

reference Sampling

number U.S. Geological Survey site name Water

(figure 1) sampling site name and number abbreviation Latitude Longitude quality Biological S I B

1 Boise River below Diversion Dam 

near Boise (13203510) . . . . . . . . . . . . . . . . . . . . . . . . . . R-DIV 43o32'23" 116o05'37" x x x

2 Boise River at Eckert Road near Boise (13203760) . . . . . . . R-ECK 43o33'57" 116o07'52" x x

3 Lander Street Wastewater Treatment Facility . . . . . . . . . . . . W-LAN 43o38'26" 116o15'32" x xx

4 Boise River at Glenwood Bridge 

near Boise (13206000) . . . . . . . . . . . . . . . . . . . . . . . . . . R-GLN 43o39'37" 116o16'41" x x x x x

5 West Boise Wastewater Treatment Facility . . . . . . . . . . . . . . W-WST 43o40'03" 116o10'20" x x x

6 Eagle Drain at Eagle (13206400) . . . . . . . . . . . . . . . . . . . . . N-EAG 43o41'38" 116o21'11" x x

7 Thurman Drain near Eagle (13208750). . . . . . . . . . . . . . . . . S-THR 43o40'18" 116o22'29" x x

8 Boise River near Middleton (13210050) . . . . . . . . . . . . . . . . R-MID 43o41'06" 116o34'22" x x x x x

9 Fifteenmile Creek at mouth 

near Middleton (13210815) . . . . . . . . . . . . . . . . . . . . . . S-FIF 43o41'16" 116o35'25" x x x

10 Mill Slough below Grade Ditch 

near Middleton (132108247) . . . . . . . . . . . . . . . . . . . . . N-MIL 43o42'04" 116o37'02" x x

11 Willow Creek at Highway 44 

at Middleton (13210835) . . . . . . . . . . . . . . . . . . . . . . . . N-WIL 43o42'24" 116o37'47" x x x

12 Mason Slough at mouth near Caldwell (13210850) . . . . . . . S-MSS 43o41'32" 116o39'56" x x

13 Mason Creek at mouth near Caldwell (13210985) . . . . . . . . S-MSC 43o41'55" 116o40'22" x x x

14 West Hartley Drain (Gulch) 

near Caldwell (13210986) . . . . . . . . . . . . . . . . . . . . . . . N-WHR 43o41'59" 116o41'95" x x x

15 East Hartley Drain (Gulch) 

near Caldwell (13210987) . . . . . . . . . . . . . . . . . . . . . . . N-EHR 43o41'56" 116o40'38" x x x

16 Boise River at Highway 20–26 crossing 

near Caldwell (13211000) . . . . . . . . . . . . . . . . . . . . . . . R-CLD 43o40'52" 116o41'18" x x

17 Caldwell Wastewater Treatment Facility . . . . . . . . . . . . . . . . W-CLD 43o40'27" 116o41'52" x xx

18 Indian Creek at mouth at Caldwell (13211445) . . . . . . . . . . S-IND 43o41'26" 116o42'05" x x x

19 Conway Gulch at Highway 20-26 crossing 

at Notus (13212550). . . . . . . . . . . . . . . . . . . . . . . . . . . . N-CON 43o43'36" 116o48'12" x x x

20 Dixie Drain near Wilder (13212890). . . . . . . . . . . . . . . . . . . S-DIX 43o43'51" 116o53'17" x x x

21 Boise River near Parma (13213000 . . . . . . . . . . . . . . . . . . . . R-PAR 43o46'54" 116o58'17" x x x

22 Boise River at mouth near Parma (13213030). . . . . . . . . . . . R-MTH 43o48'50" 117o00'55" x x

Sample collection frequency

Sample type
12 Water-Quality Conditions of the Lower Boise River, Idaho

10,000

DISCHARGE, IN CUBIC FEET PER SECOND

PERCENT OF TIME DISCHARGE WAS EQUALED OR EXCEEDED

Figure 4. Discharges at which water-quality samples were collected at Boise River sites, May 1994 through February 

(Dashed lines represent the discharge-duration curve over the period of record for the indicated site)

7,000

5,000

4,000

3,000

2,000

1,000

700

500

400

300

200

100

70

50

40

10,000

7,000

5,000

4,000

3,000

2,000

1,000

700

500

400

300

200

100

70

50

40

0.1 1 2 5 10 20 30 40 5060 70 80 90 95 98 99 99.9 0.1 1 2 5 10 20 30 40 5060 70 80 90 95 98 

Sampling site 1 Boise River below Diversion Dam near Boise Sampling site 4 Boise River at Glenwood Bridge near B

Period of record, water years 1938–96

Discharge at which

water-quality sample

was collected

Period of record, water years 1987–96

Period of record, water years 1975–96 Period of record, water years 1971–96

Sampling site 8 Boise River near Middleton Sampling site 21 Boise River near Parma

measured at each sampling site by using thermometers 

calibrated to within 0.5oC against National Institute of 

Standards and Technology standard thermometers. Additional water temperature data were collected hourly 

during the summer of 1996 using Hobo continuous temperature recorders (Onset Computer Corporation). Recorders were deployed at five main-stem Boise River 

sites (sites 1, 4, 8, 16, and 22; table 3) from July 18 

through September 5.

Total and fecal coliform bacteria concentrations 

were measured using membrane-filter methods (Britton 

and Greeson, 1987). Water samples for bacterial analysis were collected at the stream centroid.

For sites not equipped with continuous stage 

ers, instantaneous stream discharge was measure

methods described by Buchanan and Somers (1

Instantaneous loads of total nitrogen, total p

rus, and suspended sediment were calculated fo

cultural drain and river sites by multiplying the 

charge measured at the time of sampling by the 

ated concentration.

Discharge plotted on flow-duration curves f

four sites on the lower Boise River indicates tha

quality samples were collected over a range of m

low to high flows (fig. 4).
Water-Quality Condi

WATER-QUALITY CONDITIONS 

Nitrogen

Nitrogen is essential to the metabolism of aquatic 

plants. The supply-to-demand ratio for nitrogen is 

small; thus, nitrogen can limit the growth of aquatic 

plants as phosphorus often does. The nitrogen cycle in 

aquatic ecosystems is complex because most pr

involving nitrogen are biologically mediated. In 

ecosystems, nitrogen commonly exists in the fo

forms: dissolved molecular nitrogen, nitrogen-c

ing organic compounds, ammonia, ammonium, 

and nitrate. Analyses for this study included dis

ammonia (includes ammonium), dissolved and 

ammonia plus organic nitrogen (commonly call

Table 4. Statistical summary of total nitrogen concentrations and instantaneous loads in samples from sites in the lo

Boise River Basin, May 1994 through February 1997

[Sampling site locations are shown by reference number in figure 1 and are listed in table 3; N, nitrogen; WTF, wastewater treatment facility]

