Prepared in cooperation with the U.S. Environmental Protection Agency

Water-Quality, Bed-Sediment, and Biological Data (October 

2016 through September 2017) and Statistical Summaries of 

Data for Streams in the Clark Fork Basin, Montana

Open-File Report 2019–1060

U.S. Department of the Interior

U.S. Geological Survey
Cover. The Little Blackfoot River entering the Clark Fork, just downstream from the sampling site 

Clark Fork above the Little Blackfoot River near Garrison, Montana. Photograph by Hannah Nilges, 

U.S. Geological Survey.
Water-Quality, Bed-Sediment, and 

Biological Data (October 2016 through 

September 2017) and Statistical Summaries 

of Data for Streams in the Clark Fork Basin, 

Montana

By Thomas E. Cleasby, Michelle I. Hornberger, Terry L. Heinert, and 

Matthew A. Turner

Prepared in cooperation with the U.S. Environmental Protection Agency

Open-File Report 2019–1060

U.S. Department of the Interior

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

DAVID BERNHARDT, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2019

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Suggested citation:

Cleasby, T.E., Hornberger, M.I., Heinert, T.L., and Turner, M.A., 2019, Water-quality, bed-sediment, and biological 

data (October 2016 through September 2017) and statistical summaries of data for streams in the Clark Fork Basin, 

Montana: U.S. Geological Survey Open-File Report 2019–1060, 110 p., https://doi.org/10.3133/ofr20191060.

ISSN 2331-1258 (online)
iii

Contents

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

Introduction.....................................................................................................................................................1

Sampling Locations and Types of Data......................................................................................................3

Water-Quality Data........................................................................................................................................3

Methods..................................................................................................................................................3

Results ....................................................................................................................................................8

Quality Assurance.................................................................................................................................8

Bed-Sediment Data .....................................................................................................................................10

Methods................................................................................................................................................10

Results ..................................................................................................................................................11

Quality Assurance...............................................................................................................................11

Biological Data.............................................................................................................................................12

Methods................................................................................................................................................12

Results ..................................................................................................................................................12

Quality Assurance...............................................................................................................................12

Statistical Summaries of Data ...................................................................................................................13

References Cited..........................................................................................................................................14

Data................................................................................................................................................................19

Figure

1. Map showing location of the study area in the Clark Fork Basin, Montana ......................2

Tables

1. Type and period of data collection at sampling sites in the Clark Fork Basin, 

Montana .........................................................................................................................................4

2. Properties and constituents measured onsite or analyzed in water, bed-sediment, 

and biota samples from the Clark Fork Basin, Montana........................................................6

3. Data-quality objectives for analyses of water samples collected in the Clark Fork 

Basin, Montana.............................................................................................................................7

4. Water-quality data for the Clark Fork Basin, Montana, October 2016 through 

September 2017...........................................................................................................................20

5. Seasonal daily maximum, minimum, and mean turbidity, with monthly 

summary statistics, at Mill Creek at Opportunity, Montana, March through 

September 2017...........................................................................................................................40

6. Seasonal daily maximum, minimum, and mean turbidity, with monthly 

summary statistics, at Willow Creek at Opportunity, Montana, March through 

September 2017...........................................................................................................................42

7. Seasonal daily maximum, minimum, and mean turbidity, with monthly 

summary statistics, at Warm Springs Creek at Warm Springs, Montana, 

March through September 2017...............................................................................................44
iv

8. Seasonal daily maximum, minimum, and mean turbidity, with monthly 

summary statistics, at Lost Creek near Anaconda, Montana, March through 

September 2017...........................................................................................................................46

9. Analyses of field replicates for water samples, Clark Fork Basin, Montana ...................48

10. Precision of analyses of field replicates for stream water samples, 

Clark Fork Basin, Montana........................................................................................................52

11. Precision of analyses of laboratory replicates for stream water samples, 

Clark Fork Basin, Montana........................................................................................................53

12. Recovery efficiency for analyses of laboratory-spiked deionized-water 

blank samples..............................................................................................................................53

13. Recovery efficiency for analyses of laboratory-spiked stream samples, 

Clark Fork Basin, Montana........................................................................................................54

14. Analyses of field blanks for water samples ...........................................................................55

15. Bed-sediment data for the Clark Fork Basin, Montana, August 2017................................56

16. Recovery efficiency for analyses of standard reference materials for 

bed-sediment samples...............................................................................................................57

17. Analyses of procedural blanks for bed-sediment samples.................................................58

18. Biological data for the Clark Fork Basin, Montana, August 2017 .......................................59

19. Recovery efficiency for analyses of certified reference material for 

biota samples ..............................................................................................................................60

20. Analyses of procedural blanks for biota samples.................................................................61

21. Statistical summary of long-term water-quality data for the Clark Fork Basin, 

Montana, March 1985 through September 2017 ...................................................................62

22. Statistical summary of long-term bed-sediment data for the Clark Fork Basin, 

Montana, August 1986 through August 2017..........................................................................82

23. Statistical summary of long-term biological data for the Clark Fork Basin, 

Montana, August 1986 through August 2017..........................................................................87

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2)

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

°F=(1.8×°C)+32
v

Datum

Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD 27).

Supplemental Information

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

or micrograms per liter (μg/L).

Pore size is given in micrometers (μm).

Suspended-sediment sizes are given in millimeters (mm) and weights are given in grams (g).

Bottle capacities or liquid measurements are given in milliliters (mL).

Liquid-phase trace-element concentrations are given in micrograms per milliliter (μg/mL), and 

solid-phase concentrations are given in micrograms per gram (μg/g).

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

the calendar year in which it ends. For example, water year 2017 is the period from October 1, 

2016, through September 30, 2017.

Abbreviations

CRM certified reference material

ICP–MS inductively coupled plasma-mass spectrometry

LRL laboratory reporting level

MRL minimum reporting level

NIST National Institute of Standards and Technology

NRP National Research Program

NWIS National Water Information System

NWQL National Water Quality Laboratory

RSD relative standard deviation

spp. species

SRM standard reference material

USGS U.S. Geological Survey

Water-Quality, Bed-Sediment, and Biological Data 

(October 2016 through September 2017) and Statistical 

Summaries of Data for Streams in the Clark Fork Basin, 

Montana

By Thomas E. Cleasby, Michelle I. Hornberger, Terry L. Heinert, and Matthew A. Turner

Abstract

Water, bed sediment, and biota were sampled in selected 

streams from Butte to near Missoula, Montana, as part of a 

monitoring program in the Clark Fork Basin of western Montana. The sampling program was led by the U.S. Geological 

Survey, in cooperation with the U.S. Environmental Protection 

Agency, to characterize aquatic resources in the Clark Fork 

Basin and emphasize trace elements associated with historic 

mining and smelting activities. Sampling sites were on the 

Clark Fork and selected tributaries. Water samples were collected periodically at 20 sites from October 2016 through September 2017. Bed-sediment and biota samples were collected 

once at 13 sites during August 2017.

This report presents the analytical results and qualityassurance data for water-quality, bed-sediment, and biota 

samples collected at sites from October 2016 through September 2017. Water-quality data include concentrations of selected 

major ions, dissolved organic carbon, turbidity, nitrogen 

(nitrate plus nitrite), trace elements, and suspended sediment. 

Seasonal daily values of turbidity were determined at four 

sites. Bed-sediment data include trace-element concentrations in the fine-grained (less than 0.063 millimeter) fraction. 

Biological data include trace-element concentrations in wholebody tissue of aquatic benthic insects. Statistical summaries of 

water-quality, bed-sediment, and biological data for sites in the 

Clark Fork Basin are provided for the period of record.

Introduction

The Clark Fork originates near the town of Warm Springs 

in western Montana at the confluence of Silver Bow and Warm 

Springs Creeks (fig. 1). Along the 148-mile (mi) reach of 

stream from Silver Bow Creek in Butte to the Clark Fork near 

Missoula, six major tributaries enter: Blacktail Creek, Warm 

Springs Creek, Little Blackfoot River, Flint Creek, Rock 

Creek, and Blackfoot River. Principal surface-water uses in 

the 6,000-square-mile (mi2) Clark Fork Basin above Missoula 

include irrigation, stock watering, small-scale industry (Cannon and Johnson, 2004), and habitat for trout fisheries. Current 

(as of 2018) land uses are primarily cattle production, logging, 

mining, residential development, and recreation. Large-scale 

mining and smelting were prevalent land uses in the basin 

for more than 100 years but are now either discontinued or 

substantially reduced in scale.

Copper, gold, silver, and lead ores were extensively 

mined, milled, and smelted in the drainages of Silver Bow 

and Warm Springs Creeks from about the 1860s to the 1980s 

(U.S. Environmental Protection Agency, 2004). Moderate- and 

small-scale mining also took place in the basins of most of the 

major tributaries to the upper Clark Fork. Tailings produced 

during past mineral processing commonly contained large 

quantities of trace elements such as arsenic, cadmium, copper, 

lead, and zinc. Eroded tailings mixed with stream sediment 

and deposited downstream in stream channels, on flood plains, 

in the Warm Springs Ponds, and at the former Milltown Reservoir (fig. 1; Andrews, 1987), whose dam (Milltown Dam, not 

shown in figure) was breached on March 28, 2008. The presence of elevated trace-element concentrations in water and bed 

sediment can pose a health risk to aquatic biota and humans 

(U.S. Environmental Protection Agency, 2004).

Concern about the toxicity of trace elements to aquatic 

biota and human health has resulted in a comprehensive effort 

by State, Federal, Tribal, and private entities to characterize 

the aquatic resources in the Clark Fork Basin. This effort was 

designed to guide and monitor remedial cleanup activities and 

to evaluate the effectiveness of remediation. Water-quality data 

have been collected by the U.S. Geological Survey (USGS) 

at selected sites in the Clark Fork Basin since 1985 (Lambing, 1987–1991; Lambing and others, 1994, 1995; Dodge and 

others, 1996–2010, 2012, 2013, 2014a, 2014b, 2017, 2018; 

Dodge and Hornberger, 2015). Trace-element data for bed sediment and biota (aquatic benthic insects) have been collected 

intermittently at selected sites since 1986 as part of studies on 

the contamination of bed-sediment quality and bioaccumulation of metals led by the USGS National Research Program 
2 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Helena

M O N T A N A

Study area

Missoula

Butte

Anaconda

Opportunity

Galen

Deer Lodge

Garrison

Goldcreek

Drummond

Bonner

Turah

Clinton

Milltown

Reservoir

Clark

Bitterroot

River

Blackfoot

River

Fork

Rock

Creek

Flint

Little

Blackfoot

River

DIVIDE

Clark

Fork

Warm Springs

 Ponds

WarmSprings Cr

Silver

Bow

Creek

Blacktail

Cr

CONTINENTAL

12340500 12340000

12334550

12331800

12324680

12324200

12323800

12323750 12323770

12323600

12323250

Streamflow site type

 Continuous record

 Periodic measurement

Water-quality, bed-sediment,

and biota site type

 Periodic water quality

 Daily suspended sediment

 Daily turbidity

 Once-annual bed sediment

 Once-annual biota

EXPLANATION

12323700

12323720

Lost Cr 12323850

12323230

12323670

Mill

Creek

Willow

Creek

12323710

Creek

47°

12323760

Dempsey

Creek 461903112440701

461559112443301

461415112450801

Mill Creek

Willow

Creek

Cr Silver

Bow

Opportunity

Base modified from 

U.S. Geological Survey, 

State base map, 1966,

1:1,000,000

North American Datum of 1927

Site number

461903112440701 Miscellaneous site number

12324200

12323840

12324400

0 10 20 MILES

0 10 20 KILOMETERS

46°

114°

113°

Racetrack

former

Warm Springs

Figure 1. Location of the study area in the Clark Fork Basin, Montana.
Water-Quality Data 3

(NRP; Axtmann and Luoma, 1991; Cain and others, 1992, 

1995; Axtmann and others, 1997; Hornberger and others, 

1997). In March 1993, a long-term monitoring program for 

water, bed sediment, and biota in the basin was implemented 

by the USGS, in cooperation with the U.S. Environmental 

Protection Agency, to systematically quantify the seasonal and 

annual variability in selected constituents.

The purpose of this report is to present water-quality 

data from samples collected at 20 sites and bed-sediment 

and biological data from samples collected at 13 sites in the 

Clark Fork Basin from October 2016 through September 2017 

(fig. 1). Quality-assurance data are presented for water-quality, 

bed-sediment, and biota samples collected during the same 

period. Statistical summaries also are provided for all data collected for the period of record.

Sampling Locations and Types of Data

Sampling sites for the monitoring program in the Clark 

Fork Basin from Butte to near Missoula (fig. 1) are on the 

Clark Fork main stem (including Silver Bow Creek), three 

major tributaries (Blacktail Creek, Warm Springs Creek, and 

Blackfoot River), and three smaller tributaries (Mill Creek, 

Willow Creek, and Lost Creek). The sites, types of data collected, and period of record for each data type are listed in 

table 1. Main-stem sampling sites were selected to divide the 

Clark Fork into reaches of approximate uniform length and 

to have each reach encompassing either a major tributary or 

depositional environment (that is, Warm Springs Ponds or the 

former Milltown Reservoir). Major tributaries were sampled to 

describe water-quality, bed-sediment, and biological characteristics of important hydrologic sources in the Clark Fork Basin 

and to provide reference comparisons to the main stem. The 

three smaller tributaries were sampled to gain better spatial 

resolution on sources of trace elements entering the Clark 

Fork in an area of historical metal-processing activities near 

Anaconda, Montana. Water-quality samples were collected at 

20 sites, 6 to 8 times a year on a schedule designed to describe 

seasonal and hydrological variability. Seasonal daily turbidity values were computed using data measured by continuous 

turbidity monitors recording every 15 minutes at four sites. 

Bed-sediment and biological samples were collected annually 

at 13 sites, and 1 additional site (Warm Springs Creek at Warm 

Springs [12323770]) was sampled every 3 years. Continuous 

streamflow data were collected at 19 sites.

Properties measured onsite and constituents for which 

water, bed-sediment, and biota samples were analyzed are 

listed in table 2. Data-quality objectives for analyses of water 

samples are listed in table 3. Results of onsite measurements 

of stream properties; laboratory analyses of water-quality, 

bed-sediment, and biota samples; and quality-assurance 

data for water year 2017 (October 1, 2016, through September 30, 2017) are listed in tables 4 through 23 at the back of 

the report. Statistical summaries of long-term water-quality, 

bed-sediment, and biological data collected between March 

1985 and September 2017 are listed in tables 21 through 23 at 

the back of the report.

Quality assurance of data was maintained using documented procedures described in the following sections. These 

quality-assurance data were designed to provide environmentally representative data. Acceptable results of the procedures 

were verified with quality-control samples that were collected 

systematically to provide a measure of the accuracy, precision, 

and bias of the environmental data and to identify problems 

associated with sampling, processing, or analysis.

Water-Quality Data

Water-quality data consist of onsite measurements of 

selected stream properties and laboratory determination of 

concentrations of chemical and physical constituents (listed 

in table 2) in periodically collected stream samples. Water 

samples were collected at 20 sites in the Clark Fork Basin 6 to 

8 times per year on a schedule designed to describe seasonal 

and hydrologic variability. Continuous turbidity monitors were 

operated seasonally (March to September 2017) at four sites; 

turbidity data (recorded every 15 minutes) were used to compute daily mean turbidity values (table 1). Water-quality data 

are available through the USGS National Water Information 

System (NWIS) database at https://waterdata.usgs.gov/nwis/

qw (U.S. Geological Survey, 2018).

Methods

Water samples were collected and composited from 

vertical transits throughout the entire stream depth at multiple 

locations across the stream using depth- and width-integration 

methods described by Ward and Harr (1990), Edwards and 

Glysson (1999), and the U.S. Geological Survey (variously 

dated). These methods provided vertically and laterally discharge-weighted composite samples that represent the entire 

flow passing through the cross section of the stream. Samples 

were collected with isokinetic depth-integrating water-quality 

samplers (Davis and the Federal Interagency Sedimentation 

Project, 2005) constructed of plastic or coated with a nonmetallic rubber-coating paint and equipped with polytetrafluoroethylene nozzles.

Instantaneous streamflow was determined at the time of 

water sampling either by direct measurement or from stagedischarge rating tables (Rantz and others, 1982). Daily mean 

streamflow values during ice periods were labeled as estimated because backwater affected the stage-discharge relation. 

Onsite measurements of pH, specific conductance, and water 

temperature were measured during water sample collection. 

Sample processing, including filtration and preservation, was 

completed according to procedures described by Ward and 

Harr (1990), Horowitz and others (1994), and the U.S. Geological Survey (variously dated).
4 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana Table 1. Type and period of data collection at sampling sites in the Clark Fork Basin, Montana. [--, no data; P, present; D, discontinued] Site number (fig. 1) Site name Continuous- record streamflow Periodic water quality1 Daily suspended sediment Daily turbidity (seasonal) Fine-grained bed sediment2 Benthic aquatic insects2 12323230 Blacktail Creek at Harri- son Avenue, at Butte -- 03/1993–08/1995, 12/1996–08/2003, 12/2004–P -- -- -- -- 12323250 Silver Bow Creek below Blacktail Creek, at Butte 10/1983–P 03/1993–08/1995, 12/1996–P -- -- -- -- 12323600 Silver Bow Creek at Opportunity 07/1988–P 03/1993–08/1995, 12/1996–P 03/1993–09/1995, D -- 07/1992–P 07/1992, 08/1994– 08/1995, 08/1997–P 12323670 Mill Creek near Ana- conda 10/2004–P 12/2004–P -- 06/2006–09/2012, D -- -- 12323700 Mill Creek at Oppor- tunity 04/2003–P 03/2003–P -- 04/2013–P -- -- 12323710 Willow Creek near Anaconda 03/2005–P 12/2004–P -- 06/2006–09/2012, D -- -- 12323720 Willow Creek at Op- portunity 04/2003–P 03/2003–P -- 04/2013–P -- -- 12323750 Silver Bow Creek at Warm Springs 03/1972–09/1979, 04/1993–P 03/1993–P 04/1993–09/1995, D -- 07/1992–P 07/1992–P 12323760 Warm Springs Creek near Anaconda 10/1997–P 10/2005–P -- 05/2006–09/2012, D -- -- 12323770 Warm Springs Creek at Warm Springs 10/1983–P 03/1993–P -- 04/2013–P 08/1995, 08/1997, 08/1999, 08/2002, 08/2005, 08/2008, 08/2011, 08/2014, 08/2017 08/1995, 08/1997, 08/1999, 08/2002, 08/2005, 08/2008, 08/2011, 08/2014, 08/2017 12323800 Clark Fork near Galen 07/1988–P 07/1988–P -- -- 08/1987, 08/1991–P 08/1987, 08/1991–P 12323840 Lost Creek near Ana- conda 10/2004–P 12/2004–P -- 05/2006–P -- -- 12323850 Lost Creek near Galen 04/2003–P 03/2003–P -- -- -- -- 461415112450801 Clark Fork below Lost Creek, near Galen -- -- -- -- 08/1996–P 08/1996–P 461559112443301 Clark Fork at county 

bridge, near Racetrack

-- -- -- -- 08/1996–P 08/1996–P
Water-Quality Data 

5

Table 1. Type and period of data collection at sampling sites in the Clark Fork Basin, Montana.—Continued[--, no data; P, present; D, discontinued]

Site number 

(fig. 1) Site name Continuous- record streamflow Periodic water quality1 Daily suspended sediment Daily turbidity (seasonal) Fine-grained bed sediment2 Benthic aquatic insects2

461903112440701 Clark Fork at Dempsey 

Creek diversion, near Racetrack

-- -- -- -- 08/1996–P 08/1996–P

12324200 Clark Fork at Deer 

Lodge

10/1978–P 03/1985–P 03/1985–08/1986, 

04/1987–03/2003, 08/2003–2014, D

03/2016–09/2016, D 08/1986–08/1987, 

08/1990–P

08/1986–08/1987, 

08/1990–P

12324400 Clark Fork above Little 

Blackfoot River, near Garrison

02/2009–P 03/2009–P -- -- 08/2009–P 08/2009–P

12324680 Clark Fork at Goldcreek 10/1977–P 03/1993–P -- -- 07/1992–P 07/1992–P12331800 Clark Fork near Drummond 04/1993–P 03/1993–P -- -- 08/1986, 08/1987, 08/1991–P 08/1986, 08/1991–P12334550 Clark Fork at Turah 

Bridge, near Bonner

03/1985–P 03/1985–P 03/1985–03/2003, 

08/2003–09/2016, D

-- 08/1986, 08/1991–P 08/1986, 08/1991–P

12340000 Blackfoot River near 

Bonner

10/1939–P 03/1985–P 07/1986–04/1987, 

06/1988–09/1995,10/2005–09/216, D

-- 08/1986–08/1987, 

08/1991, 08/1993–08/1996, 08/1998–08/2001, 09/2003,08/2006–P

08/1986–08/1987, 

08/1991, 08/1993, 08/1996, 08/1998, 09/2000, 09/2003,08/2006–P

12340500 Clark Fork above Missoula 03/1929–P 07/1986–P3 07/1986–04/1987, 06/1988–01/1996, 

03/1996–03/2003, 08/2003–09/216, D

04/2007–09/2007, D 08/1997–P 08/1997–P

1Onsite measurements of physical properties and laboratory analyses for selected major ions, trace elements, and suspended sediment. Before March 1993, laboratory analyses included only trace elements 

and suspended sediment. In 2012, dissolved organic carbon and turbidity analyses were included at select sites. In 2013, nutrient sample analyses were included for two sites near Butte, Montana.

2Laboratory analyses of fine-grained bed sediment and aquatic benthic insects for trace elements.3Before October 1989, water-quality data for Clark Fork above Missoula included only suspended-sediment data.
6 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 2. Properties and constituents measured onsite or analyzed in water, bed-sediment, and biota 

samples from the Clark Fork Basin, Montana.

Water Bed sediment Benthic aquatic insects

Property Constituent Constituent Constituent

Streamflow Hardness (calculated) Arsenic Arsenic

pH Calcium Cadmium Cadmium

Specific conductance Magnesium Chromium Chromium

Temperature Potassium Copper Copper

Turbidity Sodium Iron Iron

Alkalinity Lead Lead

Chloride Manganese Manganese

Fluoride Nickel Nickel

Silica Zinc Zinc

Sulfate

Nitrate plus nitrite

Cadmium

Copper

Iron

Lead

Manganese

Zinc

Arsenic

Dissolved organic carbon

Suspended sediment

Concentrations of arsenic, cadmium, copper, lead, manganese, and zinc in filtered samples (0.45-micrometer [μm] 

pore size) were measured using inductively coupled plasmamass spectrometry (ICP–MS; Garbarino and others, 2006). 

Concentrations of calcium, magnesium, and iron in filtered 

samples were measured using inductively coupled plasmaatomic emission spectrometry (Fishman and Friedman, 1989). 

Calcium and magnesium concentrations were used to calculate water hardness. Concentrations of potassium, sodium, 

alkalinity, chloride, fluoride, silica, sulfate, nitrogen (nitrate 

plus nitrite), and dissolved organic carbon were measured in 

filtered samples collected at select sites in the upper Clark 

Fork Basin. Potassium was measured by Standard Method 

3120 (American Public Health Association, 1998); sodium 

and silica were analyzed by inductively coupled plasmaatomic emission spectrometry (Fishman, 1993); alkalinity was 

measured by electrometric titration (Fishman and Friedman, 

1989); chloride, fluoride, and sulfate were measured by ion 

chromatography (Fishman and Friedman, 1989); nitrogen 

(nitrate plus nitrite) was measured by colorimetric enzymatic 

reduction (Patton and Kryskalla, 2011); and dissolved organic 

carbon was measured by persulfate oxidation and infrared 

spectrometry (Brenton and Arnett, 1993). Recoverable concentrations of trace elements were measured in unfiltered samples 

that were first digested with dilute hydrochloric acid (Hoffman 

and others, 1996). For cadmium, iron, lead, and manganese, 

the digested samples were analyzed by ICP–MS as described 

by Garbarino and Struzeski (1998). For arsenic, copper, and 

zinc, the digested samples were analyzed by ICP–MS as 

described by Garbarino and others (2006). Turbidity was measured using Standard Method 2130 (American Public Health 

Association, 1998) in selected unfiltered samples. All samples 

were analyzed at the USGS National Water Quality Laboratory (NWQL) in Denver, Colorado.

Water samples for analysis of suspended sediment also 

were collected from multiple vertical transits when periodic 

water samples were collected. Water samples were analyzed 

for suspended-sediment concentration and the percentage of 

suspended-sediment mass finer than 0.062-millimeter (mm) 

diameter (silt size and smaller) by the USGS WyomingMontana Water Science Center Sediment Laboratory (hereinafter referred to as the “Wyoming-Montana Sediment Laboratory”) in Helena, Mont., according to methods described by 

Guy (1969) and Dodge and Lambing (2006).
Water-Quality Data 7

Table 3. Data-quality objectives for analyses of water samples collected in the Clark Fork Basin, Montana.

[lab, laboratory; NTRU, nephelometric turbidity ratio unit; --, not determined; mg/L, milligram per liter; μg/L, microgram per liter; mm, millimeter]

Constituent

Data-quality objectives

Detectability Precision Bias

Laboratory 

reporting 

level

Maximum relative standard 

deviation of replicate analyses 

(percent)

Maximum deviation of spike 

recovery (percent)

Turbidity, unfiltered, lab, NTRU 2.0 units 20 --

Calcium, filtered 0.022 mg/L 20 --

Magnesium, filtered 0.011 mg/L 20 --

Potassium, filtered 0.03–0.1 mg/L 20 --

Sodium, filtered 0.06–0.1 mg/L 20 --

Alkalinity, filtered, lab 4.0 mg/L 20 --

Chloride, filtered 0.02 mg/L 20 --

Fluoride, filtered 0.01 mg/L 20 --

Silica, filtered 0.018 mg/L 20 --

Sulfate, filtered 0.02 mg/L 20 --

Nitrate plus nitrite, filtered 0.01 mg/L 20 --

Cadmium, filtered 0.03 μg/L 20 25

Cadmium, unfiltered recoverable 0.03 μg/L 20 25

Copper, filtered 0.2 μg/L 20 25

Copper, unfiltered recoverable 0.2 μg/L 20 25

Iron, filtered 4-10 μg/L 20 25

Iron, unfiltered recoverable 4.6-10 μg/L 20 25

Lead, filtered 0.02 μg/L 20 25

Lead, unfiltered recoverable 0.02 μg/L 20 25

Manganese, filtered 0.4 μg/L 20 25

Manganese, unfiltered recoverable 0.4 μg/L 20 25

Zinc, filtered 2 μg/L 20 25

Zinc, unfiltered recoverable 2 μg/L 20 25

Arsenic, filtered 0.05 μg/L 20 25

Arsenic, unfiltered recoverable 0.05 μg/L 20 25

Organic carbon, filtered 0.23 mg/L 20 --

Sediment, suspended, percent finer than 0.062 mm 1 percent 20 --

Sediment, suspended 1 mg/L 20 --

Real-time turbidity was measured from early spring 

(after ice breakup) to early fall (before stream freezeup) 

using model 6136 turbidity sensors (Yellow Springs Instruments, Yellow Springs, Ohio) at four tributary sites in the 

upper Clark Fork Basin near Anaconda (table 1). Turbidity 

values were recorded every 15 minutes and are stored in the 

USGS NWIS database (U.S. Geological Survey, 2018) at 

https://waterdata.usgs.gov/mt/nwis/current?type=quality. The 

in situ values differ from the results of laboratory-measured 

turbidity in discrete water-quality samples because of differences in the instrumentation and sampling procedures. 

Continuous recordings enable determination of the minimum 

and maximum turbidity values for each day as well as a daily 

mean turbidity, which is based on the average of all values 

in a 24-hour period. Procedures for the operation of continuous turbidity monitors and for daily record computations are 

described by Wagner and others (2006).
8 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Results

Water-quality data from samples collected periodically 

during water year 2017 (October 1, 2016, through September 30, 2017) are listed in table 4. In water year 2017, there 

was one water-quality sample at Mill Creek near Anaconda 

(12323670) on April 17, 2017, with missing values for filtered 

and unfiltered copper. These copper values did not pass review 

because the filtered value was greater than the unfiltered value, 

and this issue could not be resolved by reruns. Daily maximum, minimum, and mean turbidity at four sites are listed 

in tables 5 through 8 along with monthly summary statistics. 

Water-quality data are available in the USGS NWIS database 

(U.S. Geological Survey, 2018).

Quality Assurance

Quality-assurance procedures used for the collection and 

field processing of water samples were described by Ward and 

Harr (1990), Horowitz and others (1994), Edwards and Glysson (1999), Lambing (2006), and the U.S. Geological Survey 

(variously dated). Standard procedures used by the NWQL for 

internal sample handling and quality assurance were described 

by Friedman and Erdmann (1982), Jones (1987), and Pritt 

and Raese (1995). Quality-assurance procedures used by the 

Wyoming-Montana Sediment Laboratory were described by 

Dodge and Lambing (2006). Standard procedures used for the 

calibration, measurement, and quality assurance of turbidity 

monitors were described by Anderson (2005).

The quality of analytical results reported for water 

samples was evaluated using quality-control samples that were 

sampled and analyzed concurrently with primary environmental samples. These quality-control samples consisted 

of replicates, spikes, and blanks that provided quantitative 

information on the precision and bias of the overall field and 

laboratory processes. Each type of quality-control sample was 

submitted at a proportion equivalent to about 5 percent of the 

total number of water samples; therefore, the total number of 

quality-control samples represented about 15 percent of the 

total number of water samples.

