U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2016–5128

Prepared in cooperation with Blaine County, Trout Unlimited, The Nature Conservancy, 

and the Wood River Land Trust

Aquatic Biological Communities and Associated Habitats at 

Selected Sites in the Big Wood River Watershed, 

South-Central Idaho, 2014
Cover: Big Wood River at Hailey, Idaho, looking downstream from the Bow 

Bridge with a scientist taking an invertebrate sample. Photograph by Dorene 

MacCoy, U.S. Geological Survey, September 17, 2014.

.
Aquatic Biological Communities and 

Associated Habitats at Selected Sites in the 

Big Wood River Watershed, South-Central 

Idaho, 2014

By Dorene E. MacCoy and Terry M. Short 

Prepared in cooperation with Blaine County, Trout Unlimited, The Nature 

Conservancy, and the Wood River Land Trust

Scientific Investigations Report 2016–5128

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Director

U.S. Geological Survey, Reston, Virginia: 2016

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Suggested citation:

MacCoy, D.E., and Short, T.M., 2016, Aquatic biological communities and associated habitats at selected sites in 

the Big Wood River watershed, south-central Idaho, 2014: U.S. Geological Survey Scientific Investigations Report 

2016–5128, 37 p., http://dx.doi.org/10.3133/sir20165128.

ISSN 2328-0328 (online)
iii

Contents

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

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

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

Sampling Sites.......................................................................................................................................6

Previous Investigations........................................................................................................................6

Sampling and Data Analysis Methods .......................................................................................................7

Watershed Characterization and Site Selection.............................................................................7

Hydrology ...............................................................................................................................................8

Water Quality.......................................................................................................................................10

Water-Quality Assurance and Quality Control......................................................................10

Periphyton............................................................................................................................................12

Physical Habitat ..................................................................................................................................12

Biological Communities .....................................................................................................................12

Macroinvertebrates ..................................................................................................................13

Fish ...............................................................................................................................................14

Aquatic Biological Communities and Habitats .......................................................................................14

Hydrology .............................................................................................................................................14

Water Quality.......................................................................................................................................16

Physical Habitat ..................................................................................................................................19

Biological Communities .....................................................................................................................21

Macroinvertebrates ..................................................................................................................21

Fish ...............................................................................................................................................24

Summary........................................................................................................................................................26

References Cited..........................................................................................................................................27

Appendix A. Macroinvertebrate Density Collected from Selected Sites in the Big Wood River 

and Tributaries, South-Central Idaho, September 2014 ...........................................................33

Appendix B. Relative Abundance of Fish Species Sampled from Sites in the Big Wood River 

and Tributaries, South-Central Idaho, September 2014 ...........................................................36
iv

Figures

1. Map showing major populated areas and water-quality and biological sampling

sites, Big Wood River watershed, south-central Idaho, 2014 ...............................................3

2. Graphs showing discharge and long-term median daily discharge for main-stem

sites on the Big Wood River, south-central Idaho, water year 2014....................................8

3. Photograph showing assembly of Onset® TidbiT® thermistors to be attached to

streamgage orifice line .............................................................................................................11

4. Graph showing base-flow index values for selected sampling sites in the Big Wood

River and tributaries, south-central Idaho, August 2014......................................................15

5. Graph showing continuous temperature for main-stem sites on the Big Wood River,

south-central Idaho, May–September 2014...........................................................................18

6. Graph showing ephemeroptera, plecoptera, and trichoptera (EPT) taxa richness

from samples collected at selected sites in the Big Wood River watershed,

south-central Idaho, September 2014 .....................................................................................22

7. Graphs showing temperature, suspended sediment, and nutrient tolerance values

for invertebrates at selected sites, Big Wood River, south-central Idaho........................23

8. Graphs showing trout and Wood River sculpin (Cottus leiopomus) relative

abundance from samples collected at sites in the Big Wood River watershed,

south-central Idaho, September 2014 .....................................................................................25

9. Photograph showing Wood River sculpin (Cotus leiopomus).............................................25

Tables

1. Watershed and site characteristics of Big Wood River, south-central, Idaho ..................5

2. Hydrologic measures used to characterize the flow regime for selected sites in the

Big Wood River watershed, south-central Idaho, water years 2012–15.............................9

3. Instantaneous water-quality and periphyton data collected from sampling sites in

the Big Wood River watershed, south-central Idaho, September 2014 ............................17

4. Daily mean temperatures for selected sites in the Big Wood River watershed,

south-central Idaho, June–September 2014..........................................................................19

5. Habitat data collected at selected sites, Big Wood River watershed, south-central

Idaho, September 2014 ..............................................................................................................20

6. Macroinvertebrate metrics calculated from samples collected at selected sites in

the Big Wood River watershed, south-central Idaho, September 2014 ............................21
v

Conversion Factors

International System of Units to Inch/Pound

Multiply By To obtain

Length

millimeter (mm) 0.03937 inch (in.)

micrometer (μm) 0.00004 inch (in.)

meter (m) 3.2808 foot (ft)

kilometer (km) 0.62137 mile (mi)

Area

square kilometer (km2) 0.38610 square mile (mi2)

Volume

liter (L) 0.26417 gallon (gal)

milliliter (mL) 0.00026 gallon (gal)

cubic meter (m3) 0.00081 acre-foot (acre-ft)

Flow rate

cubic meter per second (m3/s) 35.315 cubic foot per second (ft3/s)

Mass

milligram (mg) 0.00004 ounce (oz)

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

°F =(1.8×°C) + 32.

Datums

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

(NAVD 88).

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

Elevation, as used in this report, refers to distance above the vertical datum.

Supplemental Information

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius 

(μS/cm at 25 °C).

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

or micrograms per liter (μg/L).

A water year is the 12-month period from October 1 through September 30 of the following 

calendar year. The water year is designated by the calendar year in which it ends. For example, 

water year 2013 is the period from October 1, 2012, through September 30, 2013.
vi

Abbreviations

AEP annual expected probablility

BFD bankfull discharge

BFI baseflow index

BURP beneficial use reconnaissance program

BW Hailey Big Wood River at Hailey

BW Ketchum Big Wood River near Ketchum

BW Stanton Big Wood River at Stanton Crossing

CV coefficient of variation

DMF daily mean flow

East Fork East Fork Big Wood River

EWI equal width integrated

EPT ephemeroptera, plecoptera, and tricoptera

FSBI fine bed sediment index

IDAS invertebrate data analysis system

IDEQ Idaho Department of Environmental Quality

IDFG Idaho Department of Fish and Game

IDHW Idaho Department of Health and Welfare

K condition coefficient

MPN most probable number

NAWQA National Water-Quality Assessment

North Fork North Fork Big Wood River

NWIS National Water Information System

NWQL National Water Quality Laboratory

PPBV planes, plateaus, and broad valleys

RD richness/density

RK river kilometer

RPD relative percent difference

SFI stream fish index

SMI stream macroinvertebrate index

SSC suspended-sediment concentration

TMDL total maximum daily load

Trail Ck Trail Creek

EPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

Warm Sp Warm Springs Creek

WV wetted volume

WWTP wastewater treatment plant
Aquatic Biological Communities and Associated 

Habitats at Selected Sites in the Big Wood River 

Watershed, South-Central Idaho, 2014 

By Dorene E. MacCoy and Terry M. Short

Abstract 

Assessments of streamflow (discharge) parameters, 

water quality, physical habitat, and biological communities 

were completed between May and September 2014 as part 

of a monitoring program in the Big Wood River watershed 

of south-central Idaho. The sampling was conducted by the 

U.S. Geological Survey in cooperation with Blaine County, 

Trout Unlimited, the Nature Conservancy, and the Wood River 

Land Trust to help identify the status of aquatic resources 

at selected locations in the watershed. Information in this 

report provides a basis with which to evaluate and monitor 

the long-term health of the Big Wood River and its major 

tributaries. Sampling sites were co-located with existing 

U.S. Geological Survey streamgaging stations: three on the 

main stem Big Wood River and four on the North Fork Big 

Wood River (North Fork), Warm Springs Creek (Warm Sp), 

Trail Creek (Trail Ck), and East Fork Big Wood River (East 

Fork) tributaries. 

The analytical results and quality-assurance information 

for water quality, physical habitat, and biological community 

samples collected at study sites during 2 weeks in 

September 2014 are summarized. Water-quality data include 

concentrations of major nutrients, suspended sediment, 

dissolved oxygen, and fecal-coliform bacteria. To assess 

the potential effects of nutrient enrichment on algal growth, 

concentrations of periphyton biomass (chlorophyll-a and ash 

free dry weight) in riffle habitats were determined at each 

site. Physical habitat parameters include stream channel 

morphology, habitat volume, instream structure, substrate 

composition, and riparian vegetative cover. Biological data 

include taxa richness, abundance, and stream-health indicator 

metrics for macroinvertebrate and fish communities. Statistical 

summaries of the water-quality, habitat, and biological data 

are provided along with discussion of how these findings 

relate to the health of aquatic resources in the Big Wood 

River watershed.

Seasonal discharge patterns using statistical summaries of 

daily discharge from selected sites are reported for water years 

2012–15. Results showed that annual average daily mean 

discharge increased from the Big Wood River near Ketchum, 

ID (BW Ketchum) downstream to the Big Wood River at 

Hailey, ID (BW Hailey), but decreased by nearly 50 percent 

from BW Hailey downstream to Big Wood River at Stanton 

Crossing near Bellevue, ID (BW Stanton). Annual variability 

in daily mean discharge among main-stem sites was highest 

at BW Stanton, suggesting that this part of the river may be 

subject to some level of flow alteration. 

Hydrologic alterations resulting in flow reduction can 

contribute to higher water temperature, especially during the 

summer months when conditions are often most stressful to 

fish and other stream organisms. Daily water temperature 

and water temperature trends from June to September 2014 

are reported for select tributary and main-stem sites on the 

Big Wood River and can be used to assess the potential for 

biological impairment based on aquatic life temperature 

criteria for cold-water streams. The State of Idaho maximum 

temperature criteria for protection of cold-water aquatic life 

of 22 °C was exceeded at Warm Sp and BW Stanton during 

summer 2014, but at none of the other main-stem or tributary 

sites. The 13 °C critical temperature criterion for salmonid 

spawning was exceeded in early July 2014 at BW Ketchum 

and BW Hailey near the end of the rainbow trout critical 

spawning and rearing period. Temperature exceedances 

were most frequent at BW Stanton, where exceedances for 

rainbow trout and brown trout occurred from May through 

early July 2014 during most of the critical spawning and 

rearing period. 

Water quality and habitat availability did not seem to be 

limiting for fish or other aquatic organisms at most sites in 

the Big Wood River watershed. Water quality assessments in 

September 2014 determined no exceedances of total maximum 

daily load target levels. The availability and quality of habitat 

was limited at BW Stanton, where shallow-water habitat 

conditions prevailed. 

Macroinvertebrate community diversity was high at all 

sites except for BW Stanton, where low community diversity 

was attributed to low species richness and high abundances of 

a few tolerant taxa. Presence of low species diversity and high 

macroinvertebrate tolerance values at BW Stanton indicates 

that benthic community condition and stream health were 

reduced at that location. 
2 Aquatic Biological Communities and Associated Habitats, Big Wood River Watershed, South-Central Idaho, 2014

Fish surveys done in September 2014 did not indicate 

any significant reductions in native fish communities in 

the Big Wood River or its tributaries. Native rainbow trout 

(Oncorhynchus mykiss) and Wood River sculpin (Cottus 

leiopomus) were the dominant fish species in the drainage and 

were found at all tributary and main-stem sites. Non-native 

brown (Salmo trutta) and brook trout (Salvelinus fontinalis) 

were limited to lower drainage sites on the Big Wood River 

(BW Hailey and BW Stanton), and occurred in relatively 

low numbers. 

Introduction

The population of Blaine County in south-central Idaho 

nearly quadrupled from about 5,700 to 22,000 people between 

1970 and 2010 (Forstall, 1995; U.S. Census Bureau, 2011). 

Residents and resource managers of the Big Wood River 

watershed (fig. 1) are concerned about how population growth 

may affect the quantity and quality of the groundwater and 

surface-water resources. Increased human activities and 

associated demands on existing water resources could alter 

the flow, water quality, habitat, and biological properties 

of streams, threatening the health of these systems in the 

watershed. The possibility that altering natural flow regimes 

and water-use practices (such as withdrawal for irrigation, 

public supply, and commercial use) can accentuate habitat 

loss for aquatic organisms is of concern, particularly for 

native fish species, which have relatively specific habitat 

requirements with respect to flow velocity, stream depth, and 

water temperature. For example, fishery studies in the 1980s 

determined that altered stream reaches in the Big Wood River 

contained one-tenth of the trout densities that unaltered or 

“natural” reaches contained (Thurow, 1988). 

Increased residential development along river corridors 

can decrease density of riparian vegetation and increase the 

amount of impervious surfaces that often lead to increased 

storm runoff and higher and more variable peak discharge. As 

frequency and intensity of peak flows increase, the likelihood 

of streambed scouring and channel incision increases. 

Furthermore, as riparian and adjacent areas become more 

developed, there is an increased potential for decreased 

infiltration to groundwater that can lead to diminished 

discharge during dry periods when groundwater is the main 

source of discharge. 

An increase in other land-use activities in the watershed, 

such as agriculture, ranching, and logging, could potentially 

increase sediment and nutrient loading to receiving systems 

during periods of snowmelt or rainfall driven surface runoff 

events. For example, recent wildfires in the upper Big Wood 

River watershed resulted in loss of hillslope stability and 

increased debris flow and sediment input to the Big Wood 

River (Skinner, 2013). Nutrients and excess sediment loading 

to streams are a leading cause of water-quality and biological 

impairment in the Nation’s streams (U.S. Environmental 

Protection Agency, 2006). Sediment erosion from disturbed 

land surfaces and stream banks can increase turbidity 

which, when prolonged, can decrease the light penetration 

necessary for growth of important primary producers such 

as benthic algae. Additionally, turbid waters tend to absorb 

more heat from sunlight and can increase stream water 

temperatures (Waters, 1995). Sediment deposition can 

severely affect biological diversity by reducing the quality 

and quantity of stream-bottom habitat available to fish and 

other stream organisms. Similarly, excessive concentrations 

of nutrients resulting from local sources such as sewage 

outfalls, septic tanks, and livestock operations, or from 

more dispersed sources such as agriculture and associated 

fertilizer applications, are associated with altered biological 

communities in streams and rivers (U.S. Environmental 

Protection Agency, 2006; Dubrovsky and others, 2010). 

These land use practices and alteration of natural flow 

regimes in the watershed are a potential threat to the wellbeing of resident aquatic communities. Native species, such 

as the endemic Wood River sculpin (Cottus leiopomus), are 

particularly vulnerable to environmental change (Zaroban, 

2010). This small fish is a protected nongame species that 

is vulnerable primarily because of its limited range, but is 

also threatened by declining stream health resulting from 

water-quality degradation, habitat loss, invasive predatory 

fish, floodplain encroachment, and flow alteration in the Big 

Wood River (Zaroban, 2010). Although associations between 

excess nutrients and macroinvertebrate and fish communities 

are often difficult to quantify, harmful effects can occur when 

elevated nutrients result in eutrophication. Problems with 

eutrophication in streams include the negative aesthetic effect 

of excessive algal growth, associated taste and odor problems, 

adverse biological effects from low dissolved oxygen and high 

pH (Dodds and Welch, 2000), and impediments to channel 

flows from dense growths of algae or aquatic macrophytes 

(Ferreira and others, 1999). However, these effects can vary 

in degree of severity from one stream to another as a result 

of differences in patterns of discharge, amount of riparian 

shading, water temperature, water clarity, and the extent of 

groundwater and surface water exchange (Dubrovsky and 

others, 2010; Riseng and others, 2011).