Sampling Maximum

site Number concentratio

reference of instantaneo

number Site name samples 25 50 75 load

Total nitrogen, milligrams per liter as N

1 Boise River below Diversion Dam . . . . 20 0.2 0.2 0.3 0.5

3 Lander Street WTF . . . . . . . . . . . . . . . . 18 13.8 14.9 17.1 20.8

4 Boise River at Glenwood Bridge. . . . . . 25 .3 .4 .5 1.9

5 West Boise WTF . . . . . . . . . . . . . . . . . . 18 14.1 19.2 23.0 25.2

6 Eagle Drain at Eagle . . . . . . . . . . . . . . . 5 1.5 1.9 2.5 2.7

7 Thurman Drain near Eagle . . . . . . . . . . 5 2.0 2.3 3.9 4.1

8 Boise River near Middleton. . . . . . . . . . 20 .5 .7 1.9 3.1

9 Fifteenmile Creek at mouth. . . . . . . . . . 18 1.8 3.2 4.9 7.3

10 Mill Slough below Grade Ditch . . . . . . 5 2.1 2.7 4.2 4.3

11 Willow Creek at Middleton . . . . . . . . . . 18 .8 1.1 2.3 3.9

12 Mason Slough at mouth. . . . . . . . . . . . . 5 2.2 3.7 4.5 4.9

13 Mason Creek at mouth . . . . . . . . . . . . . 18 3.75 4.7 5.7 6.9

14 West Hartley Gulch near Caldwell . . . . 18 1.6 2.8 4.5 5.8

15 East Hartley Gulch near Caldwell . . . . . 18 3.0 3.9 5.1 6.0

17 Caldwell WTF . . . . . . . . . . . . . . . . . . . . 17 9.1 11.1 12.6 15.3

18 Indian Creek at mouth . . . . . . . . . . . . . . 18 3.1 4.2 7.0 7.7

19 Conway Gulch at Notus . . . . . . . . . . . . 18 3.7 4.9 5.7 6.3

20 Dixie Drain at mouth. . . . . . . . . . . . . . . 18 2.3 2.9 5.3 6.2

21 Boise River near Parma . . . . . . . . . . . . . 21 1.2 2.0 3.5 4.6

Total nitrogen, instantaneous load, pounds per day as N

1 Boise River below Diversion Dam . . . . 20 377 2,320 7,500 19,800

3 Lander Street WTF . . . . . . . . . . . . . . . . 18 1,100 1,170 1,400 1,660

4 Boise River at Glenwood Bridge. . . . . . 25 1,300 1,840 6,470 16,200

5 West Boise WTF . . . . . . . . . . . . . . . . . . 18 1,690 2,230 2,850 3,470

6 Eagle Drain at Eagle . . . . . . . . . . . . . . . 5 161 250 306 315

7 Thurman Drain near Eagle . . . . . . . . . . 5 151 221 323 360

8 Boise River near Middleton. . . . . . . . . . 20 2,470 4,080 7,630 14,900

9 Fifteenmile Creek at mouth. . . . . . . . . . 18 995 1,480 1,730 2,900

10 Mill Slough below Grade Ditch . . . . . . 5 1,480 1,600 1,700 1,730

11 Willow Creek at Middleton . . . . . . . . . . 18 153 238 382 522

12 Mason Slough at mouth. . . . . . . . . . . . . 5 204 261 555 838

13 Mason Creek at mouth . . . . . . . . . . . . . 18 1,580 2,260 2,770 3,520

14 West Hartley Gulch near Caldwell . . . . 18 173 229 276 522

15 East Hartley Gulch near Caldwell . . . . . 18 566 789 1,020 1,590

17 Caldwell WTF . . . . . . . . . . . . . . . . . . . . 17 366 431 480 563

18 Indian Creek at mouth . . . . . . . . . . . . . . 18 1,560 2,310 7,730 9,110

19 Conway Gulch at Notus . . . . . . . . . . . . 18 646 840 952 1,120

20 Dixie Drain at mouth. . . . . . . . . . . . . . . 18 2,260 2,570 3,550 5,390

21 Boise River near Parma . . . . . . . . . . . . . 21 13,400 20,800 26,500 53,500

Concentration or instantaneous

load at indicated percentile

Water-Quality Conditions
14 Water-Quality Conditions of the Lower Boise River, Idaho

100

CONCENTRATION, IN MILLIGRAMS PER LITER INSTANTANEOUS LOAD, IN POUNDS PER DAY

SAMPLING SITE NAME ABBREVIATION

Figure 5. Instantaneous concentrations and daily loads of total nitrogen in samples from 19 sites in the lower Boise R

Basin, May 1994 through February 1997. (Shaded boxes represent Boise River sites; see table 3 for sampling site na

abbreviations)

50

20

10

5

2

1

0.5

0.2

0.1

100,000

N

CON

W

CLD

S

IND

N

EHR

S

MSC

N

WHR

N

WIL

S

MSS

S

FIF

N

MIL

R

MID

N

EAG

S

THR

W

WST

W

LAN

R

GLN

R

DIV

S

DIX

50,000

20,000

10,000

5,000

2,000

1,000

500

200

100

50

20

10

20

17

17

25

5

5

20

18

5 18

5

18 18 18

18

16

18 18

Number of observations

(same for both graphs)
Water-Quality Condi

dahl nitrogen and includes ammonium), and dissolved 

nitrite plus nitrate. Total nitrogen was calculated as the 

sum of total ammonia plus organic nitrogen and dissolved nitrite plus nitrate. Dissolved nitrite plus nitrate 

was the dominant nitrogen species detected.

Median concentrations of total nitrogen among the 

19 sampling sites ranged from 0.2 mg/L (Boise River 

below Diversion Dam) to 19.2 mg/L (West Boise WTF) 

(table 4, fig. 5). Four sites were sampled only 5 times, 

whereas the other sites were sampled between 17 and 25 

times, so caution is advised when comparing median 

concentrations. Median concentrations of total nitrogen 

at the Boise River sites increased in a downstream direction and were 0.2 mg/L below Diversion Dam, 0.4 mg/L 

at Glenwood Bridge, 0.7 mg/L near Middleton, and 

2.0 mg/L near Parma. Among the six northside tributary/drains, six southside tributary/drains, and three 

WTFs, median concentrations of total nitrogen were 

2.9, 3.5, and 15.1 mg/L, respectively. Results for inorganic nitrogen were similar to those for total nitrogen 

(fig. 6).

The daily load of total nitrogen at each site was 

computed using the instantaneous discharge and associated concentration of total nitrogen. Median daily loads 

of total nitrogen among the 19 sites ranged from 221 lb/d 

(Thurman Drain near Eagle) to 20,800 lb/d (Boise River 

near Parma) (fig. 5, table 4). Median daily loads of total 

nitrogen at the four Boise River sites decreased from 

Diversion Dam (2,320 lb/d) to Glenwood Bridge (1,840 

lb/d), about doubled near Middleton (4,080 lb/d), and 

were 20,800 lb/d near Parma. Median daily loads of 

total nitrogen at three of the southside tributary/drains 

(Mason Creek at mouth, Indian Creek at mouth, and 

Dixie Drain at mouth) exceeded 2,000 lb/d, comparable 

to the 2,230-lb/d input from the West Boise WTF 

(table 4). Results for inorganic nitrogen were similar to 

those for total nitrogen (fig. 6).