Replicate data can be collected in different ways to 

provide an assessment of the precision (reproducibility) of 

analytical results. Replicate samples are two or more samples 

considered to be essentially identical in composition. Replicate 

samples can be collected in the field (field replicate) either by 

repeating the collection process (sequential or concurrent replicate) to obtain two or more independent composite samples 

or by splitting a single composite sample into two or more 

subsamples (split 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).

Precision of analytical results for field replicates can be 

affected by numerous sources of variability within the field 

and laboratory environments, including sample collection, 

processing, and analysis. Data on overall precision for samples 

exposed to field and laboratory sources of variability were provided by obtaining replicate stream samples for chemical analysis by splitting a composite stream sample. Replicate stream 

samples for suspended-sediment analysis were obtained in the 

field by collecting two independent cross-sectional samples. 

Analyses of field replicate samples indicate the reproducibility 

of environmental data that are affected by the combined potential variability introduced by field and laboratory processes.

In addition to analyzing quality-control samples submitted from the field, internal quality-assurance practices are 

performed systematically by the NWQL to provide quality 

control of analytical procedures (D.L. Stevenson, U.S. Geological Survey, written commun., 2012). These internal 

practices include analyses of 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 in which standard reference water samples prepared by the USGS Branch of Quality Systems are routinely 

inserted into the sample line for each analytical method at a 

frequency proportional to the sample load. The laboratory also 

participates in external evaluation studies and audits with the 

National Environmental Laboratory Accreditation Program, 

the U.S. Environmental Protection Agency, Environment 

Canada, and the USGS Branch of Quality Systems to assess 

analytical performance.

Precision of analytical results for laboratory replicates, 

which exclude field sources of variability, was determined 

using two independent chemical analyses of aliquots from a 

single sample selected from the group of samples constituting each analytical run. A separate analysis of the sample was 

made at the beginning and end of each analytical run to provide information on the reproducibility of laboratory analytical results independent of variability caused by field sample 

collection and processing. Laboratory replicates of suspendedsediment samples were not obtainable because the samples 

were consumed during the analysis.

Spiked samples (Boughton, 2019) were used to evaluate bias, which measures the ability of an analytical method 

to accurately quantify a known amount of analyte added to a 

sample. In the laboratory, deionized-water blank samples and 

aliquots of stream samples were spiked with known amounts 

of the same trace elements for which water samples were 

being analyzed. Analyses of spiked blanks indicate if the 

spiking procedure and analytical method are within control 

for water that is presumably free of chemical interference. 

Analyses of spiked aliquots of stream samples indicate if the 

chemical matrix of the stream water interferes with the analytical measurement and if these interferences could contribute 

substantial bias to reported trace-element concentrations for 

stream samples.

Field blank samples were submitted for every field trip 

and analyzed to identify the presence and magnitude of contamination that could potentially bias analytical results. Field 
Water-Quality Data 9

blanks consist of deionized water that is certified as constituent free and is processed in the field through clean sampling 

equipment used to collect stream samples. These blanks then 

are subjected to the same processing (sample splitting, filtration, preservation, transportation, and laboratory handling) 

as stream samples. Blank samples are analyzed for the same 

constituents as stream samples to detect contamination.

All water samples were handled in accordance with 

chain-of-custody procedures that provide documentation of 

sample identity, shipment, receipt, and laboratory handling 

(Driscoll and Hatcher, 2010). All environmental and qualitycontrol samples submitted from a sampling episode were 

stored in a secure area of the NWQL and analyzed as a discrete sample group, independent of other samples submitted 

to the NWQL. Therefore, the quality-control data apply solely 

to the analytical results for stream samples reported herein and 

provide a direct measure of data quality for this study.

Data-quality objectives (table 3) were established by the 

USGS and U.S. Environmental Protection Agency as part of 

the study plan for the expanded long-term monitoring program 

started in 1993. The objectives identify the analytical requirements of detectability and serve as a guide for identifying 

questionable data by establishing acceptable limits for precision and bias of laboratory results. Comparisons of qualitycontrol data to data-quality objectives were used to evaluate if 

sampling and analytical procedures produced environmentally 

representative data in a consistent manner. Data that did not 

meet the objectives were evaluated for acceptability; if necessary, additional quality-control samples were submitted and 

corrective action was taken.

The precision of analytical results was determined by 

calculating the standard deviation of the differences in concentrations between replicate analyses. These replicate analyses 

consisted of pairs of field replicate samples and laboratory 

replicates. Standard deviations were calculated according to 

the following equation (Taylor, 1987):

S

k

d

= Σ 2

2 (1)

where

S is the standard deviation of the difference in 

concentration between replicate analyses,

d is the difference in concentration between 

each pair of replicate analyses, and

k is the number of pairs of replicate analyses.

Precision also was expressed as a relative standard deviation (RSD), in percent, which was computed from the standard 

deviation and the mean concentration for all the replicate 

analyses. Expressing precision relative to a mean concentration standardized the comparison of precision among individual constituents. The RSD was calculated according to the 

following equation (Taylor, 1987):

RSD S

x = ×100 (2)

where

RSD is the relative standard deviation,

S is the standard deviation, and

x is the mean concentration for all replicate 

analyses.

Sample results and the corresponding field replicate data 

are listed in table 9, and the precision for each constituent 

estimated from field replicate analyses is listed in table 10. 

Precision estimates for the analytical results of field replicates 

were within the acceptable RSD limit of 20 percent for all 

constituents except filtered cadmium (table 10), which was 

21 percent. This one exceedance of the data-quality objective 

resulted from a statistical artifact of calculating the difference 

between one replicate sample pair for which one value is less 

than the laboratory reporting level (LRL).

The precision for each constituent estimated from 

laboratory replicate analyses is listed in table 11. Statistics 

summarizing the precision of analytical results for laboratory 

replicates were calculated using unrounded values stored in 

laboratory data files. Precision estimates for the laboratory 

replicates were within the acceptable 20-percent RSD limit 

for all constituents (table 11), so no adjustments were made to 

analytical data based on replicate analyses precision. Recovery 

efficiencies for analyses of constituents was determined by 

comparing a sample and a spiked aliquot of the same sample. 

The data-quality objective for acceptable spike recoveries of 

trace elements in water samples was a maximum deviation 

of 25 percent from a theoretical 100-percent recovery of an 

added constituent (table 3). At NWQL, a spiked deionizedwater blank sample and a spiked aliquot of a stream sample 

were prepared and analyzed along with the original unspiked 

sample. The differences between the spiked and unspiked 

sample concentrations were determined and used to compute 

recovery, in percent, according to equation 3:

R

D

C= ×100 (3)

where

R is the spike recovery, in percent;

D is the difference between the spiked and 

unspiked sample concentrations; and

C is the concentration of material used to spike 

the sample.

If the spike recovery of a trace element was outside a 

range of 75 to 125 percent, the instrument was recalibrated and 

the entire sample set and all spiked samples were reanalyzed 

for that element until recoveries were improved to the extent 

possible. Recovery efficiency for individual trace elements in 
10 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

spiked blank samples and in spiked stream samples is listed in 

tables 12 and 13, respectively. The mean recovery for spiked 

blank samples (table 12) ranged from 81.5 to 108 percent. The 

smallest individual constituent recovery was lead, filtered, at 

53.4 percent, and the largest was cadmium, filtered, at 122 percent. The 95-percent confidence intervals (Taylor, 1987) for 

the mean recovery for each constituent for which spiked blank 

samples were analyzed (table 12) did not exceed a 25-percent 

deviation from an expected 100-percent recovery except for 

lead, filtered (53.4 percent). The mean recovery for spiked 

stream samples (table 13) ranged from 85.9 to 106 percent. 

The smallest constituent recovery was arsenic, unfiltered 

recoverable, at 43.4 percent, and the largest was arsenic, unfiltered recoverable, at 128 percent. The 95-percent confidence 

intervals for the mean spike recovery for each constituent for 

which stream water samples were analyzed (table 13) did not 

exceed a 25-percent deviation from an expected 100-percent 

recovery except for arsenic, filtered (63.9 percent) and arsenic, 

unfiltered recoverable (43.4 and 128 percent). No adjustments were made to analytical data based on the mean spike 

recovery.

High or low bias is indicated if the 95-percent confidence interval does not include 100-percent recovery, thereby 

indicating a consistent deviation or bias, either high or low. 

Confidence intervals for percent recovery include 100 percent 

for all laboratory-spiked blank samples (table 12). Confidence 

intervals for percent recovery include 100 percent for all 

laboratory-spiked stream samples (table 13) except for iron, 

filtered (96.6–99.8 percent) and iron, unfiltered recoverable 

(79.3–96.3 percent). No adjustments were made to analytical 

results for stream samples based on spike recoveries.

Analytical results for field blanks are listed in table 14. 

Field blanks with constituent concentrations less than or equal 

to the LRL indicate that the entire process of sample collection, field processing, and laboratory analysis is presumably 

free of contamination. If detectable concentrations of trace 

elements in field blanks were greater than or equal to twice the 

LRL, the concentrations were noted during data review. Analytical results from the field blank were evaluated for evidence 

of a consistent trend that could indicate systematic contamination. Sporadic, infrequent, nonconsecutive exceedances of 

twice the LRL most likely represented random contamination 

or laboratory-instrument calibration error that was not persistent in the process and was not likely to cause positive bias in 

a long-term record of analytical results; however, if concentrations for a particular constituent exceeded twice the LRL in 

field blanks from two consecutive field trips, additional blank 

samples were collected and submitted for analysis to identify 

the source of contamination.

Constituent concentrations in field blanks (table 14) 

almost always were less than the LRL. Three sample concentrations of copper, filtered (0.22, 0.21, and 0.26 micrograms 

per liter [μg/L]) exceeded the LRL of 0.20 μg/L. One sample 

concentration of copper, unfiltered recoverable (0.2 μg/L) 

matched the LRL of 0.2 μg/L. No adjustments were made to 

water-quality sample data based on a review of these results.

Bed-Sediment Data

Bed-sediment data for the long-term monitoring program 

in the Clark Fork Basin consist of trace-element concentrations in the fine-grained (less than 0.063 mm) fraction of bedsediment samples. Bed-sediment samples were collected once 

annually at 13 sites (fig. 1; table 1) during low, stable flow 

conditions at about the same time of year as previous samples 

(typically in August) to facilitate data comparisons among 

years. Warm Springs Creek at Warm Springs is sampled once 

every 3 years rather than once annually and was sampled during water year 2017. The 2017 bed-sediment data are available 

in a machine-readable data release (Boughton, 2019). For prior 

years, bed-sediment data can be obtained in a Microsoft Excel 

format from the authors.

Methods

Fine-grained bed-sediment samples were collected in 

August 2017 using protocols described by Axtmann and 

Luoma (1991). Samples were collected from the surfaces of 

streambed deposits in areas near the edge of the stream using 

an acid-washed polypropylene scoop. Whenever possible, 

samples were collected from both sides of the stream.

Individual samples of bed sediment were collected by 

scooping material from the surfaces of three to five randomly 

selected deposits along pools or low-velocity areas. The three 

to five individual samples were combined to form a single 

composite sample. This collection process was repeated three 

times to obtain three composite samples. Each composite sample was wet sieved onsite through a 0.063-mm polyester-mesh 

sieve using ambient stream water. The fraction of bed sediment in each composite sample that was finer than 0.063 mm 

was collected in an acid-washed 500-milliliter (mL) polyethylene bottle and transported to the laboratory on ice.

Bed-sediment samples were processed and analyzed at 

the USGS NRP Ecology and Contaminants Project Laboratory in Menlo Park, California. Bed-sediment samples were 

ovendried at 60 degrees Celsius (°C) and ground into smaller 

particle sizes using an acid-washed, ceramic mortar and 

pestle. Single aliquots of about 0.5–0.6 gram (g) of sediment 

from each of the three composite bed-sediment samples were 

digested using a hot, concentrated nitric acid reflux according 

to methods described by Luoma and Bryan (1981). Laboratory replicates were analyzed by taking an aliquot from one of 

the three sieved replicate samples at each site. After a 2-week 

digestion period, the aliquots were evaporated to dryness on a 

hot plate. The dry residue was reconstituted in 10 mL of 0.6 N 

(normal) hydrochloric acid. The reconstituted aliquots were 

then filtered through a 0.45-μm pore-size filter using a syringe 

and an in-line disposable filter cartridge. The filtrate was 

diluted to a 1–10 ratio with 0.6 N hydrochloric acid. These 

final solutions were analyzed for arsenic, cadmium, chromium, copper, iron, lead, manganese, nickel, and zinc using 

inductively coupled plasma-optical emission spectrometry 
Bed-Sediment Data 11

(Hornberger and others, 1997). The smallest concentration of 

a constituent that can be reliably reported for analyses of bed 

sediment is termed the minimum reporting level (MRL).

Results

Solid-phase concentrations of trace elements measured in 

samples of fine-grained bed sediment collected during August 

2017 are listed in table 15. Liquid-phase concentrations, 

measured in micrograms per milliliter, were analyzed in the 

reconstituted aliquots of digested bed sediment. Solid-phase 

concentrations, measured in micrograms per gram, were calculated using the following equation:

μg/g (μg/mL)(volume of digested sample, in mL)

(dry weight = of sample, in grams)(dilution ratio) (4)

where

μg/g is micrograms of trace element per gram,

μg/mL is micrograms per milliliter of liquid-phase 

trace element, and

mL is milliliters.

The reported solid-phase concentrations (table 15) are 

the means of all analyses for replicate aliquots from each 

composite bed-sediment sample collected at the site. Because 

the conversion from liquid-phase to solid-phase concentration 

is dependent on the dilution ratio and the dry weight of the 

sample, MRLs for some trace elements might differ among 

sites and among years.

Quality Assurance

The USGS protocols for field collection and processing 

of bed-sediment samples are designed to prevent contamination from metal sources. Nonmetallic sampling and processing equipment (white plastic scoop, funnel-frame apparatus, 

and 500-mL sample bottles) were acid-washed and rinsed 

with deionized water before the collection of the first sample. 

Polyester-mesh sieves were washed in laboratory-grade detergent and rinsed with deionized water. All equipment received 

a field rinse onsite with stream water. Sampling equipment 

used at more than one site was field rinsed thoroughly between 

sites with site-specific stream water. Separate sieves were 

used at each site and, therefore, did not require between-site 

cleaning. Bed-sediment samples were collected sequentially at 

sites along a general increasing concentration gradient (that is, 

downstream sites have lower concentrations of contaminated 

bed sediments compared to upstream sites) to minimize effects 

from potential site-to-site carryover contamination (Axtmann 

and Luoma, 1991).

Quality assurance of analytical results for bed-sediment 

samples included laboratory-instrument calibration with 

standard solutions and analysis of quality-control samples 

designed to identify the presence and magnitude of bias (Ellen 

V. Axtmann, U.S. Geological Survey, written commun., 1994). 

Quality-control samples consisted of standard reference 

materials (SRMs) issued by the National Institute of Standards and Technology (NIST) and procedural blanks. In total, 

10 low-concentration SRMs, 10 high-concentration SRMs, 

and 13 procedural blanks were analyzed.

SRMs are commercially prepared materials that have 

certified concentrations of trace elements. Analyses of SRMs 

are used to indicate the ability of the method to accurately 

measure a known quantity of a constituent. Multiple analyses 

of SRMs are made to derive a mean and 95-percent confidence 

interval for recovery. Recovery efficiency for trace-element 

analyses of SRMs for bed sediment is listed in table 16. Two 

SRMs, consisting of agricultural soils and representing low 

and high concentrations of trace elements, were analyzed to 

test recovery efficiency for a range of concentrations like those 

discovered in the bed sediment in streams in the upper Clark 

Fork Basin.

The digestion process used to analyze bed-sediment 

samples is not a “total” digestion (does not liberate elements 

associated with crystalline lattices); therefore, 100-percent 

recovery may not be achieved for elements strongly bound to 

the sediment. The percent recovery of trace elements for SRM 

analyses that use less than a total digestion is useful to indicate 

which trace elements display strong sediment-binding characteristics in the SRM and if analytical recovery is consistent 

between multiple sets of analyses.

Although data-quality objectives have not been established for bed sediment, percent recoveries for individual 

trace elements (table 16) illustrate analytical performance. 

Metal recoveries of sediment digests were evaluated with 

NIST 2709a San Joaquin soils (hereinafter referred to as 

“SRM sample 2709A”) and NIST 2711a Montana soil II 

(hereinafter referred to as “SRM sample 2711a”). Mean recoveries in SRM sample 2709a ranged from 45.0 to 90.0 percent 

of the certified concentrations (table 16). The mean recoveries 

were within 22 percent of the 95-percent confidence interval 

for copper, iron, manganese, nickel, and zinc. Elements with 

low certified concentrations (cadmium, 0.371 μg/g) or with a 

strong association with crystalline lattices (arsenic, chromium, 

lead) had lower percent recoveries (from 45.0 to 67.6 percent). 

Mean recoveries in SRM sample 2711a ranged from 55.6 to 

97.7 percent (table 16). The percent recoveries were within 

15.2 percent of the 95-percent confidence interval for arsenic, 

cadmium, copper, iron, lead, nickel, and zinc; and 19.1 percent for manganese. Chromium had the lowest mean recovery 

(55.6 percent) because of the strong binding nature of the crystalline lattice of chromium-bearing minerals. No adjustments 

were made to trace-element concentrations in bed-sediment 

samples based on recovery efficiencies.

Procedural blanks for bed-sediment samples consisted 

of the analysis of the same reagents used for sample digestion and reconstitution. Concentrated nitric acid used for 

sample digestion was heated and evaporated to dryness. After 

evaporation, 0.6 N hydrochloric acid was added to reconstitute the dry residue. Analytical results of procedural blanks 

for bed sediment (table 17) are reported as a liquid-phase 
12 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

concentration, in micrograms per milliliter. A procedural blank 

was prepared and analyzed concurrently with bed-sediment 

samples for each site. Concentrations of trace elements in all 

procedural blanks were less than the MRL for all elements. No 

adjustments were made to analytical data based on procedural 

blanks.

Biological Data

Biological data for the long-term monitoring program 

in the Clark Fork Basin consist of trace-element concentrations in the whole-body tissue of aquatic benthic insects. 

Insect samples are collected once annually at the same 13 sites 

and on the same dates as bed-sediment samples (fig. 1; 

table 1), 10 of which have streamgages, allowing for a direct 

comparison of biological data with bed-sediment data and 

water-quality data through the years. Warm Springs Creek at 

Warm Springs is sampled once every 3 years rather than once 

annually and was sampled during water year 2017. Biological 

data for water year 2017 are available in a machine-readable 

data release (Boughton, 2019). Biological data for prior years 

are available by request in Microsoft Excel format from the 

authors.

Methods

Insect samples were collected using protocols described 

in Hornberger and others (1997). Benthic insects at immature stages were collected with a large nylon-mesh kick net. 

A single riffle at each site was sampled repeatedly until an 

adequate number of individual insects were collected to provide sufficient mass for analysis (for example, about 10 stoneflies, about 100–200 caddisflies). Two caddisfly species of the 

genus Hydropsyche (Hydropsyche cockerelli and Hydropsyche 

occidentalis) were targeted for collection in this study because 

of their occurrence at most sites. Hydropsyche species (spp.) 

that could not be positively identified were categorized as 

Hydropsyche spp. or Hydropsyche morosa group. On the few 

occasions when Hydropsyche were not present, other caddisflies, including Brachycentrus spp. and Rhyacophila spp., 

were collected. The caddisfly Arctopsyche grandis and the 

stoneflies Claassenia sabulosa and Hesperoperla spp. were 

collected where available to represent additional insect taxa 

commonly distributed in the Clark Fork Basin but with different feeding traits.

Samples of each taxon were sorted by genus in the field 

and placed in acid-washed plastic containers. Samples were 

frozen in a small amount of ambient stream water on dry ice 

within 30 minutes of collection. Between 1986 and 1998, macroinvertebrate containers were kept on ice to allow the insects 

to evacuate their gut contents (depurate) for 6 to 8 hours. 

Excess water was drained and insects were frozen for transport to the laboratory. Since 1999, samples were immediately 

frozen on dry ice in the field to reduce the possibility of metal 

loss through intracellular breakdown during depuration. A 

comparison of immediately frozen to depurated samples indicated that although no substantial difference occurred for most 

metals, concentrations of copper were about 20 percent lower 

in the depurated samples than in the samples that were immediately frozen. The data were not adjusted for this difference.

Insect samples were processed and analyzed at the 

USGS NRP Ecology and Contaminants Project Laboratory in 

Menlo Park, Calif. Insects were thawed and rinsed with ultrapure deionized water to remove particulate matter and then 

sorted to their lowest possible taxonomic level. If large numbers of specimens were collected at a site, similar-sized individuals were composited into replicate subsamples. Subsamples were placed in tared scintillation vials and ovendried at 

70 °C. Subsamples were weighed to obtain a final dry weight 

and digested by reflux using concentrated nitric acid (Cain and 

others, 1992). After digestion, insect samples were evaporated 

to dryness on a hot plate. The dry residue was reconstituted in 

0.6 N hydrochloric acid, filtered through a 0.45-μm pore-size 

filter, and analyzed undiluted by using inductively coupled 

plasma-optical emission spectrometry (Hornberger and others, 

1997) for arsenic, cadmium, chromium, copper, iron, lead, 

manganese, nickel, and zinc. The smallest concentration of a 

constituent that can be reliably reported for analyses of biota is 

termed the MRL.

Results

Concentrations of trace elements in whole-body tissue 

of aquatic insects collected during August 2017 are listed in 

table 18. The variability in the number of composite samples 

among species and among sites reflects differences in insect 

abundance (the number of composite samples increases with 

the relative abundance of insects). Liquid-phase concentrations, in micrograms per milliliter, analyzed in the reconstituted samples were converted to solid-phase concentrations, 

in micrograms per gram, using equation 4 (used earlier in this 

report to calculate solid-phase concentrations of trace elements 

in bed sediment). All tissue samples were analyzed undiluted 

(the dilution ratio was 1–1). As with MRLs for trace elements 

in bed sediment, MRLs for trace elements in insects may differ among sites because of varied sample weights. In general, 

the smaller the biological-sample weight (primarily a function 

of insect abundance), the higher the MRL; therefore, higher 

MRLs do not necessarily imply a higher trace-element concentration in tissue.

Quality Assurance

The USGS protocols for field collection and processing of biota samples are designed to prevent contamination 

from metal sources. Nonmetallic nets, sampling equipment, 

and processing equipment were used in all sample collection. 

Equipment was acid-washed and rinsed in ultrapure deionized 

water before the first sample collection. Nets and equipment 
Statistical Summaries of Data 13

were thoroughly rinsed in stream water at each main-stem site. 

Clean nets were used at each tributary site. Biota samples were 

collected sequentially at sites along an increasing concentration gradient, which was from downstream sites to upstream 

sites, to minimize effects from potential site-to-site carryover 

contamination (Hornberger and others, 1997).

Quality control of analytical results for biota samples 

included laboratory-instrument calibration with standard 

solutions and analyses of quality-control samples designed to 

quantify precision and to identify the presence and magnitude 

of bias. Quality-control samples consisted of 12 replicates of 

the certified reference material (CRM) TORT–3 (lobster hepatopancreas) purchased from the National Research Council 

Canada. Quality-control samples were analyzed in a proportion equivalent to about 20 percent of the total number of biota 

samples.

Recovery efficiencies for trace-element analyses of the 

TORT–3 CRM are listed in table 19. Data-quality objectives 

have not been established for analytical recovery in biota, 

but percent recoveries indicate analytical performance. Mean 

CRM recoveries for TORT–3 ranged from 80.4 to 185 percent 

for all constituents. The mean recoveries were within 14 percent (based on the 95-percent confidence interval) for arsenic, 

cadmium, chromium, copper, iron, manganese, and zinc; 

20 percent for nickel; and 185 percent for lead (likely because 

of the low certified concentrations in the standard). No adjustments were made to trace-element concentrations in biota 

samples based on recovery efficiencies.

Procedural blanks for biota consisted of undiluted aliquots of the same reagents used to digest and reconstitute tissue of aquatic insects. Analytical results of procedural blanks 

for biota (table 20) are reported as a liquid-phase concentration, in micrograms per milliliter. A procedural blank was prepared and analyzed concurrently with biota samples for each 

site. Concentrations of trace elements in all procedural blanks 

were less than the MRL; therefore, no adjustments to the data 

were necessary.

Statistical Summaries of Data

Statistical summaries of long-term water-quality, bedsediment, and biological data for the Clark Fork Basin are 

listed in tables 21 through 23 for the period of record at each 

site. The summaries include the period of record; number 

of samples; and maximum, minimum, mean, and median 

concentrations.

Statistical summaries of water-quality data (table 21) are 

based on results of cross-section samples collected periodically by the USGS for the long-term monitoring program in 

the Clark Fork Basin during the period of record for each site. 

The summaries do not include data for supplemental samples 

collected at selected sites that targeted high-flow conditions or 

maintenance drawdowns of Milltown Reservoir, which might 

disproportionately skew the long-term statistics relative to the 

other sites in the network. Sample results at sites that have 

been sampled for other projects can be accessed in the NWIS 

database at https://waterdata.usgs.gov/mt/nwis/qw. Statistical 

summaries of long-term bed-sediment (table 22) and biological data (table 23) are based on results of samples collected 

once each year during the indicated years. Because not all sites 

were sampled for bed sediment and biota every year, the data 

for some sites do not represent a consecutive annual record. 

Statistical summaries are not presented for discontinued sites.

Statistics for long-term bed-sediment data (table 22) are 

based on the mean trace-element concentrations determined 

for each year from the mean of the analyses of composite samples; therefore, the number of samples for bed sediment represents the number of years that the constituent was analyzed. 

The number of samples for arsenic for bed sediment is smaller 

than the number for other trace elements because sampling for 

arsenic began in September 2003. In addition, the number of 

samples analyzed for silver in bed sediment is smaller because 

analysis for this constituent was discontinued in 2004.

In contrast, statistics for long-term biological data 

(table 23) are based on individual analyses for each composite 

sample collected rather than on a single mean concentration 

for each year. Differences in the number of composited insect 

samples among species reflect differences in species abundance, both within and between sites and among years. As a 

result, the statistics for insects describe a wider range of variation in trace-element concentrations than would be evident 

if results from individual composite samples were averaged. 

Also, the number of samples for arsenic in insect samples 

is smaller than the number for other trace elements because 

sampling for arsenic began in September 2003. The abundance 

of aquatic insects at a site in a given year limits the biomass of 

the sample, which in turn, may result in varied MRLs. When 

MRLs vary among years, differences in concentration with 

time are difficult to determine, especially when a large percentage of the samples have concentrations less than MRLs.

The presence or absence of insect species at a given site 

can vary among years and may result in different taxa being 

analyzed in the long-term period of record. Because Hydropsyche insects were not sorted to the species level during 

1986–89, statistics for sites sampled during those years are 

based on the results of all Hydropsyche species combined. At 

some sites, statistics for the Hydropsyche morosa group are 

based on the combined results for two or more species because 

these samples could not clearly be identified to the species 

level, but the individual insects had morosa characteristics.
14 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

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for the examination of water and wastewater (20th ed.): 

Washington, D.C., American Public Health Association, 

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Data
20 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2016 through September 2017.