The Idaho Department of Environmental Quality (IDEQ) 

designated that beneficial uses of the Big Wood River and 

tributaries include supporting cold-water aquatic life, salmonid 

spawning, primary and secondary contact recreation, special 

resource waters, and domestic and agricultural water supply 

(Buhidar, 2002). Special resource waters outlined in Idaho 

Water-Quality Standards have special restrictions to protect 

cold water biota that include no detectable increase in ambient 

water temperature as a result of a flow alteration (Buhidar, 

2002). The Big Wood River Management Plan identified the 

Big Wood River as not meeting standards because of high 

concentrations of suspended sediment, fine substrate sediment, 

total phosphorus, bacteria, and high water temperatures 

(Buhidar, 2002). 
Introduction 3

TAC_16-1096_fig01

Big Wood River

Trail Creek

Deer Creek

Dry Creek

Croy Creek

Camp

Creek

Seamans Creek

Willow Creek

Fox Creek

Rock Creek

Corral Creek

Lava Creek

Cove Creek

Lake Creek

Greenhorn Creek

East Fork Big Wood River

Springs

Creek

Warm

Fall Creek

Wild Horse Creek

Little Wood River

Fisher Canyon

Kane Creek

Loving Creek

Silver Creek

North Fork 

Big Wood 

River

EXPLANATION

Level 4 ecoregions

 Foothill shrublands-grasslands

Camas prairie

Dry partly wooded mountains

Southern forested mountains

Site drainage basin

Sampling site

Populated area

Hot spring

Waste-water treatment plant

Hailey HS

Hailey WWTP

13140800

Hailey

IDAHO

Study

area

Sun Valley

Ketchum

Hailey

Gannett

Bellevue

Picabo

Russian John HS

Warfeild HS

Clarendon HS

Hailey HS

Easley HS

Guyer HS

Hailey

WWTP

Meadows/

Ketchum 

WWTP

Ketchum/

Sun Valley

WWTP

13140800

13139510

13138000

13137500

13137000

13135520

13135500

Sawtooth National

Recreation Area

Bellevue

Fan

114°30' 114°20' 114°10' 114°00'

43°40'

43°30'

43°20'

0 5 10 MILES

0 5 10 KILOMETERS Base from U.S. Geological Survey digital data 30 m shaded relief, 2002

75

75

20

Figure 1. Major populated areas and water-quality and biological sampling sites, Big Wood River watershed, 

south-central Idaho, 2014. Names of numbered sites are shown in table 1.
4 Aquatic Biological Communities and Associated Habitats, Big Wood River Watershed, South-Central Idaho, 2014

Stream degradation is rarely caused by a single factor, 

but is often the consequence of multiple physical, chemical, 

and biological factors interacting (Carlisle and others, 2013). 

Identifying the role of each of these factors in influencing 

ecosystem health poses a challenge to development of 

effective water-quality and biological management strategies. 

The ability of biological communities to integrate, over space 

and time, effects of multiple environmental stressors provides 

a mechanism with which to identify stressor effects from 

many sources. For example, algae, macroinvertebrate, and 

fish communities each represents a different functional role in 

the ecosystem, responds in different ways to human‐caused 

environmental change, and thus provides different and 

complementary perspectives on water-quality and stream 

health. Collectively, these communities, along with key waterand habitat-quality parameters, provide a comprehensive basis 

of understanding with which to assess long-term effects of 

multiple environmental stressors on the quality of freshwater 

resources (Karr, 1991; Lapointe and others, 2014).

Despite concerns about the sustainability of the health 

of the Big Wood River, there is a lack of long-term waterand biological-quality monitoring in the watershed (Hopkins 

and Bartolino, 2013). The information in this report is 

intended to characterize selected discharge, water quality, 

physical habitat, and biological properties of the Big Wood 

River and its major tributaries, and to provide ecologically 

relevant guidelines to help in the design and implementation 

of long-term monitoring efforts in the Big Wood River 

watershed. Assessments of discharge, water quality, physical 

habitat, and biological communities were completed in 

September 2014 by the U.S. Geological Survey, in cooperation 

with Blaine County, Trout Unlimited, the Nature Conservancy, 

and the Wood River Land Trust. Samples were collected in 

September 2014 at three sites on main stem of the Big Wood 

River: Big Wood at Ketchum (BW Ketchum), Big Wood at 

Hailey (BW Hailey), and Big Wood at Stanton Crossing (BW 

Stanton). Samples also were collected at four major tributaries 

of the Big Wood River: North Fork Big Wood River (North 

Fork), Warm Springs Creek (Warm Sp), Trail Creek (Trail 

Ck), and East Fork Big Wood River (East Fork). Sampling 

reaches were near existing U.S. Geological Survey (USGS) 

streamgaging stations where continuous daily discharge 

information was available. Daily discharge and associated 

hydrologic variables were calculated for water years 2012–15. 

Continuous daily water temperature was measured at each site 

during May–September 2014. Water‐quality samples, habitat 

measurements, and biological samples were collected during 

2 weeks in September 2014. 

Description of Study Area

The Big Wood River watershed in south-central Idaho 

has a drainage area of approximately 3,800 km2 and consists 

of three ecoregions: the Southern Forested Mountains, the Dry 

Partly Wooded Mountains, and the Camas Prairie (Omernik 

and Griffith, 2008). The Big Wood River originates in a 

mountainous area of south-central Idaho at an elevation of 

about 3,300 m and transitions from primarily forest and alpine 

meadows in the higher elevations to sagebrush steppe at the 

lower elevations of about 1,500 m (fig. 1; McGrath and others, 

2002; Tetra Tech, 2011). The climate is mild and arid during 

summer months, but cold and wet during winter, with about 

60 percent of the total annual precipitation occurring between 

the first of November and the end of March, mostly as snow. 

The growing season varies in length, ranging from about 

3 months in the cooler, high elevations near Ketchum to about 

5 months in the lower watershed. The drought conditions 

during data collection in the Big Wood River watershed are 

categorized as moderate (U.S. Geological Survey, 2016a).

The upper and lower parts of the Big Wood River 

watershed in Blaine County differ in major land use (table 1). 

Most of the population growth, land development, and 

tourism occur in the northernmost part of the county near the 

communities of Sun Valley, Ketchum, Hailey, and Bellevue. 

This area is dominated by recreational areas popular for 

skiing, fishing, and other outdoor activities. Local resorts 

and numerous fly fishing guides provide services in the area 

that attract recreationists from around the world to the Big 

Wood River. The population of Blaine County depends on 

groundwater for domestic and public supply, either from 

privately-owned or municipal-supply wells (Hopkins and 

Bartolino, 2013). In contrast, irrigation for local agriculture 

is largely dependent on surface water supplies. Three 

wastewater-treatment plants (WWTP) discharge to the Big 

Wood River: the northernmost WWTP is located within the 

City of Ketchum (Ketchum/Sun Valley), one is located south 

of Ketchum (Meadows/Ketchum WWTP), and the WWTP 

farthest south in the watershed is located within the City of 

Hailey (Hailey WWTP, fig. 1). Additionally, many homes in 

the watershed are on septic systems that percolate into the Big 

Wood River Valley aquifer (Bartolino, 2009) and may have an 

impact on water quality. 

The lower Big Wood River watershed downstream 

of Bellevue (Bellevue Fan) is primarily farms and ranches 

irrigated by groundwater and diverted surface water. Farmland 

irrigation began as early as 1900 (Jones, 1952) and has since 

expanded, with increased agricultural water needs within 

the watershed. Periodic changes in discharge for the Big 

Wood River, particularly in the downstream reaches, have 

been directly related to seasonal patterns of surface and 

groundwater withdrawal for irrigation (Hopkins and Bartolino, 

2013). Water use for irrigation typically occurs during the 

growing season between May and September, during which 

time discharge in the southwestern part of the watershed is 

diminished and portions of the river downstream of Bellevue 

can go dry. 
Introduction 

5

Table 1. Watershed and site characteristics of Big Wood River, south-central, Idaho.[Locations of sites are shown in figure 1. River kilometers above mouth: Distance from confluence of Malad and Snake Rivers, from 1:24,000 topographic map. IDEQ ecoregion: Idaho Department of Environmental Quality ecoregion based on level 4 ecoregions and associated biological communities (Tetra Tech, 2011). MT, mountain; PPBV, plains, plateaus, and broad valleys. Land use: Watershed characteristics calculated from NLCD11 and StreamStats (http://water.usgs.gov/osw/streamstats/). Abbreviations: m, meter; km2, square kilometer; NRA, National Recreation Area; USGS, U.S. Geological Survey; –, not calculated]

USGS site name Station No. Site short name Latitude (decimal degrees) Longitude (decimal degrees) River kilometers upstream of mouth Drainage area (km2) Elevation (m) IDEQ ecoregion Land use (percent) Major land use near reach location Basin slope Forest Agriculture Developed

Big Wood River nr Ketchum, Idaho 13135500 BW Ketchum 43.786 -114.425 170 355 1,902 MT 26 53.80 – 0.57 RecreationNorth Fork Big Wood River near 

Sawtooth NRA Headquarters, Idaho

13135520 North Fork 43.786 -114.419 169 104 1,908 MT 57 47.07 – – Recreation

Warm Springs Creek near Ketchum, 

Idaho

13137000 Warm Sp 43.690 -114.385 156 243 1,777 MT 44 46.32 0.07 0.50 Residential/

commercial

Trail Creek at Ketchum, Idaho 13137500 Trail Ck 43.678 -114.361 154 166 1,765 MT 51 49.72 0.48 1.85 Residential/

commercial

East Fork Big Wood River at 

Gimlet, Idaho

13138000 East Fork 43.603 -114.330 146 223 1,701 PPBV 46 33.38 0.00 0.31 Residential/

commercial

Big Wood River at Hailey, Idaho 13139510 BW Hailey 43.517 -114.322 136 1,590 1,614 PPBV 45 44.17 0.16 1.57 Residential/

commercial

Big Wood River at Stanton 

Crossing nr Bellevue, Idaho

13140800 BW Stanton 43.329 -114.319 122 1,937 1,472 PPBV 43 39.29 1.05 1.91 Agriculture
6 Aquatic Biological Communities and Associated Habitats, Big Wood River Watershed, South-Central Idaho, 2014

Sampling Sites

Locations of study sites on the Big Wood River main 

stem and major tributaries are shown in figure 1 and listed 

in table 1. The northernmost study sites in the watershed 

are the BW Ketchum (13135500) at 170 river kilometers 

(RK) upstream of the mouth and on North Fork (13135520, 

RK 169). Both sites drain relatively undeveloped lands within 

the Sawtooth National Recreation Area managed by the U.S. 

Forest Service and are 16 km upstream of local population 

centers at Sun Valley and Ketchum. Two tributary sites are 

located within the city of Ketchum, Warm Sp (13137000, 

RK 156) and Trail Ck (13137500, RK 154). The Warm Sp 

drainage area contains the Guyer Hot Springs system located 

3.2 km upstream of the sampling site (Foley and Street, 1988). 

This geothermal system provides heating to local residences 

and mixes with colder groundwater and surface water prior 

to discharging to Warm Springs Creek. A 1986 study by the 

U.S. Environmental Protection Agency (EPA) indicated that 

the geothermal waters from this system did not substantially 

increase the overall water temperature of Warm Springs Creek 

(Renk, 1986). Land use bordering these tributary sites is 

primarily light residential and commercial. Recently, increased 

surface runoff and soil erosion as a consequence of the 2013 

Beaver Creek fire (Skinner, 2013) resulted in increased 

sediment loading to the upper and middle parts of Warm 

Springs Creek prior to the 2014 sampling. The East Fork 

(13138000, RK 146) discharges to the Big Wood River main 

stem downstream of the town of Ketchum. The East Fork 

headwaters originate on land managed by the Bureau of Land 

Management that has a history of mining activity (Hopkins 

and Bartolino, 2013). The East Fork sampling site is located 

in a rural area dominated by small ranches. The BW Hailey 

study site (13139510, RK 136) is located within the City of 

Hailey at the USGS streamgaging station that has been in 

operation since 1916. The farthest downstream sampling site, 

BW Stanton (13140800, RK 122), is in the western Bellevue 

Fan area that drains about 1,900 km2. Discharges at this site 

typically decrease in the summer months owing to upstream 

surface water diversions for pasture and crop irrigation. 

Previous Investigations

Effects of altered discharge on water quality and quantity 

in the Big Wood River watershed have been documented, 

but studies targeting long-term trends in water quality and 

biological condition are lacking. The importance of long-term 

monitoring to assessing the health of streams and rivers in the 

Big Wood River watershed was recognized more than 60 years 

ago by Jones (1952, p. 1), who concluded that “records 

covering a period of many years are necessary to evaluate 

adequately the effect of vagaries of the weather and to 

determine the safe yield during drought periods.” Referenced 

here is a list of environmental studies for streams and rivers in 

the Big Wood River watershed.

• Urbanization effects on water resources in the Big 

Wood River watershed were investigated by the Idaho 

Department of Water Resources in 1975 (Castelin 

and Chapman, 1972). That study attributed increased 

water use and water-quality degradation in the Big 

Wood River valley to increased urban development 

and included mining and agriculture as contributing 

sources of pollution. The report includes historical 

records of early fisheries and provides accounts 

of large trout being caught in the Big Wood River 

as far back as 1877 and the stocking of rainbow 

(Oncorhynchus mykiss) and eastern brook (Salvelinus 

fontinalis) trout in the watershed as early as 1912. 

• Thurow (1988) determined that trout densities in the 

Big Wood River were positively correlated with the 

amount of available fish habitat cover and that reaches 

with altered habitat conditions contained one-tenth 

of the trout densities than undisturbed or “natural” 

reaches contained. Based on these findings, the author 

suggested that restoration of fish habitat was needed 

throughout the Big Wood River watershed.

• Maret and others (1997) studied fish assemblages 

and habitat conditions for a number of relatively 

undisturbed streams in the Upper Snake River 

watershed that included sites on the Big Wood River. 

The authors concluded that the major environmental 

factors determining fish distributions were stream 

gradient, watershed size, connectivity, and percentage 

of watershed covered by forest. Fish community 

properties that varied the greatest among sites were 

total number of species, number of native species, 

number of salmonid species, and percentages 

of introduced species, cottidae, and salmonids. 

Least‐disturbed streams tended to have fewer fish 

species than sites affected by human activities, where 

tolerant species have been introduced. The study 

also concluded that there was a distinct difference in 

composition of fish communities between spring-fed 

and non-spring fed stream systems in the Big Wood 

River watershed, which they attributed in part to 

differences in habitat. 

• Maret and others (2001) and Hardy and others 

(2005) summarized water-quality conditions and 

macroinvertebrate community composition for a 

number of Idaho streams and rivers and included sites 

in the Big Wood River watershed—the BW Stanton 

and Silver Creek near Sportsman Access. The reports 

concluded that biological conditions at both sites 

were indicative of healthy stream environments 

with relatively unimpaired water quality. Idaho 

bioassessment data published in Maret and others 

(2001) and subsequent samples collected as part of 

a statewide water-quality network between 1998 
Sampling and Data Analysis Methods 7

and 2008 are available in at U.S. Geological Survey 

(2016b) or U.S. Geological Survey (2016c).