Temporal trends in total nitrogen and dissolved inorganic nitrogen (fig. 7) in the Boise River near Parma 

were evaluated for the period June 1974 through February 1997. Data used prior to this study were from other 

USGS data collection programs. The LOWESS (LOcally WEighted Scatterplot Smoothing) technique was 

used to adjust concentrations on the basis of streamflow 

(Helsel and Hirsch, 1992). Streamflow adjustment eliminates trends caused solely by variations in streamflow. 

Thus, trends caused by variations in concentrations can 

be observed. Trends for total nitrogen and dissolved inorganic nitrogen do not appear to be affected by streamflow adjustment. On the basis of the adjusted tren

nitrogen concentrations declined slightly beginn

1992, whereas dissolved inorganic nitrogen con

tions began declining sharply in 1994. 

Phosphorus

Phosphorus, like nitrogen, is one of several 

tial nutrients in the metabolism of aquatic plants

phication research has focused heavily on phosp

because it is the nutrient typically found to have 

smallest supply-to-demand ratio for aquatic plant 

(Ryding and Rast, 1989). Forms of phosphorus 

aquatic ecosystems commonly include PO4 (also 

dissolved reactive phosphorus), hydrolyzable ph

rus, inorganic compounds, and organic compou

Analyses reported for this study include total ph

rus, dissolved phosphorus, and dissolved orthop

rus. The orthophosphate ion is especially import

because it is directly available for metabolic use 

aquatic plants. Dissolved orthophosphorus was 

dominant phosphorus species detected.

Median concentrations of total phosphorus 

the 19 sites ranged from 0.02 mg/L at Boise Riv

low Diversion Dam to 6.60 mg/L at West Boise 

(fig. 8, table 5). Median concentrations of total 

phorus at the four Boise River sites increased in 

stream direction—from 0.02 mg/L below Diver

Dam to 0.08 mg/L at Glenwood Bridge, nearly d

to 0.15 mg/L near Middleton, and nearly doublin

to 0.27 mg/L near Parma. Among the six norths

utary/drains, six southside tributary/drains, and 

WTFs, median concentrations of total phosphor

0.22, 0.29, and 4.9 mg/L, respectively.

Median daily loads of total phosphorus amo

19 sites ranged from 9 lb/d at Thurman Drain nea

to 2,260 lb/d at Boise River near Parma (fig. 8, t

Median daily loads of total phosphorus at the fou

River sites began at 101 lb/d below Diversion D

creased to 372 lb/d at Glenwood Bridge, nearly 

to 946 lb/d near Middleton, and were 2,260 lb/d 

Parma. Among the 15 sources of discharge to th

River, the West Boise WTF was the source of the 

median daily load of total phosphorus (810 lb/d

Drain was the source of the second-largest loa

(285 lb/d). Results for dissolved orthophosphor

(fig. 9) were similar to those for total phosphoru

Temporal trends in total phosphorus and di

orthophosphorus (fig. 10) at the Boise River nea

also were evaluated. Adjusting total phosphorus 
16 Water-Quality Conditions of the Lower Boise River, Idaho CONCENTRATION, IN MILLIGRAMS PER LITER INSTANTANEOUS LOAD, IN POUNDS PER DAY

SAMPLING SITE NAME ABBREVIATION

Figure 6. Instantaneous concentrations and daily loads of dissolved inorganic nitrogen in samples from 19 sites in the 

Boise River Basin, May 1994 through February 1997. (Shaded boxes represent Boise River sites; see table 3 for sam

site name abbreviations)

100,000

N

CON

W

CLD

S

IND

N

EHR

S

MSC

N

WHR

N

WIL

S

MSS

S

FIF

N

MIL

R

MID

N

EAG

S

THR

W

WST

W

LAN

R

GLN

R

DIV

S

DIX

50,000

20,000

10,000

5,000

2,000

1,000

500

200

100

50

20

10

20

17 17

25

5

5

20

18

5 18 5

18 18 18 18

16

18 18

Number of observations

(same for both graphs)

100

50

20

10

5

2

1

0.5

0.2

0.1

0.05

0.02

0.01
5.0

4.0

3.0

2.0

1.0

0

MILLIGRAMS PER LITER AS NITROGEN

Figure 7. Time series and trend line of concentrations of total nitrogen and dissolved inorganic nitrogen in samples from the Boise River near Parma, June 1974

through February 1997.

December

1990

June

1985

December

1979

June

1974

June

1996

DISSOLVED INORGANIC NITROGEN DISSOLVED INORGANIC NITROGEN (Streamflow adjusted) 6.0

5.0

4.0

3.0

2.0

1.0

0

December

1990

June

1985

December

1979

June

1974

June

1996

Trend

line
18 Water-Quality Conditions of the Lower Boise River, Idaho CONCENTRATION, IN MILLIGRAMS PER LITER INSTANTANEOUS LOAD, IN POUNDS PER DAY

SAMPLING SITE NAME ABBREVIATION

Figure 8. Instantaneous concentrations and daily loads of total phosphorus in samples from 19 sites in the lower Bois

River Basin, May 1994 through February 1997. (Shaded boxes represent Boise River sites; see table 3 for sampling

site name abbreviations)

20,000

10,000

N

CON

W

CLD

S

IND

N

EHR

S

MSC

N

WHR

N

WIL

S

MSS

S

FIF

N

MIL

R

MID

N

EAG

S

THR

W

WST

W

LAN

R

GLN

R

DIV

S

DIX

5,000

2,000

1,000

500

200

100

50

20

10

5

2

1

20

18

18

25 5 5

20

18

5 18

5

18

18 18

18

17

18 18 

Number of observations

(same for both graphs)

100

50

20

10

5

2

1

0.5

0.2

0.1

0.05

0.02

0.01

0.005

0.002

0.001
Water-Quality Condi

centrations by streamflow removed much of the concentration variability and noticeable trend. The more pronounced effect of flow on total phosphorus concentrations is likely the result of an increase in particulate 

transport of total phosphorus during high streamflow. 

Streamflow-adjusted concentrations of total phosphorus 

showed little discernible trend over the course of the 

study; however, dissolved orthophosphorus concentrations began declining sharply in 1994.