[hh, hours; mm, minutes; ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, 

nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; E, estimated; <, less than laboratory reporting level; μg/L, microgram 

per liter; mm, millimeter; ton/d, ton per day; --, no data]

12323230—Blacktail Creek at Harrison Avenue, at Butte

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, 

(standard 

units)

Specific 

conductance 

(μS/cm)

Water 

temperature 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/17/2016 0915 13 7.5 209 5.5 25 83.7 23.8 5.91

03/20/2017 1015 34 7.6 198 2.0 E3.9 76.5 21.7 5.40

04/17/2017 0840 19 7.6 266 5.0 E2.3 98.0 27.9 6.88

05/08/2017 0855 21 7.6 217 5.0 E3.5 84.5 24.1 5.88

05/22/2017 0945 43 7.5 207 8.0 E6.3 76.3 21.8 5.34

06/12/2017 0850 15 7.5 239 8.5 E5.4 93.7 27.0 6.41

07/10/2017 0845 7.7 7.6 296 11.5 E3.2 120 34.6 8.10

08/14/2017 0830 4.1 7.6 343 10.0 <2.0 135 38.6 9.37

Date

Nitrate plus 

nitrite, 

filtered 

(mg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

10/17/2016 0.58 0.040 0.11 4.2 20.7 90.9 1,370 0.240 6.23

03/20/2017 0.23 0.034 0.08 4.5 6.6 322 778 0.256 0.89

04/17/2017 0.39 <0.030 0.05 2.9 3.7 233 448 0.110 0.33

05/08/2017 0.32 <0.030 0.05 4.7 6.4 255 621 0.148 0.56

05/22/2017 0.15 <0.030 0.07 6.5 9.2 211 720 0.219 1.02

06/12/2017 0.50 <0.030 0.05 3.9 5.8 394 880 0.224 0.71

07/10/2017 0.92 <0.030 0.03 2.1 2.9 185 405 0.105 0.28

08/14/2017 0.96 <0.030 0.03 2.3 3.2 85.2 236 0.050 0.21

Date

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc,

 unfiltered 

recoverable 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

10/17/2016 24.7 67.1 7.2 36 2.5 4.1 94 30 1.1

03/20/2017 36.7 50.0 3.0 5 3.7 4.7 78 9 0.83

04/17/2017 31.8 35.9 2.3 3 2.3 2.9 84 3 0.15

05/08/2017 38.9 48.0 2.1 4 3.3 4.1 90 6 0.34

05/22/2017 27.7 48.1 2.6 6 4.7 5.8 82 10 1.2

06/12/2017 34.8 53.0 <2.0 <6 5.0 6.2 85 7 0.28

07/10/2017 33.1 38.6 <2.0 2 4.2 4.8 85 2 0.04

08/14/2017 33.8 43.3 2.4 4 2.6 3.0 78 1 0.01
Data 21

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2016 through September 2017.—Continued

[hh, hours; mm, minutes; ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, 

nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; E, estimated; <, less than laboratory reporting level; μg/L, microgram 

per liter; mm, millimeter; ton/d, ton per day; --, no data]

12323250—Silver Bow Creek below Blacktail Creek, at Butte

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, 

(standard 

units)

Specific 

conductance 

(μS/cm)

Water 

temperature 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/17/2016 1045 24 7.6 406 6.0 E18 143 39.9 10.6

03/20/2017 1155 48 7.7 319 3.0 E4.0 114 32.3 8.16

04/17/2017 1015 34 7.8 424 5.5 E2.4 149 41.6 10.8

05/08/2017 1025 37 7.8 373 8.0 E4.2 129 37.1 8.85

05/22/2017 1125 58 7.8 325 10.0 E5.7 109 31.3 7.52

06/12/2017 1030 30 8.2 420 10.5 E5.3 147 41.4 10.7

07/10/2017 1015 21 8.0 550 15.0 <2.0 187 52.5 13.5

08/14/2017 1005 18 7.8 575 11.0 <2.0 187 52.3 13.6

Date

Nitrate plus 

nitrite, 

filtered 

(mg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

10/17/2016 0.97 0.100 0.19 6.0 18.5 54.3 961 0.390 9.40

03/20/2017 0.59 0.053 0.14 5.7 12.5 250 728 0.315 2.12

04/17/2017 0.96 <0.090 0.12 5.0 8.8 147 426 0.137 1.03

05/08/2017 1.01 0.052 0.10 5.9 10.1 178 575 0.189 1.82

05/22/2017 0.51 0.060 0.13 7.3 14.2 157 716 0.277 3.78

06/12/2017 0.87 0.066 0.12 5.2 10.2 202 658 0.666 1.47

07/10/2017 1.00 0.083 0.10 4.3 6.4 49.3 167 0.139 0.53

08/14/2017 1.00 <0.030 0.11 4.1 6.5 22.8 93.7 0.141 0.67

Date

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

10/17/2016 58.3 120 45.3 90 3.3 5.0 98 22 1.4

03/20/2017 78.6 101 17.5 29 4.1 5.5 77 9 1.2

04/17/2017 83.7 102 24.9 32 3.0 4.1 79 7 0.65

05/08/2017 61.1 85.5 16.7 25 3.8 4.8 86 8 0.80

05/22/2017 42.5 79.0 15.7 33 4.6 6.4 83 12 1.9

06/12/2017 59.5 82.3 14.5 30 4.9 6.5 91 7 0.56

07/10/2017 52.6 65.2 28.4 36 4.6 5.4 70 2 0.11

08/14/2017 58.5 72.9 <2.0 50 3.5 3.8 84 2 0.10
22 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2016 through September 2017.—Continued

[hh, hours; mm, minutes; ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, 

nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; E, estimated; <, less than laboratory reporting level; μg/L, microgram 

per liter; mm, millimeter; ton/d, ton per day; --, no data]

12323600—Silver Bow Creek at Opportunity

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, 

(standard 

units)

Specific 

conductance 

(μS/cm)

Water 

temperature

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/17/2016 1215 43 8.5 472 6.0 E5.4 183 55.2 11.0

03/20/2017 1330 93 8.0 346 3.5 E10 127 38.0 7.77

04/17/2017 1145 79 8.5 419 5.5 E4.5 146 43.7 9.03

05/08/2017 1155 111 8.5 320 7.0 E9.4 122 37.8 6.75

05/22/2017 1255 139 8.5 308 10.5 E9.0 111 34.0 6.47

06/12/2017 1205 121 8.6 332 10.5 E4.2 128 38.9 7.42

07/10/2017 1145 61 8.5 453 16.0 <2.0 163 48.6 10.1

08/14/2017 1145 21 8.5 589 16.5 E3.4 206 60.2 13.6

Date

Potassium, 

filtered 

(mg/L)

Sodium, 

filtered 

(mg/L)

Alkalinity, 

filtered, lab 

(mg/L as CaCO3)

Chloride, 

filtered 

(mg/L)

Fluoride, 

filtered 

(mg/L)

Silica, 

filtered 

(mg/L)

Sulfate, 

filtered 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

10/17/2016 4.53 21.8 98.4 37.4 0.42 23.4 75.7 0.100 0.22

03/20/2017 4.54 17.0 82.0 22.1 0.28 22.4 50.1 0.165 0.37

04/17/2017 3.69 22.2 92.9 28.1 0.34 19.8 65.7 0.188 0.32

05/08/2017 2.83 14.6 87.2 13.7 0.26 21.2 46.0 0.095 0.26

05/22/2017 2.92 14.1 83.7 13.3 0.25 23.8 44.3 0.111 0.28

06/12/2017 2.59 14.9 93.9 16.5 0.24 21.9 44.5 0.089 0.18

07/10/2017 4.20 25.3 113 28.5 0.37 24.5 68.6 0.147 0.18

08/14/2017 5.79 34.5 122 43.6 0.50 24.6 105 0.145 0.31

Date

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

10/17/2016 6.8 13.7 20.8 287 0.130 1.80 49.6 111

03/20/2017 13.1 26.5 165 877 0.346 3.71 83.0 157

04/17/2017 11.1 18.7 66.2 355 0.177 1.41 111 137

05/08/2017 9.1 18.8 58.8 594 0.178 2.46 48.8 125

05/22/2017 13.1 23.5 115 638 0.332 2.95 42.7 109

06/12/2017 8.9 12.8 54.3 318 0.164 1.15 44.2 68.0

07/10/2017 10.4 13.6 25.1 105 0.117 0.53 36.4 56.5

08/14/2017 9.3 16.5 <10.0 308 0.139 1.67 34.2 115

Date

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Organic 

carbon, 

filtered 

(mg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 mm)

Sediment, 

suspended (mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

10/17/2016 28.0 54 5.1 5.3 3.64 93 8 0.92

03/20/2017 56.6 93 7.2 8.9 5.77 85 22 5.5

04/17/2017 47.4 80 4.9 5.9 5.35 90 10 2.1

05/08/2017 23.0 59 6.3 7.4 7.96 89 23 6.9

05/22/2017 26.6 65 8.2 9.5 9.07 89 19 7.1

06/12/2017 17.6 30 6.7 7.0 7.38 93 7 2.3

07/10/2017 18.7 29 8.3 9.1 5.98 91 3 0.49

08/14/2017 21.4 48 7.6 7.9 4.04 85 8 0.46
Data 23

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2016 through September 2017.—Continued

[hh, hours; mm, minutes; ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, 

nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; E, estimated; <, less than laboratory reporting level; μg/L, microgram 

per liter; mm, millimeter; ton/d, ton per day; --, no data]

12323670—Mill Creek near Anaconda

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, 

(standard 

units)

Specific 

conductance 

(μS/cm)

Water 

temperature 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/17/2016 1610 17 7.9 158 6.0 <2.0 78.3 21.7 5.87

03/20/2017 1630 37 7.7 125 3.0 E4.9 54.2 15.3 3.91

04/17/2017 1455 30 7.8 144 7.5 E2.5 60.4 16.6 4.63

05/08/2017 1515 120 7.6 84 8.5 E5.5 35.4 10.4 2.31

05/22/2017 1620 78 7.9 102 11.5 E3.4 42.7 12.3 2.91

06/12/2017 1535 119 7.7 82 8.0 E2.6 35.5 10.4 2.31

07/10/2017 1445 55 7.9 106 14.0 <2.0 48.4 14.0 3.25

08/14/2017 1545 21 7.9 160 14.0 <2.0 74.9 20.6 5.69

Date

Potassium, 

filtered 

(mg/L)

Sodium, 

filtered 

(mg/L)

Alkalinity, 

filtered, lab 

(mg/L as CaCO3)

Chloride, 

filtered 

(mg/L)

Fluoride, 

filtered 

(mg/L)

Silica, 

filtered 

(mg/L)

Sulfate, 

filtered 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

10/17/2016 0.84 3.96 73.6 0.42 0.33 12.8 7.98 0.050 0.07

03/20/2017 0.79 5.11 54.5 0.47 0.35 16.0 8.93 0.043 0.10

04/17/2017 0.71 5.72 62.6 0.41 0.31 15.5 8.69 0.038 0.10

05/08/2017 0.63 3.70 36.8 0.29 0.27 14.7 4.48 0.038 0.15

05/22/2017 0.62 3.66 46.0 0.25 0.28 14.8 4.83 0.038 0.09

06/12/2017 0.45 2.45 37.5 0.17 0.29 10.9 3.54 0.032 0.07

07/10/2017 0.52 2.64 48.9 0.17 0.29 10.0 4.44 0.037 0.06

08/14/2017 0.66 3.40 75.1 0.24 0.32 12.2 6.20 <0.030 0.06

Date

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

10/17/2016 1.5 1.9 70.6 111 0.090 0.25 8.62 11.1

03/20/2017 4.6 6.1 128 332 0.256 0.80 5.99 12.5

04/17/2017 -- -- 43.4 178 0.280 0.57 6.62 12.1

05/08/2017 4.2 8.1 70.3 395 0.221 1.57 6.37 23.9

05/22/2017 3.2 4.6 43.6 162 0.170 0.65 4.72 10.4

06/12/2017 2.3 3.4 34.0 169 0.180 0.48 5.26 11.0

07/10/2017 2.0 3.0 49.1 132 0.118 0.40 8.73 14.0

08/14/2017 1.5 2.2 80.0 147 0.119 0.36 10.0 13.7

Date

Zinc, 

filtered

 (μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Organic 

carbon, 

filtered 

(mg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

10/17/2016 <2.0 2 13.2 13.6 1.59 75 1 0.05

03/20/2017 2.5 4 18.0 19.9 4.06 97 2 0.2

04/17/2017 <2.0 3 18.8 20.5 2.89 81 4 0.32

05/08/2017 2.7 7 15.4 17.6 5.10 75 14 4.5

05/22/2017 <2.0 3 17.6 18.3 4.08 86 4 0.84

06/12/2017 <2.0 3 10.1 11.3 2.58 76 6 1.9

07/10/2017 <2.0 <2 13.3 14.2 2.11 60 3 0.45

08/14/2017 <2.0 <2 15.9 16.0 1.40 62 2 0.11
24 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2016 through September 2017.—Continued

[hh, hours; mm, minutes; ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, 

nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; E, estimated; <, less than laboratory reporting level; μg/L, microgram 

per liter; mm, millimeter; ton/d, ton per day; --, no data]

12323700—Mill Creek at Opportunity

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, 

(standard 

units)

Specific 

conductance 

(μS/cm)

Water 

temperature, 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/17/2016 1700 5.2 7.9 181 7.0 <2.0 83.3 23.2 6.17

03/20/2017 1720 31 7.8 138 3.0 E4.5 59.6 16.8 4.29

04/17/2017 1545 27 8.1 159 6.5 <2.0 65.9 18.2 4.99

05/08/2017 1620 79 7.6 92 9.0 E8.9 39.2 11.4 2.61

05/22/2017 1725 64 8.0 111 12.5 E3.7 45.8 13.3 3.08

06/12/2017 1645 62 7.8 86 8.5 E4.0 37.1 10.9 2.41

07/10/2017 1540 27 8.0 115 15.0 <2.0 52.0 15.0 3.53

08/14/2017 1700 4.8 8.2 177 15.0 <2.0 79.7 22.2 5.91

Date

Potassium, 

filtered 

(mg/L)

Sodium, 

filtered 

(mg/L)

Alkalinity, 

filtered, lab 

(mg/L as CaCO3)

Chloride, 

filtered 

(mg/L)

Fluoride, 

filtered 

(mg/L)

Silica, 

filtered 

(mg/L)

Sulfate, 

filtered 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

10/17/2016 0.86 5.23 76.2 0.57 0.35 13.2 15.5 0.070 0.07

03/20/2017 0.81 5.66 56.4 0.54 0.35 15.1 13.1 0.045 0.12

04/17/2017 0.75 6.40 65.3 0.49 0.32 15.3 13.0 0.035 0.10

05/08/2017 0.67 4.00 38.6 0.33 0.29 14.8 6.24 0.037 0.31

05/22/2017 0.65 4.06 48.1 0.30 0.29 14.5 6.88 0.043 0.10

06/12/2017 0.47 2.57 38.1 0.19 0.29 10.8 4.58 0.040 0.13

07/10/2017 0.55 3.10 51.2 0.22 0.30 10.2 6.30 0.039 0.08

08/14/2017 0.79 4.59 77.1 0.38 0.34 12.3 11.8 0.038 0.05

Date

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

10/17/2016 1.9 2.1 77.9 115 0.122 0.19 6.93 7.9

03/20/2017 4.6 6.7 102 360 0.249 1.08 4.05 17.5

04/17/2017 3.1 4.3 44.5 164 0.089 0.53 4.33 11.3

05/08/2017 4.6 14.0 67.6 811 0.241 3.45 7.26 61.7

05/22/2017 3.5 6.1 43.6 220 0.215 0.94 4.54 13.9

06/12/2017 2.7 5.3 39.3 325 0.209 1.17 5.68 16.5

07/10/2017 2.4 3.6 62.5 158 0.174 0.53 6.30 13.4

08/14/2017 1.8 2.2 75.8 132 0.134 0.26 5.62 7.3

Date

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Organic 

carbon, 

filtered 

(mg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

10/17/2016 2.9 3 21.0 21.9 2.44 61 1 0.01

03/20/2017 2.7 6 19.8 23.0 3.52 61 5 0.41

04/17/2017 <2.0 3 21.2 23.6 2.44 78 4 0.3

05/08/2017 2.3 14 18.4 26.0 4.86 64 31 6.6

05/22/2017 <2.0 6 20.9 23.3 3.59 71 8 1.4

06/12/2017 <2.0 5 13.2 15.5 2.61 56 12 2.0

07/10/2017 <2.0 2 20.6 21.5 2.01 77 3 0.22

08/14/2017 <2.0 <2 30.4 30.9 1.86 56 3 0.04
Data 25

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2016 through September 2017.—Continued

[hh, hours; mm, minutes; ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, 

nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; E, estimated; <, less than laboratory reporting level; μg/L, microgram 

per liter; mm, millimeter; ton/d, ton per day; --, no data]

12323710—Willow Creek near Anaconda

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, 

(standard 

units)

Specific 

conductance 

(μS/cm)

Water 

temperature, 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/17/2016 1425 2.1 7.7 121 5.0 E2.2 46.5 15.5 1.90

03/20/2017 1525 10 7.6 107 2.0 E12 42.2 14.1 1.71

04/17/2017 1345 11 7.7 100 4.0 E7.4 36.8 12.2 1.52

05/08/2017 1355 33 7.5 70 6.5 E11 24.1 8.06 0.96

05/22/2017 1505 35 7.6 73 10.0 E9.9 24.7 8.24 1.00

06/12/2017 1420 14 7.7 92 7.0 E3.0 35.4 12.1 1.29

07/10/2017 1340 5.0 7.8 105 12.0 <2.0 40.7 13.8 1.50

08/14/2017 1420 2.1 7.9 109 13.0 <2.0 40.3 13.7 1.50

Date

Potassium, 

filtered 

(mg/L)

Sodium, 

filtered 

(mg/L)

Alkalinity, 

filtered, lab 

(mg/L as CaCO3)

Chloride, 

filtered 

(mg/L)

Fluoride, 

filtered 

(mg/L)

Silica, 

filtered 

(mg/L)

Sulfate, 

filtered 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

10/17/2016 1.09 7.17 51.2 0.85 0.07 25.4 8.34 0.040 0.06

03/20/2017 1.05 6.23 42.1 0.67 0.07 25.4 10.1 <0.030 0.09

04/17/2017 0.91 6.06 38.3 0.52 0.07 26.6 8.47 <0.030 0.05

05/08/2017 0.72 4.46 29.2 0.34 0.06 23.4 4.75 <0.030 0.18

05/22/2017 0.78 4.33 30.2 0.32 0.06 25.3 4.92 <0.030 0.08

06/12/2017 0.76 4.84 40.0 0.27 0.06 23.4 5.30 <0.030 0.05

07/10/2017 0.89 5.83 46.6 0.29 0.07 25.1 5.60 <0.030 0.04

08/14/2017 0.99 6.54 48.1 0.34 0.07 26.7 5.75 0.040 0.04

Date

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

10/17/2016 2.9 3.3 119 203 0.200 0.37 12.5 17.2

03/20/2017 3.7 5.3 194 807 0.347 1.17 20.9 43.2

04/17/2017 3.0 3.7 178 526 0.240 0.64 10.6 20.2

05/08/2017 3.4 6.2 96.5 666 0.256 1.85 13.6 55.8

05/22/2017 3.2 4.7 160 469 0.311 1.21 7.89 24.8

06/12/2017 2.1 2.7 75.1 207 0.190 0.46 9.76 15.2

07/10/2017 2.0 2.4 89.7 191 0.220 0.45 7.44 14.1

08/14/2017 1.7 2.4 107 247 0.259 0.58 9.93 13.8

Date

Zinc, 

filtered

 (μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Organic 

carbon, 

filtered 

(mg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

10/17/2016 <2.0 <2 17.6 18.3 4.21 94 2 0.01

03/20/2017 2.3 4 18.1 20.1 6.65 92 9 0.25

04/17/2017 <2.0 3 17.2 19.0 5.94 84 5 0.14

05/08/2017 <2.0 8 15.2 17.9 7.19 69 26 2.3

05/22/2017 <2.0 5 15.8 16.8 7.06 62 17 1.60

06/12/2017 <2.0 <2 14.2 13.9 4.49 85 3 0.11

07/10/2017 <2.0 <2 18.6 18.7 4.63 93 3 0.04

08/14/2017 <2.0 <2 16.9 22.8 0.25 93 3 0.02
26 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2016 through September 2017.—Continued

[hh, hours; mm, minutes; ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, 

nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; E, estimated; <, less than laboratory reporting level; μg/L, microgram 

per liter; mm, millimeter; ton/d, ton per day; --, no data]

12323720—Willow Creek at Opportunity

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, 

(standard 

units)

Specific 

conductance 

(μS/cm)

Water 

temperature, 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/17/2016 1300 6.8 8.1 262 7.0 E4.1 118 34.9 7.58

03/20/2017 1410 16 7.9 212 4.0 E11 86.2 25.9 5.24

04/17/2017 1230 14 7.9 181 5.5 E8.1 72.3 21.8 4.30

05/08/2017 1235 27 7.8 128 7.0 E10 50.4 15.6 2.75

05/22/2017 1340 28 8.0 153 12.0 E6.7 60.5 18.6 3.43

06/12/2017 1245 21 8.0 254 11.0 E4.1 111 32.5 7.31

07/10/2017 1225 11 8.0 275 13.0 E2.6 126 37.0 8.04

08/14/2017 1240 7.1 8.2 259 14.0 E2.9 113 32.7 7.57

Date

Potassium, 

filtered 

(mg/L)

Sodium, 

filtered 

(mg/L)

Alkalinity, 

filtered, lab 

(mg/L as CaCO3)

Chloride, 

filtered 

(mg/L)

Fluoride, 

filtered 

(mg/L)

Silica, 

filtered 

(mg/L)

Sulfate, 

filtered 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

10/17/2016 1.58 10.6 113 2.09 0.36 24.3 21.0 0.090 0.05

03/20/2017 1.88 9.84 81.3 2.17 0.22 24.2 23.3 <0.030 0.12

04/17/2017 1.12 8.59 70.9 1.35 0.19 25.1 16.8 <0.030 0.11

05/08/2017 1.06 6.42 51.6 0.81 0.12 24.4 10.3 <0.030 0.13

05/22/2017 1.03 6.92 63.1 0.97 0.17 24.9 11.4 0.032 0.09

06/12/2017 1.50 9.24 116 1.17 0.43 26.1 13.0 0.035 0.09

07/10/2017 1.23 7.96 128 1.47 0.45 23.6 13.3 <0.030 0.05

08/14/2017 1.36 8.73 112 1.88 0.41 21.8 18.0 <0.030 0.05

Date

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

10/17/2016 2.3 4.2 42.9 247 0.229 1.12 20.8 29.5

03/20/2017 5.2 10.0 130 626 0.328 2.20 60.2 75.6

04/17/2017 3.8 9.0 92.8 500 0.246 2.32 33.3 50.9

05/08/2017 6.6 12.5 97.7 542 0.350 2.11 31.7 50.9

05/22/2017 8.8 13.0 89.0 340 0.332 1.52 21.6 32.7

06/12/2017 6.3 8.3 62.9 258 0.215 1.13 30.2 40.5

07/10/2017 3.6 5.6 46.9 172 0.203 0.84 19.4 23.6

08/14/2017 2.3 4.4 27.0 202 0.185 1.06 10.1 15.6

Date

Zinc, 

filtered

 (μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Organic 

carbon, 

filtered 

(mg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

10/17/2016 3.8 5 18.3 20.4 2.85 98 5 0.09

03/20/2017 4.0 11 23.3 28.0 5.75 98 16 0.69

04/17/2017 3.0 11 17.6 20.7 4.95 93 13 0.49

05/08/2017 4.8 12 21.8 24.4 7.79 91 19 1.4

05/22/2017 4.1 10 31.1 32.5 7.51 94 11 0.83

06/12/2017 4.4 8 72.8 72.4 7.72 96 5 0.28

07/10/2017 3.4 6 67.2 67.9 5.27 91 5 0.15

08/14/2017 <2.0 4 15.9 17.8 2.90 98 5 0.1
Data 27

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2016 through September 2017.—Continued

[hh, hours; mm, minutes; ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, 

nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; E, estimated; <, less than laboratory reporting level; μg/L, microgram 

per liter; mm, millimeter; ton/d, ton per day; --, no data]

12323750—Silver Bow Creek at Warm Springs

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, 

(standard 

units)

Specific 

conductance 

(μS/cm)

Water 

temperature, 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/18/2016 1035 35 8.6 495 6.0 E2.3 204 57.1 14.8

03/21/2017 0930 161 8.7 407 3.5 E6.4 160 46.3 10.7

04/18/2017 1035 121 8.3 431 6.0 E3.8 165 48.1 10.9

05/09/2017 1045 189 9.0 324 8.0 E5.1 123 36.4 7.87

05/23/2017 1035 249 9.2 341 11.0 E3.5 132 39.9 7.80

06/13/2017 0945 385 7.9 406 9.5 E7.7 167 48.4 11.1

07/11/2017 1010 89 9.2 317 14.0 E2.8 134 39.3 8.60

08/15/2017 1150 29 9.4 418 15.0 <2.0 180 52.2 12.0

Date

Potassium, 

filtered 

(mg/L)

Sodium, 

filtered 

(mg/L)

Alkalinity, 

filtered, lab 

(mg/L as CaCO3)

Chloride, 

filtered 

(mg/L)

Fluoride, 

filtered 

(mg/L)

Silica, 

filtered 

(mg/L)

Sulfate, 

filtered 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

10/18/2016 4.09 21.2 106 22.1 0.80 13.4 111 <0.030 0.05

03/21/2017 3.91 18.7 90.3 23.2 0.55 11.5 75.2 0.036 0.15

04/18/2017 3.94 18.4 97.7 21.5 0.58 14.1 79.5 <0.030 0.12

05/09/2017 2.97 14.5 77.0 15.6 0.47 15.3 55.6 0.037 0.14

05/23/2017 2.88 14.2 89.7 15.6 0.43 15.6 57.8 0.103 0.21

06/13/2017 3.76 15.5 98.1 10.2 0.54 17.1 88.1 0.065 0.21

07/11/2017 1.91 11.7 89.2 8.97 0.48 13.5 56.8 <0.030 0.05

08/15/2017 2.46 15.2 102 11.9 0.63 17.8 94.8 <0.090 0.04

Date

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

10/18/2016 1.9 3.1 16.9 105 0.030 0.45 5.03 66.0

03/21/2017 4.1 12.8 52.1 391 0.213 2.88 33.8 88.1

04/18/2017 2.8 7.6 31.2 274 0.127 1.60 116 150

05/09/2017 4.8 9.6 39.2 365 0.151 1.81 86.5 134

05/23/2017 9.1 13.5 31.5 246 0.144 1.25 77.3 107

06/13/2017 8.2 16.1 103 583 0.391 3.15 110 146

07/11/2017 4.1 5.2 30.0 101 0.115 0.39 39.2 57.8

08/15/2017 2.4 2.8 24.7 85.3 0.088 0.29 31.0 64.9

Date

Zinc, 

filtered

 (μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Organic 

carbon, 

filtered 

(mg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

10/18/2016 <2.0 4 17.8 18.8 4.04 84 1 0.1

03/21/2017 4.5 22 11.7 14.9 3.84 95 10 4.3

04/18/2017 3.8 15 10.9 13.9 4.76 92 7 2.3

05/09/2017 2.2 12 18.0 20.7 5.23 82 12 6.1

05/23/2017 12 23 17.4 19.5 6.08 89 5 3.4

06/13/2017 7.1 21 47.5 48.0 9.29 83 20 21

07/11/2017 <2.0 3 26.8 27.6 4.89 90 2 0.48

08/15/2017 <6.0 2 25.9 26.9 4.71 35 6 0.46
28 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2016 through September 2017.—Continued

[hh, hours; mm, minutes; ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, 

nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; E, estimated; <, less than laboratory reporting level; μg/L, microgram 

per liter; mm, millimeter; ton/d, ton per day; --, no data]

12323760—Warm Springs Creek near Anaconda

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, 

(standard 

units)

Specific 

conductance 

(μS/cm)

Water 

temperature, 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/18/2016 0840 64 8.2 262 4.5 <2.0 132 38.7 8.56

04/18/2017 0845 52 8.4 275 4.0 E2.1 133 39.1 8.65

05/09/2017 0855 123 8.2 213 5.0 E3.0 103 31.6 5.92

05/23/2017 0840 135 8.2 200 6.0 E2.6 95.6 29.4 5.39

07/11/2017 0820 156 8.3 202 9.5 <2.0 98.6 29.9 5.82

08/15/2017 0905 78 8.4 251 8.5 <2.0 122 36.3 7.66

Date

Potassium, 

filtered 

(mg/L)

Sodium, 

filtered 

(mg/L)

Alkalinity, 

filtered, lab 

(mg/L as CaCO3)

Chloride, 

filtered 

(mg/L)

Fluoride, 

filtered 

(mg/L)

Silica, 

filtered 

(mg/L)

Sulfate, 

filtered 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

10/18/2016 1.36 3.42 120 1.21 0.41 11.1 16.9 0.035 0.04

04/18/2017 1.24 3.60 126 1.43 0.39 10.5 15.4 <0.030 0.05

05/09/2017 1.03 2.15 98.5 0.84 0.33 9.94 10.8 <0.030 0.06

05/23/2017 0.89 1.95 92.6 0.78 0.31 9.47 9.99 <0.030 0.06

07/11/2017 0.95 2.16 88.5 0.87 0.38 9.60 14.3 0.034 0.05

08/15/2017 1.19 2.90 114 1.22 0.39 11.1 13.8 0.040 0.04

Date

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

10/18/2016 0.70 1.3 4.6 37.9 0.020 0.11 0.68 1.9

04/18/2017 0.68 1.6 <5.0 58.1 <0.020 0.20 0.50 2.9

05/09/2017 1.3 3.4 12.8 154 0.022 0.42 1.18 8.7

05/23/2017 1.00 3.7 <10.0 118 <0.020 0.35 1.28 7.4

07/11/2017 0.97 2.2 <10.0 63.2 <0.020 0.18 3.86 8.4

08/15/2017 0.70 1.8 <10.0 56.1 <0.020 0.19 0.92 4.2

Date

Zinc, 

filtered

 (μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Organic 

carbon, 

filtered 

(mg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

10/18/2016 <2.0 3 1.9 2.1 0.90 75 2 0.35

04/18/2017 <2.0 2 2.0 2.3 0.83 70 4 0.56

05/09/2017 <2.0 6 1.6 2.1 3.19 74 9 3.0

05/23/2017 <2.0 6 2.1 2.3 2.31 74 7 2.6

07/11/2017 4.4 10 2.1 2.4 1.56 79 2 0.84

08/15/2017 <2.0 3 1.9 2.1 1.04 63 2 0.42
Data 29

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2016 through September 2017.—Continued

[hh, hours; mm, minutes; ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, 

nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; E, estimated; <, less than laboratory reporting level; μg/L, microgram 

per liter; mm, millimeter; ton/d, ton per day; --, no data]

12323770—Warm Springs Creek at Warm Springs

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, 

(standard 

units)

Specific 

conductance 

(μS/cm)

Water 

temperature, 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/18/2016 0950 28 8.2 338 4.5 <2.0 171 51.2 10.5

03/21/2017 0845 46 8.1 333 3.0 <2.0 170 50.7 10.5

04/18/2017 0955 36 8.2 346 5.0 <2.0 168 50.1 10.5

05/09/2017 1005 84 8.1 262 6.0 E6.2 128 39.5 7.17

05/23/2017 0950 86 8.2 257 8.0 E3.7 122 37.5 6.80

06/13/2017 1055 366 7.8 173 7.0 E13 81.5 25.0 4.62

07/11/2017 0925 97 8.0 232 11.0 E2.7 112 34.2 6.46

08/15/2017 1035 37 8.3 306 10.5 <2.0 148 44.8 8.87

Date

Potassium, 

filtered 

(mg/L)

Sodium, 

filtered 

(mg/L)