• Since 1993, the IDEQ Beneficial Use Reconnaissance 

Program (BURP; Idaho Department of Environmental 

Quality, 2016) has collected biological and habitat 

data from Idaho streams to support beneficial use 

determinations. Surveys of algae, macroinvertebrate, 

and fish communities and physical habitat are 

conducted each summer mainly on small streams 

throughout Idaho. Survey sites are selected 

randomly and systematically to ensure that results 

are representative of a broad range of conditions 

throughout Idaho’s streams. Additionally, biological 

indices were developed to characterize and evaluate 

biological community conditions (Grafe, 2002a, 

2002b; Tetra Tech, 2011). Sample collection in the 

main stem and tributary sites in the Big Wood River 

watershed was conducted by BURP in 2014 (Idaho 

Department of Environmental Quality, 2014).

• To meet Federal Clean Water Act requirements, the 

state of Idaho set water-quality standards to ensure 

the waters of Idaho are fishable and swimmable. 

IDEQ evaluated existing water-quality concerns and 

pollution sources in the Big Wood River watershed and 

published findings in the Big Wood River Watershed 

Management Plan (Buhidar, 2002). Total maximum 

daily load (TMDL) limits set for the upper Big 

Wood River watershed were published in both the 

management plan and the Agriculture Implementation 

Plan (Buhidar, 2002; Pentzer 2006). The TMDL 

documents describe segments of the Big Wood River 

that do not support one or more beneficial uses. Since 

the development of the TMDL, there has been no 

consistent and continuous monitoring of water-quality 

and biological integrity in the Big Wood River and 

tributaries. A 5-year review of the Big Wood TMDL 

is being done by IDEQ and this report will contribute 

to the analysis of existing data and the updating of the 

TMDL. Data collected by BURP will also be used in 

TMDL development and evaluation. 

• The USGS, in cooperation with several local 

government agencies and organizations, has published 

a number of reports on the quality and quantity of 

water resources in the Big Wood River watershed. 

These reports include (1) a description of trends in 

surface and groundwater hydrology (Skinner and 

others, 2007), (2) the development of a groundwater 

budget (Bartolino, 2009), (3) a hydrogeologic 

framework for the Wood River Valley aquifer system 

(Bartolino and Adkins, 2012), (4) a stream seepage 

and groundwater levels study (Bartolino, 2014), and 

(5) an evaluation of the quality of groundwater and 

surface-water supplies (Hopkins and Bartolino, 2013). 

Overall, these studies concluded that most of the water 

supply in the Big Wood River watershed is relatively 

unimpaired, with low concentrations of nutrients 

and low levels of fecal contamination, although 

elevated nutrient concentrations were reported in 

groundwater in the eastern part of the watershed. 

The studies furthermore concluded that the demand 

for water could eventually affect the quality and 

quantity of groundwater and surface water resources in 

the watershed. 

• The Idaho Department of Fish and Game (2013) 

published information on the status of the fishery 

for the Big Wood River and select tributaries. Idaho 

Department of Fish and Game manages the Big Wood 

River as a cold-water fishery and continues to assess 

fish population on a 3-year rotation. The Big Wood 

River upstream of North Fork and parts of Trail Creek 

and Warm Springs Creek are managed as a put-andtake fishery. Downstream of North Fork to downstream 

of Bellevue, the river is managed as a wild-trout 

trophy fishery.

Sampling and Data Analysis Methods

U.S. Geological Survey water quality and bioassessment 

sampling protocols were used to collect data at selected sites 

in the Big Wood River watershed. Specific sampling protocol 

details and data analysis methods are discussed.

Watershed Characterization and Site Selection

Watershed characteristics were summarized using USGS 

StreamStats (U.S. Geological Survey, 2016d), a Web-based 

geographic information system application that delineates 

drainage areas and uses physical features such as slope, land 

use, surface geology, and discharge from national datasets to 

calculate statistics for a selected watershed and the National 

Land Cover Database 2011 (Homer and others, 2015; table 1). 

River kilometer, drainage area, and elevation are from U.S. 

Geological Survey (2016e).

Given the significant influence of stream hydrology on 

water quality, physical habitat, and biological communities 

(Carlisle and others, 2013), monitoring sites in the Big 

Wood River and tributaries were located near existing 

USGS streamgaging stations. Additionally, monitoring site 

locations were selected to represent as best as possible the 

range of existing conditions within the Big Wood River 

watershed, to include land and water uses, water-quality, and 

biological diversity. 
8 Aquatic Biological Communities and Associated Habitats, Big Wood River Watershed, South-Central Idaho, 2014

Hydrology

Information on daily stream stage was 

used to estimate continuous discharge using a 

stage-discharge relation described by Mueller 

and Wagner (2009) and Turnipseed and Sauer 

(2010). Discharge records for this period were 

computed according to methods described in 

Rantz and others (1982) and are available at 

U.S. Geological Survey (2016e). Continuous 

discharge for water year 2014 and the 

long-term median daily discharge for the period 

of record for each main-stem site are presented 

in figure 2. 

The magnitude and variability of 

discharge are important factors affecting 

the occurrence and composition of fish and 

invertebrate communities (Sheldon and 

Thoms, 2006; Zuellig and others, 2007; Monk 

and others, 2008; Naiman and others, 2008). 

Changes from natural discharge could cause 

washout or stranding of aquatic species, timing 

of seasonal peaks may disrupt fish migration 

cues, prolonged low flow may decrease 

available habitat, and prolonged high flow may 

result in loss of riffle habitat (Poff and others, 

1997). Human-caused alterations to these and 

other natural flow parameters can occur as 

increased frequency of high flows (or flood 

flows), fluctuations in flow between seasonal 

periods of high and low flows that usually 

occur during storm run-off, and increased 

variability in daily flows (Konrad and Booth, 

2005). Ultimately, disruption of natural flow 

regimes can result in loss of physical habitat 

and promote conditions that favor the spread 

of non-native and invasive species (Poff and 

others, 1997; Olden and Poff, 2003). To help 

identify and evaluate flow-related disturbances, 

table 2 presents hydrologic measures that may 

be useful for future evaluation of instream 

flow alteration in the Big Wood River and 

tributaries. Annual and monthly (June and 

September) flow magnitude and variability 

statistics were calculated using discharge 

data from water years 2012 to 2015 and are 

summarized as annual average daily mean 

flow (DMF) and coefficient of variation (CV) 

of annual average DMF (table 2). The CV 

represents the variability of flow relative to the 

magnitude of the mean flow and is calculated 

as the standard deviation divided by the annual 

or monthly average DMF and expressed as 

a percentage. 

TAC_16-1096_fig02

20

0

5

10

15

50

45

40

35

30

25

20

15

10

5

0

30

25

20

15

10

5

0

Discharge, in cubic meters per second

A. USGS 13135500 Big Wood River near Ketchum, Idaho discharge, water year 2014 

B. USGS 13135500 Big Wood River at Hailey, Idaho discharge, water year 2014 

C. USGS 13135500 Big Wood River at Stanton Crossing near Bellevue, Idaho

 discharge, water year 2014 

Oct. 1 Nov. 1 Dec. 1 Jan. 1 Feb. 1 Mar. 1 Apr. 1 May 1 June 1 July 1 Aug. 1 Sept. 1

Oct. 1 Nov. 1 Dec. 1 Jan. 1 Feb. 1 Mar. 1 Apr. 1 May 1 June 1 July 1 Aug. 1 Sept. 1

Oct. 1 Nov. 1 Dec. 1 Jan. 1 Feb. 1 Mar. 1 Apr. 1 May 1 June 1 July 1 Aug. 1 Sept. 1

EXPLANATION

Long term median daily

 discharge (27 years)

Biological sampling

Continuous discharge

EXPLANATION

Long term median daily

 discharge (100 years)

Biological sampling

Continuous discharge

EXPLANATION

Long term median daily

 discharge (19 years)

Continuous discharge

Figure 2. Discharge and long-term median daily discharge for mainstem sites on the Big Wood River, south-central Idaho, water year 2014.
Sampling and Data Analysis Methods 

9

Table 2. Hydrologic measures used to characterize the flow regime for selected sites in the Big Wood River watershed, south-central Idaho, water years 2012–15.[Full site names are shown in table 1. Abbreviations: AEP, annual exceedance probability; CV, coefficient of variation; DMF, daily mean flow; m3/s, cubic meter per second; –, not calculated]

Hydrologic measures

Site name

BW Ketchum North Fork Warm Sp Trail Ck East Fork BW Hailey BW Stanton

Annual average DMF (m3/s) 3.67 1.37 1.97 0.85 0.90 9.88 4.37Annual average CV DMF (variability of annual DMF)

(percent)

26 20 17 27 33 24 46

June average annual DMF (m3/s) 9.22 4.62 3.09 3.47 3.21 24.4 11.0June average annual CV DMF (percent) 28 20 24 21 24 24 42September average DMF (m3/s) 1.84 0.69 1.15 0.19 0.30 4.56 1.12September CV DMF (percent) 5 5 9 55 13 18 73Base-flow index, ratio of base flow (usually summer low 

flow conditions) to total flow for a given period of record

0.93 0.94 0.94 0.88 0.92 0.93 0.91

Bankfull discharge, 67 percent annual expected (m3/s)

probability (m3/s) (AEP, or 1.5-year recurrence interval)1

22 – – – – 28 –

Bankfull discharge, 43 percent AEP (m3/s) (or 2.33-year 

recurrence interval)1

52 – – – – 72 –

1Based on methods described Hortness and Berenbrock (2003) and calculations presented in Wood and others (2016).
10 Aquatic Biological Communities and Associated Habitats, Big Wood River Watershed, South-Central Idaho, 2014

Bankfull discharge (BFD) and base-flow index (BFI) are 

additional hydrologic measures that can correlate strongly 

with occurrence and distribution patterns of stream biota 

(Petts and Maddock, 1997; Sheldon and Thoms, 2006; 

Munn and others, 2010). A BFD is considered the dominant 

channel‐forming flow and hence is a key factor in structuring 

habitat conditions for fish and other stream organisms 

(Knighton, 1998; Doyle and others, 2005; Naiman and others, 

2008). Only the USGS streamgages at BW Ketchum and 

BW Hailey had sufficient periods of record to calculate BFD. 

The BFD reported here is the 67 percent annual expected 

probability (AEP; or 1.5‐year recurrence interval) and 43 

percent AEP (or 2.33-year recurrence interval) based on 

methods described by Hortness and Berenbrock (2003) and 

calculations presented in Wood and others (2016). Base-flow 

index is a ratio of base flow (typically summer low-flow 

conditions) to total flow for a given period of record and 

represents the relative contribution of groundwater flow to 

total discharge. A BFI value of 0 indicates that all flow is 

derived from surface water and a value of 1 indicates that all 

flow comes from groundwater. Importance of groundwater 

flows in moderating physical‐chemical properties of streams 

and influencing biological properties such as algal biomass 

accrual and invertebrate community composition has been 

well-documented (Constantz and others, 1994; Pepin and 

Hauer, 2002; Brown and others, 2007). BFI was calculated 

using the local minimum method of hydrograph separation 

or the separation of the base flow from the total flow over 

the discharge hydrograph (Lim and others, 2005). BFI has 

been used previously to evaluate trends in discharge and 

groundwater and surface water relations in the Big Wood 

River watershed (Skinner and others, 2007). 

Water Quality

Surface-water samples were collected and composited 

from vertical transits throughout the entire stream depth using 

depth- and equal-width-increment (EWI) methods described in 

the “USGS National Field Manual” (U.S. Geological Survey, 

variously dated). The EWI samples were collected with an 

isokinetic DH-81 sampler. Water samples were consolidated 

in a plastic churn splitter and dispensed into separate bottles. 

In accordance with the ”USGS National Field Manual,” the 

churn and sampling equipment were cleaned in soapy water, 

rinsed in tap water, and triple rinsed with deionized water 

between sites. Sites were sampled in downstream order 

starting at the farthest upstream site. At the time of EWI 

water sample collection, field parameters (temperature, pH, 

specific conductance, and dissolved oxygen) were determined 

in accordance with USGS procedures (Turnipseed and 

Sauer, 2010; U.S. Geological Survey, variously dated) using 

a six‐series multiparameter water-quality sonde (Yellow 

Springs, Inc.). Instruments were calibrated prior to and 

following sampling using methods described in Wagner and 

others (2006).

Unfiltered water samples for total nutrient analysis were 

acidified with sulfuric acid and chilled at 4 °C. Water samples 

to be analyzed for dissolved nutrients were filtered through 

0.45-μm-pore-size capsule filters certified to be free from 

contamination, acidified with sulfuric acid, and chilled at 4 °C. 

All the nutrient samples were shipped on ice to the USGS 

National Water-Quality Laboratory (NWQL) for analysis. 

Water concentrations of total nitrogen and phosphorus were 

determined using colorimetric analysis following alkaline 

persulfate digestion as described by Fishman (1993) and by 

Patton and Kryskalla (2003 and 2011) and in accordance with 

laboratory quality-assurance and quality-control protocols 

described by Pritt and Raese (1995). Unfiltered suspended 

sediment samples were homogenized, stored at room 

temperature, and shipped to the USGS Cascades Volcano 

Observatory Sediment Laboratory for analysis. Samples were 

analyzed for suspended-sediment concentration (SSC) and 

percentage of particles less than 0.0625 mm (fines) using 

wet sieving and filtration methods described by Guy (1969) 

and the American Society for Testing and Materials (2002) 

method D3977-97. Unfiltered water samples for fecal indicator 

analysis (Escherichia coli [E. coli]) were homogenized, 

chilled at 4 °C, and delivered to the Idaho Department of 

Health and Welfare (IDHW), Bureau of Laboratories in Boise, 

Idaho within 24 hours. The most probable number (MPN) 

of organisms per milliliter (E. coli and total coliform) was 

determined for each water sample using method number 

9223B as described in Standard Methods (Eaton and 

others, 1999). 

Continuous water temperature was recorded using two 

Onset® TidbiT® thermistors (fig. 3) attached to the USGS 

streamgage orifice line at each site—one was the main 

thermistor and one was used as a backup. Temperature 

calibration, temperature checks, record compilation, and 

reporting followed USGS standard procedures (Wagner and 

others, 2006). Continuous temperature was recorded every 

15 minutes to the nearest 0.1 °C between May 2014 and 

September 2014. Monthly statistics were calculated from daily 

average continuous temperature measurements.

Water-Quality Assurance and Quality Control

Quality-assurance procedures used for the collection and 

field processing of water samples were described by Ward and 

Harr (1990) and U.S. Geological Survey (variously dated). 

The NWQL follows systematic internal quality-assurance 

practices as described in Friedman and Erdmann (1982) 

and Pritt and Raese (1995) to ensure laboratory analytical 

accuracy. These practices include quality-control samples 

such as calibration standard samples, standard reference water 

samples, replicate samples, deionized-water blank samples, or 

spiked samples at a proportion equivalent to at least 10 percent 

of the sample load. The NWQL participates in a blind‐sample 

program using samples prepared by the USGS Branch of 
Sampling and Data Analysis Methods 11

Figure 3. Assembly of Onset® TidbiT® thermistors to be attached to streamgage orifice 

line. Photograph by Dorene E. MacCoy, U.S. Geological Survey.

Quality Systems (U.S. Geological Survey, 2016f) that are 

routinely inserted into the sample line. The laboratory also 

participates in external evaluation studies and audits with the 

National Environmental Laboratory Accreditation Program to 

assess analytical performance. 

Suspended sediment processing and analysis by 

Cascades Volcano Observatory adheres to quality-control 

and quality-assurance procedures described by Knott and 

others (1993). These include frequent instrument calibration, 

standard conductivity and reagent checks, as well as split, 

spiked, blank, and reference sample analysis. 