Nitrogen-to-Phosphorus Ratios

Concentrations of nitrogen and phosphorus, 

as the ratio of their biologically available forms

give an indication of which nutrient is potential

ing to algal growth in a water body. Literature s

that nuisance levels of algal growth in streams ca

if concentrations of inorganic nitrogen (the sum 

ammonia, nitrite, and nitrate as nitrogen) and so

Table 5. Statistical summary of total phosphorus concentrations and instantaneous loads in samples from sites in th

lower Boise River Basin, May 1994 through February 1997

[Sampling site locations are shown by reference number in figure 1 and are listed in table 3; P, phosphorus; WTF, wastewater treatment facility]

Sampling Maximum

site Number concentration o

reference of instantaneous

number Site name samples 25 50 75 load

Total phosphorus, milligrams per liter as P

1 Boise River below Diversion Dam . . . . 20 0.01 0.02 0.03 0.09

3 Lander Street WTF . . . . . . . . . . . . . . . . 18 3.50 3.70 4.60 6.50

4 Boise River at Glenwood Bridge . . . . . . 25 .05 .08 .11 .30

5 West Boise WTF . . . . . . . . . . . . . . . . . . 18 5.52 6.60 8.00 12.00

6 Eagle Drain at Eagle . . . . . . . . . . . . . . . 5 .15 .17 .22 .23

7 Thurman Drain near Eagle. . . . . . . . . . . 5 .09 .13 .17 .19

8 Boise River near Middleton . . . . . . . . . . 20 .07 .15 .40 .85

9 Fifteenmile Creek at mouth . . . . . . . . . . 18 .25 .30 .33 .41

10 Mill Slough below Grade Ditch. . . . . . . 5 .17 .20 .25 .27

11 Willow Creek at Middleton . . . . . . . . . . 18 .17 .19 .29 .34

12 Mason Slough at mouth . . . . . . . . . . . . . 5 .16 .35 .49 .62

13 Mason Creek at mouth. . . . . . . . . . . . . . 18 .20 .22 .40 .93

14 West Hartley Gulch near Caldwell . . . . 18 .20 .31 .39 .45

15 East Hartley Gulch near Caldwell . . . . . 18 .23 .26 .29 .37

17 Caldwell WTF . . . . . . . . . . . . . . . . . . . . 17 3.70 4.50 4.90 6.70

18 Indian Creek at mouth . . . . . . . . . . . . . . 18 .36 .43 .52 .82

19 Conway Gulch at Notus. . . . . . . . . . . . . 18 .17 .19 .35 .44

20 Dixie Drain at mouth . . . . . . . . . . . . . . . 18 .27 .33 .39 .55

21 Boise River near Parma . . . . . . . . . . . . . 21 .17 .27 .38 .55

Total phosphorus, instantaneous load, pounds per day as P

1 Boise River below Diversion Dam . . . . 20 48 101 483 3,250

3 Lander Street WTF . . . . . . . . . . . . . . . . 18 245 267 412 782

4 Boise River at Glenwood Bridge . . . . . . 25 237 372 847 2,690

5 West Boise WTF . . . . . . . . . . . . . . . . . . 18 659 810 971 1,260

6 Eagle Drain at Eagle . . . . . . . . . . . . . . . 5 12 23 34 36

7 Thurman Drain near Eagle. . . . . . . . . . . 5 6 9 21 30

8 Boise River near Middleton . . . . . . . . . . 20 505 946 1,350 3,710

9 Fifteenmile Creek at mouth . . . . . . . . . . 8 63 135 207 365

10 Mill Slough below Grade Ditch. . . . . . . 5 74 127 159 169

11 Willow Creek at Middleton . . . . . . . . . . 18 22 34 68 124

12 Mason Slough at mouth . . . . . . . . . . . . . 5 12 17 90 141

13 Mason Creek at mouth. . . . . . . . . . . . . . 18 65 92 299 607

14 West Hartley Gulch near Caldwell . . . . 18 17 21 44 76

15 East Hartley Gulch near Caldwell . . . . . 18 27 48 95 138

17 Caldwell WTF . . . . . . . . . . . . . . . . . . . . 17 146 164 192 242

18 Indian Creek at mouth . . . . . . . . . . . . . . 18 175 247 529 944

19 Conway Gulch at Notus. . . . . . . . . . . . . 18 20 36 89 115

20 Dixie Drain at mouth . . . . . . . . . . . . . . . 18 156 285 449 918

21 Boise River near Parma . . . . . . . . . . . . . 21 1,620 2,260 3,650 7,960

Concentration or instantaneous

load at indicated percentile
20 Water-Quality Conditions of the Lower Boise River, Idaho CONCENTRATION, IN MILLIGRAMS PER LITER INSTANTANEOUS LOAD, IN POUNDS PER DAY

SAMPLING SITE NAME ABBREVIATION

Figure 9. Instantaneous concentrations and daily loads of dissolved orthophosphorus in samples from 19 sites in the 

Boise River Basin, May 1994 through February 1997. (Shaded boxes represent Boise River sites; see table 3 for sam

site name abbreviations)

10,000

N

CON

W

CLD

S

IND

N

EHR

S

MSC

N

WHR

N

WIL

S

MSS

S

FIF

N

MIL

R

MID

N

EAG

S

THR

W

WST

W

LAN

R

GLN

R

DIV

S

DIX

5,000

2,000

1,000

500

200

100

50

20

10

5

2

1

20

18

18

25

5 5

20

18

5

18 5 18 18

18

18

17

18

18

Number of observations

(same for both graphs)

100

50

20

10

5

2

1

0.5

0.2

0.1

0.05

0.02

0.01

0.005

0.002

0.001
0.8

0.6

0.4

0.2

0

MILLIGRAMS PER LITER AS PHOSPHORUS

Figure 10. Time series and trend line of concentrations of total phosphorus and dissolved orthophosphorus in samples from the Boise River near Parma,

June 1974 through February 1997.

December

1990

June

1985

December

1979

June

1974

June

1996

DISSOLVED ORTHOPHOSPHORUS DISSOLVED ORTHOPHOSPHORUS (Streamflow adjusted)

December

1990

June

1985

December

1979

June

1974

June

1996

Trend

line

1.0

0.8

0.6

0.4

0.2

0
22 Water-Quality Conditions of the Lower Boise River, Idaho

25

20

15

10

5

0

MASS-BASED NITROGEN-TOPHOSPHORUS RATIO

SAMPLING SITE

Figure 11. Mass ratios of dissolved inorganic nitrog

solved orthophosphorus, grouped by Boise River sit

1994 through February 1997.

Diversion Dam Glenwood Middleton 

Mass ratio of N:P = 7.2

20

25

20

Number of observations

phosphorus exceed 0.3 and 0.01 mg/L, respectively, at 

the start of the growing season (Sawyer, 1947, as cited 

in Mackenthun, 1969). Mackenthun (1969) recommended that total phosphorus concentrations in streams 

not exceed 0.1 mg/L in order to prevent nuisance levels 

of algal growth. In addition to their concentrations, the 

calculated mass ratio of dissolved inorganic nitrogen to 

dissolved orthophosphorus (N:P) can be compared to a 

preference ratio for algal uptake of 7.2 μg of nitrogen 

per 1 μg of phosphorus (7.2N:1P) (Ryding and Rast, 

1989). If algal populations utilize nitrogen and phosphorus in this ideal ratio, any deviation from the ratio 

can be used as an additional tool to determine the potential for nutrient limitation. If N:P is greater than 7.2, 

phosphorus is the potential limiting nutrient; if N:P is 

less than 7.2, nitrogen is the potential limiting nutrient.

Only once did concentrations of inorganic nitrogen 

exceed 0.3 mg/L, and never did concentrations of total 

phosphorus exceed 0.1 mg/L in water samples collected 

at the Diversion Dam site on the Boise River from May 

1994 to February 1997. However, N:P greater than 7.2 

in most of the water samples suggests a potential for 

phosphorus-limiting conditions at the Diversion Dam 

site (fig. 11). As nutrient concentrations increased 

downstream, N:P fell below 7.2 at the Glenwood and 

Middleton sites, and any potential phosphorus limitation in the river was eliminated. Inorganic nitrogen concentrations in water samples from Glenwood and 

Middleton were often smaller than 0.3 mg/L and, on the 

basis of the N:P, nitrogen could be limiting algal growth 

in that reach of the river during some parts of the year. 