Alkalinity, 

filtered, lab 

(mg/L as CaCO3)

Chloride, 

filtered 

(mg/L)

Fluoride, 

filtered 

(mg/L)

Silica, 

filtered 

(mg/L)

Sulfate, 

filtered 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

10/18/2016 1.60 3.96 135 1.58 0.44 11.9 41.3 <0.030 0.04

03/21/2017 1.43 4.09 137 1.84 0.41 10.8 37.6 <0.030 0.06

04/18/2017 1.41 4.14 138 1.70 0.42 10.4 38.6 0.031 0.06

05/09/2017 1.23 2.74 111 1.09 0.36 10.4 21.9 0.030 0.12

05/23/2017 1.11 2.53 109 1.07 0.34 9.54 22.8 <0.030 0.08

06/13/2017 1.32 1.84 61.4 0.87 0.33 9.21 22.6 0.046 0.18

07/11/2017 1.06 2.45 96.1 1.48 0.39 9.84 20.6 0.036 0.07

08/15/2017 1.33 3.44 126 1.42 0.42 11.1 30.1 0.034 0.04

Date

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

10/18/2016 1.7 3.7 13.4 55.4 0.026 0.21 42.2 64.3

03/21/2017 1.9 4.7 13.9 67.7 <0.020 0.29 57.1 77.6

04/18/2017 2.1 4.7 15.2 61.8 <0.020 0.28 46.6 76.9

05/09/2017 4.6 31.0 13.8 389 0.069 2.00 29.2 130

05/23/2017 2.7 11.5 <10.0 167 0.031 1.00 36.2 92.3

06/13/2017 7.1 39.0 28.7 893 0.102 4.58 25.6 111

07/11/2017 2.3 8.3 20.2 128 0.047 0.61 34.3 52.4

08/15/2017 2.1 4.8 14.1 69.6 0.054 0.30 28.1 40.9

Date

Zinc, 

filtered

 (μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Organic 

carbon, 

filtered 

(mg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

10/18/2016 <2.0 2 5.1 5.3 1.10 74 1 0.08

03/21/2017 <2.0 3 4.0 4.3 1.35 78 2 0.25

04/18/2017 <2.0 3 4.0 4.6 1.59 72 3 0.29

05/09/2017 <2.0 13 4.7 7.8 3.07 81 17 3.9

05/23/2017 <2.0 6 4.5 5.7 2.35 74 8 1.9

06/13/2017 4.8 23 6.5 11.3 4.27 70 42 42

07/11/2017 3.0 7 5.2 6.1 1.91 75 3 0.79

08/15/2017 <2.0 3 5.2 5.6 1.14 87 1 0.10
30 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2016 through September 2017.—Continued

[hh, hours; mm, minutes; ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, 

nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; E, estimated; <, less than laboratory reporting level; μg/L, microgram 

per liter; mm, millimeter; ton/d, ton per day; --, no data]

12323800—Clark Fork near Galen

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, 

(standard 

units)

Specific 

conductance 

(μS/cm)

Water 

temperature, 

(°C)

Hardness, 

filtered 

(mg/L as CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/18/2016 1205 80 8.4 434 6.0 190 55.0 12.9

03/21/2017 1115 203 8.5 391 4.5 161 47.3 10.4

04/18/2017 1210 155 8.3 405 7.0 168 49.3 10.9

05/09/2017 1220 278 8.6 286 10.0 119 35.6 7.21

05/23/2017 1215 337 8.9 315 13.0 127 38.5 7.40

06/13/2017 1220 725 7.9 319 9.0 131 38.8 8.37

07/11/2017 1150 186 8.9 273 15.5 123 36.8 7.48

08/15/2017 1400 69 9.0 363 16.5 163 47.7 10.6

Date

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

10/18/2016 0.030 0.04 4.2 5.40 9.60 57.7 0.04 0.29

03/21/2017 0.037 0.14 4.1 12.6 26.8 376 0.127 2.56

04/18/2017 <0.030 0.11 2.9 11.8 23.5 315 0.093 1.77

05/09/2017 0.035 0.16 4.7 17.7 26.1 468 0.117 2.68

05/23/2017 0.076 0.17 6.9 16.2 15.6 288 0.084 1.53

06/13/2017 0.052 0.27 8.0 41.9 66.8 1,270 0.252 5.74

07/11/2017 0.032 0.06 3.9 6.8 17.8 95.5 0.070 0.42

08/15/2017 <0.090 0.05 3.4 5.5 13.7 77.3 0.087 0.43

Date

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

 filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 mm)

Sediment,

 suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

10/18/2016 10.1 25.8 <2.0 4 9.9 12.5 78 1 0.22

03/21/2017 39.5 107 3.9 18 10.0 12.6 84 12 6.6

04/18/2017 74.6 140 3.4 15 9.8 12.7 85 9 3.8

05/09/2017 47.0 142 <2.0 17 14.1 17.3 76 21 16

05/23/2017 49.3 98.7 3.1 19 14.6 16.9 75 9 8.2

06/13/2017 65.8 179 5.4 35 26.3 33.8 55 59 115

07/11/2017 25.6 45.6 <2.0 5 15.5 16.5 90 3 1.5

08/15/2017 23.5 48.9 <6.0 3 15.3 15.8 76 4 0.75
Data 31

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2016 through September 2017.—Continued

[hh, hours; mm, minutes; ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, 

nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; E, estimated; <, less than laboratory reporting level; μg/L, microgram 

per liter; mm, millimeter; ton/d, ton per day; --, no data]

12323840—Lost Creek near Anaconda

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, 

(standard 

units)

Specific 

conductance 

(μS/cm)

Water 

temperature, 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness,

filtered 

(mg/L as CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/18/2016 0745 6.1 8.0 230 5.0 <2.0 114 34.0 7.04

03/21/2017 0745 5.2 8.1 213 3.0 <2.0 104 31.2 6.31

04/18/2017 0745 4.9 8.0 225 4.0 <2.0 107 31.8 6.73

05/09/2017 0735 2.7 7.7 174 5.0 E2.5 82.6 24.9 4.94

05/23/2017 0740 4.8 7.9 183 7.0 E2.7 85.6 26.2 4.91

06/13/2017 0740 35 7.8 139 6.5 23 66.3 20.3 3.81

07/11/2017 0740 4.1 8.0 223 10.0 <2.0 109 33.7 6.11

08/15/2017 0750 9.1 8.2 234 9.0 <2.0 114 34.5 6.73

Date

Potassium, 

filtered 

(mg/L)

Sodium, 

filtered 

(mg/L)

Alkalinity, 

filtered, lab 

(mg/L as CaCO3)

Chloride, 

filtered 

(mg/L)

Fluoride, 

filtered 

(mg/L)

Silica, 

filtered 

(mg/L)

Sulfate, 

filtered 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

10/18/2016 1.46 3.52 111 0.82 0.44 13.0 9.29 0.030 0.03

03/21/2017 1.27 2.73 102 0.75 0.43 11.3 9.95 <0.030 0.06

04/18/2017 1.27 2.95 105 0.79 0.45 11.4 10.2 <0.030 0.06

05/09/2017 1.19 2.35 81.3 0.56 0.35 11.4 7.19 <0.030 0.06

05/23/2017 1.07 2.38 85.6 0.56 0.36 11.1 7.21 <0.030 0.06

06/13/2017 1.38 2.27 63.3 0.56 0.30 10.7 5.77 <0.030 0.27

07/11/2017 1.24 3.18 108 0.74 0.39 11.9 7.41 <0.030 0.03

08/15/2017 1.33 2.92 112 0.72 0.40 12.4 7.97 <0.030 0.04

Date

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

10/18/2016 1.6 2.2 13.6 41.2 0.040 0.13 0.98 1.8

03/21/2017 1.6 5.4 9.4 128 0.023 0.60 0.77 6.7

04/18/2017 1.5 4.6 11.8 108 0.023 0.47 1.17 5.5

05/09/2017 3.3 8.2 14.1 136 0.045 0.67 1.47 5.5

05/23/2017 2.3 5.6 14.1 127 0.033 0.57 1.04 6.0

06/13/2017 7.7 56.6 78.6 2,040 0.234 7.85 7.11 51.2

07/11/2017 2.3 3.6 16.3 50.2 0.054 0.19 1.38 3.1

08/15/2017 1.7 5.0 20.5 129 <0.020 0.43 0.96 7.4

Date

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Organic 

carbon, 

filtered 

(mg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

10/18/2016 <2.0 <2 6.3 6.3 1.40 63 1 0.02

03/21/2017 <2.0 3 3.8 4.3 1.39 78 8 0.11

04/18/2017 <2.0 2 3.7 4.4 1.24 69 5 0.07

05/09/2017 <2.0 4 4.7 5.1 3.78 75 5 0.04

05/23/2017 <2.0 3 4.6 4.9 2.92 78 6 0.08

06/13/2017 2.5 28 10.7 17.1 7.10 39 130 12

07/11/2017 <2.0 <2 7.8 7.6 2.36 64 1 0.01

08/15/2017 <2.0 <2 1.9 7.2 1.40 74 4 0.1
32 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2016 through September 2017.—Continued

[hh, hours; mm, minutes; ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, 

nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; E, estimated; <, less than laboratory reporting level; μg/L, microgram 

per liter; mm, millimeter; ton/d, ton per day; --, no data]

12323850—Lost Creek near Galen

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, 

(standard 

units)

Specific 

conductance 

(μS/cm)

Water 

temperature, 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/18/2016 1125 54 8.1 537 5.0 <2.0 267 77.7 17.6

03/21/2017 1030 45 8.1 621 4.0 E3.2 318 92.8 20.9

04/18/2017 1130 40 8.2 621 5.5 E3.0 308 89.6 20.4

05/09/2017 1140 17 8.3 647 9.5 E2.8 319 94.2 20.3

05/23/2017 1130 16 8.4 705 12.0 E2.2 355 102 24.1

06/13/2017 0850 45 8.0 667 8.5 E13 320 90.3 23.0

07/11/2017 1115 1.7 8.3 593 16.0 E3.1 247 64.2 20.9

08/15/2017 1315 1.7 8.4 594 16.5 <2.0 244 62 21.7

Date

Potassium, 

filtered 

(mg/L)

Sodium, 

filtered 

(mg/L)

Alkalinity, 

filtered, lab 

(mg/L as CaCO3)

Chloride, 

filtered 

(mg/L)

Fluoride, 

filtered 

(mg/L)

Silica, 

filtered 

(mg/L)

Sulfate, 

filtered 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

10/18/2016 2.09 10.3 174 3.96 0.49 15.4 108 <0.030 0.03

03/21/2017 2.44 12.8 192 4.89 0.48 16.5 139 <0.030 0.09

04/18/2017 2.17 12.9 186 4.69 0.46 15.8 137 <0.030 0.08

05/09/2017 2.23 13.1 181 4.60 0.45 16.1 159 <0.030 0.06

05/23/2017 2.46 14.1 193 4.96 0.50 16.6 183 <0.090 0.05

06/13/2017 3.81 17.1 184 5.32 0.58 18.7 167 <0.090 0.19

07/11/2017 3.80 32.2 232 5.90 0.88 23.5 84.1 <0.030 0.04

08/15/2017 3.75 33.3 226 5.47 0.90 20.6 88.4 <0.030 0.05

Date

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

10/18/2016 1.5 2.9 10.2 53.6 <0.020 0.17 5.09 5.90

03/21/2017 1.9 7.7 22.4 193 0.048 0.75 20.3 26.6

04/18/2017 1.3 6.5 16.7 176 0.031 0.74 14.0 22.2

05/09/2017 1.5 5.4 14.6 152 0.039 0.58 19.7 26.2

05/23/2017 3.3 4.0 22.2 97.8 0.087 0.32 25.7 27.3

06/13/2017 5.7 22.4 55.0 760 0.108 2.55 28.8 74.3

07/11/2017 2.2 3.8 24.4 107 0.223 0.32 18.3 22.2

08/15/2017 2.0 3.4 <10.0 66.5 0.048 0.22 4.92 10.9

Date

Zinc, 

filtered

 (μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Organic 

carbon, 

filtered 

(mg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

10/18/2016 <2.0 2 9.3 9.9 1.41 69 2 0.29

03/21/2017 <2.0 5 11 13 1.89 74 13 1.6

04/18/2017 <2.0 4 8.5 9.9 1.99 81 8 0.86

05/09/2017 <2.0 4 8.7 10.1 1.99 63 17 0.78

05/23/2017 <6.0 2 14.2 18.6 2.78 47 24 1.0

06/13/2017 <6.0 13 26.3 26.7 7.18 71 43 5.2

07/11/2017 <2.0 <2 11.5 11.5 3.36 74 6 0.03

08/15/2017 <2.0 <2 7.6 7.4 2.80 65 4 0.02
Data 33

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2016 through September 2017.—Continued

[hh, hours; mm, minutes; ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, 

nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; E, estimated; <, less than laboratory reporting level; μg/L, microgram 

per liter; mm, millimeter; ton/d, ton per day; --, no data]

12324200—Clark Fork at Deer Lodge

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, 

(standard 

units)

Specific 

conductance 

(μS/cm)

Water 

temperature, 

(°C)

Hardness, 

filtered 

(mg/L as CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/18/2016 1320 212 8.4 506 7.0 233 67.9 15.5

03/21/2017 1225 342 8.2 435 5.5 197 58.1 12.5

04/18/2017 1335 295 8.5 470 8.0 202 58.8 13.5

05/09/2017 1345 351 8.3 356 12.0 148 44.6 8.97

05/23/2017 1355 369 8.3 395 15.5 165 48.4 10.7

06/13/2017 1440 1,180 7.9 344 10.0 139 41.1 8.73

07/11/2017 1310 200 8.6 356 18.0 156 47.1 9.31

08/15/2017 1545 83 8.3 477 18.5 204 60.1 13.1

Date

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper,

 unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

10/18/2016 0.030 0.11 5.3 16.3 7.1 214 0.040 1.78

03/21/2017 0.062 0.28 8.1 56.9 19.1 922 0.136 7.37

04/18/2017 0.060 0.17 6.2 26.3 16.3 417 0.081 3.40

05/09/2017 0.060 0.29 9.2 60.3 24.1 883 0.181 6.88

05/23/2017 0.080 0.32 11.3 72.4 18.6 937 0.201 7.76

06/13/2017 0.145 1.86 41.2 538 91.4 9,990 0.753 85.1

07/11/2017 0.061 0.10 10.1 19.0 11.7 158 0.162 1.34

08/15/2017 0.051 0.09 8.4 15.0 16.3 122 0.154 0.97

Date

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

10/18/2016 9.60 70.5 4.3 15 11.7 12.8 87 8 4.6

03/21/2017 29.4 127 7.0 49 9.9 17.6 71 37 34

04/18/2017 28.6 93.0 4.6 23 11.4 14.5 80 16 13

05/09/2017 23.4 157 4.9 47 14.6 22.7 82 36 34

05/23/2017 21.1 127 7.1 57 18.7 27.1 69 37 37

06/13/2017 91.4 714 21.8 434 22.8 91.5 53 469 1,490

07/11/2017 23.9 39.7 3.5 12 17.9 18.7 87 6 3.2

08/15/2017 19.5 44.0 4.9 11 14.8 15.0 86 5 1.1
34 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2016 through September 2017.—Continued

[hh, hours; mm, minutes; ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, 

nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; E, estimated; <, less than laboratory reporting level; μg/L, microgram 

per liter; mm, millimeter; ton/d, ton per day; --, no data]

12324400—Clark Fork above Little Blackfoot River, near Garrison

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, 

(standard 

units)

Specific 

conductance 

(μS/cm)

Water 

temperature, 

(°C)

Hardness, 

filtered 

(mg/L as CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/18/2016 1440 226 8.7 496 8.0 227 65.8 15.2

03/21/2017 1340 370 8.4 435 6.0 197 58.2 12.5

04/18/2017 1440 280 8.8 471 9.5 204 59.3 13.6

05/09/2017 1505 329 8.6 365 14.0 154 46.2 9.28

05/23/2017 1520 387 8.5 409 17.0 171 50.1 11.2

06/13/2017 1640 1,640 8.0 360 11.0 145 40.5 10.6

07/11/2017 1425 205 8.4 394 20.0 173 51.3 11.0

08/15/2017 1700 78 8.5 461 20.0 190 53.9 13.6

Date

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

10/18/2016 0.050 0.08 5.8 13.8 5.6 175 0.060 1.35

03/21/2017 0.054 0.34 8.5 71.2 20.5 1,150 0.170 9.98

04/18/2017 0.048 0.18 7.4 34.5 14.5 450 0.104 3.90

05/09/2017 0.049 0.30 10.5 62.8 15.9 872 0.172 7.87

05/23/2017 0.076 0.32 12.1 75.5 16.5 0 0.220 8.18

06/13/2017 0.102 3.25 36.6 869 105 17,300 0.955 132

07/11/2017 0.082 0.14 11.5 23.6 17.2 224 0.132 2.40

08/15/2017 <0.030 <0.03 8.3 10.2 <10.0 21.9 0.059 0.16

Date

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

 filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

10/18/2016 28.0 81.9 2.6 11 12.9 13.7 88 6 3.7

03/21/2017 34.7 170 6.6 61 10.9 19.0 73 51 51

04/18/2017 29.4 94.8 3.3 27 11.8 15.6 82 20 15

05/09/2017 24.0 166 3.0 49 16.4 22.9 88 37 33

05/23/2017 25.5 141 6.0 58 20.8 28.1 83 38 40

06/13/2017 164 1,060 17.8 800 27.4 138 61 836 3,700

07/11/2017 29.9 58.5 8.4 18 19.6 20.4 74 8 4.4

08/15/2017 2.7 6.4 <2.0 <2 16.8 17.1 89 7 1.5
Data 35

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2016 through September 2017.—Continued

[hh, hours; mm, minutes; ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, 

nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; E, estimated; <, less than laboratory reporting level; μg/L, microgram 

per liter; mm, millimeter; ton/d, ton per day; --, no data]

12324680—Clark Fork at Goldcreek

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, 

(standard 

units)

Specific 

conductance 

(μS/cm)

Water 

temperature, 

(°C)

Hardness, 

filtered 

(mg/L as CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/18/2016 1545 306 8.7 444 8.0 205 60.0 13.5

03/21/2017 1450 617 8.3 352 5.5 155 45.4 10.0

04/18/2017 1535 519 8.8 363 9.0 158 46.4 10.1

05/09/2017 1605 784 8.5 281 13.5 122 36.8 7.39

05/23/2017 1640 1170 8.4 282 15.0 119 35.6 7.23

06/14/2017 0815 3,370 7.9 305 9.5 121 35.1 8.09

07/11/2017 1520 403 8.5 375 20.0 169 51.0 10.1

08/16/2017 0730 161 8.1 442 13.0 191 56.2 12.2

Date

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

10/18/2016 0.040 0.05 4.6 8.5 <4.0 87.2 0.040 0.68

03/21/2017 0.038 0.24 6.1 45.8 49.4 906 0.216 8.03

04/18/2017 <0.030 0.12 4.5 18.6 11.2 354 0.054 2.35

05/09/2017 0.032 0.21 6.3 36.2 27.8 833 0.152 4.89

05/23/2017 0.037 0.20 6.5 34.0 47.0 870 0.220 4.86

06/14/2017 0.102 1.35 30.9 295 106 8,760 0.734 44.1

07/11/2017 0.051 0.09 7.6 14.2 15.8 184 0.094 1.13

08/16/2017 <0.030 0.06 5.0 17.3 16.4 123 0.070 0.71

Date

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

 filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

10/18/2016 10.4 33.0 <2.0 7 9.9 10.4 88 4 3.3

03/21/2017 22.3 122 4.7 42 7.8 13.2 77 37 62

04/18/2017 13.9 58.3 <2.0 17 7.8 9.9 84 16 22

05/09/2017 14.0 121 2.1 35 9.8 13.8 87 36 76

05/23/2017 14.1 95.0 3.2 32 10.6 14.2 74 41 130

06/14/2017 46.6 647 13.4 317 19.3 49.9 60 394 3,590

07/11/2017 18.2 45.6 <6.0 12 13.8 13.8 89 8 8.7

08/16/2017 17.7 53.1 2.5 8 10.8 11.8 85 9 3.9
36 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2016 through September 2017.—Continued

[hh, hours; mm, minutes; ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, 

nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; E, estimated; <, less than laboratory reporting level; μg/L, microgram 

per liter; mm, millimeter; ton/d, ton per day; --, no data]

12331800—Clark Fork near Drummond

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, 

(standard 

units)

Specific 

conductance 

(μS/cm)

Water 

temperature, 

(°C)

Hardness, 

filtered 

(mg/L as CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/19/2016 0805 520 8.2 473 7.0 220 62.6 15.4

03/22/2017 0830 868 8.1 383 6.0 174 50.4 11.8

04/19/2017 0750 742 8.3 391 8.0 171 48.6 12.1

05/10/2017 0805 1120 8.1 282 11.0 124 36.6 8.02

05/24/2017 0745 1,350 8.0 298 13.0 125 36.8 7.92

06/14/2017 0945 5,500 7.8 276 9.5 113 32.7 7.62

07/12/2017 0745 593 8.2 432 17.0 199 58.3 13.0

08/16/2017 0835 241 8.1 542 15.0 244 68.9 17.6

Date

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

10/19/2016 0.030 0.08 2.9 9.4 <4.0 206 0.040 1.37

03/22/2017 <0.030 0.27 5.4 45.4 38.4 1120 0.211 7.67

04/19/2017 <0.030 0.16 4.1 22.8 12.0 553 0.075 4.22

05/10/2017 <0.030 0.26 5.9 37.1 42.6 1,080 0.301 8.18

05/24/2017 0.037 0.28 6.7 46.6 42.5 1,380 0.287 8.74

06/14/2017 0.067 2.20 18.8 330 177 14,000 1.54 78.2

07/12/2017 0.050 0.10 6.6 15.4 11.0 248 0.098 1.53

08/16/2017 <0.030 0.05 4.4 8.3 <10.0 103 0.078 0.59

Date

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

 filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

10/19/2016 9.25 50.4 3.5 13 8.9 9.1 81 10 14

03/22/2017 14.7 142 5.7 55 8.2 14.0 62 60 141

04/19/2017 12.2 90.4 3.7 29 8.2 11.4 72 33 66

05/10/2017 9.33 181 4.7 56 9.4 16.0 80 57 172

05/24/2017 8.96 160 4.7 60 10.4 16.2 54 86 313

06/14/2017 77.0 1,240 14.7 575 26.5 79.1 55 759 11,300

07/12/2017 13.4 60.0 3.6 17 14.0 15.4 85 11 18

08/16/2017 13.7 40.7 3.1 9 11.6 12.2 87 6 3.9
Data 37

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2016 through September 2017.—Continued

[hh, hours; mm, minutes; ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, 

nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; E, estimated; <, less than laboratory reporting level; μg/L, microgram 

per liter; mm, millimeter; ton/d, ton per day; --, no data]

12334550—Clark Fork at Turah Bridge, near Bonner

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, 

(standard 

units)

Specific 

conductance 

(μS/cm)

Water 

temperature, 

(°C)

Hardness, 

filtered 

(mg/L as CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/19/2016 0935 820 8.1 370 7.0 171 47.9 12.4

03/22/2017 1010 2,110 8.0 251 5.0 109 30.8 7.71

04/19/2017 1230 1,670 8.4 258 9.0 111 31.2 7.99

05/10/2017 0955 3,840 7.8 144 9.0 63.0 17.8 4.50

05/24/2017 0945 3,860 8.0 174 11.5 73.1 21.0 5.04

06/14/2017 1120 8,670 7.8 170 9.0 71.4 20.3 5.00

07/12/2017 1050 1,400 8.3 273 15.5 124 35.6 8.51

08/16/2017 0945 540 8.2 327 13.0 149 41.2 11.3

Date

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

10/19/2016 <0.030 0.05 1.8 6.2 4.7 191 0.030 0.89

03/22/2017 <0.030 0.18 3.3 25.3 72.6 799 0.188 4.30

04/19/2017 <0.030 0.08 2.7 11.4 23.4 306 0.072 1.68

05/10/2017 <0.030 0.15 3.1 22.9 56.6 820 0.172 3.83

05/24/2017 <0.030 0.15 3.7 22.4 47.2 713 0.174 3.82

06/14/2017 0.057 1.71 10.9 244 203 10,700 0.977 50.5

07/12/2017 <0.030 0.05 3.4 6.5 11.0 128 0.051 0.52

08/16/2017 <0.030 0.04 2.3 3.7 <10.0 56.9 0.034 0.22

Date

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

 filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

10/19/2016 3.36 30.3 2.3 12 5.7 6.3 84 10 22

03/22/2017 7.96 85.6 4.1 33 4.2 7.2 70 40 228

04/19/2017 6.09 37.3 <2.0 14 4.2 5.4 77 16 72

05/10/2017 7.63 81.5 3.4 34 3.4 5.9 50 67 695

05/24/2017 8.02 72.6 3.3 32 4.4 7.0 53 56 584

06/14/2017 48.3 871 11.3 430 10.2 37.4 54 692 16,200

07/12/2017 8.08 25.2 2.1 8 6.6 6.8 79 6 23

08/16/2017 4.59 14.8 2.0 5 5.5 5.4 77 4 5.8
38 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2016 through September 2017.—Continued

[hh, hours; mm, minutes; ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, 

nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; E, estimated; <, less than laboratory reporting level; μg/L, microgram 

per liter; mm, millimeter; ton/d, ton per day; --, no data]

12340000—Blackfoot River near Bonner

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, 

(standard 

units)

Specific 

conductance 

(μS/cm)

Water 

temperature, 

(°C)

Hardness, 

filtered 

(mg/L as CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/19/2016 1120 615 8.3 252 7.5 131 33.1 11.8

04/19/2017 1430 3,240 8.4 182 8.0 87.9 22.7 7.55

05/10/2017 1200 7,210 8.1 164 9.0 82.3 21.7 6.85

05/24/2017 1340 6,930 8.2 164 11.5 80.7 21.5 6.57

07/12/2017 1255 1,330 8.5 239 17.5 121 30.9 10.6

08/16/2017 1120 672 8.5 264 14.0 134 33.0 12.4

Date

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

10/19/2016 <0.030 <0.03 -- -- 5.3 53.8 -- --

04/19/2017 <0.030 <0.03 0.80 1.1 30.8 218 0.025 0.21

05/10/2017 <0.030 <0.03 0.80 3.3 28.8 829 0.038 1.07

05/24/2017 <0.030 <0.03 0.79 2.6 22.4 714 0.033 0.95

07/12/2017 <0.030 <0.03 0.81 0.6 <10.0 48.5 0.022 0.05

08/16/2017 <0.030 <0.03 0.38 0.5 <10.0 31.2 0.021 0.04

Date

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

 filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

10/19/2016 1.51 5.1 <2.0 <2 1.1 1.1 80 3 5

04/19/2017 3.75 15.2 <2.0 <2 0.72 0.9 86 11 96

05/10/2017 3.63 52.4 <2.0 5 0.84 1.5 83 69 1,340

05/24/2017 3.27 43.0 <2.0 <8 0.85 1.5 85 61 1,140

07/12/2017 1.84 6.1 <2.0 <2 1.3 1.3 90 4 14

08/16/2017 1.54 4.8 <2.0 <2 1.2 1.4 82 3 5.4
Data 39

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2016 through September 2017.—Continued

[hh, hours; mm, minutes; ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, 

nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; E, estimated; <, less than laboratory reporting level; μg/L, microgram 

per liter; mm, millimeter; ton/d, ton per day; --, no data]

12340500—Clark Fork above Missoula

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH 

(standard 

units)

Specific 

conductance 

(μS/cm)

Water 

temperature, 

(°C)

Hardness, 

filtered 

(mg/L as CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/19/2016 1320 1,480 8.4 318 7.5 155 41.8 12.3

03/22/2017 1240 5,490 8.0 207 5.0 94.2 25.6 7.36

04/19/2017 1030 5,070 8.2 209 6.5 95.2 25.6 7.60

05/10/2017 1350 10,900 8.0 157 10.0 75.1 20.5 5.82

05/24/2017 1145 10,400 8.1 170 11.0 79.1 21.6 6.14

06/14/2017 1345 15,400 7.9 173 10.5 78.6 21.6 5.96

07/12/2017 0930 2,730 8.2 255 15.5 122 33.4 9.34

08/16/2017 1225 1170 8.5 287 14.5 134 35.0 11.4

Date

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper, 

filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

10/19/2016 <0.030 0.03 1.5 3.5 7.0 120 0.020 0.48

03/22/2017 <0.030 0.08 2.0 10.4 87.5 559 0.144 1.89

04/19/2017 <0.030 0.05 1.4 4.4 24.2 260 0.041 0.75

05/10/2017 <0.030 0.08 1.8 9.2 38.4 848 0.093 1.94

05/24/2017 <0.030 0.08 2.2 9.8 31.6 707 0.088 1.92

06/14/2017 0.033 1.02 8.0 155 150 5,770 0.724 27.8

07/12/2017 <0.030 0.03 2.2 4.3 10.9 95.2 0.037 0.33

08/16/2017 <0.030 <0.03 1.5 2.1 <10.0 70.8 0.036 0.14

Date

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

 filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Sediment, 

suspended 

(percent finer 

than 0.062 mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

10/19/2016 5.36 19.8 <2.0 6 3.7 4.0 82 6 24

03/22/2017 7.94 49.6 2.3 15 2.5 3.4 76 28 415

04/19/2017 5.34 24.5 <2.0 7 1.9 2.4 81 14 192

05/10/2017 6.80 62.9 <2.0 15 1.9 3.1 76 65 1,910

05/24/2017 5.50 50.6 <2.0 19 2.4 3.5 75 50 1,400

06/14/2017 44.6 479 8.6 259 7.2 23.7 65 350 14,600

07/12/2017 6.28 18.6 <2.0 5 4.0 4.0 86 6 44

08/16/2017 5.62 12.6 <2.0 3 3.1 3.4 84 2 6.3
40 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 5. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics, at Mill Creek at Opportunity, 

Montana (12323700), March through September 2017.