The IDHW follows standard operating procedures 

(SOP) for simultaneous detection or enumeration of total 

coliform and E. coli using defined substrate (Colilert®

and Colilert-18®). Biological controls and sterility checks 

are used to calibrate and check instrumentation. Colilert 

reagent is checked with a known concentration of a control 

organism before use and then quarterly, until the reagent is 

completely consumed or reaches expiration, with a target 

concentration of approximately 100 organisms/100 mL. 

Additionally, each batch of testing vessels is checked for 

sterility, volumetric accuracy, and auto-fluorescence before 

use. Reagent and testing materials are rejected if quality 

control parameters are not met (Standard operating procedure 

MIC-SM9223B, version 6.0, Ernest Bader, written commun., 

January 19, 2016).

The quality of analytical results reported for water 

samples was evaluated using quality-control samples that 

were submitted concurrently with environmental samples. 

Water-quality sample results were reviewed after receipt 

of the laboratory analysis. Data validation included use of 

a relative percent difference (RPD) to evaluate the relation 

between the dissolved nutrient concentrations and whole-water 

concentrations. RPDs were calculated using the absolute value 

of the difference between the result pair, divided by the mean 

of the result pair, multiplied by 100. Expressing precision 

relative to a mean concentration standardizes comparison of 

precision among individual constituents. Laboratory analyses 

are rerun and (or) verified when the dissolved fraction 

exceeded the whole-water fraction with an RPD greater than 

10 percent. Nutrient, suspended sediment, and bacteria results 

were reviewed for anomalies in relation to historical results at 

the same location if data were available. 

Replicate data were used to assess the precision 

(reproducibility) of the analytical results. Replicate samples 

are two or more samples considered to be essentially identical 

in composition. Replicate samples can be obtained in the field 

(field replicate) by either repeating the collection process 

to obtain two or more independent composite samples 

(concurrent field replicate) or by splitting a single composite 

sample into two or more subsamples (split field replicate). 

The individual replicate samples are then analyzed separately. 

Likewise, a single sample can be analyzed two or more times 

in the laboratory to obtain a measure of analytical precision 

(laboratory replicate). All replicate samples collected as 

part of this study were split field replicates and were used to 

indicate the reproducibility of environmental data that are 

affected by variability potentially introduced by field and 
12 Aquatic Biological Communities and Associated Habitats, Big Wood River Watershed, South-Central Idaho, 2014

laboratory processes. The precision of the analytical results 

was determined using the RPD between the environmental 

sample and the split replicate. An RPD of less than 25 percent 

was considered acceptable because of the low concentrations 

of constituents (near analytical detection), especially for 

nutrients. The RPD was evaluated for split replicate total 

coliform and E. coli bacteria samples. However, because those 

results are reported as an MPN, no specific RPD acceptability 

value was targeted. 

Blank samples identify the presence and magnitude of 

potential contamination that could bias analytical results. 

Field blanks are aliquots of deionized water that are certified 

as contaminant-free and are processed through the sampling 

equipment used to collect stream samples. All blanks were 

collected as field blanks. Field blanks are subjected to the 

same processing (sample splitting, filtration, preservation, 

transportation, and laboratory handling) as environmental 

samples. Blank samples were analyzed for the same 

constituents as the environmental samples.

Replicate samples for suspended sediment and E. coli

were collected at Trail Ck. Replicate samples for nutrient 

analysis were collected at both Trail Ck and BW Stanton. 

All replicate samples met data-quality objectives and did not 

exceed the 25 percent RPD criteria. Additionally, equipment 

blanks collected at BW Stanton were analyzed for nutrient 

contamination, with no detectable results. 

Periphyton

Samples of periphyton (biofilm attached to rock surfaces) 

were collected from as many as 25 cobbles in or near each 

riffle targeted for macroinvertebrate collections using methods 

described in Moulton and others (2002). Periphyton samples 

were removed from cobbles by using the bottom portion 

of a 30-mL syringe fitted with a neoprene O-ring to form a 

watertight seal against a rock surface. Filtered stream water 

(5 mL) was added to the syringe barrel, and attached materials 

were dislodged from the rock surface with a stiff-bristle brush 

and collected with a hand pipette. Individual samples were 

composited and total sample volume determined. A 5–10 mL 

aliquot of the composited sample was filtered through 

a 0.7-μm glass-fiber filter. Filters were then wrapped in 

aluminum foil and frozen until analyzed for concentrations of 

chlorophyll-a and biomass (ash-free dry weight) by the Bureau 

of Reclamation, Pacific Northwest Regional Laboratory in 

Boise, Idaho, using standard analytical methods (standard 

method 10200H; Eaton and others, 1999).

Physical Habitat

Measures of physical habitat include discharge, channel 

morphology, substrate composition, habitat cover, and 

riparian canopy density and are based on methods described 

in Fitzpatrick and others (1998). Eleven equidistant transects 

perpendicular to the direction of flow were established within 

the longitudinal boundaries (150–400 m) of each sampling 

reach. Wetted channel width was measured at each transect 

location and averaged for the entire length of the reach. Wetted 

depth and flow velocity were measured at five locations along 

each transect and an average value reported for each study 

reach. Streambed substrate composition was quantified at 

each transect location using a modification of the Wolman 

pebble count technique (Wolman, 1954). At each transect, 

the presence of habitat cover type (over-hanging vegetation, 

undercut banks, woody debris, boulders, macrophytes, 

artificial structures) that could provide refuge for fish or other 

organisms was recorded at channel margins near the edge of 

water and at three other locations in the main channel. The 

proportion of cover types occurring within a stream reach 

was calculated as percent cover. Riparian vegetation density 

(percent) was measured near stream channel margins at each 

transect location using a hemispherical densitometer (Platts 

and others, 1987). 

The amount of variability among habitat measures such 

as channel wetted width, depth of water, flow velocity, and 

substrate particle size can be used to evaluate overall habitat 

conditions occurring along the length of a study reach. 

Stream channels where dimensions of physical properties are 

relatively uniform throughout the reach (low variability), such 

as might occur in highly channelized streams, typically are 

less biologically diverse than streams where conditions are 

more heterogeneous throughout (Kaufmann and others, 1999). 

Variability among physical habitat parameters was determined 

as the CV of the total individual transect-based determinations 

collected in each reach (55 determinations per reach). The 

product of reach length and reach-averaged wetted width and 

depth is the wetted volume (WV) for a given length of stream 

channel, and this measure can be used to estimate the total 

amount of available habitat space for a defined stream reach 

(Gordon and others, 1993). This metric provides a general 

indication of the potential habitat capacity of a stream—

essentially the habitable space of a stream region available to 

support populations of fish and other organisms. Streams with 

a relatively large WV are more likely to have greater numbers 

of fish than smaller streams with more limited habitat areas. 

Because WV will increase with increasing reach length, the 

WV was calculated based on a standard reach length of 150 m. 

Biological Communities

Benthic macroinvertebrate and fish communities were 

sampled using protocols developed by the USGS National 

Water-Quality Assessment (NAWQA) Program (Moulton 

and others, 2002). The USGS NAWQA sampling protocols 

have been thoroughly tested in streams and rivers throughout 

the conterminous United States, Alaska, and Hawaii, and 

are designed using nationally consistent sampling and 

analytical methods. 
Sampling and Data Analysis Methods 13

Macroinvertebrates

Quantitative macroinvertebrate samples were collected 

from rock substrates using a modified D-frame net fitted with 

a 500 μm-mesh net and a detachable collection receptacle. 

Macroinvertebrates were collected from a 0.25-m2 area 

immediately upstream of the sampler by systematically 

removing attached organisms from rocks and other substrate 

surfaces. Individual samples were collected from five locations 

distributed in riffle regions throughout each stream reach and 

composited into a single sample. Each sample was cleaned 

of extraneous inorganic and organic materials by elutriation, 

preserved in ethanol, and shipped to EcoAnalysts in Moscow, 

Idaho, for taxonomic identification and enumeration. 

The EcoStandard West procedure was used to identify 

macroinvertebrates to the lowest taxonomic level possible 

(usually genus or species) and all biological community data 

were uploaded to the USGS BioData website (U.S. Geological 

Survey, 2016b).

Macroinvertebrate assemblage data was summarized 

using USGS Invertebrate Data Analysis System (IDAS) 

software (Cuffney and Brightbill, 2011). IDAS provides 

methods of resolving ambiguous taxa and calculating 

macroinvertebrate metrics and specific indices. Metrics 

selected for analysis were those that have been effective in 

diagnosing macroinvertebrate community health in Idaho 

streams. Among these were mayflies [ephemeroptera]; 

stoneflies [plecoptera]; and caddisflies [trichoptera], EPT taxa 

richness and total taxa richness (number of unique taxa in 

a sample). Generally, least disturbed streams in Idaho have 

higher EPT and taxa richness and can be used as indicators of 

healthy cold-water streams (Maret and others, 2001). 

Disturbance effects on benthic macroinvertebrate 

communities often manifest as alterations in community 

composition (Resh and others, 1988), although compositional 

characteristics such as taxa richness and density can generate 

opposite patterns of community response to disturbance 

(McCabe and Gotelli, 2000) depending on the intensity, areal 

extent, and frequency of the disturbance (Resh and others 

1988; Townsend and others, 1997). Community responses 

to conditions of water quality and physical habitat were 

examined by comparing taxa richness and density ratios (RD) 

among sampling locations. Taxa richness and density values 

for each site were log transformed prior to calculation of RD. 

Environmental framework documents were developed 

in 2002 by IDEQ in order to evaluate the biological 

integrity of Idaho streams and rivers (Grafe, 2002a, 2002b). 

This document stated that multiple indices of biological 

communities (algae, macroinvertebrates, fish, and habitat) 

would help the State of Idaho identify waters that may or may 

not be in full support of their designated beneficial uses of 

fishable and swimmable. In 2011, IDEQ began the process 

to update the 2002 water-body assessment framework using 

BURP data collected from more than 3,000 sites in Idaho. 

For this evaluation, Idaho streams were categorized into three 

groups based on level 4 ecoregions listed in figure 1 and 

associated macroinvertebrate community data (Tetra Tech, 

2011). The stream-based ecoregions (IDEQ ecoregions) were 

designated Mountain, Foothills, and, collectively, Plains, 

Plateaus, and Broad Valleys (PPBV). The Big Wood River 

sites are in both the Mountain and PPBV IDEQ ecoregions. 

A stream macroinvertebrate index (SMI2) was developed for 

each IDEQ ecoregion using species trait characteristics that 

are meant to be the most responsive to regional environmental 

conditions. The PPBV SMI2 metrics include Simpson’s 

D (species diversity index), percent non-insects, percent 

filter feeders, percent tolerant species, percent clingers, and 

number of semi‐voltine taxa (taxa that take more than 1 year 

to complete their life-cycle, considered to be long-lived). 

The Mountain SMI2 include the number of clinger taxa, 

percent ephemeroptera and plecoptera, number of EPT taxa, 

percent filterers, modified Hilsenhoff Biotic Index (diversity 

index based on sensitivity to organic pollution), number 

of semi‐voltine taxa, and total number of taxa. As of 2016, 

the State of Idaho has not developed scoring criteria for 

SMI2, and the values published in this report are for future 

reference. The SMI2 values generally range from 0 (most 

disturbed conditions) to 100 (least disturbed conditions). 

The reference values calculated for PPBV SMI2 are between 

50 and 94, and for the Mountains SMI2 between 33 and 94 

(Jason Papanni, Idaho Department of Environmental Quality, 

written commun., September 2015). See Tetra Tech (2011) for 

a more detailed description of IDEQ ecoregion groupings and 

SMI2 development.

Tolerance metrics and biological indices help identify 

macroinvertebrate communities that may be susceptible 

to individual or combinations of physical and chemical 

stressors. Relations between macroinvertebrate assemblages 

and compositional characteristics of streambed substrates 

can be examined using the Fine Bed Sediment Index (FBSI) 

developed by Relyea and others (2012). The FSBI is based on 

occurrence patterns of macroinvertebrate taxa in northwestern 

streams having markedly different substrate compositional 

characteristics. High FSBI values are indicative of streams 

with a relatively low percentage of substrate fines and high 

abundance of fine sediment sensitive species, whereas low 

FSBI values indicate streams with a high percentage of species 

not sensitive to substrates dominated by fine-grained particles. 

In the Northern Mountains level 3 ecoregion, the typical FSBI 

values range between 0 and 350, with the lowest values (<50) 

containing as much as 100 percent fine sediment (defined as 

particles <2 mm in Relyea, 2012). 

Macroinvertebrate indicator values (tolerances) for 

nutrients, water temperature, and suspended sediment were 

based on ecological trait information provided by U.S. 

Environmental Protection Agency (2012). Tolerance values 

range from 0 (lowest tolerance) to 10 (highest tolerance). 
14 Aquatic Biological Communities and Associated Habitats, Big Wood River Watershed, South-Central Idaho, 2014

Tolerance values were abundance weighted to account for 

differences among sites in macroinvertebrate densities and 

to normalize tolerance values for among-site comparisons. 

Tolerance categories were arbitrarily defined and based on 

ranges of tolerance values where low was less than or equal to 

3, moderate was 3–6, and high was greater than 6–10. 

Fish

Fish communities were sampled during base-flow 

conditions in September 2014 using pulsed direct-current 

backpack and barge electrofishing as described in Moulton 

and others (2002). For most sites, electrofishing began at the 

downstream boundary of the sampling reach and a single pass 

was done in an upstream direction. For the larger BW Hailey 

site barge, electrofishing was used and sampling conducted 

in a downstream direction. All habitats were systematically 

surveyed along the entire length of the sampling reach. All 

captured fish were identified to species, counted, measured 

for length and weight, and examined for external anomalies. 

Voucher specimens, primarily Wood River sculpin, were 

verified at the Orma J. Smith Academy of Sciences museum 

at the College of Idaho in Caldwell, Idaho. All fish species 

and sampling information was entered into BioData at U.S. 

Geological Survey (2016b).

The environmental framework documents developed by 

IDEQ to evaluate the biological integrity of Idaho’s streams 

and rivers (Grafe, 2002a, 2002b) included the original River 

Fish Index (2002 RFI) and the Stream Fish Index (2002 SFI). 

The 2002 RFI and SFI were revised and IDEQ developed 

the new 2011 river and stream fish indices (RFI2 and SFI2; 

Tetra Tech, 2011). Similar to the SMI2, the SFI2 used metrics 

specific to IDEQ ecoregions (Tetra Tech, 2011). The Big 

Wood River is mainly in the PPBV IDEQ ecoregion with 

the upstream-most sites in the Mountains IDEQ ecoregion. 

The PPBV SFI2 includes the number of native fish taxa, and 

the percentages non-native fish taxa, minnows, lithophilic 

spawners (fish that spawn in gravel), invertivores (fish feeding 

on invertebrates), and piscivores (fish feeding on other fish). 

The Mountains SFI2 includes number of native fish taxa, 

individuals per native taxon, percent invertivores, percent 

lithophilic spawners, and percent native intolerant individuals 

(Tetra Tech, 2011). The State of Idaho has not finalized scoring 

criteria for the SFI2, and the values published in this report are 

for general reference. SFI2 values reported here range from 0 

(most disturbed conditions) to 100 (least disturbed conditions). 

The reference values calculated for PPBV SFI2 are between 

61 and 99, and for the Mountains SFI2 between 30 and 100 

(Jason Papanni, Idaho Department of Environmental Quality, 

written commun., October 2015).