At the Parma site, concentrations of inorganic nitrogen 

and total phosphorus were nearly always in excess of 

limiting concentrations, so algal growth did not appear 

to be limited by nutrient availability in that reach of the 

river. 

Suspended Sediment

Suspended sediment is defined as “the velocityweighted concentration of suspended sediment in the 

sampled zone (from the water surface to a point approximately 0.3 feet above the bed) expressed as milligrams 

of dry sediment per liter of water-sediment mixture” 

(Brennan and others, 1996). The suspended sediment 

concentration, multiplied by the stream discharge, multiplied by 0.0027 yields suspended sediment discharge, 

expressed as tons per day.

Median concentrations of suspended sedim

among the 19 river and tributary/drain sites ran

from 5 mg/L at Boise River below Diversion D

112 mg/L at Mason Slough at mouth (fig. 12, ta

Median concentrations of suspended sediment a

four Boise River sites ranged from 5 mg/L below 

sion Dam, to 12 mg/L at Glenwood Bridge, dec

to 7 mg/L near Middleton, and increased to 47 

near Parma. Among the six northside tributary/d

six southside tributary/drains, and three WTFs, 

concentrations of suspended sediment were 57, 

9 mg/L, respectively.

Median daily loads of suspended sediment 

the 19 river and tributary/drain sites ranged from 

0.42 ton/d at Thurman Drain near Eagle to 299 

at Boise River near Parma (fig. 12, table 6). Me

daily loads of suspended sediment at the four B

River sites were 24.5 ton/d below Diversion Da

decreased slightly to 23.6 ton/d at Glenwood B

decreased further to 10 ton/d near Middleton, th

increased to 299 ton/d near Parma. The reason f

decreasing trend in loads from Diversion Dam t

dleton is the diversion of water from the river b

these sites during the irrigation season. Among 

sources of discharge to the Boise River, Dixie Dr

the source of the largest median daily load of sus

sediment (26.4 ton/d); Mason Creek was the so

the second-largest load (23.3 ton/d).
Water-Quality Condi

CONCENTRATION, IN MILLIGRAMS PER LITER INSTANTANEOUS LOAD, IN POUNDS PER DAY

SAMPLING SITE NAME ABBREVIATION

Figure 12. Instantaneous concentrations and daily loads of suspended sediment in samples from 19 sites in the lowe

River Basin, May 1994 through February 1997. (Shaded boxes represent Boise River sites; see table 3 for sampling

site name abbreviations)

N

CON

W

CLD

S

IND

N

EHR

S

MSC

N

WHR

N

WIL

S

MSS

S

FIF

N

MIL

R

MID

N

EAG

S

THR

W

WST

W

LAN

R

GLN

R

DIV

S

DIX

10,000

5,000

2,000

1,000

500

200

100

50

20

10

5

2

1

19

16

16

23

5

5

19

18

5

18

5

18

18

18 18

16

18 18

Number of observations 

(same for both graphs)

1,000

500

200

100

50

20

10

5

2

1

0.5

0.2

0.1

0.05

0.02

0.01
24 Water-Quality Conditions of the Lower Boise River, Idaho

Temporal trends in suspended sediment (fig. 13) in 

the Boise River near Parma also were evaluated. The 

streamflow-adjusted trend for suspended sediment was 

similar to the unadjusted trend, thereby indicating a lack 

of strong influence by streamflow on the trend. Streamflow-adjusted concentrations of suspended sediment 

showed little discernible trend over the course of the 

study.

Nitrogen and Phosphorus Loads

Nitrogen and phosphorus loads entering the 

River between the Diversion Dam and Parma w

mated using measurements of discharge and nu

made at the four main-stem river sites, six north

tributary/drains, six southside tributary/drains, a

three WTFs. Measurements were made during 

Table 6. Statistical summary of suspended sediment concentrations and instantaneous loads in samples from site

the lower Boise River Basin, May 1994 through February 1997

[Sampling site locations are shown by reference number in figure 1 and are listed in table 3; WTF, wastewater treatment facility]