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 90 plus or minus 

2.5 degrees to incident beam, reported in formazin nephelometric units (FNU). --, no data]

Day

Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean

March April May June

1 -- -- -- 5.1 4.2 4.5 6.1 4.3 4.8 25 16 19

2 -- -- -- 5.7 4.3 4.7 5.8 4.3 4.9 33 14 21

3 -- -- -- 6.2 4.3 4.6 6.5 4.1 4.7 45 31 38

4 -- -- -- 7.2 4.2 4.6 6.5 4.4 5.1 224 31 59

5 -- -- -- 5.3 4.0 4.4 13 5.7 7.3 616 129 354

6 -- -- -- 5.1 4.2 4.5 33 13 18 -- -- --

7 -- -- -- 6.4 4.5 5.0 64 26 38 -- -- --

8 -- -- -- 5.8 4.3 4.8 -- -- -- -- -- --

9 -- -- -- 6.8 4.1 4.6 16 7.9 9.5 -- -- --

10 -- -- -- 4.8 3.8 4.2 58 7.4 16 8.5 5.8 6.5

11 -- -- -- 4.6 3.9 4.1 95 18 32 6.7 4.9 5.6

12 -- -- -- 6.4 4.0 4.5 211 41 123 19 4.4 7.7

13 -- -- -- 5.5 4.2 4.6 74 17 32 48 12 24

14 -- -- -- 5.3 4.3 4.7 42 8.4 18 33 7.8 11

15 -- -- -- 4.8 4.0 4.4 56 7.0 16 9.9 5.5 7.0

16 -- -- -- 5.7 3.9 4.4 16 7.0 10 7.5 4.9 5.8

17 -- -- -- 5.7 3.8 4.4 15 6.0 8.2 11 5.4 7.4

18 -- -- -- 5.4 3.9 4.5 8.2 5.8 6.3 10 4.4 6.0

19 -- -- -- 6.0 4.2 4.7 8.2 6.2 6.9 7.6 3.5 4.6

20 -- -- -- 5.8 4.5 5.0 15 6.1 8.1 21 5.0 11

21 -- -- -- 5.9 4.4 4.9 11 4.7 6.7 -- -- --

22 -- -- -- 6.2 4.3 4.9 12 4.3 5.7 -- -- --

23 -- -- -- 6.0 4.6 5.2 8.0 4.8 5.9 -- -- --

24 -- -- -- 6.7 4.9 5.7 12 6.4 8.0 -- -- --

25 -- -- -- 6.3 4.6 5.3 11 6.7 7.9 -- -- --

26 -- -- -- 5.9 4.4 5.1 9.1 5.2 6.1 -- -- --

27 -- -- -- 5.7 4.0 4.5 7.1 4.5 5.4 -- -- --

28 -- -- -- 5.2 3.8 4.2 7.2 4.1 5.1 -- -- --

29 -- -- -- 4.7 3.7 4.2 8.4 5.1 6.1 -- -- --

30 5.4 4.5 4.9 5.5 4.3 4.8 13 6.3 8.5 -- -- --

31 5.3 4.3 4.7 -- -- -- 21 8.4 13 -- -- --

Month1 5.4 4.3 4.8 7.2 3.7 4.7 211 4.1 15 616 3.5 37
Data 41

Table 5. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics, at Mill Creek at 

Opportunity, Montana (12323700), March through September 2017.—Continued

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle 

of 90 plus or minus 2.5 degrees to incident beam, reported in formazin nephelometric units (FNU). --, no data]

Day

Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean

July August September

1 -- -- -- 4.0 1.5 1.9 3.8 1.6 1.8

2 -- -- -- 4.0 1.7 2.0 3.5 1.7 2.3

3 -- -- -- 3.1 1.8 2.2 4.6 2.1 2.4

4 -- -- -- 4.3 1.9 2.2 3.6 2.1 2.4

5 -- -- -- 3.7 1.8 2.1 2.5 1.9 2.1

6 -- -- -- 2.5 1.6 1.9 2.7 1.7 1.8

7 5.5 2.5 3.2 4.9 1.7 1.9 3.7 1.5 1.8

8 4.5 2.2 3.0 2.5 1.5 1.8 3.3 1.7 2.0

9 3.9 2.5 3.1 3.5 1.6 1.8 3.5 1.7 1.9

10 4.5 2.3 3.0 2.8 1.6 1.8 2.6 1.7 1.9

11 4.1 2.3 2.9 2.3 1.6 1.8 2.5 1.8 2.0

12 4.3 2.3 3.0 2.5 1.6 1.8 2.7 1.8 2.1

13 4.2 2.2 3.0 4.1 1.7 2.1 2.4 1.2 2.1

14 5.1 2.3 3.1 2.6 1.6 2.0 3.3 2.1 2.5

15 4.9 2.4 3.1 2.2 1.6 1.7 4.1 2.2 3.1

16 4.6 2.1 2.8 3.0 1.6 1.8 3.6 2.1 2.6

17 3.6 2.1 2.7 4.4 1.6 1.8 3.3 1.4 2.3

18 3.1 1.8 2.4 2.9 1.4 1.7 3.4 1.9 2.2

19 3.7 1.8 2.3 2.7 1.4 1.6 4.7 1.9 2.3

20 3.1 1.9 2.3 2.6 1.4 1.6 9.8 2.2 3.9

21 3.0 1.8 2.3 3.9 1.4 1.8 6.7 1.5 3.0

22 3.1 1.6 2.0 2.8 1.5 1.8 3.7 1.6 2.1

23 2.8 1.6 2.0 2.7 1.4 2.1 3.7 1.6 2.0

24 2.9 1.5 2.1 3.3 1.8 2.3 2.5 1.1 1.8

25 3.4 1.5 2.1 4.4 2.0 2.4 3.7 1.4 1.7

26 9.0 1.5 3.1 4.5 1.9 2.2 2.8 1.6 2.0

27 8.5 1.4 2.7 4.7 2.0 2.5 3.0 1.8 2.2

28 3.8 1.4 1.9 14 2.1 4.3 3.4 1.9 2.4

29 3.1 1.3 1.8 7.7 2.0 2.6 3.2 2.0 2.5

30 2.6 1.3 1.8 2.2 1.6 1.8 3.1 1.4 2.0

31 2.9 1.2 1.7 2.7 1.5 1.7 -- -- --

Month1 9.0 1.2 2.5 14 1.4 2.0 9.8 1.1 2.2

1

For months with missing daily values, the means are calculated using available values.
42 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 6. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics, at Willow Creek at Opportunity, 

Montana (12323720), March through September 2017.

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 90 plus or minus 

2.5 degrees to incident beam, reported in formazin nephelometric units (FNU). --, no data]

Day

Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean

March April May June

1 -- -- -- 14 10 12 11 7.8 8.8 8.0 5.9 6.8

2 -- -- -- 15 10 12 19 7.6 9.4 9.7 6.1 7.3

3 -- -- -- 15 10 12 14 7.7 9.3 7.8 6.0 6.7

4 -- -- -- 16 11 12 13 7.8 8.7 16 6.0 8.5

5 -- -- -- 14 11 11 12 8.4 9.7 14 6.3 8.8

6 -- -- -- 14 10 11 19 11 14 8.1 5.0 6.5

7 -- -- -- 14 9.9 11 20 14 15 7.7 5.3 6.3

8 -- -- -- 15 9.9 11 18 12 14 8.5 5.2 6.6

9 -- -- -- 16 9.8 11 13 9.8 11 8.3 5.4 6.4

10 -- -- -- 14 9.8 11 11 8.2 8.9 44 5.2 7.6

11 -- -- -- 13 9.3 11 10 8.0 8.5 8.0 4.9 5.8

12 -- -- -- 13 9.3 10 10 7.6 8.3 38 4.6 10

13 -- -- -- 12 8.8 9.8 11 8.4 9.3 38 7.1 15

14 -- -- -- 14 9.2 10 12 8.0 9.0 8.8 5.8 6.6

15 -- -- -- 13 9.0 10 9.6 7.5 8.1 7.5 5.6 6.3

16 -- -- -- 12 9.0 10 8.5 6.4 7.1 7.6 5.9 6.6

17 -- -- -- 13 9.2 10 10 7.5 8.6 8.7 5.2 6.5

18 -- -- -- 15 9.0 11 9.0 5.7 7.0 8.7 5.5 6.3

19 -- -- -- 15 9.2 11 19 4.8 6.3 20 5.6 7.8

20 -- -- -- 24 9.2 11 7.6 5.6 6.2 9.0 4.7 6.4

21 -- -- -- 15 9.9 11 8.9 6.6 7.4 9.3 4.6 6.0

22 -- -- -- 16 9.4 11 12 7.5 8.1 11 4.3 6.2

23 -- -- -- 19 9.2 11 8.8 7.4 8.0 16 4.0 5.7

24 -- -- -- 13 9.5 11 9.0 7.4 8.1 39 4.1 5.7

25 -- -- -- 14 9.4 11 9.2 7.8 8.5 39 4.0 6.5

26 -- -- -- 13 9.2 10 13 7.0 7.9 11 4.0 5.7

27 -- -- -- 13 9.0 10 11 6.7 7.5 14 4.0 6.3

28 -- -- -- 12 8.6 9.9 12 6.4 7.4 16 5.2 8.3

29 -- -- -- 12 8.4 9.5 11 5.9 7.2 15 3.2 8.2

30 13 10 11 14 8.1 9.2 8.7 6.0 7.0 11 3.2 6.3

31 16 11 12 -- -- -- 9.2 6.2 6.7 -- -- --

Month1 16 10 12 24 8.1 11 20 4.8 8.7 44 3.2 7.1
Data 43

Table 6. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics, at Willow 

Creek at Opportunity, Montana (12323720), March through September 2017.—Continued

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle 

of 90 plus or minus 2.5 degrees to incident beam, reported in formazin nephelometric units (FNU). --, no data]

Day

Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean

July August September

1 13 3.6 6.1 5.3 3.2 4.1 4.9 2.3 3.1

2 -- -- -- 5.3 3.7 4.4 4.2 2.5 3.1

3 8.1 3.5 4.4 6.7 3.7 4.9 4.6 2.4 3.1

4 7.8 3.4 5.1 6.8 3.5 4.6 4.1 2.2 2.9

5 14 3.3 6.2 5.9 3.6 4.5 4.4 2.5 3.2

6 9.6 3.2 4.3 5.5 3.7 4.4 5.8 2.4 3.5

7 4.9 3.0 3.8 5.9 3.3 4.5 5.8 2.3 3.5

8 6.3 3.1 3.9 6.2 3.2 4.4 7.7 2.4 3.6

9 6.4 2.8 4.4 6.8 3.4 4.1 4.4 2.3 3.0

10 7.0 2.9 4.0 4.8 2.9 3.7 4.6 2.4 3.1

11 5.9 3.1 4.2 8.7 2.9 4.1 5.1 2.8 3.5

12 6.7 2.7 4.2 5.7 3.2 4.2 5.2 2.4 3.5

13 5.2 2.5 3.6 6.0 3.0 4.1 5.3 2.6 3.4

14 4.2 2.8 3.3 6.5 2.9 3.6 5.2 3.0 3.7

15 5.4 3.1 4.1 6.0 2.7 3.7 6.7 3.7 4.8

16 6.1 2.8 4.0 4.4 2.9 3.5 5.6 3.2 4.3

17 7.8 2.7 4.2 5.1 3.1 3.8 4.5 3.3 3.8

18 5.8 2.6 3.9 5.0 2.9 3.3 6.0 3.1 4.0

19 6.5 3.9 4.7 4.5 2.8 3.3 8.6 3.3 4.3

20 -- -- -- 4.9 2.9 3.5 5.9 3.5 4.3

21 -- -- -- 5.7 3.0 3.6 6.7 3.3 4.3

22 -- -- -- 4.5 2.9 3.4 8.3 3.2 4.6

23 -- -- -- 3.7 2.6 3.1 6.8 3.3 4.3

24 -- -- -- 4.9 2.6 3.1 7.0 3.4 4.8

25 -- -- -- 6.3 2.6 3.2 7.0 3.5 4.5

26 9.0 4.4 6.0 5.9 3.0 3.5 6.2 3.5 4.9

27 9.0 3.9 5.3 4.3 2.6 3.1 7.6 4.1 5.5

28 11 3.5 5.0 5.4 2.6 3.3 6.3 3.5 5.1

29 9.2 3.4 4.8 4.6 2.5 3.2 8.1 4.9 6.0

30 11 3.5 5.3 3.8 2.2 2.9 8.8 4.7 6.4

31 9.7 3.3 5.1 4.0 2.4 2.9 -- -- --

Month1 14 2.5 4.6 8.7 2.2 3.7 8.8 2.2 4.1

1

For months with missing daily values, the means are calculated using available values.
44 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 7. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics, at Warm Springs Creek at Warm 

Springs, Montana (12323770), March through September 2017.

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 90 plus or minus

2.5 degrees to incident beam, reported in formazin nephelometric units (FNU). --, no data]

Day

Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean

March April May June

1 -- -- -- 2.5 1.4 1.8 5.1 3.6 4.2 32 16 24

2 -- -- -- 2.8 1.5 1.8 6.7 3.7 4.4 -- -- --

3 -- -- -- 2.1 1.5 1.8 5.8 3.5 4.0 -- -- --

4 -- -- -- 3.0 1.5 1.8 5.2 3.4 4.1 -- -- --

5 -- -- -- 3.3 1.5 1.8 4.9 3.7 4.2 -- -- --

6 -- -- -- 2.0 1.5 1.7 9.1 4.3 6.3 -- -- --

7 -- -- -- 2.3 1.6 1.9 29 9.1 21 21 11 13

8 -- -- -- 2.2 1.6 1.8 18 7.3 11 12 9.6 11

9 -- -- -- 2.4 1.6 1.9 11 6.1 7.5 12 8.3 9.3

10 -- -- -- 2.3 1.6 1.9 12 6.5 7.8 9.5 7.4 8.0

11 -- -- -- 2.6 1.5 1.8 18 7.9 13 8.1 6.3 7.0

12 -- -- -- 2.9 1.8 2.2 23 10 15 23 5.8 8.6

13 -- -- -- 2.9 1.8 2.2 26 13 18 47 13 25

14 -- -- -- 3.1 1.9 2.3 13 6.6 8.6 44 15 24

15 -- -- -- 2.5 1.8 2.1 7.3 5.0 6.0 16 10 12

16 -- -- -- 2.9 1.6 2.1 6.1 4.3 5.0 12 8.4 9.4

17 -- -- -- 2.9 2.0 2.3 6.0 4.2 5.2 8.8 7.3 7.7

18 -- -- -- 3.5 2.0 2.4 5.7 3.5 4.2 7.8 6.1 6.7

19 -- -- -- 3.8 1.9 2.4 5.0 3.2 4.0 8.1 6.0 6.5

20 -- -- -- 3.3 1.9 2.4 4.7 3.0 3.7 7.4 5.8 6.4

21 -- -- -- 3.0 1.8 2.4 4.5 2.8 3.5 7.6 5.5 6.2

22 -- -- -- 3.6 1.9 2.6 4.5 3.0 3.7 6.2 4.8 5.5

23 -- -- -- 4.3 3.1 3.6 5.2 3.6 4.4 6.0 4.5 5.2

24 -- -- -- 7.8 3.5 4.1 49 4.4 12 6.0 4.3 4.9

25 -- -- -- 5.1 3.1 3.8 20 9.0 14 5.7 3.9 4.6

26 -- -- -- 5.1 3.2 3.7 9.1 5.7 6.8 5.8 4.0 4.7

27 -- -- -- 5.3 3.4 3.8 6.4 4.3 5.2 5.9 3.8 4.4

28 -- -- -- 4.7 3.5 3.9 6.0 4.6 5.2 4.8 3.5 3.9

29 -- -- -- 4.7 3.4 3.9 9.4 5.7 7.4 8.6 3.3 4.3

30 2.9 1.7 2.1 4.6 3.4 3.8 18 8.0 13 5.7 3.3 3.9

31 3.1 1.5 1.9 -- -- -- 31 13 20 -- -- --

Month1 3.1 1.5 2.0 7.8 1.4 2.5 49 2.8 8.1 47 3.3 9.0
Data 45

Table 7. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics, at Warm Springs Creek 

at Warm Springs, Montana (12323770), March through September 2017.—Continued

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 

90 plus or minus 2.5 degrees to incident beam, reported in formazin nephelometric units (FNU). --, no data]

Day

Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean

July August September

1 5.0 3.1 3.8 2.6 1.1 1.6 3.1 1.3 2.1

2 -- -- -- 2.4 1.2 1.5 2.6 1.1 1.9

3 -- -- -- 2.3 0.8 1.4 3.2 1.1 1.7

4 -- -- -- 2.6 0.8 1.3 3.0 1.0 1.5

5 -- -- -- 2.1 0.8 1.2 2.7 0.9 1.6

6 -- -- -- 1.8 0.8 1.2 2.3 0.9 1.4

7 13 2.6 3.8 2.1 0.7 1.2 2.9 0.6 1.2

8 3.5 2.3 2.9 -- -- -- -- -- --

9 3.6 2.3 2.8 -- -- -- -- -- --

10 -- -- -- 3.2 1.0 1.7 -- -- --

11 4.5 2.2 2.9 2.6 1.0 1.5 2.8 1.0 1.4

12 3.5 2.0 2.5 2.4 0.9 1.4 2.5 1.0 1.5

13 4.0 1.7 2.5 2.2 1.0 1.4 2.6 0.9 1.6

14 3.7 1.8 2.5 3.3 0.8 1.8 3.2 1.0 1.7

15 980 1.8 22 4.9 0.8 1.5 3.8 1.0 1.8

16 1,070 6.2 91 2.3 0.9 1.5 2.2 0.7 1.3

17 7.5 4.2 5.6 2.0 0.8 1.3 2.2 0.6 1.1

18 5.8 3.3 4.1 2.0 0.7 1.2 -- -- --

19 4.9 2.7 3.6 2.7 0.7 1.3 -- -- --

20 5.6 2.6 3.8 2.0 0.7 1.2 -- -- --

21 4.8 2.1 2.9 2.3 0.7 1.3 -- -- --

22 4.2 1.6 2.6 3.9 1.2 2.2 -- -- --

23 4.0 1.6 2.4 4.1 0.9 1.6 -- -- --

24 5.1 2.3 2.8 1.9 0.7 1.2 -- -- --

25 5.1 2.0 3.0 2.2 0.6 1.1 2.4 0.6 1.2

26 10 2.4 3.5 1.9 0.5 1.0 4.1 0.7 1.7

27 5.9 2.5 3.6 -- -- -- 6.1 0.9 1.7

28 3.3 1.5 2.2 -- -- -- 2.3 0.7 1.2

29 2.9 1.3 1.9 -- -- -- 2.0 0.5 1.0

30 2.8 1.3 1.8 1.9 0.5 0.9 1.9 0.6 1.1

31 2.6 1.3 1.7 3.8 0.7 1.6 -- -- --

Month1 1,070 1.3 7.3 4.9 0.5 1.4 6.1 0.5 1.5

1

For months with missing daily values, the means are calculated using available values.
46 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 8. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics, at Lost Creek near Anaconda, 

Montana (12323840), March through September 2017.

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 90 plus or minus 

2.5 degrees to incident beam, reported in formazin nephelometric units (FNU). --, no data]

Day

Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean

March April May June

1 -- -- -- 17 3.5 5.8 6.1 1.7 3.1 70 6.9 12

2 -- -- -- -- -- -- 7.9 1.5 2.7 14 5.9 8.8

3 -- -- -- 9.4 2.5 4.2 5.3 1.6 2.6 15 6.0 8.5

4 -- -- -- 15 2.8 5.1 7.7 1.4 2.7 23 5.3 8.4

5 -- -- -- 6.8 3.2 3.8 7.3 1.7 3.3 90 9.7 20

6 -- -- -- 9.1 3.3 4.6 8.9 2.5 4.2 12 5.4 8.3

7 -- -- -- 6.7 2.8 3.7 259 5.2 18 8.1 4.1 6.3

8 -- -- -- 9.7 2.6 4.0 18 4.6 8.9 9.1 4.7 5.9

9 -- -- -- 16 2.8 5.0 13 1.9 4.1 17 4.9 7.8

10 -- -- -- 7.3 2.4 3.3 9.5 2.2 5.1 11 3.9 5.9

11 -- -- -- 6.9 2.5 3.3 8.3 2.4 4.6 16 3.8 6.5

12 -- -- -- 12 2.9 4.3 81 4.8 9.9 168 4.2 21

13 -- -- -- 12 3.2 6.1 44 5.4 9.8 88 26 51

14 -- -- -- 4.7 2.9 3.7 12 3.4 5.2 29 12 18

15 -- -- -- 8.6 2.4 4.0 6.3 3.2 4.1 12 7.2 9.4

16 -- -- -- 6.3 2.5 3.4 4.7 2.7 3.4 12 5.7 7.9

17 -- -- -- 6.7 2.7 3.9 13 3.2 5.3 17 6.0 8.5

18 -- -- -- -- -- -- 23 2.4 4.9 14 5.4 7.1

19 -- -- -- 7.7 2.7 3.5 4.1 1.4 2.6 13 4.6 6.8

20 -- -- -- 8.1 2.9 4.1 3.6 2.2 2.8 -- -- --

21 -- -- -- 8.7 3.3 4.8 5.5 2.1 2.9 7.9 2.1 3.8

22 -- -- -- 9.1 3.9 5.1 5.1 2.3 3.4 6.1 1.8 3.1

23 -- -- -- 12 3.3 5.9 12 2.5 5.1 9.4 1.6 2.9

24 -- -- -- 6.4 2.5 4.1 46 5.8 11 8.7 1.7 3.1

25 -- -- -- 6.5 2.1 3.5 21 6.2 9.9 9.0 2.4 3.5

26 -- -- -- 8.9 2.8 4.2 13 4.3 6.2 6.7 2.7 3.5

27 -- -- -- 107 3.3 11 28 3.8 6.7 6.2 1.6 3.4

28 -- -- -- 24 4.4 12 12 2.8 4.4 4.0 1.4 2.5

29 -- -- -- 25 2.7 4.6 8.1 3.4 4.9 5.2 1.8 3.3

30 21 4.1 8.0 7.9 3.3 4.3 8.8 1.7 5.6 6.6 0.5 3.3

31 11 3.6 5.5 -- -- -- 14 3.9 6.4 -- -- --

Month1 21 3.6 6.8 107 2.1 4.8 259 1.4 5.6 168 0.5 9.0
Data 47

Table 8. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics, at Lost Creek near 

Anaconda, Montana (12323840), March through September 2017.—Continued

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 

90 plus or minus 2.5 degrees to incident beam, reported in formazin nephelometric units (FNU). --, no data]

Day

Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean

July August September

1 4.3 1.4 2.2 3.7 2.4 2.9 2.4 0.5 1.5

2 4.9 1.9 2.6 75 2.2 6.9 2.0 1.0 1.6

3 4.8 1.8 2.6 3.9 2.2 2.8 2.2 0.5 1.1

4 3.3 1.1 2.2 91 2.2 8.5 2.4 0.5 1.1

5 3.9 1.9 2.5 7.1 4.1 5.4 3.3 0.5 1.1

6 3.3 1.8 2.4 8.9 3.4 4.1 2.2 0.5 0.9

7 4.3 1.4 2.2 6.6 3.3 3.9 1.9 0.5 1.1

8 3.4 1.3 1.9 5.4 3.0 3.6 -- -- --

9 4.4 1.2 2.1 5.7 3.2 3.7 -- -- --

10 2.6 1.3 1.8 4.5 2.8 3.3 -- -- --

11 3.9 1.0 2.0 5.8 3.1 3.8 -- -- --

12 3.0 1.9 2.2 13 3.3 4.1 -- -- --

13 3.3 2.0 2.3 5.4 3.3 3.9 -- -- --

14 3.3 1.6 2.3 4.4 3.0 3.5 -- -- --

15 1,080 1.8 148 6.1 3.1 3.7 -- -- --

16 125 8.6 18 5.3 2.9 3.7 -- -- --

17 28 4.0 7.8 5.5 3.2 3.7 -- -- --

18 5.9 2.9 4.0 4.5 3.1 3.6 -- -- --

19 15 2.1 5.6 4.9 3.1 3.6 -- -- --

20 5.6 1.2 3.4 4.6 2.9 3.5 -- -- --

21 5.2 2.7 3.2 5.7 3.2 3.9 -- -- --

22 6.0 2.0 2.7 5.8 3.1 4.0 -- -- --

23 6.1 2.0 2.7 6.4 2.7 3.7 -- -- --

24 3.4 1.9 2.4 3.8 2.3 2.9 8.3 0.5 1.1

25 4.3 1.9 2.3 5.8 2.2 2.7 5.5 0.7 1.2

26 3.1 1.4 2.1 3.5 2.2 2.6 2.4 1.1 1.4

27 3.0 1.5 1.9 2.6 2.0 2.3 2.2 1.5 1.8

28 5.2 1.3 1.8 3.3 1.9 2.2 3.0 1.7 2.0

29 3.8 1.8 2.0 3.5 1.8 2.1 4.4 2.1 2.3

30 6.1 1.7 2.3 2.6 1.2 1.8 2.9 2.1 2.2

31 6.0 2.3 3.2 2.1 1.1 1.5 -- -- --

Month1 1,080 1.0 7.9 91 1.1 3.6 8.3 0.5 1.5

1

For months with missing daily values, the means are calculated using available values.
48 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana Table 9. Analyses of field replicates for water samples, Clark Fork Basin, Montana. [hh, hours; mm, minutes; lab, laboratory; NTRU, nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; --, no data; <, less than laboratory reporting level; E, estimated] Site number (fig. 1) Site name Date Time (hhmm) Turbidity, unfiltered, lab (NTRU) Hardness, filtered (mg/L as CaCO3

)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

Potassium, 

filtered 

(mg/L)

Sodium, 

filtered 

(mg/L)

Alkalinity, 

filtered, lab 

(mg/L as CaCO3

)

12324680 Clark Fork at Goldcreek 10/18/2016 1545 -- 205 60.0 13.5 -- -- --

10/18/2016 1550 -- 210 61.6 13.6 -- -- --

12323250 Silver Bow Creek below 

Blacktail Creek

03/20/2017 1155 E4.0 114 32.3 8.16 -- -- --03/20/2017 1200 E4.4 116 32.8 8.26 -- -- --

12324400 Clark Fork above Little 

Blackfoot, near Garrison

03/21/2017 1340 -- 197 58.2 12.5 -- -- --03/21/2017 1345 -- 191 56.0 12.5 -- -- --

12323840 Lost Creek near Anaconda 04/18/2017 0745 <2.0 107 31.8 6.73 1.27 2.95 105

04/18/2017 0750 <2.0 108 32.2 6.79 1.29 2.96 105

12324200 Clark Fork at Deer Lodge 05/09/2017 1345 -- 148 44.6 8.97 -- -- --

05/09/2017 1350 -- 152 46.2 8.97 -- -- --

12334550 Clark Fork at Turah Bridge, 

near Bonner

05/24/2017 0945 -- 73.1 21.0 5.04 -- -- --05/24/2017 0950 -- 74.3 21.2 5.19 -- -- --

12340500 Clark Fork above Missoula 06/14/2017 1345 -- 78.6 21.6 5.96 -- -- --

06/14/2017 1350 -- 78.0 21.6 5.84 -- -- --

12323750 Silver Bow Creek at 

Warm Springs

07/11/2017 1010 E2.8 134 39.3 8.60 1.91 11.7 89.207/11/2017 1015 E3.0 137 40.2 8.80 1.98 11.9 89.5

12323700 Mill Creek at Opportunity 08/14/2017 1700 <2.0 79.7 22.2 5.91 0.79 4.59 77.1

08/14/2017 1705 <2.0 79.2 22.1 5.85 0.80 4.48 76.9
Data 49

Table 9. Analyses of field replicates for water samples, Clark Fork Basin, Montana.—Continued[hh, hours; mm, minutes; lab, laboratory; NTRU, nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; --, no data; <, less than laboratory reporting level; E, estimated]

Site number 

(fig. 1) Site name Date Time (hhmm) Chloride, filtered (mg/L) Flouride, filtered (mg/L) Silica, filtered (mg/l) Sulfate, filtered (mg/L) Nitrate plus nitrite, filtered (mg/L) Cadmium, filtered (μg/L) Cadmium, unfiltered recoverable (μg/L) Copper, filtered (μg/L) Copper, unfiltered recoverable (μg/L)

12324680 Clark Fork at Goldcreek 10/18/2016 1545 -- -- -- -- -- 0.040 0.05 4.6 8.5

10/18/2016 1550 -- -- -- -- -- <0.030 0.05 4.7 8.8

12323250 Silver Bow Creek below 

Blacktail Creek

03/20/2017 1155 -- -- -- -- 0.59 -- -- -- --03/20/2017 1200 -- -- -- -- 0.58 -- -- -- --

12324400 Clark Fork above Little 

Blackfoot, near Garrison

03/21/2017 1340 -- -- -- -- -- 0.054 0.34 8.5 71.203/21/2017 1345 -- -- -- -- -- 0.057 0.33 8.4 76.0