Aquatic Biological Communities and 

Habitats

Hydrologic, water quality, and physical habitat data 

associated with the 2014 biological community samples 

provide information about the environment available for 

aquatic organisms in the Big Wood River watershed. It is 

important to note that this was a one-time sampling event 

and that aquatic organisms integrate these and possibly more 

parameters over time. Findings from this initial assessment are 

given below.

Hydrology

Seasonal flow patterns for the Big Wood River and 

tributaries are typical of a snow-melt driven system with 

peak flows usually occurring during spring runoff (fig. 2). 

Peak discharges during WY 2014 occurred in late May and 

early June for the main-stem sites, with peak discharge of 

15 m3/s at BW Ketchum, 39 m3/s at BW Hailey, and 24 m3/s at 

BW Stanton. Lower peak flows downstream of the BW Hailey 

site at the BW Stanton site may have resulted from water 

diversion upstream of BW Stanton during the beginning of 

the irrigation season. Peak flows for the Big Wood River in 

2014 occurred somewhat earlier than historical occurrences 

based on the period of record for these sites (fig. 2) and reflect 

a more recent pattern of earlier snowmelt runoff occurring 

in rivers throughout the Western United States (Stewart and 

others, 2004; McCabe and Clark, 2005; Clow, 2008).

Average DMF for water years 2012–15 for sites on 

the Big Wood River increased in magnitude downstream 

of BW Ketchum (3.67 m3/s) to BW Hailey (9.88 m3/s), 

but decreased to 4.37 m3/s at BW Stanton (table 2). Flow 

variability (expressed as the coefficient of variation of 

annual DMF) was similar for BW Ketchum and BW Hailey 

(26 and 24 percent, respectively), but increased to 46 percent 

at BW Stanton (table 2). Generally, with the exception of 

BW Stanton, differences among tributary and main-stem sites 

in annual variability of DMF were not remarkable (ranging 

between 17 and 33 percent), and probably reflect naturally 

occurring seasonal changes in discharge (table 2). Discharges 

are typically greatest during late spring to early summer, and 

on the Big Wood River, average DMF for June was 9.22 m3/s 

at BW Ketchum and 24.4 m3/s downstream at BW Hailey 

(table 2). In unaltered systems, discharge typically increases 

downstream as corresponding drainage area increases; 

however, June DMF downstream of BW Hailey decreased 

by one-half at BW Stanton to 11.0 m3/s (fig. 2, table 2). 
Aquatic Biological Communities and Habitats 15

Additionally, flow variability for June was highest among sites 

at BW Stanton (DMF CV of 42 percent, table 2). Reduced 

and more variable June flows occurring at BW Stanton likely 

result from flow diversions downstream of BW Hailey to 

support increased agricultural demands during early summer 

and possible leakage to groundwater (Bartolino, 2014).

On average, September DMF for main-stem sites on the 

Big Wood River was about 16 percent of the June DMF, with 

the highest flows (4.56 m3/s) recorded at BW Hailey. Flows 

decreased downstream at the BW Stanton site to 1.12 m3/s 

during this time. Tributary flows in September also were at 

their seasonal low and ranged between 0.19 m3/s at Trail Ck 

to 1.15 m3/s at Warm Sp. The CV in DMF was lower at most 

sites in the month of September compared to June and is 

indicative of the time of year when daily discharge is greatly 

reduced and antecedent flow conditions are relatively stable 

(table 2). However, flow conditions in the lower part of the 

watershed can be highly variable depending on water use 

patterns during the end of the irrigation season, as evident at 

BW Stanton with a CV DMF of 73 percent for September. 

High flow variability (CV DMF of 55 percent) for the Trail Ck 

site (table 2) may have been partly due to summer storms, 

which are frequent in the upper part of the watershed.

The BFD estimates for BW Ketchum and BW Hailey 

reported in table 2 represent conditions when the stream 

channels are at capacity with the water at the top of the 

channel bank at the level of the floodplain. For most streams 

this typically occurs in the spring as a result of rain- or 

snowmelt-driven runoff events, and has a recurrence interval 

between 1 and 2 years (Leopold, 1994). Differences in BFD 

between BW Ketchum and BW Hailey largely result from 

differences in drainage areas (table 1), with BFD increasing 

with increasing drainage area. Estimates of BFD reported in 

table 2 are included as a reference for comparing magnitudes 

of peak flows for streams in the watershed and the potential of 

these flows as channel- and habitat-forming events. 

Annual BFI values for sites in the Big Wood River 

watershed indicated that discharge is dominated by 

groundwater throughout most of the year (BFI near 1, table 2). 

However, in August 2014 significant contributions of surfacewater inputs to total daily discharge (where surface water is 

greater than 50 percent of total flow) were apparent at the Trail 

Ck tributary and at BW Stanton (fig. 4). For these sites, 36 and 

13 percent, respectively, of the total daily flows during August 

were derived primarily from surface water inputs (fig. 4), 

possibly from late summer storms in the Trail Ck drainage or 

return flows for BW Stanton.

0

0.2

0.4

0.6

0.8

1.0

1.2

Base-flow index

Surface water Groundwater

BW Ketchum North Fork Warm Sp Trail Ck East Fork BW Hailey BW Stanton

EXPLANATION

Daily value

Daily average

Figure 4. Base-flow index values for selected sampling sites in the Big Wood River and tributaries, 

south-central Idaho, August 2014. Full site names are shown in table 1.
16 Aquatic Biological Communities and Associated Habitats, Big Wood River Watershed, South-Central Idaho, 2014

Water Quality

Samples collected in September 2014 consisted of 

a single sampling event and was intended to characterize 

water‐quality conditions at the time of sampling and not to 

provide information on long-term water-quality conditions or 

potential effects to aquatic communities. Nevertheless, these 

initial results provide information on water-quality for streams 

in the Big Wood River watershed during base flow when 

conditions are often most stressful to stream organisms. 

Water-quality and recommended TMDL values for the 

upper Big Wood River watershed are presented in table 3. 

Suspended-sediment concentrations were low and ranged 

from 1 mg/L at the North Fork and East Fork sites to 13 mg/L 

at Warm Sp, well within the recommended TMDL target 

concentration for suspended sediment of less than 25 mg/L 

(Buhidar, 2002). Similarly, nutrient concentrations among the 

tributary and main-stem sites were low. Nitrate plus nitrite 

concentrations ranged from less than 0.04 to 0.073 mg/L 

and were within the recommended TMDL of less than 

0.30 mg/L. Total phosphorus concentrations were within the 

TMDL target of less than 0.050 mg/L for all sites with the 

exception of Warm Sp with a total phosphorus concentration 

of 0.055 mg/L. This value is within the 20 percent analytical 

variability for total phosphorus and may not be considered 

as exceeding TMDL. Periphyton accrual was limited at all 

main-stem and tributary sites as evident by low concentrations 

of chlorophyll-a and biomass (ash free dry weight) (table 3). 

Chlorophyll-a concentrations ranged from 2 mg/ m2 at 

BW Ketchum to 86 mg/m2 at Trail Ck, and biomass 

concentrations were near detection limits at most locations. 

Although physical factors such as flow velocity, riparian 

shading, and substrate composition can affect algal accrual 

rates (Biggs, 2000; Munn and others, 2010), nutrients assume 

a greater influence on algal growth during periods of relatively 

low and stable streamflow (Biggs and Close, 1989; Lohman 

and others, 1992), as was present during the September 

sampling. Results of the periphyton sampling suggest that 

nutrient and organic enrichment was not a significant factor 

affecting water quality at the sampling locations. E. coli

concentrations were also low in stream water at all, sites with 

the highest levels of 43 MPN/100 mL at Trail Ck. The E. coli

recommended TMDL concentration is based on a geometric 

mean value of five samples collected within a month (primary 

and secondary contact less than 126 most probable number per 

100 milliliters [MPN/100 mL]) and on an instantaneous value 

(primary contact, less than 406 MPN/100 mL and secondary 

contact, less than 576 MPN/100mL). Concentrations of E. coli

in the Big Wood River and tributary sites were well within 

TMDL target levels.

The State of Idaho has designated the Big Wood River 

subbasin as cold water (Buhidar, 2002), and as such it is 

required to meet cold-water aquatic life criteria. Streams 

designated as cold water are those having a daily maximum 

temperature less than 22 °C or a daily average temperature of 

less than 19 °C (Idaho Department of Environmental Quality, 

2013; 2015). The state daily maximum temperature criterion 

of 22 °C is applicable during the index period between May 4 

and September 24. This value was exceeded only at Warm Sp 

and BW Stanton during summer 2014 (table 4, fig. 5). The 

salmonid spawning criteria of 13 °C applies during the critical 

spawning and rearing periods (critical periods) for species 

that occur in a watershed (Buhidar, 2002; Miller and others, 

2014). Exceedance of temperature criteria will differ based 

on salmonid reproductive behavior. For autumn spawners in 

Idaho, such as brown trout (Salmo trutta) in the Big Wood 

River, the critical period is during spawning and early stages 

of incubation and emergence when stream temperatures begin 

to cool, approximately October 1 through June 30 (Miller 

and others, 2014). The opposite is true for spring spawners, 

such as rainbow trout, where the later stages of incubation 

through emergence are a more critical period, approximately 

March 15–July 15. The temperature critical period was 

exceeded for rainbow trout in early July 2014 at BW Ketchum 

and BW Hailey, and was exceeded May through July during 

most of the rainbow and brown trout critical period at 

BW Stanton (fig. 5). 

Various hydrological, topographical, and meteorological 

factors are responsible for temperature patterns in streams 

and rivers (Allan, 1995). The direction of discharge 

(whether the stream channel is predominantly parallel or 

perpendicular to the angle of the sun during daylight hours), 

the amount of streamside vegetation (which affects the 

amount of shading), and the channel shape (for example, 

deep and narrow versus wide and shallow), all affect stream 

temperature by influencing the amount of sunlight reaching 

the water surface. Precipitation in the form of rain or snow 

also can have a warming or cooling influence on stream 

temperature. One of the most important factors affecting 

stream temperature is the influence of groundwater, which 

tends to have a moderating effect on temperature extremes 

(Findlay, 1995). For streams in the Big Wood River watershed, 

groundwater contributes greater than 85 percent of the total 

flow during summer when streams are at or near base-flow 

(table 2). Increased groundwater withdrawal, combined with 

variable surface water reallocation, can have a significant 

effect on stream temperatures in the watershed by increasing 

average daily water temperatures and the frequency of high 

temperature periods. 
Aquatic Biological Communities and Habitats 17

Table 3. Instantaneous water-quality and periphyton data collected from sampling sites in the Big Wood River watershed, south-central Idaho, September 2014.[Site short name: Full site names are shown in table 1. Dissolved oxygen: TMDL dissolved oxygen target >6 mg/L. Instantaneous temperature: TMDL instantaneous temperature target >22. Nitrate plus nitrite: TMDL total nitrate plus nitrite target <0.30 mg/L. pH: TMDL pH target between 6.5 and 9.5. Suspended sediment: TMDL suspended sediment target <25 mg/L total suspended solids. Total phosphorus: TMDL total phosphorus target <0.050 mg/L. Abbreviations: E. Coli, Escherichia coli; °C, degrees Celsius; m3/s, cubic meter per second; μS/cm at 25 °C, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligram per liter; mg/m2, milligram per square meter; mm, millimeter; MPN/100 mL , most probable number per 100 milliliters; N, nitrogen; P, phosphorus; TMDL, total maximum daily load from Buhidar (2002); USGS, U.S. Geological Survey; –, no sample taken; <, less than; >, greater than] 

Site 

short name

USGS

site 

No.

Date Time Rated discharge (m3/s) Instantaneous temperature (°C) Dissolved oxygen (mg/L) pH (standard units) Specific conductance (μS/cm at 25 °C) Suspended sediment (mg/L) Suspended sediment <0.0625 mm (percent) Ammonia (mg/L)

BW Ketchum 13135500 09-02-14 1210 2.0 9.1 9.6 7.1 161 12 83 <0.010North Fork 13135520 09-02-14 1400 0.7 12.1 8.9 7.9 244 1 58 <0.010Warm Sp 13137000 09-02-14 1530 1.2 18.4 8.1 8.3 239 13 74 <0.010Trail Ck 13137500 09-03-14 0940 0.2 10.1 9.4 8.2 408 6 19 <0.010East Fork 13138000 09-03-14 1300 0.3 11.1 9.3 8.3 278 1 58 <0.010BW Hailey 13139510 09-03-14 1445 4.3 15.5 9.5 8.7 256 6 84 <0.010BW Stanton 13140800 09-04-14 1000 0.7 11.1 8.6 7.6 290 3 87 <0.010

Site 

short name

USGS 

site 

No.

Date Time

Nitrate plus 

nitrite

(mg/L as N)

Total 

nitrogen

(mg/L)

Orthophosphate

(mg/L as P)

Total 

phosphorus 

(mg/L as P)

E. coli

(MPN/100 mL)

Date of 

collection

Chlorophyll-a

(mg/m2)

Biomass, ash 

free dry weight 

(mg/m2)

BW Ketchum 13135500 09-02-14 1210 <0.04 0.077 0.007 0.024 2 09-17-14 2 1North Fork 13135520 09-02-14 1400 <0.04 <0.05 <0.004 <0.01 1 09-03-14 14 6Warm Sp 13137000 09-02-14 1530 <0.04 0.139 0.031 0.055 13 09-04-14 24 8Trail Ck 13137500 09-03-14 0940 0.073 0.102 0.005 <0.01 43 09-03-14 86 18East Fork 13138000 09-03-14 1300 <0.04 0.155 <0.004 0.011 15 09-04-14 10 8BW Hailey 13139510 09-03-14 1445 <0.04 0.101 0.005 0.016 10 09-17-14 15 8BW Stanton 13140800 09-04-14 1000 <0.04 0.102 0.009 0.016 18 09-02-14 5 13
18 Aquatic Biological Communities and Associated Habitats, Big Wood River Watershed, South-Central Idaho, 2014

tac16-1096_fig05

5

10

15

20

25

Temperature, water, degrees Celsius

0

5

10

15

20

25

Temperature, water, degrees Celsius

0

5

10

15

20

25

Temperature, water, degrees Celsius

22 °C daily maximum stream criteria

13 °C daily 

maximum salmonid 

spawning criteria

22 °C daily maximum stream criteria

13 °C daily maximum

salmonid spawning 

criteria

22 °C daily maximum stream criteria

13 °C daily maximum

salmonid spawning 

criteria

Brown trout critical spawning and rearing period

Rainbow trout critical spawning and rearing period

0

5/14 5/21 5/28 6/4 6/11

2014

6/18 6/25 7/2 7/9 7/16 7/23 7/30 8/6 8/13 8/20 8/27 9/3 9/10 9/17

5/14 5/21 5/28 6/4 6/11

2014

6/18 6/25 7/2 7/9 7/16 7/23 7/30 8/6 8/13 8/20 8/27 9/3 9/10 9/17

5/14 5/21 5/28 6/4 6/11

2014

6/18 6/25 7/2 7/9 7/16 7/23 7/30 8/6 8/13 8/20 8/27 9/3 9/10 9/17

A. Big Wood River near Ketchum continuous temperature May 14–September 20, 2014 

B. Big Wood River at Hailey continuous temperature May 14–September 23, 2014 

C. Big Wood River at Stanton Crossing continuous temperature 

 May 14–September 23, 2014 

Brown trout critical spawning and rearing period

Rainbow trout critical spawning and rearing period

Brown trout critical spawning and rearing period

Rainbow trout critical spawning and rearing period

Figure 5. Continuous temperature for main-stem sites on the Big Wood 

River, south-central Idaho, May–September 2014. Full site names are 

shown in table 1.
Aquatic Biological Communities and Habitats 19

Table 4. Daily mean temperatures for selected sites in the Big Wood River watershed, south-central Idaho, June–September 2014.