Sampling Maximum

site Number concentratio

reference of instantaneo

number Site name samples 25 50 75 load

Suspended sediment, milligrams per liter

1 Boise River below Diversion Dam . . . . 20 2 5 7 38

3 Lander Street WTF . . . . . . . . . . . . . . . . 18 6 9 12 17

4 Boise River at Glenwood Bridge. . . . . . 25 4 12 23 67

5 West Boise WTF . . . . . . . . . . . . . . . . . . 18 4 7 9 11

6 Eagle Drain at Eagle . . . . . . . . . . . . . . . 5 9 64 82 90

7 Thurman Drain near Eagle . . . . . . . . . . 5 11 11 16 20

8 Boise River near Middleton. . . . . . . . . . 20 4 7 18 211

9 Fifteenmile Creek at mouth. . . . . . . . . . 18 18 66 156 518

10 Mill Slough below Grade Ditch . . . . . . 5 26 48 57 62

11 Willow Creek at Middleton . . . . . . . . . . 18 13 59 133 357

12 Mason Slough at mouth. . . . . . . . . . . . . 5 64 112 165 202

13 Mason Creek at mouth . . . . . . . . . . . . . 18 42 100 209 525

14 West Hartley Gulch near Caldwell . . . . 18 11 25 79 248

15 East Hartley Gulch near Caldwell . . . . . 18 31 55 79 157

17 Caldwell WTF . . . . . . . . . . . . . . . . . . . . 17 8 11 14 20

18 Indian Creek at mouth . . . . . . . . . . . . . . 18 35 43 81 176

19 Conway Gulch at Notus . . . . . . . . . . . . 18 37 89 217 425

20 Dixie Drain at mouth. . . . . . . . . . . . . . . 18 29 69 128 460

21 Boise River near Parma . . . . . . . . . . . . . 21 19 47 84 245

Suspended sediment, instantaneous load, tons per day

1 Boise River below Diversion Dam . . . . 20 5.19 24.5 79.6 718

3 Lander Street WTF . . . . . . . . . . . . . . . . 18 .26 .38 .50 .66

4 Boise River at Glenwood Bridge. . . . . . 25 4.54 23.6 258 1,020

5 West Boise WTF . . . . . . . . . . . . . . . . . . 18 .25 .45 .65 .80

6 Eagle Drain at Eagle . . . . . . . . . . . . . . . 5 .48 1.9 7.40 7.78

7 Thurman Drain near Eagle . . . . . . . . . . 5 .36 .42 1.01 1.56

8 Boise River near Middleton. . . . . . . . . . 20 4.44 10.0 183 2,066

9 Fifteenmile Creek at mouth. . . . . . . . . . 18 1.67 21.9 53.2 165

10 Mill Slough below Grade Ditch . . . . . . 5 4.59 16.0 22.1 26.3

11 Willow Creek at Middleton . . . . . . . . . . 18 1.08 5.26 20.7 117

12 Mason Slough at mouth. . . . . . . . . . . . . 5 2.67 6.34 7.40 8.27

13 Mason Creek at mouth . . . . . . . . . . . . . 18 7.10 23.3 66.2 171

14 West Hartley Gulch near Caldwell . . . . 18 .24 .59 6.85 26.8

15 East Hartley Gulch near Caldwell . . . . . 18 2.63 5.37 15.2 27.10

17 Caldwell WTF . . . . . . . . . . . . . . . . . . . . 17 .15 .21 .28 .43

18 Indian Creek at mouth . . . . . . . . . . . . . . 18 8.91 16.8 25.2 86.6

19 Conway Gulch at Notus . . . . . . . . . . . . 18 1.83 9.52 26.1 59.6

20 Dixie Drain at mouth. . . . . . . . . . . . . . . 18 10.30 26.4 60.3 459

21 Boise River near Parma . . . . . . . . . . . . . 21 48.50 299 978 1,565

Concentration or instantaneous

load at indicated percentile
Water-Quality Condi

MILLIGRAMS PER LITER

500

400

300

200

100

0

SUSPENDED SEDIMENT

500

400

300

200

100

0

Figure 13. Time series and trend line of concentrations of suspended sediment in samples from the Boise River near 

June 1974 through February 1997.

SUSPENDED SEDIMENT (Streamflow adjusted)

Trend

line

December

1990

June

1985

December

1979

June

1974

J

1
Water-Quality Condi

rounds in each of four synoptic sampling periods: May 

1995 and May 1996 (irrigation, or high-flow, season) 

and November 1994 and December 1995 (post-irrigation, or low-flow, season). The discharge and nutrient 

loads measured at the 15 tributary/drains and WTFs 

were compared with the differences in discharge and 

loads measured in the Boise River between the Diversion Dam and Parma (fig. 14).

In general, loads of total nitrogen and total phosphorus entering the river from tributary/drains and 

WTFs were similar to the differences in loads measured 

at the Diversion Dam and Parma. However, because 

water is diverted from the river during the irrigation season, comparisons between discharge and nutrient loads 

entering the river at all measured sites during the highflow sampling periods could be misleading. Diversions 

from the Boise River during the May 1995 and May 

1996 sampling periods account for the loss of discharge 

between the Diversion Dam and Parma, as indicated in 

figure 14. During the May 1995 sampling period, there 

was less water in the Boise River at Parma site than at 

the Diversion Dam site. A more accurate comparison 

between discharge and nutrient loads entering the river 

at measured sites could be made if samples were collected from the diversions, as well as from tributary/

drains. During the post-irrigation season, water is not 

diverted from the Boise River, and nutrient loads can be 

compared directly with discharge.

During the post-irrigation (low-flow) season, discharge measured at the tributary/drains and WTFs constituted about 80 percent of the discharge in the Boise 

River between Diversion Dam and Parma. Unmeasured 

ground-water inflow probably constituted most of the 

remaining 20 percent. Nitrogen and phosphorus loads 

measured at the tributary/drains and WTFs during lowflow sampling were near, or exceeded, the loads in the 

Boise River between Diversion Dam and Parma. Loss 

of nitrogen and phosphorus once these nutrients enter 

the river probably is attributable to biotic uptake, partitioning, and sedimentation. Southside tributary/drains 

contributed most of the discharge and total nitrogen to 

the Boise River during the low-flow sampling periods; 

WTFs contributed most of the total phosphorus.

Although the total measured discharge entering the 

Boise River from tributary/drains and WTFs was substantially larger during high-flow sampling than during 

low-flow sampling, the nitrogen and phosphorus loads 

were not. Total nitrogen and total phosphorus loads 

were relatively constant in discharge from WTFs during 

all four sampling periods and were only slightly larger 

in discharge from the northside tributary/drains 

the high-flow sampling periods. Total nitrogen a

phosphorus loads from the southside tributary/d

did not correlate well with the season; the total n

load from southside tributary/drains was largest 

the December 1995 period, and the total phosph

load was largest during the May 1996 period.

Selected Water-Quality Constituents

DISSOLVED OXYGEN

The concentration of dissolved oxygen in s

water is a measure of the amount of unbound ox

and is affected by temperature, barometric pres

biological processes (photosynthesis, respiratio

decomposition of organic material) and stream 

State of Idaho water-quality standards speci

solved oxygen concentrations exceeding 6 mg/L 

times” (Idaho Department of Health and Welfare

State water-quality standards further specify tha

waters of the Boise River from Veterans State Pa

mouth will have dissolved oxygen concentration

(6) mg/L or seventy-five percent (75%) of satur

whichever is greater, during the spawning perio

monid fishes inhabiting those waters” (Idaho D

ment of Health and Welfare, 1993). Dissolved o

concentrations ranged from 6.9 mg/L in the Bois

near Parma on August 16, 1995, to 14.8 mg/L i

teenmile Creek on February 13, 1997. No disso

oxygen concentrations violated State standards

tical characteristics of dissolved oxygen measur

river and tributary/drain sites in the lower Boise 

Basin from May 1994 through February 1997 a

marized in figure 15.

pH

The water-quality variable pH represents th

tive base-10 log of the hydrogen-ion activity in 

per liter (Hem, 1985). The pH scale ranges from 

standard units; at neutrality, pH equals 7. Value

less than 7 are considered acidic, and values grea

7 are considered basic. Unpolluted river water ge

has a pH within the range 6.5 to 8.5 (Hem, 198

State of Idaho water-quality standards for p

coldwater biota specify “hydrogen ion concentr

(pH) values within the range of six point five (6
Water-Quality Condi

1,400

1,200

1,000

800

600

400

200

0

DISCHARGE, IN CUBIC FEET PER SECOND

30,000

25,000

20,000

15,000

10,000

5,000

0

6,000

5,000

4,000

3,000

2,000

1,000

0

November 1994

(low flow)

May 1995

(high flow)

Figure 14. Discharge and nutrient loads entering the Boise River from wastewater treatment facilities and tributary/dra

during four synoptic sampling rounds, November 1994 through May 1996.