12323840 Lost Creek near Anaconda 04/18/2017 0745 0.79 0.45 11.4 10.2 -- <0.030 0.06 1.5 4.6

04/18/2017 0750 0.79 0.45 11.4 10.2 -- <0.030 0.07 1.5 5.2

12324200 Clark Fork at Deer Lodge 05/09/2017 1345 -- -- -- -- -- 0.060 0.29 9.2 60.3

05/09/2017 1350 -- -- -- -- -- 0.053 0.28 9.3 55.8

12334550 Clark Fork at Turah 

Bridge, near Bonner

05/24/2017 0945 -- -- -- -- -- <0.030 0.15 3.7 22.405/24/2017 0950 -- -- -- -- -- <0.030 0.17 3.6 24.6

12340500 Clark Fork above Missoula 06/14/2017 1345 -- -- -- -- -- 0.033 1.02 8.0 155

06/14/2017 1350 -- -- -- -- -- 0.031 1.03 7.3 144

12323750 Silver Bow Creek at 

Warm Springs

07/11/2017 1010 8.97 0.48 13.5 56.8 -- <0.030 0.05 4.1 5.207/11/2017 1015 8.97 0.48 13.7 56.8 -- <0.030 0.08 4.0 5.3

12323700 Mill Creek at Opportunity 08/14/2017 1700 0.38 0.34 12.3 11.8 -- 0.038 0.05 1.8 2.2

08/14/2017 1705 0.38 0.34 11.8 11.8 -- 0.036 0.06 1.8 2.3
50 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana Table 9. Analyses of field replicates for water samples, Clark Fork Basin, Montana.—Continued [hh, hours; mm, minutes; lab, laboratory; NTRU, nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; --, no data; <, less than laboratory reporting level; E, estimated] Site number (fig. 1) Site name Date Time (hhmm) Iron, filtered (μg/L) Iron, unfiltered recoverable (μg/L) Lead, filtered (μg/L) Lead, unfiltered recoverable (μg/L) Manganese, filtered (μg/L) Manganese, unfiltered recoverable (μg/L) Zinc, filtered (μg/L) Zinc, unfiltered recoverable (μg/L) 12324680 Clark Fork at Goldcreek 10/18/2016 1545 <4.0 87.2 0.040 0.68 10.4 33.0 -- -- 10/18/2016 1550 4.1 88.6 <0.020 0.68 10.4 35.1 -- -- 12323250 Silver Bow Creek below Blacktail Creek 03/20/2017 1155 -- -- -- -- -- -- -- -- 03/20/2017 1200 -- -- -- -- -- -- -- -- 12324400 Clark Fork above Little Blackfoot, near Garrison 03/21/2017 1340 20.5 1,150 0.170 9.98 34.7 170 6.6 61 03/21/2017 1345 19.1 1,190 0.160 9.73 35.1 161 6.5 63 12323840 Lost Creek near Anaconda 04/18/2017 0745 11.8 108 0.023 0.47 1.17 5.5 <2.0 2 04/18/2017 0750 11.6 105 0.025 0.63 1.15 7.0 <2.0 2 12324200 Clark Fork at Deer Lodge 05/09/2017 1345 24.1 883 0.181 6.88 23.4 157 4.9 47 05/09/2017 1350 28.2 897 0.189 6.95 23.5 157 5.1 46 12334550 Clark Fork at Turah Bridge, near Bonner 05/24/2017 0945 47.2 713 0.174 3.82 8.02 72.6 3.3 32 05/24/2017 0950 47.6 754 0.179 4.08 7.36 71.9 3.3 32 12340500 Clark Fork above Missoula 06/14/2017 1345 150 5,770 0.724 27.8 44.6 479 8.6 259 06/14/2017 1350 144 6,030 0.678 27.6 43.0 481 7.9 257 12323750 Silver Bow Creek at Warm Springs 07/11/2017 1010 30.0 101 0.115 0.39 39.2 57.8 <2.0 3 07/11/2017 1015 34.6 106 0.112 0.40 39.3 57.8 <2.0 4 12323700 Mill Creek at Opportunity 08/14/2017 1700 75.8 132 0.134 0.26 5.62 7.30 <2.0 <2 08/14/2017 1705 79.2 136 0.139 0.26 5.38 7.50 <2.0 <2
Data 51

Table 9. Analyses of field replicates for water samples, Clark Fork Basin, Montana.—Continued[hh, hours; mm, minutes; lab, laboratory; NTRU, nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; --, no data; <, less than laboratory reporting level; E, estimated]

Site number 

(fig. 1) Site name Date Time (hhmm) Arsenic, filtered (μg/L) Arsenic, unfiltered recoverable (μg/L) Organic carbon, filtered (mg/L) Sediment suspended (percent finer than 0.062 mm) Sediment suspended (mg/L)

12324680 Clark Fork at Goldcreek 10/18/2016 1545 9.9 10.4 -- 88 4

10/18/2016 1550 10.1 10.7 -- 87 4

12323250 Silver Bow Creek below 

Blacktail Creek

03/20/2017 1155 -- -- -- 77 903/20/2017 1200 -- -- -- 75 9

12324400 Clark Fork above Little 

Blackfoot, near Garrison

03/21/2017 1340 10.9 19.0 -- 73 5103/21/2017 1345 10.9 19.9 -- 76 48

12323840 Lost Creek near Anaconda 04/18/2017 0745 3.7 4.4 1.24 69 5

04/18/2017 0750 3.6 4.3 1.24 72 4

12324200 Clark Fork at Deer Lodge 05/09/2017 1345 14.6 22.7 -- 82 36

05/09/2017 1350 14.9 21.7 -- 83 35

12334550 Clark Fork at Turah Bridge, 

near Bonner

05/24/2017 0945 4.4 7.0 -- 53 5605/24/2017 0950 4.4 7.3 -- 55 54

12340500 Clark Fork above Missoula 06/14/2017 1345 7.2 23.7 -- 65 350

06/14/2017 1350 7.0 23.4 -- 65 345

12323750 Silver Bow Creek at 

Warm Springs

07/11/2017 1010 26.8 27.6 4.89 90 207/11/2017 1015 27.7 29.1 5.07 88 1

12323700 Mill Creek at Opportunity 08/14/2017 1700 30.4 30.9 1.86 56 3

08/14/2017 1705 28.9 30.1 1.81 64 1
52 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 10. Precision of analyses of field replicates for stream water samples, Clark Fork Basin, Montana. 

[lab, laboratory; NTRU, nephelometric turbidity ratio unit; mg/L, milligram per liter; μg/L, microgram per liter; mm, millimeter]

Constituent and reporting unit Number of 

replicate pairs

Standard deviation1

(listed units)

Relative standard 

deviation 

(percent)

Within limits2 of 

data-quality objective

Turbidity, unfiltered, lab, NTRU 4 0.16 7.0 Yes

Calcium, filtered, mg/L 9 0.79 2.1 Yes

Magnesium, filtered, mg/L 9 0.08 0.91 Yes

Potassium, filtered, mg/L 3 0.03 2.2 Yes

Sodium, filtered, mg/L 3 0.09 1.5 Yes

Alkalinity, filtered, lab, mg/L 3 0.15 0.16 Yes

Chloride, filtered, mg/L 3 0.00 0.00 Yes

Fluoride, filtered, mg/L 3 0.00 0.00 Yes

Silica, filtered, mg/L 3 0.22 1.8 Yes

Sulfate, filtered, mg/L 3 0.00 0.00 Yes

Cadmium, filtered, μg/L 8 0.01 21 No3

Cadmium, unfiltered recoverable, μg/L 8 0.01 4.2 Yes

Copper, filtered, μg/L 8 0.18 3.6 Yes

Copper, unfiltered recoverable, μg/L 8 3.3 8.0 Yes

Iron, filtered, μg/L 8 2.4 5.3 Yes

Iron, unfiltered recoverable, μg/L 8 66 5.8 Yes

Lead, filtered, μg/L 8 0.01 7.5 Yes

Lead, unfiltered recoverable, μg/L 8 0.11 1.8 Yes

Manganese, filtered, μg/L 8 0.45 2.2 Yes

Manganese, unfiltered recoverable, μg/L 8 2.4 2.0 Yes

Zinc, filtered, μg/L 7 0.20 5.3 Yes

Zinc, unfiltered recoverable, μg/L 7 0.85 1.5 Yes

Arsenic, filtered, μg/L 8 0.45 3.3 Yes

Arsenic, unfiltered recoverable, μg/L 8 0.56 3.1 Yes

Organic carbon, filtered, mg/L 3 0.08 2.8 Yes

Sediment, suspended, percent finer than 0.062 mm 9 2.3 3.2 Yes

Sediment, suspended, mg/L 9 1.6 2.5 Yes

1

Standard deviation is calculated using one-half of the laboratory reporting level for censored values (less than the laboratory reporting level).

2

The data-quality objective for an acceptable level of precision is a maximum relative standard deviation of 20 percent for field replicate analyses (table 3).

3

Exceedence of the data-quality objective resulted from a statistical artifact of calculating the difference between one replicate sample pair for which one value 

is less than the laboratory reporting level. Because analytical variation, in percent, can be large at very low concentrations, the precision may not be representative of analytical performance at detectable concentrations.
Data 53

Table 11. Precision of analyses of laboratory replicates for stream water samples, Clark Fork Basin, Montana.

[mg/L, milligram per liter; μg/L, microgram per liter]

Constituent and reporting unit Number of 

replicate pairs

Standard deviation, 

in listed units

Relative standard deviation, in 

percent

Within limits1 of 

data-quality objective

Calcium, filtered, mg/L 7 0.22 0.65 Yes

Magnesium, filtered, mg/L 7 0.04 0.58 Yes

Cadmium, filtered, μg/L 8 0.00 10 Yes

Cadmium, unfiltered recoverable, μg/L 8 0.00 1.94 Yes

Copper, filtered, μg/L 8 0.07 1.37 Yes

Copper, unfiltered recoverable, μg/L 8 1.7 4.34 Yes

Iron, filtered, μg/L 7 1.4 2.60 Yes

Iron, unfiltered recoverable, μg/L 8 7.8 0.67 Yes

Lead, filtered, μg/L 8 0.00 1.33 Yes

Lead, unfiltered recoverable, μg/L 8 0.07 1.14 Yes

Manganese, filtered, μg/L 7 0.19 0.90 Yes

Manganese, unfiltered recoverable, μg/L 8 0.73 0.59 Yes

Zinc, filtered, μg/L 8 0.17 4.94 Yes

Zinc, unfiltered recoverable, μg/L 8 1.1 2.21 Yes

Arsenic, filtered, μg/L 8 0.14 1.07 Yes

Arsenic, unfiltered recoverable, μg/L 8 0.22 1.21 Yes

1

The data-quality objective for an acceptable level of precision is a maximum relative standard deviation of 20 percent for laboratory replicate analyses 

(table 3).

Table 12. Recovery efficiency for analyses of laboratory-spiked deionized-water blank samples.

[μg/L, microgram per liter]

Constituent and reporting unit Number of 

samples

95-percent confidence 

interval for spike recovery, 

in percent

Mean spike recovery, 

in percent

Within limits1 of 

data-quality objective

Cadmium, filtered, μg/L 5 94.0–122 108 Yes

Cadmium, unfiltered recoverable, μg/L 5 97.8–104 101 Yes

Copper, filtered, μg/L 5 87.3–117 102 Yes

Copper, unfiltered recoverable, μg/L 5 99.8–114 107 Yes

Iron, filtered, μg/L 5 97.3–103 100 Yes

Iron, unfiltered recoverable, μg/L 5 99.4–107 103 Yes

Lead, filtered, μg/L 5 53.4–110 81.5 No2

Lead, unfiltered recoverable, μg/L 5 95.3–103 99.2 Yes

Manganese, filtered, μg/L 5 88.9–104 96.3 Yes

Manganese, unfiltered recoverable, μg/L 5 96.4–106 101 Yes

Zinc, filtered, μg/L 5 97.2–109 103 Yes

Zinc, unfiltered recoverable, μg/L 5 95.3–109 102 Yes

Arsenic, filtered, μg/L 5 93.6–103 98.5 Yes

Arsenic, unfiltered recoverable, μg/L 5 96.0–102 99.1 Yes

1

The data-quality objective for acceptable bias is a maximum deviation of 25 percent from a theoretical 100-percent recovery (table 3).

2

Exceedance of the data-quality objective resulted from two samples having low recoveries of 60.0 and 59.8 percent.
54 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 13. Recovery efficiency for analyses of laboratory-spiked stream samples, Clark Fork Basin, Montana.

[μg/L, microgram per liter]

Constituent and reporting unit Number of 

samples

95-percent confidence 

interval for spike recovery, 

in percent

Mean spike recovery, 

in percent

Within limits1 of

data-quality objective

Cadmium, filtered, μg/L 5 85.6–108 96.6 Yes

Cadmium, unfiltered recoverable, μg/L 5 95.1–100 97.8 Yes

Copper, filtered, μg/L 5 90.3–108 99.2 Yes

Copper, unfiltered recoverable, μg/L 5 79.0–106 92.3 Yes

Iron, filtered, μg/L 5 96.6–99.8 98.2 Yes

Iron, unfiltered recoverable, μg/L 5 79.3–96.3 87.8 Yes

Lead, filtered, μg/L 5 91.9–105 98.3 Yes

Lead, unfiltered recoverable, μg/L 5 86.2–101 93.4 Yes

Manganese, filtered, μg/L 5 88.0–106 97.1 Yes

Manganese, unfiltered recoverable, μg/L 5 92.2–105 98.5 Yes

Zinc, filtered, μg/L 5 96.1–116 106 Yes

Zinc, unfiltered recoverable, μg/L 5 95.0–103 99.0 Yes

Arsenic, filtered, μg/L 5 63.9–112 87.8 No2

Arsenic, unfiltered recoverable, μg/L 5 43.4–128 85.9 No3

1

The data-quality objective for acceptable bias is a maximum deviation of 25 percent from a theoretical 100-percent recovery (table 3).

2

Exceedance of the data-quality objective resulted from one sample having a recovery of 65.5 percent. When data from this one spiked-sample set are 

removed from the 95-percent confidence interval calculation, filtered arsenic meets the data-quality objective limit (78.1–108 percent).

3

Exceedance of the data-quality objective resulted from one sample having a recovery of 29.6 percent. When data from this one spiked-sample set are 

removed from the 95-percent confidence interval calculation, filtered arsenic meets the data-quality objective limit (75.2–125 percent).
Data 55

Table 14. Analyses of field blanks for water samples.[hh, hours; mm, minutes; μS/cm, microsiemens per centimeter at 25 degrees Celsius; lab, laboratory; NTRU, nephelometric turbidity ratio unit; mg/L, milligram per liter; <, less than laboratory reporting level; --, no data; μg/L, microgram per liter]

Date Time (hhmm) pH, onsite (standard units) Specific conduc- tance, onsite (μS/cm) Turbidity, unfiltered, lab (NTRU) Calcium, filtered (mg/L) Magnesium, filtered (mg/L) Potassium, filtered (mg/L) Sodium, filtered (mg/L) Alkalinity, filtered, lab (mg/L) Chloride, filtered (mg/L)

10/17/2016 1420 5.3 2 <2.0 <0.022 <0.011 <0.03 <0.06 <4.0 <0.02103/13/2017 1200 5.6 2 <2.0 <0.022 <0.011 <0.06 <0.10 <4.0 <0.0204/19/2017 1025 5.4 2 -- <0.022 <0.011 -- -- -- --05/09/2017 0730 5.5 2 <2.0 <0.022 <0.011 <0.06 <0.10 <4.0 <0.0205/23/2017 1350 5.5 2 -- <0.022 <0.011 -- -- -- --06/14/2017 0940 5.4 2 -- <0.022 <0.011 -- -- -- --07/10/2017 2000 5.5 2 -- <0.022 <0.011 -- -- -- --08/15/2017 1145 5.6 2 <2.0 <0.022 <0.011 <0.10 <0.10 <4.0 <0.02

Date

Fluoride, 

filtered 

(mg/L)

Silica, 

filtered 

(mg/L)

Sulfate, 

filtered 

(mg/L)

Nitrate plus 

nitrite, 

filtered 

(mg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

Copper,

 filtered 

(μg/L)

Copper, 

unfiltered 

recoverable 

(μg/L)

Iron, 

filtered 

(μg/L)

Iron, 

unfiltered 

recoverable 

(μg/L)

10/17/2016 <0.01 <0.018 <0.02 -- <0.030 <0.03 0.22 <0.2 <4.0 <4.6103/13/2017 <0.01 <0.018 <0.02 <0.01 <0.030 <0.03 <0.20 <0.2 <5.0 <4.604/19/2017 -- -- -- -- <0.030 <0.03 <0.20 <0.2 <5.0 <10.005/09/2017 <0.01 0.031 <0.02 -- <0.030 <0.03 <0.20 <0.2 <5.0 <10.005/23/2017 -- -- -- -- <0.030 <0.03 <0.20 <0.2 <10.0 <10.006/14/2017 -- -- -- -- <0.030 <0.03 0.21 <0.2 <10.0 <10.007/10/2017 -- -- -- -- <0.030 <0.03 0.26 <0.2 <10.0 <10.008/15/2017 <0.01 <0.018 <0.02 -- <0.030 <0.03 <0.20 0.2 <10.0 <10.0

Date

Lead, 

filtered 

(μg/L)

Lead, 

unfiltered 

recoverable 

(μg/L)

Manganese, 

filtered 

(μg/L)

Manganese, 

unfiltered 

recoverable 

(μg/L)

Zinc, 

filtered 

(μg/L)

Zinc, 

unfiltered 

recoverable 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Arsenic, 

unfiltered 

recoverable 

(μg/L)

Organic 

carbon, 

filtered 

(mg/L)

10/17/2016 <0.020 <0.02 <0.40 <0.4 <2.0 <2 <0.05 <0.1 <0.23103/13/2017 <0.020 <0.02 <0.40 <0.4 <2.0 <2 <0.05 <0.1 <0.2304/19/2017 <0.020 <0.02 <0.40 <0.4 <2.0 <2 <0.05 <0.1 --05/09/2017 <0.020 <0.02 <0.40 <0.4 <2.0 <2 <0.05 <0.1 <0.2305/23/2017 <0.020 <0.02 <0.40 <0.4 <2.0 <2 <0.05 <0.1 --06/14/2017 <0.020 <0.02 <0.40 <0.4 <2.0 <2 <0.05 <0.1 --07/10/2017 <0.020 <0.02 <0.40 <0.4 <2.0 <2 <0.05 <0.1 --08/15/2017 <0.020 <0.02 <0.40 <0.4 <2.0 <2 <0.05 <0.1 <0.23

1Annual office equipment blank collected before any equipment was used in the field.
56 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana Table 15. Bed-sediment data for the Clark Fork Basin, Montana, August 2017. [Trace-element concentrations in bed sediment were determined for the fine-grained fraction (material less than 0.063 millimeter in diameter). Reported concentrations are the mean of all replicate aliquot analyses from each composite sample. μg/g, microgram per gram of dry sample weight; <, less than laboratory reporting level] Site number (fig. 1) Site name Number of composite samples Concentration (μg/g) Arsenic Cadmium Chromium Copper Iron Lead Manganese Nickel Zinc 12323600 Silver Bow Creek at Opportunity 3 16.4 7.1 25.8 452 30,200 95.6 3,250 14.8 1,350 12323750 Silver Bow Creek at Warm Springs

3 75.2 5.3 19.3 257 22,900 75.6 5,120 14.7 609

12323770 Warm Springs Creek at Warm 

Springs

3 59.6 2.7 31.4 771 22,700 78.7 2,790 34.3 442

12323800 Clark Fork near Galen 3 102 4.0 30.6 780 26,300 105 4,920 29.1 765461415112450801 Clark Fork below Lost Creek, 

near Galen 

3 119 4.7 25.2 1,440 29,700 195 2,190 15.2 1,170

461559112443301 Clark Fork at county bridge, near 

Racetrack 

3 75.7 4.6 20.0 1,040 25,200 140 2,210 12.9 975

461903112440701 Clark Fork at Demspey Creek 

diversion, near Racetrack 

3 59.2 3.8 13.5 718 18,800 104 1,580 9.0 875

12324200 Clark Fork at Deer Lodge 3 78.2 4.3 32.6 1,090 27,600 150 1,240 13.2 98112324400 Clark Fork above Little Blackfoot 

River, near Garrison

3 59.1 3.6 30.1 940 24,300 139 1,820 13.0 964

12324680 Clark Fork at Goldcreek 3 31.9 2.2 23.2 415 17,900 77.7 1,360 9.5 57912331800 Clark Fork near Drummond 3 41.4 5.1 23.1 442 20,400 82.0 1,440 13.0 1,10012334550 Clark Fork at Turah Bridge, near 

Bonner 

3 26.1 2.0 24.0 284 20,800 58.4 1,220 13.1 628

12340000 Blackfoot River near Bonner 3 5.5 <0.04 18.0 16.4 17,900 9.9 397 10.9 59.912340500 Clark Fork above Missoula 3 16.4 1.2 21.2 162 19,000 38.4 602 12.0 417
Data 57

Table 16. Recovery efficiency for analyses of standard reference materials for bed-sediment samples.

[Dilution ratio is the proportion of initial volume of concentrated nitric acid used as a digesting reagent to final volume 

of solution after addition of 0.6N (normal) hydrochloric acid used for reconstituting dried residue. μg/g, microgram per 

gram of dry sample weight; SRM, standard reference material (agricultural soils)]

Constituent Number of 

analyses

Dilution 

ratio

Certified 

concentration 

(μg/g)

Mean SRM 

recovery

(percent)

95-percent confidence 

interval for SRM recovery 

(percent)

SRM sample 2709a

Arsenic 10 1:10 10.5 50.2 47.1–53.3

Cadmium 10 1:10 0.371 53.6 51.7–55.5

Chromium 10 1:10 130 67.6 66.1–69.0

Copper 10 1:10 33.9 76.4 74.8–78.0

Iron 10 1:10 33,600 87.4 86.6–88.3

Lead 10 1:10 17.3 45.0 43.9–46.1

Manganese 10 1:10 529 84.9 83.6–86.3

Nickel 10 1:10 85 87.7 87.2–88.1

Zinc 10 1:10 103 90.0 89.5–90.5

SRM sample 2711a

Arsenic 10 1:10 107 89.7 86.8–92.5

Cadmium 10 1:10 54.1 97.7 96.6–99.0

Chromium 10 1:10 52.3 55.6 54.3–56.9

Copper 10 1:10 140 91.9 90.6–93.2

Iron 10 1:10 28,200 83.7 82.6–84.8

Lead 10 1:10 1,400 97.4 96.5–98.3

Manganese 10 1:10 675 79.3 77.7–80.9

Nickel 10 1:10 21.7 88.0 87.1–88.9

Zinc 10 1:10 414 94.6 93.6–95.6
58 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana Table 17. Analyses of procedural blanks for bed-sediment samples. [Dilution ratio is the proportion of initial volume of concentrated nitric acid used as a digesting reagent to final volume of solution after addition of 0.6N (normal) hydrochloric acid used for reconstituting dried residue. μg/mL, microgram per milliliter; <, less than minimum reporting level for liquid-phase concentration, in micrograms per milliliter] Site number (fig. 1) Site name Dilution ratio Concentration (μg/mL) Arsenic Cadmium Chromium Copper Iron Lead Manganese Nickel Zinc 12323600 Silver Bow Creek at Opportunity 1:10 <0.002 <0.0001 <0.008 <0.008 <0.08 <0.005 <0.0007 <0.0008 <0.006 12323750 Silver Bow Creek at Warm Springs 1:10 <0.002 <0.0001 <0.008 <0.008 <0.08 <0.005 <0.0007 <0.0008 <0.006 12323800 Clark Fork near Galen 1:10 <0.002 <0.0001 <0.008 <0.008 <0.08 <0.005 <0.0007 <0.0008 <0.006 12323770 Warm Springs Creek at Warm Springs 1:10 <0.002 <0.0001 <0.008 <0.008 <0.08 <0.005 <0.0007 <0.0008 <0.006 461415112450801 Clark Fork below Lost Creek, near Galen 1:10 <0.002 <0.0001 <0.008 <0.008 <0.08 <0.005 <0.0007 <0.0008 <0.006 461559112443301 Clark Fork at county bridge, near Racetrack 1:10 <0.002 <0.0001 <0.008 <0.008 <0.08 <0.005 <0.0007 <0.0008 <0.006 461903112440701 Clark Fork at Dempsey Creek diversion, near Racetrack 1:10 <0.002 <0.0001 <0.008 <0.008 <0.08 <0.005 <0.0007 <0.0008 <0.006 12324200 Clark Fork at Deer Lodge 1:10 <0.002 <0.0001 <0.008 <0.008 <0.08 <0.005 <0.0007 <0.0008 <0.006 12324400 Clark Fork above Little Blackfoot River, near Garrison 1:10 <0.002 <0.0001 <0.02 <0.008 <0.7 <0.005 <0.003 <0.009 <0.006 12324680 Clark Fork at Goldcreek 1:10 <0.002 <0.0001 <0.008 <0.008 <0.08 <0.005 <0.0007 <0.0008 <0.006 12331800 Clark Fork near Drummond 1:10 <0.002 <0.0001 <0.008 <0.008 <0.08 <0.005 <0.0007 <0.0008 <0.006 12334550 Clark Fork at Turah Bridge, near Bonner 1:10 <0.002 <0.0001 <0.008 <0.008 <0.08 <0.005 <0.0007 <0.0008 <0.006 12340000 Blackfoot River near Bonner 1:10 <0.002 <0.0001 <0.008 <0.008 <0.08 <0.005 <0.0007 <0.0008 <0.006 12340500 Clark Fork above Missoula 1:10 <0.002 <0.0001 <0.008 <0.008 <0.08 <0.005 <0.0007 <0.0008 <0.006
Data 59

Table 18. Biological data for the Clark Fork Basin, Montana, August 2017.

[Analyses are for the whole-body tissue of aquatic insects. Composite samples were made by combining similar-sized insects of the same species into a sample 

of sufficient mass for analysis. Concentrations for biota samples composed of two or more composite samples are the means of all analyses. All tissues were 

analyzed undiluted (dilution ratio 1:1). μg/g, microgram per gram of dry sample weight]

Taxon

Number of 

composite 

samples

Concentration (μg/g)

Arsenic Cadmium Chromium Copper Iron Lead Manganese Nickel Zinc

12323600—Silver Bow Creek at Opportunity

Hydropsyche cockerelli 2 5.1 3.1 3.5 133 2,200 11.5 3,130 3.3 489

Hydropscyhe species 1 3.5 1.0 <6.8 71.0 1,250 9.4 2,750 3.6 380

12323750—Silver Bow Creek at Warm Springs

Hydropsyche cockerelli 2 8.5 0.4 0.9 30.7 703 2.6 1,040 1.4 152

Hydropscyhe occidentalis 1 15.6 1.0 1.9 42.0 1,670 6.5 2,320 2.6 186

12323770—Warm Springs Creek at Warm Springs

Arctopscyhe grandis 2 8.2 2.7 <3.0 115 1,290 6.3 1,590 7.0 325

Hesperoperla pacifica 2 2.4 0.9 4.1 52.3 403 1.6 332 1.6 457

Hydropsyche species 1 13.1 1.3 3.5 155 2,260 11.3 2,030 8.8 214

12323800—Clark Fork near Galen

Hydropsyche cockerelli 2 10.4 1.5 2.9 79.3 1,460 7.6 2,020 3.4 210

Hydropsyche species 1 7.2 1.2 0.6 55.9 1,090 6.4 1,920 3.9 208

461415112450801—Clark Fork below Lost Creek, near Galen

Hydropsyche cockerelli 2 14.4 2.1 2.6 155 2,030 17.6 1,600 3.2 243

Hydropscyhe occidentalis 1 13.6 1.6 <8.9 167 2,080 19.5 2,170 6.4 266

461559112443301--Clark Fork at county bridge, near Racetrack

Hydropsyche cockerelli 2 11.5 1.3 3.0 137 1,730 11.1 1,590 2.8 233

Hydropscyhe occidentalis 1 15.0 1.7 1.8 168 2,070 14.6 2,820 5.7 311

461903112440701—Clark Fork at Dempsey Creek diversion, near Racetrack

Arctopscyhe grandis 1 5.8 2.2 0.5 80.8 661 5.1 956 1.4 202

Hydropsyche cockerelli 2 9.3 1.6 2.9 118 1,720 9.9 997 1.6 193

Hydropsyche species 2 8.7 1.4 2.3 115 1,420 7.7 983 1.5 188

12324200—Clark Fork at Deer Lodge

Hydropsyche cockerelli 2 11.9 2.8 4.1 181 2,060 16.2 1,350 2.1 252

Hydropscyhe occidentalis 1 10.0 1.6 3.0 152 1,750 14.6 1,230 2.6 250

12324400—Clark Fork above Little Blackfoot River, near Garrison

Arctopscyhe grandis 2 3.6 1.0 <0.6 42.1 359 4.2 645 0.6 180

Hydropsyche cockerelli 2 6.4 1.3 1.3 111 1,030 10.8 1,060 1.5 208

Hydropscyhe occidentalis 1 7.5 1.6 <1.5 120 1,190 12.6 1,340 1.9 240

12324680—Clark Fork at Goldcreek

Arctopscyhe grandis 2 7.9 1.0 1.2 61.0 807 4.5 966 1.2 163

Hydropsyche cockerelli 3 10.2 1.2 3.2 114 1,750 9.7 1,260 2.0 201

Hydropscyhe occidentalis 1 8.9 1.0 3.5 81.0 1,200 8.0 1,230 2.0 181

12331800—Clark Fork near Drummond

Arctopscyhe grandis 1 3.6 1.3 0.1 37.5 390 3.3 687 0.7 177

Claassenia sabulosa 1 1.4 0.8 0.3 60.6 212 1.1 143 0.6 240

Hydropsyche cockerelli 1 7.6 1.2 1.6 84.6 1,690 8.2 1,070 2.0 203

Hydropscyhe occidentalis 1 6.5 1.0 2.1 70.7 1,420 8.0 1,240 2.3 231

Hydropsyche species 2 7.8 1.2 3.1 92.6 2,190 10.4 1,380 2.4 239
60 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 18. Biological data for the Clark Fork Basin, Montana, August 2017.—Continued

[Analyses are for the whole-body tissue of aquatic insects. Composite samples were made by combining similar-sized insects of the same species into a sample 

of sufficient mass for analysis. Concentrations for biota samples composed of two or more composite samples are the means of all analyses. All tissues were 

analyzed undiluted (dilution ratio 1:1). μg/g, microgram per gram of dry sample weight]

Taxon

Number of 

composite 

samples

Concentration (μg/g)

Arsenic Cadmium Chromium Copper Iron Lead Manganese Nickel Zinc

12334550—Clark Fork at Turah Bridge, near Bonner

Arctopscyhe grandis 2 4.1 1.8 0.9 34.7 770 3.8 659 1.2 228

Claassenia sabulosa 1 0.8 1.3 <0.6 42.3 106 0.5 96.7 0.4 228

Hydropsyche cockerelli 2 5.6 1.5 3.5 64.9 1,840 7.5 715 2.1 219

Hydropsyche species 1 4.4 1.1 2.6 50.5 1,430 5.9 980 1.7 231

12340000—Blackfoot River near Bonner

Arctopscyhe grandis 1 3.3 0.3 2.0 16.9 1,240 1.4 522 2.2 153

Hydropsyche cockerelli 1 3.8 0.2 5.4 16.2 2,400 2.6 572 2.6 148

Hydropsyche species 1 3.1 0.2 4.4 19.9 2,100 2.0 623 2.4 160

12340500—Clark Fork above Missoula

Arctopscyhe grandis 2 2.4 1.4 <1.1 19.5 501 1.8 784 0.8 191

Claassenia sabulosa 1 1.3 1.4 2.4 35.7 273 1.6 263 1.5 344

Hydropsyche cockerelli 2 4.5 1.1 3.7 42.9 1,770 5.5 1,010 2.3 216

Hydropsyche species 1 3.3 1.0 <3.4 45.4 1,140 4.6 1,180 2.8 223

Table 19. Recovery efficiency for analyses of certified reference material for biota samples.