[Site short name: Full site names are shown in table 1. Daily mean temperature and range (minimum to maximum), in degrees Celsius]

Site

short name

June July August September Mean summer 

temperatures Mean June–September Range Mean Range Mean Range Mean Range

BW Ketchum 8.5 3.5–14.7 12.8 6.4–19.2 11.9 6.6–17.5 9.8 3.8–14.7 10.7

North Fork 6.9 3.3–12.5 10.7 5.5–16.6 10.8 6.9–17.0 9.0 3.9–14.5 9.4

Warm Sp 12.6 6.8–19.3 17.9 11.5–23.5 16.8 11.4–23.0 14.8 9.0–19.7 15.5

Trail Ck 8.7 4.9–12.3 13.6 9.4–17.2 13.4 9.2–17.6 11.8 6.7–15.7 11.9

East Fork 9.1 4.3–14.5 14.4 7.8–19.9 14.1 9.2–19.8 11.2 5.4–15.3 12.2

BW Hailey 10.8 6.1–15.3 15.4 10.3–20.0 15.1 10.3–20.4 12.9 7.7–17.3 13.6

BW Stanton 13.2 7.2–19.9 17.3 11.3–24.2 17.1 12.2–24.1 14.6 9.6–20.9 15.6

Physical Habitat

Sampling reaches for the Big Wood River main-stem sites 

were between 300 and 400 m long and for the tributary sites 

between 150 and 200 m (table 5). Wetted channel widths were 

relatively uniform among sampling reaches (CV < 30 percent), 

whereas stream depth varied within and among streams, 

with CV of mean channel depth ranging from 19 percent 

at BW Ketchum to 60 percent at Trail Ck (table 5). Among 

Big Wood River sites, wetted volume (table 5) in September 

2014 was greatest at BW Hailey (1,395 m3) compared to 

BW Ketchum (627 m3) and BW Stanton (411 m3). The 

relatively lower wetted volume and high width to depth ratio 

of 69 (indicating a wider and shallower stream) at BW Stanton 

suggests that availability of fish habitat may be the most 

limited of the main-stem sites. Mean water column velocity 

during the September 2014 sampling for the Trail Ck and East 

Fork tributaries was less than 0.5 m/s, and sampling reach 

wetted volumes were correspondingly low (156 and 140 m3, 

respectively). Wetted volumes for sampling reaches on North 

Fork and Warm Sp sites (357 and 390 m3, respectively) were 

larger and similar in size to BW Stanton. 

Streambed substrate composition was similar among all 

sites and dominated by small to large cobble-size particles 

(table 5). There was little evidence of extensive sedimentation 

at most of the sampling sites, and overall fine-grained particles 

(<2 mm diameter) were less than 10 percent of the substrate 

composition, except for the two tributary sites at Warm Sp 

(24 percent) and Trail Ck (14 percent). 

Riparian vegetation is especially important to the health 

of stream ecosystems because it stabilizes stream banks and 

reduces soil erosion, provides food and habitat structure 

for stream organisms in the form of leaf litter and woody 

debris, and mitigates seasonal temperature extremes through 

shading of the stream channel (Carlisle and others, 2013). The 

average amount of riparian vegetative cover was greater than 

30 percent for all study sites in the Big Wood River watershed 

with the highest densities (>60 percent) occurring at the North 

Fork, Warm Sp, and East Fork, and BW Stanton sites.

The complexity and stability of fish and other 

communities in a stream environment are in large part a 

function of the numbers and types of habitat cover occurring 

within the stream channel (Cummins, 1979; Maddock, 1999; 

Rosenfeld, 2003). The amount of habitat cover is critical to the 

well-being of fish and other stream organisms and has been 

shown to be directly related to trout survival in cold-water 

streams (Penaluna and others, 2015). Abundance of habitat 

cover (percent over-hanging vegetation, undercut banks, 

woody debris, boulders, macrophytes, or artificial structures 

within a reach) for the tributary sites ranged from 33 percent 

at Trail Ck to 87 percent at the North Fork and East Fork sites 

(table 5). Habitat cover was abundant at BW Ketchum and 

BW Hailey (100 and 71 percent, respectively), but limited at 

BW Stanton (7 percent). 
20 Aquatic Biological Communities and Associated Habitats, Big Wood River Watershed, South-Central Idaho, 2014 Table 5. Habitat data collected at selected sites, Big Wood River watershed, south-central Idaho, September 2014.

[Site short name: Full names are shown in table 1. Values are the mean of 11 transect measurements within each site reach. See figure 1 for drainage basin.. Instream fish cover: Percentage of fish cover was determined by identifying fish cover at five equidistant points across the transect. Fish cover included overhanging vegetation, boulder, undercut banks, and (or) woody debris. Wetted volume: Mean wetted width × mean wetted depth × reach length, normalized to 150-m reach. Abbreviations: CV, coefficient of variation (standard deviation/mean); m3, cubic meter; ft, foot; m, meter; mm, millimeter; m/s, meter per second]

Site

short name

Sampling 

date

Reach length 

(m)

Mean 

channel 

wetted 

width 

(m)

CV mean 

width 

(percent)

Mean 

channel 

depth

(m)

CV mean 

depth 

(percent)

Width/

depth 

ratio

Wetted 

volume

(m3

)

Mean water 

column 

velocity 

(m/s)

CV water 

column 

velocity 

(percent)

Median 

particle 

size 

(mm)

Percent 

<2 mm 

(fines)

Dominant 

particle 

size 

category

Riparian 

vegetation 

cover 

(percent)

Instream 

fish cover 

(percent)

BW Ketchum 09-17-14 300 12.3 15 0.34 19 36 627 0.62 32 180 7 Small 

cobble

45 100

North Fork 09-03-14 150 8.5 19 0.28 33 30 357 0.55 40 250 0 Large 

cobble

86 87

Warm Sp 09-04-14 200 10.4 10 0.25 29 42 390 0.56 41 140 24 Small 

cobble

78 45

Trail Ck 09-03-14 150 4.0 26 0.26 60 15 156 0.36 67 115 14 Small 

cobble

46 33

East Fork 09-04-14 150 5.2 28 0.18 48 29 140 0.42 69 160 0 Small 

cobble

66 87

BW Hailey 09-17-14 400 22.7 20 0.41 49 55 1,395 0.55 44 100 6 Small 

cobble

37 71

BW Stanton 09-02-14 300 13.7 21 0.20 46 69 411 0.40 50 90 5 Small 

cobble

66 7
Aquatic Biological Communities and Habitats 21

Biological Communities

Macroinvertebrates

The number of aquatic insect taxa (EPT) is commonly 

used as an indicator of water-quality and biological condition, 

with decreasing EPT values indicating a loss of species 

that are generally sensitive to environmental degradation. 

EPT richness was highest at sites in the upper drainage at 

the North Fork tributary and BW Ketchum (33 and 24 EPT 

taxa respectively), and generally decreased downstream 

with the lowest number of EPT taxa with 7 observed at 

BW Stanton (table 6). The relative contributions of individual 

taxonomic groups to the overall EPT richness for each site 

are summarized in figure 6. Although stream-health standards 

based on EPT values are not well-defined and vary among 

environmental settings, an assessment of macroinvertebrate 

communities in Idaho streams by Maret and others (2001) 

reported an average EPT value of 18 for systems that were 

relatively undisturbed by human-caused perturbations. During 

the Maret study (1996–98), BW Stanton had an EPT value of 

16 and at the time was considered relatively unimpaired. 

Designation of a cold-water stream is partly based 

on the presence of organisms that have relatively narrow 

thermal requirements for growth and reproduction and 

where cold‐water environments are an inherent part of their 

life‐history strategy (U.S. Environmental Protection Agency, 

2012). Low abundance or absence of macroinvertebrate 

species that are limited in their distributions to cold-water 

streams are indications that streams may be warming. 

Development of temperature optima for macroinvertebrates in 

Idaho streams will facilitate temperature-based designations 

of Idaho streams and rivers and help identify impaired 

systems (Richards and others, 2013). Macroinvertebrate 

taxa that occur in the 95th percentile of Idaho streams with 

water temperatures below 20 °C were used to identify 

Table 6. Macroinvertebrate metrics calculated from samples collected at selected sites in the Big Wood River watershed, 

south-central Idaho, September 2014.

[Short site name: Full site names are in table 1. Abundance weighted tolerance: Tolerance values from Carlisle and others (2007). FSBI: Fine 

Sediment Biotic Index; score is the sum of corresponding invertebrate grouping values presented in Reylea and others (2012). Cold-water taxa: 

Cold water species derived from Richards and others (2013). Simpson’s D: Diversity index, scored 0–1, with values closer to 1 with higher diversity. 

Abbreviations: EPT, ephemeroptera, plecoptera, trichoptera; organisms/m2, organisms per square meter; mg/L, milligram per liter; PPBV, plains, 

plateaus, and broad valleys; RD, richness and density ratio; SMI, stream macroinvertebrate index (Tetra Tech, 2011); oC, degree Celsius]

Site short 

name

Sample

collection 

date

 Taxa 

richness

EPT 

richness

Density 

(organisms/m2

)

Natural log richness/ 

natural log density 

(RD)

Cold-water taxa

Number Percent

BW Ketchum 09-17-14 40 24 1,869 0.49 19 40

North Fork 09-03-14 51 33 1,379 0.55 26 50

Warm Sp 09-04-14 36 12 1,816 0.47 6 2

Trail Ck 09-03-14 40 12 1,687 0.50 10 25

East Fork 09-03-14 45 18 4,508 0.46 11 24

BW Hailey 09-17-14 34 8 3,386 0.43 4 12

BW Stanton 09-02-14 23 7 7,797 0.35 0 0

Site short 

name

Sample

collection 

date

Abundance weighted tolerance

Three 

dominant taxa 

(percent)

Simpson’s 

D

PPBV 

SMI2

Mountains

SMI2 FSBI

Nutrients

Water 

temperature

(oC)

Suspended 

sediment

(mg/L)

BW Ketchum 09-17-14 3.8 3.0 3.5 46 0.90 85 63 190

North Fork 09-03-14 3.3 2.5 3.4 44 0.91 79 77 210

Warm Sp 09-04-14 5.7 4.2 5.5 49 0.90 78 37 70

Trail Ck 09-03-14 6.1 2.9 4.7 56 0.83 73 37 80

East Fork 09-03-14 6.2 2.8 4.2 43 0.91 70 47 90

BW Hailey 09-17-14 4.2 2.8 3.9 51 0.85 71 30 75

BW Stanton 09-02-14 7.7 6.6 8.5 92 0.22 71 11 35
22 Aquatic Biological Communities and Associated Habitats, Big Wood River Watershed, South-Central Idaho, 2014

tac16-1096_fig06

0

5

10

15

20

25

30

35

BW Ketchum North Fork Warm Sp Trail Ck East Fork BW Hailey BW Stanton

EPT taxa richness

Average of reference (Maret and others, 2001)

Upstream Downstream

EXPLANATION

Ephemeroptera richness

Plecoptera richness

Trichoptera richness

Figure 6. Ephemeroptera, plecoptera, and trichoptera (EPT) taxa richness from samples collected at 

selected sites in the Big Wood River watershed, south-central Idaho, September 2014. Full site names are 

shown in table 1.

cold-water taxa collected as part of this investigation. 

Thirty-three cold‐water macroinvertebrate taxa were found 

among the tributary and main-stem sites of the Big Wood 

River, 13 of which consisted of mayfly, stonefly, and 

caddisfly taxa (appendix A). The highest numbers of coldwater macroinvertebrate taxa (19 and 26, respectively) 

were collected at the BW Ketchum and North Fork sites. 

Macroinvertebrate community samples collected at BW 

Hailey and at the Warm Sp, Trail Ck, and East Fork sites each 

contained less than 12 cold‐water macroinvertebrate taxa. No 

macroinvertebrates designated as cold-water species were 

collected at BW Stanton. 

Although occurrence patterns of cold-water 

macroinvertebrate taxa may be an indication of stream thermal 

properties, it is recognized that stream organisms integrate 

stressor effects from multiple sources that typically act in 

concert to affect stream communities. For streams in the 

Big Wood River watershed, effects from groundwater and 

surface water abstraction, nutrient enrichment, elevated stream 

temperatures, and increased sediment loading collectively, 

can potentially influence local biological condition to 

varying degrees depending on adjacent land-use and water 

management practices in the watershed. To examine different 

stressor effects, macroinvertebrate community tolerances to 

nutrient enrichment, elevated water temperature, and high 

concentrations of suspended sediment were used to determine 

whether sites in the Big Wood River watershed may be subject 

to one or more physical or chemical perturbations affecting 

water-quality and overall stream health. Despite the fact that 

nutrient concentrations were not markedly elevated in stream 

water (table 3), tolerance values for macroinvertebrates 

sensitive to nutrient enrichment indicated that water-quality at 

the East Fork and Trail Ck tributaries, and at BW Stanton, may 

be subject to some levels of nutrient enrichment or other forms 

of organic pollution (fig. 7). Macroinvertebrate community 

responses to enrichment represent a time-integrated effect 

likely occurring over an exposure period of weeks or months, 

and may not be consistent with results of water-quality 

determinations based on a single sampling event.

Relative abundances of temperature tolerant 

macroinvertebrate taxa were low at most sites, except for 

Warm Sp and BW Stanton (table 6, fig. 7). Higher temperature 

tolerance values for macroinvertebrate communities at these 

sites corresponded to mean summer water temperatures 

(May to September), which were the highest (15.5 and 

15.6 °C, respectively) among the study sites (table 4). 

Additionally, Warm Sp and BW Stanton both experienced 

temperature exceedances of 22 °C during the summer months 

(table 4).

 Elevated levels of suspended sediment are a naturally 

occurring event in most stream systems and, accordingly, 

stream macroinvertebrates as a group are relatively tolerant 

of periodic increases in SSC (Ward, 1992). Although SSC 

were low at all sites during the September 2014 water-quality 
Aquatic Biological Communities and Habitats 23

0

1

2

3

4

5

6

7

8

9

10

BW Ketchum North Fork Warm Sp Trail Ck East Fork BW Hailey BW Stanton

Tolerance value

High

Moderate

Low

EXPLANATION

Temperature

Suspended sediment

Nutrients

tac16-1096_fig07

Figure 7. Temperature, suspended sediment, and nutrient tolerance values for invertebrates at selected 

sites, Big Wood River, south-central Idaho.

assessment (table 3), suspended-sediment tolerance values 

were high at BW Stanton (8.5) compared to other sites in the 

drainage (values ranging from 3.4 to 5.5) (fig. 7, table 6). 

Given the lack of long-term water quality monitoring data for 

these locations, responses of macroinvertebrate communities 

to these multiple stressors can only be inferred, and may be 

part of a more generalized response to a broader array of 

environmental conditions. Nevertheless, elevated tolerance 

values for macroinvertebrate communities at BW Stanton 

suggest the likelihood of some impairment caused by stream 

conditions. Species diversity index values (Simpson’s D) 

were high (>0.80) among tributary and main-stem sites of 

the Big Wood River except BW Stanton (0.22) (table 6). 