December 1995

(low flow)

May 1996

(high flow)

TOTAL PHOSPHORUS, IN POUNDS PER DAY TOTAL NITROGEN, IN POUNDS PER DAY

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Wastewater treatment facilities

Southside tributary drains

Northside tributary drains

Difference between Boise

 River at Diversion Dam

 and Parma

Difference is

-230 cubic feet

per second

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28 Water-Quality Conditions of the Lower Boise River, Idaho DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER

20

18

16

14

12

10

8

6

35

30

25

20

15

10

5

0

50,000

FECAL COLIFORM, IN COLONIES

PER 100 MILLILITERS

WATER TEMPERATURE, IN

DEGREES CELSIUS

SAMPLING SITE NAME ABBREVIATION

Figure 15. Concentrations of selected water-quality constituents in samples from 16 sites in the lower Boise River Ba

1994 through February 1997. (Shaded boxes represent Boise River sites; see table 3 for sampling site name abbrevia

N

CON

W

CLD

S

IND

N

EHR

S

MSC

N

WHR

N

WIL

S

MSS

S

FIF

N

MIL

R

MID

N

EAG

S

THR

W

WST

W

LAN

R

GLN

R

DIV

S

DIX

20,000

10,000

50

20

10

5,000

2,000

1,000

5

2

1

500

200

100

20

18

25

5

5 20 17

5

18

5 18 18 18 18

18

(Maximum instantaneous) 

20 25 18

5

5

19

17

5

18

5

18

17

18

18

17

19

17

24

5 5

19

17

5

17

4

17 17

18 17

17

(Maximum

instantaneous,

secondary

contact)

(Maximum

instantaneous,

primary

contact)

Number of observations
Water-Quality Condi

nine point five (9.5)” (Idaho Department of Health and 

Welfare, 1993). Values of pH ranged from 6.6 in the 

Boise River below Diversion Dam on August 21, 1996, 

to 8.9 in the Boise River near Parma on March 21, 1995 

(Brennan and others, 1996, 1997). No pH values violated State standards.

SPECIFIC CONDUCTANCE

Specific conductance, a measure of electrical conductivity in water, is generally proportional to the concentration of total dissolved solids. Surface water has a 

wide range of specific conductance values, ranging from 

about 50 μS/cm in freshwater to about 50,000 μS/cm in 

seawater (Hem, 1985). Specific conductance values 

ranged from 59 μS/cm in the Boise River below Diversion Dam on June 12, 1996, to 845 μS/cm in Dixie 

Drain on February 11, 1997 (Brennan and others, 1996, 

1997). 

WATER TEMPERATURE

Water temperature is an important considera

aquatic biota. State of Idaho water-quality stand

coldwater biota specify “water temperatures of 

two (22) degrees C or less with a maximum dai

age of no greater than nineteen (19) degrees C” 

Department of Health and Welfare, 1993). A sta

summary of water temperatures measured at riv

tributary/drain sites in the lower Boise River Bas

May 1994 through February 1997 is shown in fi

Daily mean water temperature data over a 5

period between July 18 and September 5, 1996

lected using Hobo continuous temperature reco

are plotted in figure 16. The State of Idaho stand

coldwater biota was exceeded by 34 percent at 

ton, 48 percent at Caldwell, and 80 percent near 

26

25

24

23

22

21

20

19

18

17

16

15

14

13

DAILY MEAN TEMPERATURE, IN DEGREES CELSIUS

DATE

July August Se

Figure 16. Daily mean water temperatures at five Boise River sites between July 18 and September 5, 1996.

18 20 25 31 5 10 15 20 25 31 

Coldwater biota

maximum daily average

Eckert Road samplin

Glenwood sampling s

Middleton sampling 

Caldwell sampling si

Parma sampling site 
30 Water-Quality Conditions of the Lower Boise River, Idaho

FECAL COLIFORM BACTERIA

Fecal coliform bacteria counts, expressed as number of colonies per 100 mL of water, are useful in determining the probability of harmful levels of pathogens in 

water and for classifying the suitability of that water for 

primary and secondary contact recreation and other 

uses. State of Idaho water-quality standards specify that 

“waters designated for primary contact recreation are 

not to contain fecal coliform bacteria significant to the 

public health in concentrations exceeding 500/100 mL 

at any time” (800/100 mL standard for secondary contact recreation; Idaho Department of Health and Welfare, 1993). Violations of State standards for primary 

and secondary contact recreation were observed at all 

tributary/drains and in the Boise River near Parma. 

Median instantaneous concentrations of fecal coliform 

bacteria exceeded State standards for primary contact 

recreation at five tributary/drains and exceeded standards for secondary contact recreation at one tributary/

drain (Dixie Drain). Fecal coliform bacteria concentrations at river and tributary/drain sites are summarized in 

figure 15. 

SUMMARY

Agricultural land and water use, wastewater treatment facility (WTF) discharges, land development, road 

construction, urban runoff, confined-animal feeding 

operations, reservoir operation, and river channelization 

affect the water quality and biotic integrity of the lower 

Boise River. The U.S. Geological Survey began a comprehensive water-quality and biotic integrity assessment 

of the river in 1994. This study, being conducted in three 

phases, is designed to describe water quality of the 

lower Boise River and its tributaries and drains, assess 

the biotic integrity of the river, and monitor the longterm trends in water quality and biotic integrity of the 

river.

Phases 1 and 2 of the study consisted of 5 synoptic 

and 13 interval sampling rounds to determine major 

sources, concentrations, and relative loads of nutrients 

and suspended sediment entering the Boise River from 

its major tributary/drains and from WTFs. 

In the Boise River, median concentrations of total 

nitrogen increased downstream, ranging from 0.2 milligrams per liter (mg/L) below Diversion Dam to 2.0 mg/L 

near Parma. The largest median concentration measured 

was 19.2 mg/L at the West Boise WTF. Median daily 

loads of total nitrogen in the Boise River ranged 

1,840 pounds per day (lb/d) at Glenwood Bridg

20,800 lb/d near Parma. Median daily loads of 

nitrogen in tributary/drains ranged from 221 lb/

Thurman Drain to 2,570 lb/d at Dixie Drain. Th

the southside tributary/drains and one WTF cont

a median daily load of more than 2,000 lb/d. Tre

ysis using LOcally WEighted Scatterplot Smoo

(LOWESS) techniques indicated that total nitrog

centrations in the Boise River declined slightly 

ning in 1992, whereas dissolved inorganic nitro

began declining sharply in 1994.

Median concentrations of total phosphorus 

Boise River also increased downstream, ranging 

0.02 mg/L below Diversion Dam to 0.27 mg/L 

Parma. The largest median concentration measu

6.60 mg/L at the West Boise WTF. Median dail

of total phosphorus in the Boise River ranged f

101 lb/d below Diversion Dam to 2,260 lb/d ne

Parma. Median daily loads of total phosphorus 

utary/drains ranged from 9 lb/d at Thurman Dr

285 lb/d at Dixie Drain. Among the 15 sources 

charge to the Boise River, the West Boise WTF 

uted the largest median daily load of total phosp

(810 lb/d); Dixie Drain contributed the second-

load (285 lb/d). Trend analysis using LOWESS 

niques indicated little discernible trend in total 

phorus concentrations in the Boise River, where

dissolved orthophosphorus began declining sha

1994.

Nitrogen-to-phosphorus ratios at the four riv

were calculated to ascertain which nutrient mig

limiting algal growth at each site. If algal popul

are assumed to utilize inorganic nitrogen and so

phosphorus in the ratio 7.2N:1P, phosphorus co

limiting algal growth at the Diversion Dam site

as nitrogen could be limiting algal growth at the 

wood and Middleton sites during some parts of t

Algal growth in the Boise River near Parma did 

appear to be nutrient limited.