[μg/g, microgram per gram of dry sample weight; CRM, certified reference material (lobster hepatopancreas)]

Constituent Number of 

analyses

Certified 

concentration 

(μg/g)

Mean CRM 

recovery

(percent)

95-percent confidence 

interval for CRM recovery

(percent)

CRM sample TORT–3

Arsenic 12 59.5 108 107–108

Cadmium 12 42.3 86.4 89.2–84.0

Chromium 12 1.95 86.6 84.0–89.2

Copper 12 497 91.9 91.4–92.4

Iron 12 179 92.4 92.1–92.8

Lead 12 0.225 185 182–187

Manganese 12 15.6 92.2 91.4–93.0

Nickel 12 5.3 80.4 79.9–80.9

Zinc 12 136 86.8 86.1–87.4
Data 61

Table 20. Analyses of procedural blanks for biota samples.[Procedural blanks were not diluted before analyses. μg/mL, microgram per milliliter; <, less than minimum reporting level for liquid-phase concentration, in micrograms per milliliter]

Site number 

(fig. 1) Site name Dilution ratio Concentration (μg/mL) Arsenic Cadmium Chromium Copper Iron Lead Manganese Nickel Zinc

12323600 Silver Bow Creek at Opportunity 1:1 <0.002 <0.003 <0.03 <0.02 <0.03 <0.003 <0.01 <0.003 <0.0112323750 Silver Bow Creek at Warm 

Springs

1:1 <0.002 <0.003 <0.03 <0.02 <0.03 <0.003 <0.01 <0.003 <0.01

12323770 Warm Springs Creek at Warm 

Springs

1:1 <0.002 <0.003 <0.03 <0.02 <0.03 <0.003 <0.01 <0.003 <0.01

12323800 Clark Fork near Galen 1:1 <0.002 <0.003 <0.03 <0.02 <0.03 <0.003 <0.01 <0.003 <0.01461415112450801 Clark Fork below Lost Creek, 

near Galen

1:1 <0.002 <0.003 <0.03 <0.02 <0.03 <0.003 <0.01 <0.003 <0.01

461559112443301 Clark Fork at county bridge, near 

Racetrack

1:1 <0.002 <0.003 <0.03 <0.02 <0.03 <0.003 <0.01 <0.003 <0.01

461903112440701 Clark Fork at Dempsey Creek 

diversion, near Racetrack

1:1 <0.002 <0.003 <0.03 <0.02 <0.03 <0.003 <0.01 <0.003 <0.01

12324200 Clark Fork at Deer Lodge 1:1 <0.002 <0.003 <0.03 <0.02 <0.03 <0.003 <0.01 <0.003 <0.0112324400 Clark Fork above Little Blackfoot River, near Garrison 1:1 <0.002 <0.003 <0.03 <0.02 <0.03 <0.003 <0.01 <0.003 <0.0112324680 Clark Fork at Goldcreek 1:1 <0.002 <0.003 <0.03 <0.02 <0.03 <0.003 <0.01 <0.003 <0.0112331800 Clark Fork near Drummond 1:1 <0.002 <0.003 <0.03 <0.02 <0.03 <0.003 <0.01 <0.003 <0.0112334550 Clark Fork at Turah Bridge, near 

Bonner

1:1 <0.002 <0.003 <0.03 <0.02 <0.03 <0.003 <0.01 <0.003 <0.01

12340000 Blackfoot River near Bonner 1:1 <0.002 <0.003 <0.03 <0.02 <0.03 <0.003 <0.01 <0.003 <0.0112340500 Clark Fork above Missoula 1:1 <0.002 <0.003 <0.03 <0.02 <0.03 <0.003 <0.01 <0.003 <0.01
62 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 21. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through September 2017.

[ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, nephelometric turbidity 

ratio unit; <, less than laboratory reporting level1; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; ton/d, ton 

per day; --, no data]

Property or constituent and reporting unit Number of samples Maximum Minimum Mean Median

12323230—Blacktail Creek at Harrison Avenue, at Butte

Period of record for water-quality data: March 1993–August 1995, December 1996–August 2003, December 2004–September 2017

Streamflow, instantaneous (ft3/s) 187 156 1.9 16 9.7

pH, onsite (standard units) 187 8.4 7.3 7.7 7.7

Specific conductance, onsite (μS/cm) 187 412 116 261 261

Temperature, water (°C) 187 18 1.0 7.9 8.0

Turbidity, unfiltered, lab (NTRU) 31 25 <2.0 1

4.5 3.5

Hardness, filtered (mg/L as CaCO3) 187 153 37.7 104 104

Calcium, filtered (mg/L) 187 42.9 10.6 29.6 29.7

Magnesium, filtered (mg/L) 187 11.1 2.71 7.21 7.16

Potassium, filtered (mg/L) 49 6.4 2 2.75 2.57

Sodium, filtered (mg/L) 49 18 6.4 10.6 10.2

Alkalinity, filtered, lab (mg/L) 21 124 54.5 85.5 78.4

Chloride, filtered (mg/L) 49 18 2.8 8.5 8

Fluoride, filtered (mg/L) 49 0.6 0.18 0.28 0.3

Silica, filtered (mg/L) 49 32 14 24.3 24.4

Sulfate, filtered (mg/L) 49 40.2 14.7 26.2 26

Nitrate plus nitrite, filtered (mg/L) 31 1.24 0.15 0.6 0.5

Cadmium, filtered (μg/L) 185 0.5 <0.03 1

0.04 0.02

Cadmium, unfiltered recoverable (μg/L) 187 0.12 <0.02 1

0.04 <1.00

Copper, filtered (μg/L) 186 10 0.8 3.5 3

Copper, unfiltered recoverable (μg/L) 187 52 0.91 6.22 4.9

Iron, filtered (μg/L) 187 739 15.2 198 180

Iron, unfiltered recoverable (μg/L) 187 4,220 123 660 592

Lead, filtered (μg/L) 187 2.8 <0.03 1

0.18 0.08

Lead, unfiltered recoverable (μg/L) 187 47 <1.00 1

1.51 0.64

Manganese, filtered (μg/L) 187 144 14.2 43.6 38.6

Manganese, unfiltered recoverable (μg/L) 187 240 23.5 60.4 52.7

Zinc, filtered (μg/L) 185 11 <1.00 1

3.14 2.4

Zinc, unfiltered recoverable (μg/L) 187 130 <3.00 1

7.42 4

Arsenic, filtered (μg/L) 186 13 1 4 3

Arsenic, unfiltered recoverable (μg/L) 187 18 1 5 5

Organic carbon, filtered (mg/L) 21 9.52 1.4 4.7 4.3

Sediment, suspended (percent finer than 0.062 mm) 187 97 50 83 85

Sediment, suspended concentration (mg/L) 187 139 1 11 7

Sediment, suspended discharge (ton/d) 187 59 0.01 0.88 0.17
Data 63

Table 21. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through September 

2017.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, nephelometric turbidity 

ratio unit; <, less than laboratory reporting level1; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; ton/d, ton 

per day; --, no data]

Property or constituent and reporting unit Number of samples Maximum Minimum Mean Median

12323250—Silver Bow Creek below Blacktail Creek, at Butte

Period of record for water-quality data: March 1993–August 1995, December 1996–September 2017

Streamflow, instantaneous (ft3/s) 195 202 13 31 26

pH, onsite (standard units) 195 8.2 7.2 7.6 7.6

Specific conductance, onsite (μS/cm) 195 691 209 456 457

Temperature, water (°C) 195 20 1.0 10 10

Turbidity, unflitered, lab (NTRU) 31 18 <2.0 1

4.3 4

Hardness, filtered (mg/L as CaCO3) 195 217 66 147 149

Calcium, filtered (mg/L) 195 62.7 19 41.8 42

Magnesium, filtered (mg/L) 195 16.1 4.51 10.4 10.7

Potassium, filtered (mg/L) 49 35 3.64 7.50 5.7

Sodium, filtered (mg/L) 49 66 12 25 25

Alkalinity, filtered, lab (mg/L) 21 119 66.9 87.7 88.6

Chloride, filtered (mg/L) 48 88 6.7 23.8 21.2

Fluoride, filtered (mg/L) 48 0.8 0.26 0.41 0.4

Silica, filtered (mg/L) 48 28 17 22 22

Sulfate, filtered (mg/L) 48 96 35 71 74

Nitrate plus nitrite, filtered (mg/L) 31 4.4 0.34 1.04 0.96

Cadmium, filtered (μg/L) 195 6.2 0.03 0.74 0.13

Cadmium, unfiltered recoverable (μg/L) 195 6 0.06 1.00 0.23

Copper, filtered (μg/L) 195 303 2.6 25.5 10.5

Copper, unfiltered recoverable (μg/L) 195 550 6.4 58.8 20.9

Iron, filtered (μg/L) 195 392 9.6 103 83.7

Iron, unfiltered recoverable (μg/L) 195 7,400 85.4 743 538

Lead, filtered (μg/L) 195 2.4 <0.50 1

0.40 0.24

Lead, unfiltered recoverable (μg/L) 195 250 0.53 9.13 2.3

Manganese, filtered (μg/L) 195 1,700 20.7 255 113

Manganese, unfiltered recoverable (μg/L) 195 1,600 25.9 292 139

Zinc, filtered (μg/L) 195 2,200 2 241 50.4

Zinc, unfiltered recoverable (μg/L) 195 2,200 20.5 293 62

Arsenic, filtered (μg/L) 195 13.4 2.3 5.7 5.2

Arsenic, unfiltered recoverable (μg/L) 195 45 3 9.0 7.6

Organic carbon, filtered (mg/L) 21 9.97 4.93 7.16 7.21

Sediment, suspended (percent finer than 0.062 mm) 194 98 42 83 85

Sediment, suspended concentration (mg/L) 194 405 2 18 9

Sediment, suspended discharge (ton/d) 194 70 0.08 2.06 0.61
64 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 21. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through September 

2017.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, nephelometric turbidity 

ratio unit; <, less than laboratory reporting level1; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; ton/d, ton 

per day; --, no data]

Property or constituent and reporting unit Number of samples Maximum Minimum Mean Median

12323600—Silver Bow Creek at Opportunity

Period of record for water-quality data: March 1993–August 1995, December 1996–September 2017

Streamflow, instantaneous (ft3/s) 195 648 13 78 56

pH, onsite (standard units) 197 9.5 7.2 8.4 8.3

Specific conductance, onsite (μS/cm) 197 633 202 414 403

Temperature, water (°C) 197 24 –1.0 9.5 9.5

Turbidity, unfiltered, lab (NTRU) 31 12 2 5.8 5.2

Hardness, filtered (mg/L as CaCO3) 197 248 60.2 150 147

Calcium, filtered (mg/L) 197 75 18.5 44.4 44

Magnesium, filtered (mg/L) 197 15 3.42 9.44 9.06

Potassium, filtered (mg/L) 68 16 1.79 4.46 4.1

Sodium, filtered (mg/L) 68 34.5 5.06 18.8 17.6

Alkalinity, filtered, lab (mg/L) 39 122 71.6 93.8 92.9

Chloride, filtered (mg/L) 67 63.9 3.2 18.6 15

Fluoride, filtered (mg/L) 67 0.8 0.16 0.39 0.4

Silica, filtered (mg/L) 67 28 9.56 20.5 21

Sulfate, filtered (mg/L) 67 190 32 65 62

Cadmium, filtered (μg/L) 196 41 0.07 0.84 0.40

Cadmium, unfiltered recoverable (μg/L) 197 49 0.17 1.53 0.87

Copper, filtered (μg/L) 195 450 6.5 35.1 25.4

Copper, unfiltered recoverable (μg/L) 197 3,900 12.1 149 79.6

Iron, filtered (μg/L) 197 397 3 51.5 30.8

Iron, unfiltered recoverable (μg/L) 196 24,100 105 1,300 646

Lead, filtered (μg/L) 197 5.1 <0.50 1

0.60 0.30

Lead, unfiltered recoverable (μg/L) 197 650 0.53 27.8 12.4

Manganese, filtered (μg/L) 197 9,300 25.5 320 227

Manganese, unfiltered recoverable (μg/L) 197 10,000 55.3 425 314

Zinc, filtered (μg/L) 196 13,000 11.2 215 97

Zinc, unfiltered recoverable (μg/L) 197 15,000 27 381 204

Arsenic, filtered (μg/L) 197 34 1 10 9.3

Arsenic, unfiltered recoverable (μg/L) 197 235 5.3 20.6 15.1

Organic carbon, filtered (mg/L) 36 9.07 3.06 5.68 5.66

Sediment, suspended (percent finer than 0.062 mm) 198 95 37 79 84

Sediment, suspended concentration (mg/L) 198 801 3 43 18

Sediment, suspended discharge (ton/d) 195 781 0.18 18.6 2.5
Data 65

Table 21. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through September 

2017.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, nephelometric turbidity 

ratio unit; <, less than laboratory reporting level1; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; ton/d, ton 

per day; --, no data]

Property or constituent and reporting unit Number of samples Maximum Minimum Mean Median

12323670—Mill Creek near Anaconda

Period of record for water-quality data: December 2004–September 2017

Streamflow, instantaneous (ft3/s) 103 309 7.4 64 38

pH, onsite (standard units) 104 8.6 7.5 8.0 7.9

Specific conductance, onsite (μS/cm) 104 213 56 128 129

Temperature, water (°C) 104 17 0.0 8.6 9.0

Turbidity, unfiltered, lab, (NTRU) 97 21 <2.0 1

2.4 <2.0

Hardness, filtered (mg/L as CaCO3) 104 98 23.7 56.4 52.9

Calcium, filtered (mg/L) 104 26.7 7 15.7 14.9

Magnesium, filtered (mg/L) 104 8.01 1.45 4.18 3.88

Potassium, filtered (mg/L) 31 0.84 0.45 0.63 0.63

Sodium, filtered (mg/L) 31 6.04 2.14 3.82 3.64

Alkalinity, filtered, lab (mg/L) 31 85.1 30.8 54.4 52.5

Chloride, filtered (mg/L) 31 0.54 0.16 0.30 0.26

Fluoride, filtered (mg/L) 31 0.37 0.27 0.31 0.3

Silica, filtered (mg/L) 31 16 9.27 12.6 12.5

Sulfate, filtered (mg/L) 31 13.9 3.12 6.17 5.37

Cadmium, filtered (μg/L) 103 0.11 0.02 0.05 0.04

Cadmium, unfiltered recoverable (μg/L) 104 0.19 0.03 0.08 0.07

Copper, filtered (μg/L) 103 5.1 0.72 2.26 2.1

Copper, unfiltered recoverable (μg/L) 103 10.6 1.3 3.71 3.1

Iron, filtered (μg/L) 104 128 21.2 49.7 43.5

Iron, unfiltered recoverable (μg/L) 104 730 64.9 194 156

Lead, filtered (μg/L) 104 0.36 0.02 0.12 0.11

Lead, unfiltered recoverable (μg/L) 104 3.12 0.15 0.70 0.53

Manganese, filtered (μg/L) 104 12 3.09 5.96 5.85

Manganese, unfiltered recoverable (μg/L) 104 36.6 6.2 13.4 11.8

Zinc, filtered (μg/L) 104 4.3 <1.40 1

1.64 1.2

Zinc, unfiltered recoverable (μg/L) 104 9.2 <2.00 1

3.00 2.6

Arsenic, filtered (μg/L) 104 32.9 7.3 15.9 15.1

Arsenic, unfiltered recoverable (μg/L) 104 34.8 7.8 17.1 15.9

Organic carbon, filtered (mg/L) 31 5.1 1.26 2.43 2.35

Sediment, suspended (percent finer than 0.062 mm) 104 97 14 65 68

Sediment, suspended concentration (mg/L) 104 42 1 6 4

Sediment, suspended discharge (ton/d) 103 28 0.02 1.94 0.36
66 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 21. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through September 

2017.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, nephelometric turbidity 

ratio unit; <, less than laboratory reporting level1; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; ton/d, ton 

per day; --, no data]

Property or constituent and reporting unit Number of samples Maximum Minimum Mean Median

12323700—Mill Creek at Opportunity

Period of record for water-quality data: March 2003–September 2017

Streamflow, instantaneous (ft3/s) 118 261 0.43 37 17

pH, onsite (standard units) 120 8.3 7.5 7.9 8

Specific conductance, onsite (μS/cm) 120 242 59 145 142

Temperature, water (°C) 120 20 –1.0 9.3 9.5

Turbidity, unfiltered, lab (NTRU) 38 9.1 <2.0 1

2.5 <2.0

Hardness, filtered (mg/L as CaCO3) 120 112 24 62.3 59.8

Calcium, filtered (mg/L) 120 31 7.01 17.5 16.9

Magnesium, filtered (mg/L) 120 8.44 1.56 4.51 4.34

Potassium, filtered (mg/L) 38 1.02 0.47 0.70 0.72

Sodium, filtered (mg/L) 38 8.15 2.29 4.41 4.13

Alkalinity, filtered, lab (mg/L) 38 88.2 31.9 57.0 55.6

Chloride, filtered (mg/L) 38 0.82 0.18 0.38 0.34

Fluoride, filtered (mg/L) 38 0.4 0.29 0.33 0.32

Silica, filtered (mg/L) 38 16.9 9.47 12.5 12.3

Sulfate, filtered (mg/L) 38 27.7 4.11 10.2 9.4

Cadmium, filtered (μg/L) 120 0.13 0.02 0.06 0.06

Cadmium, unfiltered recoverable (μg/L) 120 0.86 0.03 0.13 0.09

Copper, filtered (μg/L) 120 6.1 1 2.8 2.5

Copper, unfiltered recoverable (μg/L) 120 38.8 1.5 5.9 4.0

Iron, filtered (μg/L) 120 108 15.9 49.2 43.8

Iron, unfiltered recoverable (μg/L) 120 1,960 44.3 284 162

Lead, filtered (μg/L) 120 0.35 <0.04 1

0.14 0.13

Lead, unfiltered recoverable (μg/L) 120 12.7 0.07 1.28 0.53

Manganese, filtered (μg/L) 120 32.8 2.13 6.45 5.05

Manganese, unfiltered recoverable (μg/L) 120 113 2.9 17.5 12.1

Zinc, filtered (μg/L) 119 7.7 <1.40 1

2.61 2.4

Zinc, unfiltered recoverable (μg/L) 120 41 <2.00 1

5.85 4

Arsenic, filtered (μg/L) 120 55.1 9 20.8 18.9

Arsenic, unfiltered recoverable (μg/L) 120 53.5 10 23.4 21.8

Organic carbon, filtered (mg/L) 38 4.86 1.33 2.46 2.44

Sediment, suspended (percent finer than 0.062 mm) 120 91 26 69 71

Sediment, suspended concentration (mg/L) 120 107 1 11 4

Sediment, suspended discharge (ton/d) 118 55 <0.1 2.91 0.20
Data 67

Table 21. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through September 

2017.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, nephelometric turbidity 

ratio unit; <, less than laboratory reporting level1; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; ton/d, ton 

per day; --, no data]

Property or constituent and reporting unit Number of samples Maximum Minimum Mean Median

12323710—Willow Creek near Anaconda

Period of record for water-quality data: December 2004–September 2017

Streamflow, instantaneous (ft3/s) 94 114 1.0 15 9.2

pH, onsite (standard units) 97 8.2 7.5 7.7 7.7

Specific conductance, onsite (μS/cm) 97 151 65 102 105

Temperature, water (°C) 97 16.0 0.0 7.4 7.5

Turbidity, unfiltered, lab (NTRU) 90 39 <2.0 1

5.3 3.2

Hardness, filtered (mg/L as CaCO3) 97 56.3 21.5 37.5 38.5

Calcium, filtered (mg/L) 97 18.3 7.22 12.5 13

Magnesium, filtered (mg/L) 97 2.6 0.78 1.50 1.48

Potassium, filtered (mg/L) 31 1.13 0.7 0.91 0.91

Sodium, filtered (mg/L) 31 7.94 4.33 5.87 5.99

Alkalinity, filtered, lab (mg/L) 31 55.4 26.3 41.4 40

Chloride, filtered (mg/L) 31 0.85 0.27 0.46 0.37

Fluoride, filtered (mg/L) 31 0.08 0.06 0.07 0.07

Silica, filtered (mg/L) 31 26.9 20.9 24.6 24.8

Sulfate, filtered (mg/L) 31 15.7 4.75 7.21 6.29

Cadmium, filtered (μg/L) 95 0.05 <0.02 1

0.03 0.03

Cadmium, unfiltered recoverable (μg/L) 97 0.33 <0.03 1

0.05 0.05

Copper, filtered (μg/L) 97 5.5 0.82 2.3 2.2

Copper, unfiltered recoverable (μg/L) 97 16.8 1 3.6 3

Iron, filtered (μg/L) 97 277 28 94.9 84.2

Iron, unfiltered recoverable (μg/L) 97 2,380 85.7 353 235

Lead, filtered (μg/L) 97 0.39 0.03 0.18 0.17

Lead, unfiltered recoverable (μg/L) 97 7.96 0.1 0.82 0.53

Manganese, filtered (μg/L) 97 34.5 6.04 13.3 11.7

Manganese, unfiltered recoverable (μg/L) 97 99.9 12.8 24.7 21.4

Zinc, filtered (μg/L) 97 3.3 <1.40 1

1.64 1.2

Zinc, unfiltered recoverable (μg/L) 97 17.8 <2.00 1

3.04 2

Arsenic, filtered (μg/L) 97 25.7 7.7 16.0 15.2

Arsenic, unfiltered recoverable (μg/L) 97 27.9 9.8 17.1 15.6

Organic carbon, filtered (mg/L) 31 7.19 0.25 4.85 4.63

Sediment, suspended (percent finer than 0.062 mm) 97 97 25 78 85

Sediment, suspended concentration (mg/L) 97 195 1 13 4

Sediment, suspended discharge (ton/d) 94 50 <0.1 1.66 0.11
68 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 21. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through September 

2017.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, nephelometric turbidity 

ratio unit; <, less than laboratory reporting level1; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; ton/d, ton 

per day; --, no data]

Property or constituent and reporting unit Number of samples Maximum Minimum Mean Median

12323720—Willow Creek at Opportunity

Period of record for water-quality data: March 2003–September 2017

Streamflow, instantaneous (ft3/s) 120 116 4.5 17 10

pH, onsite (standard units) 120 9.0 7.6 8.1 8.0

Specific conductance, onsite (μS/cm) 120 380 116 259 275

Temperature, water (°C) 120 24.0 0.0 10.9 11.0

Turbidity, unfiltered, lab (NTRU) 38 11 <2.0 1

4.4 3.8

Hardness, filtered (mg/L as CaCO3) 120 173 50.4 113 118

Calcium, filtered (mg/L) 120 48.4 15.6 32.9 34.9

Magnesium, filtered (mg/L) 120 12.8 2.75 7.41 7.88

Potassium, filtered (mg/L) 38 2.73 0.94 1.46 1.39

Sodium, filtered (mg/L) 38 16.7 6.12 9.40 9.16

Alkalinity, filtered, lab (mg/L) 38 175 51.6 101 111

Chloride, filtered (mg/L) 38 3.28 0.79 1.75 1.65

Fluoride, filtered (mg/L) 38 0.66 0.12 0.35 0.38

Silica, filtered (mg/L) 38 30.8 18.4 23.5 23.5

Sulfate, filtered (mg/L) 38 36.5 9.21 18.4 18.4

Cadmium, filtered (μg/L) 120 0.12 <0.03 1

0.04 0.03

Cadmium, unfiltered recoverable (μg/L) 119 0.52 0.02 0.10 0.07

Copper, filtered (μg/L) 120 21.4 0.87 5.08 3.65

Copper, unfiltered recoverable (μg/L) 119 48.8 2.6 10.2 7.8

Iron, filtered (μg/L) 120 274 6.1 54.6 48.4

Iron, unfiltered recoverable (μg/L) 119 1,670 27.4 290 241

Lead, filtered (μg/L) 120 0.89 0.04 0.24 0.21

Lead, unfiltered recoverable (μg/L) 119 14.4 0.27 2.05 1.43

Manganese, filtered (μg/L) 120 200 3.3 32.1 25.7

Manganese, unfiltered recoverable (μg/L) 119 228 4.7 44.9 38

Zinc, filtered (μg/L) 120 19.8 <1.40 1

4.68 3.8

Zinc, unfiltered recoverable (μg/L) 119 68 1.2 11.2 9

Arsenic, filtered (μg/L) 120 164 9.3 37.5 25.7

Arsenic, unfiltered recoverable (μg/L) 120 164 11.4 39.8 27.4

Organic carbon, filtered (mg/L) 38 12.9 1.6 5.05 5.11

Sediment, suspended (percent finer than 0.062 mm) 120 99 54 87 90

Sediment, suspended concentration (mg/L) 120 87 1 10 6

Sediment, suspended discharge (ton/d) 120 11 0.01 0.81 0.18
Data 69

Table 21. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through September 

2017.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, nephelometric turbidity 

ratio unit; <, less than laboratory reporting level1; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; ton/d, ton 

per day; --, no data]

Property or constituent and reporting unit Number of samples Maximum Minimum Mean Median

12323750—Silver Bow Creek at Warm Springs

Period of record for water-quality data: March 1993–September 2017

Streamflow, instantaneous (ft3/s) 204 1,030 16 139 91

pH, onsite (standard units) 202 9.6 7.9 8.8 8.8

Specific conductance, onsite (μS/cm) 202 783 182 451 455

Temperature, water (°C) 203 25.0 0.0 10.3 10.0

Turbidity, unfiltered, lab (NTRU) 31 11 <2.0 1

3.7 3

Hardness, filtered (mg/L as CaCO3) 202 314 74.9 187 189

Calcium, filtered (mg/L) 202 90.4 22.5 54.2 54.1

Magnesium, filtered (mg/L) 202 21.4 4.52 12.4 12.2

Potassium, filtered (mg/L) 62 8.3 1.72 3.81 3.81

Sodium, filtered (mg/L) 62 23 8.2 16.1 16.8

Alkalinity, filtered, lab (mg/L) 34 113 69.2 91.3 94.0

Chloride, filtered (mg/L) 62 26.2 1.3 11.6 10.4

Fluoride, filtered (mg/L) 62 1.2 0.41 0.66 0.64

Silica, filtered (mg/L) 62 20 6.3 12.9 12.7

Sulfate, filtered (mg/L) 62 210 39.2 97.8 91.3

Cadmium, filtered (μg/L) 202 0.31 <0.03 1

0.06 0.03

Cadmium, unfiltered recoverable (μg/L) 202 0.57 <0.03 1

0.12 0.07

Copper, filtered (μg/L) 202 40 1.6 6.9 5

Copper, unfiltered recoverable (μg/L) 202 96.8 2.4 14.1 10

Iron, filtered (μg/L) 202 103 <5.00 1

21.9 18.4

Iron, unfiltered recoverable (μg/L) 202 3,000 35.8 306 237

Lead, filtered (μg/L) 202 1 <0.08 1

0.14 0.06

Lead, unfiltered recoverable (μg/L) 202 41.8 <1.00 1

2.14 1.24

Manganese, filtered (μg/L) 202 875 5.03 107 72.9

Manganese, unfiltered recoverable (μg/L) 202 899 24 163 127

Zinc, filtered (μg/L) 202 73 <1.00 1

6.25 3.5

Zinc, unfiltered recoverable (μg/L) 202 180 2 25.9 14.1

Arsenic, filtered (μg/L) 202 60 6.8 22.6 21.9

Arsenic, unfiltered recoverable (μg/L) 202 94 9.9 26 24.3

Organic carbon, filtered (mg/L) 31 9.29 2.88 4.93 4.86

Sediment, suspended (percent finer than 0.062 mm) 203 98 35 83 86

Sediment, suspended concentration (mg/L) 204 229 1 9 6

Sediment, suspended discharge (ton/d) 204 279 0.05 5.54 1.45
70 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 21. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through September 