Diversity index values increase as the abundance of individual 

taxa of the entire community assemblage becomes more 

equitable (Magurran, 1988). The low diversity index value 

(0.22) at BW Stanton compared to the other study sites is 

a result of relatively low species richness (22) and high 

macroinvertebrate density (7,797 organisms/m2). These 

relations are exemplified in the comparisons of species RD 

shown in table 6, which provides an indication of relative 

evenness between the numbers and kinds of taxa at a 

sampling location. Richness-density ratios were highest for 

macroinvertebrate communities at the North Fork tributary 

(RD = 0.55) and lowest for communities at BW Stanton (RD = 

0.35). The low RD and diversity values at BW Stanton were 

largely a result of the numerical dominance of the generally 

tolerant caddisfly Hydropsyche spp., which comprised 

88 percent of the total macroinvertebrate density at that 

location (appendix A). The decrease and periodic loss of 

channel connectivity (Bartolino, 2014) and presumably 

upstream recruitment pools caused by flow alterations may 

partly be responsible for the relatively low number of taxa at 

the BW Stanton site.

The Idaho State SMI2 values calculated for the Big 

Wood River and tributary sites all were within the reference 

range for the PPBV ecoregion (50 and 94, table 6). The 

Mountains ecoregion SMI2 values were outside the reference 

range (33 and 94) at BW Hailey (Mountains SMI2 = 30) and 

BW Stanton (Mountains SMI2 = 11; Jason Pappani, Idaho 

Department of Environmental Quality, written commun., 

October 2015; table 6). The combination of metrics that are 

used for calculating the SMI2 collectively do not appear 

to be as sensitive as the individual abundance weighted 

tolerance values and diversity metrics in identifying potential 

effects to stream invertebrates for sites in the Big Wood 

River watershed. However, a multi-metric index of this type 

is inherently more robust than single metric indices and, as 

such, is often more representative of overall stream health. 

Moreover, it is important to note that the scoring criteria of 

the SMI2 for PPBV and Mountains IDEQ ecoregions has 

not been finalized as of 2016 and that the index may undergo 

additional refinement. 
24 Aquatic Biological Communities and Associated Habitats, Big Wood River Watershed, South-Central Idaho, 2014

The Fine Sediment Biotic Index (FSBI) is designed 

as a stressor-specific biomonitoring index to assess fine 

sediment impacts on macroinvertebrate communities, with 

higher index values indicating greater abundance of more 

sediment-sensitive taxa and, by inference, better water-quality 

conditions. The highest FSBI values were at the BW Ketchum 

and the North Fork sites, and the lowest FSBI value occurred 

at BW Stanton (table 6), with the macroinvertebrate 

community at BW Stanton consisting of comparatively 

higher densities of fine-sediment tolerant taxa. The FSBI 

values for the Big Wood River main-stem and tributary sites 

were consistent with suspended-sediment tolerance values in 

terms of characterizing general patterns of macroinvertebrate 

sediment sensitivity. Ultimately, the SMI2 and FSBI will be 

used to evaluate beneficial use designations for streams in the 

Big Wood River watershed (Tetra Tech, 2011).

Fish

The Big Wood River and tributaries provide habitat for 

native Catostomidae (bridgelip sucker), Cyprinidae (redside 

shiner, longnose dace and speckled dace), Salmonidae 

(rainbow trout and mountain whitefish), and Cottidae (Wood 

River sculpin). Introduced species include brook trout and 

brown trout (appendix B). Although introduced brook trout 

and brown trout often are considered desirable in supporting 

local recreational fisheries, when abundant they have the 

potential to alter habitat suitability for native species and 

diminish food resource availability. Of concern to the health 

of the native fishery is that as streams and rivers become 

altered as a result of land- and water-use practices, potential 

loss of habitat and biological complexity favors proliferation 

of more tolerant non-native and invasive species (Peipoch and 

others, 2015). Fish surveys in September 2014 determined that 

occurrence of non-native species was limited to sites on the 

main stem of the Big Wood River (appendix B). Non-native 

brook trout and brown trout were observed at BW Hailey, but 

both occurred in relatively low numbers (0.6 and 4.7 percent 

of fish relative abundance, respectively). Brown trout were 

the only non-native fish collected at BW Stanton, but were 

present in somewhat higher numbers (14.6 percent of the 

total fish abundance). Typical for many relatively undisturbed 

Western streams (Whittier and others, 2007), the total number 

of fish taxa was generally low overall with three or fewer 

species collected at BW Ketchum, North Fork, Trail Ck, and 

East Fork. The highest numbers of fish species were collected 

at Warm Sp (five), BW Hailey (four), and BW Stanton (six). 

Native rainbow and brown trout and Wood River sculpin were 

the dominant fish species in the drainage and were found at all 

tributary and main-stem sites (figs. 8 and 9). 

Fish size (length and weight) has been shown to be a 

good indicator of fish health, where low weight-to-length 

ratios are indicative of potential impairment of health and 

overall well-being (Anderson and Gutreuter, 1983). Indices 

of fish condition that rely on size parameters, such as the 

condition coefficient (K), are commonly used as diagnostic 

measures of fish condition (Williams, 2000). The IDFG uses 

several different measures for evaluating fish condition that 

include examination of relative weight and age-related growth 

(Idaho Department of Fish and Game, 2013). Fish population 

data from the September 2014 survey alone are not sufficient 

to quantitatively assess fish health for the Big Wood River 

and tributaries; however, fish collected as part of this study 

appeared in good health at all sampling locations, with few if 

any instances of external anomalies (deformities, eroded fins, 

lesions, and tumors) that might be indicative of environmental 

stress. These observations are consistent with earlier studies 

that considered the Big Wood River to be of high biotic 

integrity (Maret, 1997; Mebane and others, 2003). 

Although preliminary SFI2 values for the Big Wood 

River sites (appendix B) were within the range of reference 

values for the PPBV (61–100) and Mountains (30–100), 

between-site differences in index values were not great enough 

to indicate any potential effect to the fishery. The State of 

Idaho is finalizing scoring criteria for the SFI2 to help refine 

designated site use attainability. 

The strong positive relation between fish production 

and fluvial habitat availability (as estimated by WV) attests 

to the importance of preserving as best as possible natural 

flow regimes for streams and rivers in the Big Wood River 

watershed. Among all study sites, fish biomass (total 

weight of all fish normalized to a reach length of 150 m) 

was strongly correlated with wetted volume (rho = 0.86, 

P = 0.006), with the highest fish biomass and wetted 

volume occurring at BW Hailey (table 5; appendix B). In 

comparison, owing to reduced discharge, wetted volume at 

BW Stanton was 29 percent of that upstream at BW Hailey, 

and, correspondingly, fish biomass was 25 percent of that at 

BW Hailey. 
Aquatic Biological Communities and Habitats 25

tac16-1096_fig08

A. Trout relative abundance

B. Wood River Sculpin relative abundance

0

50

100

150

200

250

300

350

400

450

BW

Ketchum

North Fork Warm Sp Trail Ck East Fork BW Hailey BW

Stanton

BW

Ketchum

North Fork Warm Sp Trail Ck East Fork BW Hailey BW

Stanton

0

50

100

150

200

250

300

350

400

Number of fish captured per reach

EXPLANATION

Rainbow trout

<100 mm rainbow trout

Hatchery rainbow trout

Brown trout

<100 mm brown trout

Figure 8. Trout and Wood River sculpin 

(Cottus leiopomus) relative abundance 

from samples collected at sites in the Big 

Wood River watershed, south-central Idaho, 

September 2014. Full site names are shown 

in table 1. 

Figure 9. Wood River sculpin (Cotus leiopomus). 

Photograph by Don Zaroban, Orma J. Smith 

Museum of Natural Science, Caldwell, Idaho.
26 Aquatic Biological Communities and Associated Habitats, Big Wood River Watershed, South-Central Idaho, 2014

Summary

Land-use development and population growth will 

likely play an increasingly important role in affecting the 

quality of freshwater resources in the Big Wood River 

watershed. Increased demands on surface water and 

groundwater resources pose a serious challenge to long-term 

water management and resource conservation strategies in 

the watershed. Fundamental to meeting this challenge is 

establishing scientifically sound water quality and biological 

monitoring programs to support informed management 

decisions. Results presented here are a synopsis of existing 

key physical, chemical, and biological properties of the 

Big Wood River and its major tributaries. This information 

provides a basis with which to evaluate and monitor the 

long‐term health of surface-water resources in the Big Wood 

River watershed. Natural flows are characterized by temporal 

and spatial variability in the magnitude, frequency, and 

duration of discharge. The occurrence and distribution of 

fish and macroinvertebrates in the Big Wood River and its 

tributaries are determined in part by these flow parameters. 

Comparison of daily discharge patterns for water years 

2012–15 for sites on the Big Wood River showed that flow 

magnitude increased downstream from BW Ketchum to 

BW Hailey, but decreased from BW Hailey to BW Stanton by 

more than half during this period. 

Annual and seasonal flow variability for the Big Wood 

River increased in a downstream direction with the highest 

variability observed at BW Stanton. Reduced and more 

variable summer flows (46 percent) occurring at BW Stanton 

likely result from flow diversions downstream of the City of 

Bellevue to support increased agriculture demands during the 

summer months. With the exception of BW Stanton, annual 

variability of daily mean flows among tributary and main-stem 

sites was generally low (ranging between 17 to 33 percent), 

and probably reflect naturally occurring seasonal changes 

in streamflow.

Examination of annual base-flow index values for sites on 

the Big Wood River and tributaries showed that groundwater 

contributes greater than 85 percent of the total flow during 

late summer, when streamflow is typically at its lowest and 

when conditions are often most stressful to aquatic organisms. 

Groundwater discharge is particularly important in moderating 

stream temperature extremes, which is critical to maintaining 

a cold-water fishery in the Big Wood River. During August 

2014, decreases in groundwater contributions to total 

discharge were evident only at Trail Ck (36 percent of total 

flow) and BW Stanton (13 percent of total flow). Increased 

surface-water contributions to total discharge at these sites 

may have resulted from late summer rainfall in the Trail Ck 

drainage and from irrigation return flows for BW Stanton. 

Among the Big Wood River and tributary sites, the 

highest mean daily water temperatures for June–September 

2014 occurred at Warm Sp (15.5 °C) and BW Stanton 

(15.6 °C). The presence of greater numbers of high 

temperature tolerant invertebrate taxa at these locations is 

consistent with the temperature findings. Additionally, the State 

of Idaho maximum temperature criterion for the protection of 

cold-water aquatic life of 22 °C was exceeded at both these 

locations during the period from June to August, but at none 

of the other study sites. The critical temperature criterion for 

salmonid spawning of 13 °C was exceeded in early July 2014 at 

both BW Ketchum and BW Hailey near the end of the rainbow 

trout critical period. Spawning temperature exceedances were 

most frequent at BW Stanton where exceedances for both 

rainbow and brown trout were observed from May through July 

during most of the critical periods for both species. 

Water-quality assessments in September 2014 determined 

no direct evidence of water-quality impairment resulting from 

elevated concentrations of suspended sediment or nutrients. 

Suspended sediment and nutrient concentrations were generally 

low in streams throughout the watershed and within the 

accepted TMDL water-quality guidelines. Absence of organic 

enrichment for the Big Wood River and tributaries was also 

evident by the presence of low concentrations of algal biomass. 

Similarly, fecal indicator analysis concluded that concentrations 

of E. coli were well within TMDL target levels at all sites. 

Despite the fact that nutrient concentrations were not elevated 

in stream water, tolerance values for macroinvertebrates 

sensitive to nutrient enrichment indicated that water quality 

at the East Fork and Trail Ck sites and at BW Stanton may be 

periodically subject to some nutrient enrichment or other forms 

of organic pollution. Macroinvertebrate responses to enrichment 

are based on exposure periods of weeks to months and may not 

be consistent with results from water-quality assessments based 

on a single sampling event. Observed biological responses 

may be indicative of possible enrichment occurrences prior to 

the September 2014 water-quality sampling. Relatively high 

suspended-sediment tolerance values also were determined 

for macroinvertebrate communities at BW Stanton in contrast 

to other sites in the drainage. Given the lack of long-term 

water-quality monitoring data for sites on the Big Wood River 

and tributaries, responses of macroinvertebrate communities 

to nutrient, suspended sediment, and temperature stressors 

can only be inferred, and may be part of a more generalized 

response to a broader array of environmental conditions. 

Nevertheless, high tolerance values for macroinvertebrate 

communities at BW Stanton suggest some impairment of 

biological condition and decline in stream health at that site. 

Habitat availability and quality did not seem to be limiting 

for fish or other organisms at sites on the Big Wood River and 

tributaries with the exception of BW Stanton. Lower wetted 

volume and high width-to-depth ratio at BW Stanton compared 

to the other main-stem sites are indicative of relatively shallowwater habitat conditions that may result in low fish abundances. 

Indeed, fish biomass at BW Stanton was only 25 percent of that 

upstream at BW Hailey. Additionally, the amount of instream 

structure and other features that provide needed refuge for fish 

and other organisms was severely lacking at the BW Stanton 

site, and comprised only 7 percent of the total possible cover 

availability compared to 100 and 71 percent for BW Ketchum 

and BW Hailey, respectively. 
References Cited 27

For streams within the Big Wood River watershed, 

potential effects from groundwater and surface water 

abstraction, nutrient enrichment, elevated stream temperatures 

and increased sediment loading collectively influence local 

biological conditions. Biological communities integrate 

disturbance effects from multiple sources and species-specific 

responses provide a means with which to assess the relative 

contribution of individual stressors to overall health of the 

system. Numbers of stressor sensitive macroinvertebrate 

EPT taxa were highest in the upper drainage on the North 

Fork and BW Ketchum (31 and 24 EPT taxa, respectively), 

and generally decreased downstream with the lowest number 

of EPT taxa (7 EPT taxa) observed at BW Stanton. The 

EPT richness at BW Stanton in September 2014 was less 

than one-half that in a 1998 study of biological integrity 

for Idaho streams. High macroinvertebrate diversity index 

values (>0.80 for Simpson’s D) are generally indicative of 

a healthy stream environment. Macroinvertebrate diversity 

values for tributary and main-stem sites ranged from 0.83 

to 0.91 except for BW Stanton with a diversity value of 

0.22. The low diversity index value for macroinvertebrate 

communities at BW Stanton was a result of relatively low taxa 

richness and high abundances of a few taxa, in particular the 

caddisfly (Hydropsyche spp.), which was the most numerically 

dominant taxa. The reduction and periodic loss of channel 

connectivity and presumably upstream recruitment pools as 

a result of flow alterations may in part be responsible for the 

relatively low number of macroinvertebrate taxa observed at 

the BW Stanton site. 

Native fish communities are one of the most important 

assets to the Big Wood River and its tributaries. Alteration of 

natural flow regimes in the Big Wood River watershed can 

potentially result in a loss of habitat and biological complexity 

that favors proliferation of non-native and invasive species, 

and ultimately lead to a reduction in the number of native 

species and overall fish health. Fish surveys conducted in 

September 2014 did not find any significant decrease in 

occurrence of native fish communities in the Big Wood 

River or its tributaries. Native rainbow trout and Wood River 

sculpin were the dominant fish species in the drainage and 

were found at all tributary and main-stem sites. Additionally, 

fish communities at all sites appeared to be in relatively good 

health with few instances of external anomalies or diminished 

size that might be indicative of environmental stress. 

The September 2014 assessments of macroinvertebrate 

and fish communities represent a single sampling period and, 

as such, do not provide information on intrinsic variability 

(seasonal and annual changes) in community assemblages; 

therefore, there was not enough information to effectively 

calculate and compare biological metrics using the Idaho State 

macroinvertebrate (SMI2) and fish indices (SFI2). However, 

the biological indices are valuable tools that can be used to 

assess the ecological condition and health of stream resources 

in the Big Wood River watershed; the information in this 

report will contribute to that effort. 