In the Boise River, median concentrations o

pended sediment increased downstream, rangin

5 mg/L below Diversion Dam to 47 mg/L near 

The largest median concentration measured wa

112 mg/L in Mason Slough. Median daily load

suspended sediment in the Boise River ranged f

23.6 tons per day (ton/d) near Glenwood Bridge 

299 ton/d near Parma. Median daily loads of sus

sediment in tributary/drains ranged from 0.42 to

Thurman Drain to 26.4 ton/d at Dixie Drain. Th

Summary
References C

the southside tributary/drains contributed median daily 

loads of more than 20 ton/d. Trend analysis using LOWESS techniques indicated little discernible trend in suspended sediment concentrations in the Boise River.

Nitrogen and phosphorus loads entering the Boise 

River between Diversion Dam and Parma were estimated using measurements of discharge and nutrients 

made at the four main-stem river sites, six northside 

tributary/drains, six southside tributary/drains, and 

three WTFs. During low-flow sampling periods, discharge measured at the tributary/drains and WTFs constituted about 80 percent of the discharge in the Boise 

River between Diversion Dam and Parma. Unmeasured 

ground-water inflow probably constituted most of the 

remaining 20 percent. Nitrogen and phosphorus loads 

measured at the tributary/drains and WTFs during lowflow sampling were near, or exceeded, the loads in the 

Boise River between Diversion Dam and Parma. Loss 

of nitrogen and phosphorus once these nutrients enter 

the river probably is attributable to biotic uptake, partitioning, and sedimentation. Southside tributary/drains 

contributed most of the discharge and total nitrogen to 

the Boise River during the low-flow sampling periods; 

WTFs contributed most of the total phosphorus.

Concentrations of dissolved oxygen and values of 

pH during May 1994 through February 1997 did not 

violate State standards. Maximum daily mean water 

temperatures collected during a 50-day period between 

July 18 and September 5, 1996, exceeded the Idaho 

State standard for coldwater biota by 34 percent at Middleton, 48 percent at Caldwell, and 80 percent near 

Parma.

Median instantaneous concentrations of fecal 

coliform bacteria exceeded State standards for primary 

and secondary contact recreation at all tributary/drains 

and in the Boise River near Parma. Median concentrations exceeded State standards for primary contact recreation at five tributary/drains and exceeded standards 

for secondary contact recreation at one tributary/drain 

(Dixie Drain).

REFERENCES CITED

Brennan, T.S., O’Dell, I., Lehmann, A.K., and Tungate, A.M., 

1996, Water Resources Data—Idaho, water year 1995, 

v. 2, Upper Columbia River Basin and Snake River 

Basin below King Hill: U.S. Geological Survey WaterData Report ID–95–2, 357 p.

Brennan, T.S., Lehmann, A.K., O’Dell, I., and Tungat

1997, Water resources data—Idaho, water year 

v. 2, Upper Columbia River Basin and Snake R

Basin below King Hill: U.S. Geological Survey 

Data Report ID–96–2, 377 p.

Britton, L.J., and Greeson, P.E., eds., 1987, Methods 

lection and analysis of aquatic biological and m

logical samples: U.S. Geological Survey Techn

of Water-Resources Investigations, book 5, cha

363 p.

Buchanan, T.J., and Somers, W.P., 1969, Discharge m

ments at gaging stations: U.S. Geological Surv

niques of Water-Resources Investigations, book 

chap. A8, 65 p.

Bureau of Reclamation, 1977, Water quality study, B

valley, v. 2: Bureau of Reclamation, 117 p.

Clark, W.H., and Bauer, S.B., 1983, Water quality st

report, lower Boise River drains, Canyon Count

Idaho Department of Health and Welfare, Divis

Environment, Water Quality Series no. 50, 101 

Edwards, T.K., and Glysson, G.D., 1998, Field meth

measurement of fluvial sediment: U.S. Geologi

vey Techniques of Water Resources Investigatio

Book 3, Chap. C2, 80 p.

Fishman, M.J., 1993, Methods of analysis by the U.

logical Survey National Water Quality Laborato

determination of inorganic and organic constitu

water and fluvial sediments: U.S. Geological S

Open-File Report 93–125, 217 p.

Friedman, L.C., and Erdmann, D.E., 1982, Quality a

practices for the chemical and biological analy

water and fluvial sediments: U.S. Geological S

Techniques of Water-Resources Investigations, 

chap. A6, 181 p.

Guy, H.P., 1969, Laboratory theory and methods for s

analysis: U.S. Geological Survey Techniques o

Resources Investigations, book 5, chap. C1, 58 

Helsel, D.R., and Hirsch, R.M., 1992, Statistical me

water resources: New York, Elsevier, 522 p.

Hem, J.D., 1985, Study and interpretation of the che

characteristics of natural water (3d ed.): U.S. Ge

Survey Water-Supply Paper 2254, 264 p.

Idaho Department of Health and Welfare, 1989, Idah

quality status report and nonpoint source assess

1988: Idaho Department of Health and Welfare, 

of Environmental Quality, variously paged.

———1992, The 1992 Idaho water quality status re

Idaho Department of Health and Welfare, Divis

Environmental Quality, variously paged.

———1993, Idaho water quality standards and was

treatment requirements: Boise, Idaho Depart-m

Health and Welfare.

Ingham, M., 1993, Conway Gulch, Canyon County, 

1958–1989: Idaho Department of Health and W

References Cited
32 Water-Quality Conditions of the Lower Boise River, Idaho

Division of Environmental Quality, State Agricultural 

Water Quality Program Water Quality Status Report 

no. 104, 76 p.

Kjelstrom, L.C., 1995, Data for and adjusted regional regression models of volume and quality of urban storm-water 

runoff in Boise and Garden City, Idaho, 1993–94: U.S. 

Geological Survey Water-Resources Investigations 

Report 95–4228, 36 p.

Mackenthun, K.M., 1969, The practice of water pollution 

biology: U.S. Department of the Interior, Federal Water 

Pollution Control Administration, Divi-sion of Technical Support, 281 p.

Nace, R.L., West, S.W., and Mower, R.W., 1957, Feasibility 

of ground-water features of the alternate plan for the 

Mountain Home Project, Idaho: U.S. Geological Survey 

Water-Supply Paper 1376, 121 p.

Naylor, D.V., Lewis, G.C., Busch, J.R., and Fitzsimmons, 

D.W., 1976, Quality of irrigation and drainage waters in 

the Boise Valley: Moscow, Agricul-tural Experiment 

Station, University of Idaho, College of Agriculture, 

22 p.

Pritt, J.W., and Raese, J.W., eds., 1995, Quality assurance/

quality control manual: National Water Quality Laboratory, U.S. Geological Survey Open-File Report 95–443, 

35 p.

Ryding, S.O., and Rast, Walter, eds., 1989, The cont

eutrophication of lakes and reservoirs, v. 1 of P

gramme on man and the biosphere series: Cam

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stream-water samples for the National Water-Q

Assessment Program: U.S. Geological Survey O

File Report 94–455, 42 p

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streamflow and ground-water conditions in the 

River Valley, Idaho: U.S. Geological Survey W

Resources Investigations Report 38–74, 56 p.

U.S. Environmental Protection Agency, 1994, List o

still requiring total maximum daily loads (TMD

paragraph 303(d) list for the State of Idaho Dec

Document, October 7, 1994, 13 p. plus app.

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