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Appendix A 33

Table A1. Macroinvertebrate density collected from selected sites in the Big Wood River and tributaries, south-central Idaho, September 2014.[Full site names are shown in table 1. Full taxanomic name and taxon reference are available in U.S. Geological Survey (2016b); taxa list in this appendix was modified to remove ambiguous taxa prior to data analysis. In addition, Naididae species have been consolidated into family and Arachnida have been consolidated into the subclass Acari prior to analysis. Taxa in bold are those that occur in the 95th percentile of Idaho streams with water temperatures below 20 °C (Richards and others, 2013)]

Class Order BioData taxon name

Density at sites, in organisms per square meter

BW

Ketchum North Fork Warm Sp Trail Ck East Fork BW Hailey BW Stanton

Nemata 0 3 0 3 0 13 0

Maxillopoda Ostracoda 0 118 0 3 129 0 0Turbellaria Turbellaria Polycelis 0 0 0 17 9 0 0Gastropoda Basommatophora Physa 0 0 0 3 0 0 0Gastropoda Basommatophora Lymnaeidae 0 0 0 3 0 0 0Oligochaeta Enchytraida Enchytraeidae 7 0 4 17 276 13 0Oligochaeta Opithopora Lumbricina 0 0 4 0 0 0 0Oligochaeta Tubificida Naididae 0 0 25 17 61 26 0Arachnida Trombidiformes Acari 8 41 46 27 103 59 31Insecta Ephemeroptera Acentrella turbida 0 3 0 0 0 0 0Insecta Ephemeroptera Ameletus 0 3 0 0 0 0 0Insecta Ephemeroptera Baetis bicaudatus 0 11 0 0 0 0 0Insecta Ephemeroptera Baetis tricaudatus 89 283 285 116 276 270 124Insecta Ephemeroptera Caudatella hystrix 395 0 0 0 0 0 0Insecta Ephemeroptera Caudatella 0 16 0 0 0 0 0Insecta Ephemeroptera Cinygmula 7 19 0 0 69 0 0Insecta Ephemeroptera Diphetor hageni 0 0 0 0 17 0 0Insecta Ephemeroptera Drunella coloradensis/flavilinea 0 22 0 0 0 0 0Insecta Ephemeroptera Drunella doddsii 122 41 0 0 0 0 0Insecta Ephemeroptera Drunella grandis 4 8 0 40 9 26 0Insecta Ephemeroptera Ecdyonurus 0 0 0 0 0 0 15Insecta Ephemeroptera Epeorus deceptivus 15 93 0 0 0 0 0Insecta Ephemeroptera Epeorus grandis 4 0 0 0 0 0 0Insecta Ephemeroptera Epeorus 0 0 0 3 0 0 0Insecta Ephemeroptera Ephemerellidae 74 21 0 0 226 0 0Insecta Ephemeroptera Ephemerella tibialis 0 25 4 7 0 0 0Insecta Ephemeroptera Leptophlebiidae 0 16 0 0 0 0 0Insecta Ephemeroptera Rhithrogena 133 199 0 10 0 0 0Insecta Ephemeroptera Tricorythodes 0 0 0 0 0 0 77Insecta Plecoptera Capniidae 7 3 0 0 0 0 0Insecta Plecoptera Hesperoperla pacifica 41 3 0 0 9 0 46

Appendix A. Macroinvertebrate Density Collected from Selected Sites in the Big Wood River and Tributaries, South-Central Idaho, September 2014.
34 Aquatic Biological Communities and Associated Habitats, Big Wood River Watershed, South-Central Idaho, 2014 Table A1. Macroinvertebrate density collected from selected sites in the Big Wood River and tributaries, south-central Idaho, September 2014.—Continued Class Order BioData taxon name Density at sites, in organisms per square meter BW Ketchum North Fork Warm Sp Trail Ck East Fork BW Hailey BW Stanton Insecta Plecoptera Perlodidae 15 5 0 13 0 0 0 Insecta Plecoptera Perlidae 0 0 0 0 26 0 0 Insecta Plecoptera Leuctridae 0 11 0 0 0 0 0 Insecta Plecoptera Skwala 0 0 7 0 0 7 31 Insecta Plecoptera Sweltsa 11 115 0 3 17 0 0 Insecta Plecoptera Zapada cinctipes 15 0 0 0 17 0 0 Insecta Plecoptera Zapada oregonensis group 0 16 0 0 0 0 0 Insecta Trichoptera Apatania 0 3 0 0 0 0 0 Insecta Trichoptera Arctopsyche grandis 307 22 11 0 17 269 0 Insecta Trichoptera Brachycentrus americanus 11 5 29 0 34 72 0 Insecta Trichoptera Ceraclea 0 0 0 0 0 0 15 Insecta Trichoptera Ceratopsyche/Hydropsyche 7 63 352 27 34 257 6,890 Insecta Trichoptera Glossosoma 111 22 14 0 17 0 0 Insecta Trichoptera Hydroptilidae 0 3 0 0 9 0 0 Insecta Trichoptera Hydroptila 0 0 85 99 0 0 0 Insecta Trichoptera Lepidostoma 18 0 93 0 172 1,172 0 Insecta Trichoptera Micrasema 44 3 0 43 26 0 0 Insecta Trichoptera Ochrotrichia 0 0 256 0 0 0 0 Insecta Trichoptera Oligophlebodes 11 11 0 0 0 0 0 Insecta Trichoptera Protoptila 0 0 25 0 0 0 0 Insecta Trichoptera Rhyacophila 0 0 0 7 0 13 0 Insecta Trichoptera Rhyacophila betteni group 0 17 0 0 0 0 0 Insecta Trichoptera Rhyacophila brunnea/vemna groups 59 19 0 3 60 0 0 Insecta Trichoptera Rhyacophila coloradensis group 7 0 14 0 9 0 0 Insecta Trichoptera Rhyacophila hyalinata group 0 3 0 0 0 0 0 Insecta Trichoptera Rhyacophila narvae 0 3 0 0 0 0 0 Insecta Trichoptera Rhyacophila sibirica group 4 19 0 0 0 0 0 Insecta Lepidoptera Petrophila 0 0 0 0 0 0 31 Insecta Coleoptera Cleptelmis addenda 11 0 4 50 26 7 0 Insecta Coleoptera Heterlimnius corpulentus 55 22 0 47 17 0 0 Insecta Coleoptera Narpus 11 0 0 3 0 0 0 Insecta Coleoptera Optioservus 0 0 0 70 0 0 0 Insecta Coleoptera Optioservus quadrimaculatus 41 0 146 0 595 138 46 Insecta Coleoptera Oreodytes 0 0 4 0 0 0 0 Insecta Coleoptera Zaitzevia 0 0 0 0 9 0 0 Insecta Coleoptera Zaitzevia parvula 0 0 29 0 0 66 0 Insecta Diptera Antocha 7 3 75 0 0 20 170
Appendix A 35

Table A1. Macroinvertebrate density collected from selected sites in the Big Wood River and tributaries, south-central Idaho, September 2014.—Continued

Class Order BioData taxon name

Density at sites, in organisms per square meter

BW

Ketchum North Fork Warm Sp Trail Ck East Fork BW Hailey BW Stanton

Insecta Diptera Atherix 0 0 7 0 0 7 0

Insecta Diptera Bezzia/Palpomyia 4 0 0 3 0 0 0

Insecta Diptera Bibiocephala 0 3 0 0 0 0 0

Insecta Diptera Brillia 0 19 0 33 0 0 0

Insecta Diptera Cardiocladius 0 0 4 0 0 0 15

Insecta Diptera Chelifera/Metachela 0 0 0 7 7 0 0

Insecta Diptera Cricotopus 0 3 0 0 0 0 0

Insecta Diptera Cricotopus nostocicola 0 0 0 33 0 0 15

Insecta Diptera Cricotopus trifascia group 0 0 21 0 0 7 0

Insecta Diptera Cricotopus/Orthocladius 0 3 21 13 190 20 93

Insecta Diptera Eukiefferiella 0 3 0 0 0 0 0

Insecta Diptera Eukiefferiella brehmi group 7 0 75 0 112 20 15

Insecta Diptera Eukiefferiella claripennis group 4 0 4 33 43 99 0

Insecta Diptera Eukiefferiella devonica group 0 3 14 17 17 47 15

Insecta Diptera Eukiefferiella gracei group 15 3 0 13 69 79 0

Insecta Diptera Hexatoma 11 0 0 0 0 20 15

Insecta Diptera Micropsectra 0 3 0 20 431 20 0

Insecta Diptera Nanocladius 0 0 0 0 0 0 15

Insecta Diptera Neoplasta 0 0 0 0 0 20 0

Insecta Diptera Orthocladius 0 0 17 3 0 59 15

Insecta Diptera Orthocladius (Euorocladius) 0 0 0 7 0 0 15

Insecta Diptera Orthocladius rivicola group 0 0 18 0 0 39 0Insecta Diptera Orthocladius rivulorum 0 0 0 0 0 7 0

Insecta Diptera Pagastia 7 5 0 199 129 26 0

Insecta Diptera Parametriocnemus 0 0 36 0 9 53 0

Insecta Diptera Pentaneurini 0 0 0 0 17 0 0

Insecta Diptera Pericoma/Telmatoscopus 0 5 0 0 9 0 0

Insecta Diptera Polypedilum 11 0 11 3 129 0 31

Insecta Diptera Procladius 0 0 4 0 0 0 0

Insecta Diptera Rheocricotopus 0 8 0 0 34 0 0

Insecta Diptera Rheotanytarsus 0 0 0 0 0 0 15

Insecta Diptera Simulium 152 14 57 622 845 191 62

Insecta Diptera Stempellinella 0 0 0 0 34 0 0

Insecta Diptera Thienemanniella 0 0 4 0 9 0 0

Insecta Diptera Thienemannimyia group 0 0 0 0 0 7 0

Insecta Diptera Tipula 0 0 0 7 0 0 0

Insecta Diptera Tvetenia bavarica group 7 14 11 43 121 237 0

Insecta Diptera Wiedemannia 0 0 0 0 34 0 0
36 Aquatic Biological Communities and Associated Habitats, Big Wood River Watershed, South-Central Idaho, 2014 Appendix B. Relative Abundance of Fish Species Sampled from Sites in the Big Wood River and Tributaries, South-Central Idaho, September 2014. Table B1. Relative abundance of fish species sampled from sites in the Big Wood River and tributaries, south-central Idaho, September 2014. [Full site names are shown in table 1; ( ), for more than one salmonidae and cottidae total length range in millimeters (mm). Additional sampling and individual fish information can be found on the BioData Web site at https://aquatic.biodata.usgs.gov. Abbreviations: CPU, number of fish caught/electrofishing seconds; g, grams; Mountains, combined mountain Idaho Department of Environmental Quality ecoregion; NR, not recorded; PPBV, Plains, Plateaus, and Broad Valley Idaho Department of Environmental Quality ecoregion; RFI, 2002 Idaho river fish index; SFI2, 2011 Idaho stream fish index; - , no fish found in sample] Metric Site name BW Ketchum North Fork Warm Sp Trail Ck East Fork BW Hailey BW Stanton USGS site ID 13135500 13135520 13137000 13137500 13138000 13139510 13140800 Sampling date 09-18-14 09-03-14 09-04-14 09-03-14 09-04-14 09-18-14 09-02-14 Reach length (meters) 300 150 200 150 150 400 300 Method Backpack Backpack Backpack Backpack Backpack Towed barge Backpack Electrofishing time (seconds) 4,833 1,708 2,279 1,317 2,157 2,780 3,605 Number of netters 4 4 4 4 4 6 4 Description Catostomidae (suckers) Bridgelip Sucker Catostomus columbianus

–

– 1 –

– 8 6

Cyprinidae 

(minnows)

Redside Shiner 

Richardsonius balteatus

–

–

–

–

–

– 19

Longnose Dace 

Rhinichthys cataractae

–

– 4 –

–

– 102

Speckled Dace 

Rhinichthys osculus

–

–

–

–

–

– 15

Salmonidae 

(trout)

Rainbow Trout 

Oncorhynchus mykiss

28 (1–410) 12 (40–376) 71 (45–320) 69 (35–320) 87 (30–320) 380 (45–385) 20 (52–360)

Brook Trout 

Salvelinus fontinalis

1 5 (85–175)

Brown Trout 

Salmo trutta

39 (80–400) 21 (58–430)

Mountain Whitefish 

Prosopium williamsoni

1 1 29 (80–410)

Cottidae 

(sculpin)

Wood River Sculpin 

Cottus leiopomus

54 (30–105) 4 (88–95) 32 (65–125) 136 (52–110) 29 (20–87) 386 (20–105) 99 (NR)

Total number 

of fish

84 16 109 205 116 847 282

CPUE 0.02 0.01 0.05 0.16 0.05 0.30 0.08Total fish weight 

(g, biomass)

5,358 2,172 5,467 4,389 898 22,410 5,638
Appendix B 37

Table B1. Relative abundance of fish species sampled from sites in the Big Wood River and tributaries, south-central Idaho, September 2014.—Continued

Metric

Site name BW Ketchum North Fork Warm Sp Trail Ck East Fork BW Hailey BW Stanton

USGS site ID 13135500 13135520 13137000 13137500 13138000 13139510 13140800

Sampling date 09-18-14 09-03-14 09-04-14 09-03-14 09-04-14 09-18-14 09-02-14

Reach length (meters) 300 150 200 150 150 400 300

Method Backpack Backpack Backpack Backpack Backpack Towed barge Backpack

Electrofishing time (seconds) 4,833 1,708 2,279 1,317 2,157 2,780 3,605

Number of netters 4 4 4 4 4 6 4

Description

2002 RFI metrics Cold-water native taxa 1 1 2 1 1 2 1

Number of cottid (sculpin) age classes 5 1 4 4 5 5 4Percent sensitive native individuals 64 25 29 66 25 46 35Number of alien taxa 2 1 1 1 1 3 2Percent common carp 0 0 0 0 0 0 0Number of salmonid age classes 5 5 5 4 4 5 5Cold water taxa caught per minute of 

electrofishing

1.0 0.6 2.7 9.3 3.2 18.1 2.3

Percent anomalies 0 0 0 0 0 0 0RFI 84 69 88 88 84 86 79

2011 PPBV 

SFI2 metrics

Non-native percent of taxa 33 0 0 0 0 33 14

Percent invertivore individuals 60 25 34 65 50 49 83Percent lithophilic individuals 40 75 69 35 50 51 63Percent minnow individuals 0 0 4 0 0 0 48Native taxa 2 2 5 2 2 4 6Percent piscivore individuals 40 75 65 35 50 51 15Total taxa 3 2 5 2 2 6 7PPBV SFI2 65 89 100 79 81 78 94

2011 Mountains 

SFI2 metrics

Number of fish taxa 3 2 5 2 2 6 7

Individuals per native taxon 24 5 18 65 58 166 40Percent invertivore individuals 60 25 34 65 50 49 83Percent lithophilic spawners 40 75 69 35 50 51 63Percent native intolerant individuals 99 100 95 100 100 91 42Mountains SFI2 92 100 93 80 80 78 74

Publishing support provided by the U.S. Geological Survey 

Science Publishing Network, Tacoma Publishing Service Center

For more information concerning the research in this report, contact the 

Director, Idaho Water Science Center

U.S. Geological Survey 

230 Collins Road

Boise, Idaho 83702

http://id.water.usgs.gov
MacCoy and Short—Aquatic Biological Communities and Associated Habitats, Big Wood River Watershed, South-Central Idaho, 2014—Scientific Investigations Report 2016–5128

ISSN 2328-0328 (online)

http://dx.doi.org/10.3133/sir20165128