2017.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, nephelometric turbidity 

ratio unit; <, less than laboratory reporting level1; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; ton/d, ton 

per day; --, no data]

Property or constituent and reporting unit Number of samples Maximum Minimum Mean Median

12323760—Warm Springs Creek near Anaconda

Period of record for water-quality data: October 2005–September 2017

Streamflow, instantaneous (ft3/s) 72 573 41 134 93

pH, onsite (standard units) 72 8.8 7.8 8.4 8.4

Specific conductance, onsite (μS/cm) 72 278 125 222 237

Temperature, water (°C) 72 16.0 0.5 8.0 8.0

Turbidity, unfiltered, lab (NTRU) 66 18 <2.00 1

1.94 <2.00

Hardness, filtered (mg/L as CaCO3) 72 145 58.5 109 115

Calcium, filtered (mg/L) 72 42.8 18.5 32.7 34.3

Magnesium, filtered (mg/L) 72 9.34 2.96 6.66 6.99

Potassium, filtered (mg/L) 23 1.37 0.8 1.11 1.17

Sodium, filtered (mg/L) 23 3.6 1.54 2.64 2.83

Alkalinity, filtered, lab (mg/L) 23 127 60.3 102 111

Chloride, filtered (mg/L) 23 1.53 0.49 1.01 1.06

Fluoride, filtered (mg/L) 23 0.42 0.29 0.37 0.38

Silica, filtered (mg/L) 23 11.7 8.25 10.1 9.94

Sulfate, filtered (mg/L) 23 16.9 7.98 12.8 13.5

Cadmium, filtered (μg/L) 72 0.05 <0.02 1

0.02 0.02

Cadmium, unfiltered recoverable (μg/L) 72 0.14 <0.02 1

0.03 0.03

Copper, filtered (μg/L) 71 6.4 <0.80 1

1.08 0.88

Copper, unfiltered recoverable (μg/L) 72 28 <0.80 1

3.11 2.1

Iron, filtered (μg/L) 72 37 <4.00 1

7.82 6.2

Iron, unfiltered recoverable (μg/L) 72 1,000 19.1 119 75.1

Lead, filtered (μg/L) 72 0.11 <0.02 1

0.02 <0.08

Lead, unfiltered recoverable (μg/L) 72 3.51 0.07 0.39 0.25

Manganese, filtered (μg/L) 72 4.2 0.13 1.30 1.1

Manganese, unfiltered recoverable (μg/L) 72 45.2 0.9 5.94 4.2

Zinc, filtered (μg/L) 72 5.6 <1.4 1

1.1 <2.0

Zinc, unfiltered recoverable (μg/L) 72 20.1 <2.0 1

3.6 2

Arsenic, filtered (μg/L) 72 3.9 1.3 2.2 2.1

Arsenic, unfiltered recoverable (μg/L) 72 5.6 1.5 2.6 2.4

Organic carbon, filtered (mg/L) 23 3.19 0.77 1.48 1.28

Sediment, suspended (percent finer than 0.062 mm) 72 84 32 66 67

Sediment, suspended concentration (mg/L) 72 65 1 7 4

Sediment, suspended discharge (ton/d) 72 68 0.13 3.92 0.92
Data 71

Table 21. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through September 

2017.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, nephelometric turbidity 

ratio unit; <, less than laboratory reporting level1; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; ton/d, ton 

per day; --, no data]

Property or constituent and reporting unit Number of samples Maximum Minimum Mean Median

12323770—Warm Springs Creek at Warm Springs

Period of record for water-quality data: March 1993–September 2017

Streamflow, instantaneous (ft3/s) 160 420 2.8 95 57

pH, onsite (standard units) 159 8.7 7.4 8.2 8.2

Specific conductance, onsite (μS/cm) 159 795 139 291 299

Temperature, water (°C) 160 20.0 0.0 8.2 8.0

Turbidity, unfiltered, lab (NTRU) 38 13 <2.0 1

2.7 <2.0

Hardness, filtered (mg/L as CaCO3) 159 415 39.8 142 146

Calcium, filtered (mg/L) 159 130 10.5 43.2 44.1

Magnesium, filtered (mg/L) 159 22 3.29 8.25 8.38

Potassium, filtered (mg/L) 57 4.7 0.83 1.45 1.35

Sodium, filtered (mg/L) 57 19.2 1.78 3.64 3.31

Alkalinity, filtered, lab (mg/L) 40 149 60.1 114 125

Chloride, filtered (mg/L) 57 3.6 0.5 1.3 1.2

Fluoride, filtered (mg/L) 57 0.6 0.3 0.4 0.4

Silica, filtered (mg/L) 57 13 8.4 10.4 10.1

Sulfate, filtered (mg/L) 57 270 15.3 44.4 35.4

Cadmium, filtered (μg/L) 158 0.1 <0.03 1

0.04 0.03

Cadmium, unfiltered recoverable (μg/L) 158 0.41 <0.03 1

0.08 0.04

Copper, filtered (μg/L) 158 16 1 3.12 2.65

Copper, unfiltered recoverable (μg/L) 158 147 2.3 17.7 8.6

Iron, filtered (μg/L) 159 36.8 <5.00 1

12.5 11.2

Iron, unfiltered recoverable (μg/L) 159 2,110 17.2 286 120

Lead, filtered (μg/L) 158 1.8 <0.02 1

0.06 <1.00

Lead, unfiltered recoverable (μg/L) 158 14 <1.00 1

1.73 0.61

Manganese, filtered (μg/L) 158 570 18.8 98.7 68.7

Manganese, unfiltered recoverable (μg/L) 158 1,400 37.1 173 128

Zinc, filtered (μg/L) 158 10 <1.00 1

1.95 1.1

Zinc, unfiltered recoverable (μg/L) 159 60 <2.00 1

8.32 3.1

Arsenic, filtered (μg/L) 158 14 2 5.01 4.5

Arsenic, unfiltered recoverable (μg/L) 158 27 3 7.06 5.9

Organic carbon, filtered (mg/L) 38 4.27 0.88 1.71 1.52

Sediment, suspended (percent finer than 0.062 mm) 160 95 43 71 71

Sediment, suspended concentration (mg/L) 160 127 1 16 7

Sediment, suspended discharge (ton/d) 160 87 0.03 7.57 0.99
72 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 21. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through September 

2017.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, nephelometric turbidity 

ratio unit; <, less than laboratory reporting level1; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; ton/d, ton 

per day; --, no data]

Property or constituent and reporting unit Number of samples Maximum Minimum Mean Median

12323800—Clark Fork near Galen

Period of record for water-quality data: July 1988–September 2017

Streamflow, instantaneous (ft3/s) 244 1,380 14 223 148

pH, onsite (standard units) 232 9.2 7.5 8.5 8.6

Specific conductance, onsite (μS/cm) 233 720 182 403 407

Temperature, water (°C) 244 23.5 0.0 9.8 10.0

Hardness, filtered (mg/L as CaCO3) 231 365 76.4 175 178

Calcium, filtered (mg/L) 231 110 23.2 51.9 52.5

Magnesium, filtered (mg/L) 231 22 4.44 11.2 11.4

Potassium, filtered (mg/L) 32 5.9 2 3.5 3.3

Sodium, filtered (mg/L) 32 19 3.6 12.0 12.5

Alkalinity, filtered, lab (mg/L) 3 117 84.4 96.3 87.4

Chloride, filtered (mg/L) 32 11 2 6.47 6.22

Fluoride, filtered (mg/L) 32 1.1 0.4 0.62 0.6

Silica, filtered (mg/L) 32 17 8.1 11.7 11.8

Sulfate, filtered (mg/L) 32 220 34 97 99

Cadmium, filtered (μg/L) 231 1 <0.03 1

0.06 0.03

Cadmium, unfiltered recoverable (μg/L) 231 3 <0.100 1

0.17 0.07

Copper, filtered (μg/L) 231 50 1.4 7.0 5.1

Copper, unfiltered recoverable (μg/L) 230 240 4.1 24.7 14.4

Iron, filtered (μg/L) 231 110 <3.00 1

17.0 13.3

Iron, unfiltered recoverable (μg/L) 231 9,200 56.2 441 265

Lead, filtered (μg/L) 231 3 <0.08 1

0.14 0.04

Lead, unfiltered recoverable (μg/L) 231 31 <1.00 1

3.10 1.75

Manganese, filtered (μg/L) 231 460 10.1 94.2 67.1

Manganese, unfiltered recoverable (μg/L) 231 1,400 25.8 197 150

Zinc, filtered (μg/L) 231 110 <1.00 1

7.58 3.4

Zinc, unfiltered recoverable (μg/L) 231 360 2.7 32.1 19

Arsenic, filtered (μg/L) 231 53 4 15.0 14

Arsenic, unfiltered recoverable (μg/L) 231 78 3 18.8 16.8

Sediment, suspended (percent finer than 0.062 mm) 244 97 32 76 77

Sediment, suspended concentration (mg/L) 245 338 1 17 8

Sediment, suspended discharge (ton/d) 244 459 0.12 19.0 2.9
Data 73

Table 21. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through September 

2017.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, nephelometric turbidity 

ratio unit; <, less than laboratory reporting level1; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; ton/d, ton 

per day; --, no data]

Property or constituent and reporting unit Number of samples Maximum Minimum Mean Median

12323840—Lost Creek near Anaconda

Period of record for water-quality data: December 2004–September 2017

Streamflow, instantaneous (ft3/s) 103 73 0.37 12 8.5

pH, onsite (standard units) 103 8.6 7.4 8.1 8.1

Specific conductance, onsite (μS/cm) 103 253 121 200 212

Temperature, water (°C) 103 17.0 0.0 7.5 7.5

Turbidity, unfiltered, lab (NTRU) 103 24,200 <2.00 1

237 <2.00

Hardness, filtered (mg/L as CaCO3) 103 122 50.4 96.2 102

Calcium, filtered (mg/L) 103 37.1 15.7 29.1 30.8

Magnesium, filtered (mg/L) 103 7.47 2.71 5.68 6.01

Potassium, filtered (mg/L) 38 1.51 0.88 1.24 1.27

Sodium, filtered (mg/L) 38 3.68 1.87 2.87 2.87

Alkalinity, filtered, lab (mg/L) 38 118 59.5 96.2 102

Chloride, filtered (mg/L) 38 2.13 0.51 0.76 0.72

Fluoride, filtered (mg/L) 38 0.5 0.28 0.39 0.4

Silica, filtered (mg/L) 38 13 9.65 11.4 11.3

Sulfate, filtered (mg/L) 38 13.8 5.77 8.60 8.01

Cadmium, filtered (μg/L) 101 0.90 <0.02 1

0.04 0.02

Cadmium, unfiltered recoverable (μg/L) 102 147 <0.02 1

1.49 0.04

Copper, filtered (μg/L) 102 90.5 0.8 2.82 1.7

Copper, unfiltered recoverable (μg/L) 102 29,100 1.3 292 4.55

Iron, filtered (μg/L) 102 78.6 3.6 11.4 9.85

Iron, unfiltered recoverable (μg/L) 103 99,700 9.4 1,165 115

Lead, filtered (μg/L) 102 0.23 <0.02 1

0.04 0.02

Lead, unfiltered recoverable (μg/L) 103 1,290 0.04 13.4 0.48

Manganese, filtered (μg/L) 102 42.4 0.2 1.84 1.38

Manganese, unfiltered recoverable (μg/L) 103 8,830 1 93.0 5.2

Zinc, filtered (μg/L) 101 30 <1.40 1

1.55 <2.00

Zinc, unfiltered recoverable (μg/L) 101 7,780 <2.00 1

80.5 2.2

Arsenic, filtered (μg/L) 102 156 1.8 5.79 3.6

Arsenic, unfiltered recoverable (μg/L) 102 3,860 2 42.7 4.25

Organic carbon, filtered (mg/L) 38 7.1 0.87 1.94 1.66

Sediment, suspended (percent finer than 0.062 mm) 103 97 22 59 62

Sediment, suspended concentration (mg/L) 103 58,900 1 584 6

Sediment, suspended discharge (ton/d) 103 1,320 <0.01 13.6 0.11
74 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 21. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through September 

2017.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, nephelometric turbidity 

ratio unit; <, less than laboratory reporting level1; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; ton/d, ton 

per day; --, no data]

Property or constituent and reporting unit Number of samples Maximum Minimum Mean Median

12323850—Lost Creek near Galen

Period of record for water-quality data: March 2003–September 2017

Streamflow, instantaneous (ft3/s) 118 71 1.3 25 18

pH, onsite (standard units) 120 8.7 7.9 8.3 8.3

Specific conductance, onsite (μS/cm) 120 934 537 637 627

Temperature, water (°C) 120 26.5 0.0 10.2 10.0

Turbidity, unfiltered, lab (NTRU) 31 13 <2.00 1

2.25 <2.00

Hardness, filtered (mg/L as CaCO3) 120 451 203 304 302

Calcium, filtered (mg/L) 120 122 48.5 86.1 86.7

Magnesium, filtered (mg/L) 120 35.7 17.3 21.5 20.9

Potassium, filtered (mg/L) 31 3.81 1.89 2.62 2.43

Sodium, filtered (mg/L) 31 33.3 10.1 16.7 12.9

Alkalinity, filtered, lab (mg/L) 31 232 166 192 188

Chloride, filtered (mg/L) 31 5.90 3.90 4.80 4.79

Fluoride, filtered (mg/L) 31 0.90 0.43 0.56 0.50

Silica, filtered (mg/L) 31 23.9 11.7 17.0 16.6

Sulfate, filtered (mg/L) 31 200 84.1 136 135

Cadmium, filtered (μg/L) 118 0.05 <0.02 1

0.03 0.02

Cadmium, unfiltered recoverable (μg/L) 120 0.19 <0.02 1

0.04 0.04

Copper, filtered (μg/L) 120 6.7 0.8 2.1 1.8

Copper, unfiltered recoverable (μg/L) 120 22.5 1.5 5.2 4.2

Iron, filtered (μg/L) 120 84.5 4.0 15.2 12.1

Iron, unfiltered recoverable (μg/L) 120 760 14.0 114 86.2

Lead, filtered (μg/L) 119 0.33 <0.02 1

0.06 0.03

Lead, unfiltered recoverable (μg/L) 120 2.55 0.04 0.42 0.31

Manganese, filtered (μg/L) 120 54 1.91 16.0 15.3

Manganese, unfiltered recoverable (μg/L) 120 74.3 2.2 21.4 20.6

Zinc, filtered (μg/L) 119 3.8 <1.00 1

1.46 0.84

Zinc, unfiltered recoverable (μg/L) 120 13 <2.00 1

3.01 2

Arsenic, filtered (μg/L) 120 41.8 6 13.8 12.5

Arsenic, unfiltered recoverable (μg/L) 120 43 6 14.7 13.0

Organic carbon, filtered (mg/L) 31 7.18 1.28 2.38 2.07

Sediment, suspended (percent finer than 0.062 mm) 120 94 18 62 65

Sediment, suspended concentration (mg/L) 120 79 2 16 15

Sediment, suspended discharge (ton/d) 118 5.2 0.01 1.05 0.76
Data 75

Table 21. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through September 

2017.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, nephelometric turbidity 

ratio unit; <, less than laboratory reporting level1; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; ton/d, ton 

per day; --, no data]

Property or constituent and reporting unit Number of samples Maximum Minimum Mean Median

12324200—Clark Fork at Deer Lodge

Period of record for water-quality data: March 1985–September 2017

Streamflow, instantaneous (ft3/s) 297 2,000 23 307 230

pH, onsite (standard units) 245 8.9 7.4 8.3 8.3

Specific conductance, onsite (μS/cm) 280 642 228 462 486

Temperature, water (°C) 296 23.0 0.0 10.2 10.5

Hardness, filtered (mg/L as CaCO3) 237 282 94.9 196 206

Calcium, filtered (mg/L) 237 82 28.2 58.0 60.4

Magnesium, filtered (mg/L) 237 18.7 5.53 12.5 13.2

Potassium, filtered (mg/L) 31 6.3 2.4 3.6 3.6

Sodium, filtered (mg/L) 31 25 8.6 14.9 14

Alkalinity, filtered, lab (mg/L) 3 142 105 119 109

Chloride, filtered (mg/L) 31 12 1.2 7.00 7.1

Fluoride, filtered (mg/L) 31 0.7 0.1 0.6 0.6

Silica, filtered (mg/L) 31 34 11 17 16

Sulfate, filtered (mg/L) 31 140 44 96 98

Cadmium, filtered (μg/L) 246 2 <0.10 1

0.08 0.04

Cadmium, unfiltered recoverable (μg/L) 246 5 <0.10 1

0.4 0.1

Copper, filtered (μg/L) 247 120 3.2 10.3 7.8

Copper, unfiltered recoverable (μg/L) 245 1,500 8.2 74.3 34

Iron, filtered (μg/L) 247 190 <3.00 1

16.0 10

Iron, unfiltered recoverable (μg/L) 247 29,000 27.2 1,324 494

Lead, filtered (μg/L) 247 6 <0.04 1

0.28 0.04

Lead, unfiltered recoverable (μg/L) 247 200 0.23 9.82 4.08

Manganese, filtered (μg/L) 247 400 1 39.3 31

Manganese, unfiltered recoverable (μg/L) 247 4,600 6.8 207 120

Zinc, filtered (μg/L) 247 230 <2.00 1

10.5 7

Zinc, unfiltered recoverable (μg/L) 245 1,700 3 75.2 35.8

Arsenic, filtered (μg/L) 247 39 6 14.4 13.4

Arsenic, unfiltered recoverable (μg/L) 246 215 4.8 23.0 17.1

Sediment, suspended (percent finer than 0.062 mm) 288 99 31 72 74

Sediment, suspended concentration (mg/L) 297 2,250 1 63 21

Sediment, suspended discharge (ton/d) 297 8,690 0.18 132 12
76 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 21. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through September 

2017.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, nephelometric turbidity 

ratio unit; <, less than laboratory reporting level1; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; ton/d, ton 

per day; --, no data]

Property or constituent and reporting unit Number of samples Maximum Minimum Mean Median

12324400—Clark Fork above Little Blackfoot River, near Garrison

Period of record for water-quality data: March 2009–September 2017

Streamflow, instantaneous (ft3/s) 70 2,310 66 429 306

pH, onsite (standard units) 70 8.9 7.9 8.4 8.4

Specific conductance, onsite (μS/cm) 70 530 249 417 443

Temperature, water (°C) 70 22.0 1.0 12.1 12.8

Hardness, filtered (mg/L as CaCO3) 70 236 104 184 196

Calcium, filtered (mg/L) 70 69.4 31.8 53.6 56.8

Magnesium, filtered (mg/L) 70 15.8 5.93 12.1 13.2

Cadmium, filtered (μg/L) 70 0.23 0.02 0.07 0.07

Cadmium, unfiltered recoverable (μg/L) 70 3.25 0.03 0.28 0.18

Copper, filtered (μg/L) 70 40.6 2.8 9.63 8

Copper, unfiltered recoverable (μg/L) 70 869 9.7 66.0 34.6

Iron, filtered (μg/L) 69 105 4.5 18.6 14.5

Iron, unfiltered recoverable (μg/L) 70 17,300 21.5 1,043 541

Lead, filtered (μg/L) 70 0.96 0.04 0.17 0.13

Lead, unfiltered recoverable (μg/L) 70 132 0.15 8.71 4.08

Manganese, filtered (μg/L) 70 164 2.68 29.2 24.1

Manganese, unfiltered recoverable (μg/L) 70 1,060 6.4 127 101

Zinc, filtered (μg/L) 70 37.1 <2.00 1

5.70 4.9

Zinc, unfiltered recoverable (μg/L) 70 800 2 54.7 28.9

Arsenic, filtered (μg/L) 70 36.7 7.8 15.3 15.3

Arsenic, unfiltered recoverable (μg/L) 70 138 10.5 22.5 18.2

Sediment, suspended (percent finer than 0.062 mm) 70 92 42 74 76

Sediment, suspended concentration (mg/L) 70 836 1 50 22

Sediment, suspended discharge (ton/d) 70 3,700 0.31 122 22
Data 77

Table 21. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through September 

2017.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, nephelometric turbidity 

ratio unit; <, less than laboratory reporting level1; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; ton/d, ton 

per day; --, no data]

Property or constituent and reporting unit Number of samples Maximum Minimum Mean Median

12324680—Clark Fork at Goldcreek

Period of record for water-quality data: March 1993–September 2017

Streamflow, instantaneous (ft3/s) 203 4,450 87 763 513

pH, onsite (standard units) 202 9.1 7.9 8.4 8.3

Specific conductance, onsite (μS/cm) 202 510 206 365 375

Temperature, water (°C) 203 23.0 0.0 10.4 10.5

Hardness, filtered (mg/L as CaCO3) 202 232 86 161 168

Calcium, filtered (mg/L) 202 68 25.9 47.5 49.4

Magnesium, filtered (mg/L) 202 15 5.15 10.3 10.6

Potassium, filtered (mg/L) 28 6.9 2 3.11 3

Sodium, filtered (mg/L) 28 19 6.9 11.5 12

Chloride, filtered (mg/L) 28 7.2 2.5 4.73 4.4

Fluoride, filtered (mg/L) 28 0.6 0.1 0.43 0.4

Silica, filtered (mg/L) 28 25.0 14.0 18.3 18.0

Sulfate, filtered (mg/L) 28 88.0 31.0 59.5 55.5

Cadmium, filtered (μg/L) 202 0.2 <0.02 1

0.04 0.03

Cadmium, unfiltered recoverable (μg/L) 202 2 <0.10 1

0.17 0.08

Copper, filtered (μg/L) 201 36 2.1 6.58 5.3

Copper, unfiltered recoverable (μg/L) 201 440 5.2 38.4 21.4

Iron, filtered (μg/L) 201 106 <3.00 1

20.4 14

Iron, unfiltered recoverable (μg/L) 202 12,000 27.3 829 411

Lead, filtered (μg/L) 199 0.73 <0.04 1

0.12 0.04

Lead, unfiltered recoverable (μg/L) 201 73 0.14 5.32 2.76

Manganese, filtered (μg/L) 202 57.3 3.98 18.5 16.4

Manganese, unfiltered recoverable (μg/L) 202 1,100 9.3 112 80.3

Zinc, filtered (μg/L) 202 26 <1.00 1

5.06 3.4

Zinc, unfiltered recoverable (μg/L) 202 510 2 40.2 26.3

Arsenic, filtered (μg/L) 202 22.5 5.6 10.1 9.85

Arsenic, unfiltered recoverable (μg/L) 202 75 7 14.5 12

Sediment, suspended (percent finer than 0.062 mm) 203 94 43 76 78

Sediment, suspended concentration (mg/L) 203 752 1 45 19

Sediment, suspended discharge (ton/d) 203 7,960 0.55 197 27
78 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 21. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through September 

2017.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, nephelometric turbidity 

ratio unit; <, less than laboratory reporting level1; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; ton/d, ton 

per day; --, no data]

Property or constituent and reporting unit Number of samples Maximum Minimum Mean Median

12331800—Clark Fork near Drummond

Period of record for water-quality data: March 1993–September 2017

Streamflow, instantaneous (ft3/s) 203 5,540 149 1,045 768 

pH, onsite (standard units) 202 8.7 7.8 8.3 8.2

Specific conductance, onsite (μS/cm) 202 630 189 406 417

Temperature, water (°C) 203 22.5 0.5 11.0 11.0

Hardness, filtered (mg/L as CaCO3) 202 298 73.9 183 189

Calcium, filtered (mg/L) 202 83 21 52.5 54.3

Magnesium, filtered (mg/L) 202 22 5.2 12.6 13.0

Potassium, filtered (mg/L) 28 10 2.1 3.67 3.4

Sodium, filtered (mg/L) 28 20 5.6 11.5 12

Chloride, filtered (mg/L) 28 7.8 2.7 4.83 4.65

Fluoride, filtered (mg/L) 28 0.5 0.2 0.39 0.4

Silica, filtered (mg/L) 28 24 10 18.7 18.5

Sulfate, filtered (mg/L) 28 130 25 64.8 64.5

Cadmium, filtered (μg/L) 201 0.30 <0.03 1

0.05 0.03

Cadmium, unfiltered recoverable (μg/L) 202 2.2 <0.03 1

0.22 0.09

Copper, filtered (μg/L) 199 21 1 6.22 4.9

Copper, unfiltered recoverable (μg/L) 200 360 4.6 40.5 22

Iron, filtered (μg/L) 202 177 <3.00 1

19.5 10.3

Iron, unfiltered recoverable (μg/L) 201 14,000 19.7 979 461

Lead, filtered (μg/L) 198 1.54 <0.04 1

0.17 0.05

Lead, unfiltered recoverable (μg/L) 198 78.2 0.17 7.24 3.45

Manganese, filtered (μg/L) 201 77 3.3 16.6 14.2

Manganese, unfiltered recoverable (μg/L) 202 1,240 8.04 138 89.3

Zinc, filtered (μg/L) 202 21 <1.40 1

5.53 4.2

Zinc, unfiltered recoverable (μg/L) 202 575 2.9 55.3 30

Arsenic, filtered (μg/L) 202 26.5 3.2 10.5 10

Arsenic, unfiltered recoverable (μg/L) 202 79.1 7.7 15.7 13

Sediment, suspended (percent finer than 0.062 mm) 203 93 38 74 75

Sediment, suspended concentration (mg/L) 203 759 2 60 25

Sediment, suspended discharge (ton/d) 203 11,300 1.7 332 47
Data 79

Table 21. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through September 

2017.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, nephelometric turbidity 

ratio unit; <, less than laboratory reporting level1; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; ton/d, ton 

per day; --, no data]

Property or constituent and reporting unit Number of samples Maximum Minimum Mean Median

12334550—Clark Fork at Turah Bridge, near Bonner

Period of record for water-quality data: March 1985–September 2017

Streamflow, instantaneous (ft3/s) 300 10,600 296 1,971 1,215 

pH, onsite (standard units) 246 8.8 7.4 8.2 8.2

Specific conductance, onsite (μS/cm) 275 483 139 295 305

Temperature, water (°C) 299 22.0 0.0 9.6 10.0

Hardness, filtered (mg/L as CaCO3) 236 205 53.6 129 130

Calcium, filtered (mg/L) 236 59 14.9 36.4 36.9

Magnesium, filtered (mg/L) 236 14 3.95 9.32 9.33

Potassium, filtered (mg/L) 32 5.7 1.51 2.45 2.45

Sodium, filtered (mg/L) 32 12 3.34 7.95 8.45

Alkalinity, filtered, lab (mg/L) 4 155 52.5 108 111

Chloride, filtered (mg/L) 32 5.6 1.5 3.13 2.95

Fluoride, filtered (mg/L) 32 0.4 0.17 0.29 0.3

Silica, filtered (mg/L) 32 19 12 14.9 15

Sulfate, filtered (mg/L) 32 68 12.6 41.8 41

Nitrate plus nitrite, filtered (mg/L) 8 0.069 <0.013 1

0.027 0.012

Phosphorus, unfiltered (mg/L) 10 0.24 0.014 0.080 0.068

Total nitrogen, unfiltered (mg/L) 2 0.49 0.38 -- --

Cadmium, filtered (μg/L) 244 0.1 <0.02 1

0.03 <1.00

Cadmium, unfiltered recoverable (μg/L) 245 4 <0.01 1

0.22 0.04

Copper, filtered (μg/L) 244 25 1.1 4.52 3.4

Copper, unfiltered recoverable (μg/L) 243 500 2.7 30.7 14

Iron, filtered (μg/L) 245 359 <3.00 1

25.4 14.5

Iron, unfiltered recoverable (μg/L) 245 19,000 32.6 925 356

Lead, filtered (μg/L) 241 7 <0.02 1

0.25 <5.00

Lead, unfiltered recoverable (μg/L) 241 100 <1.00 1

6.12 2.3

Manganese, filtered (μg/L) 245 48.6 1 8.44 7

Manganese, unfiltered recoverable (μg/L) 245 2,000 8.8 109 57.3

Zinc, filtered (μg/L) 243 39 <2.00 1

5.36 3.7

Zinc, unfiltered recoverable (μg/L) 245 1,100 2.9 51.6 22

Arsenic, filtered (μg/L) 245 17 2.7 5.95 5.5

Arsenic, unfiltered recoverable (μg/L) 245 110 3 9.26 7

Sediment, suspended (percent finer than 0.062 mm) 289 98 27 74 76

Sediment, suspended concentration (mg/L) 300 1,370 2 53 18

Sediment, suspended discharge (ton/d) 300 34,700 3 619 60
80 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 21. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through September 

2017.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, nephelometric turbidity 

ratio unit; <, less than laboratory reporting level1; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; ton/d, ton 

per day; --, no data]

Property or constituent and reporting unit Number of samples Maximum Minimum Mean Median

12340000—Blackfoot River near Bonner

Period of record for water-quality data: March 1985–September 2017

Streamflow, instantaneous (ft3/s) 220 13,400 344 2,769 1,375 

pH, onsite (standard units) 180 8.7 7.5 8.3 8.3

Specific conductance, onsite (μS/cm) 197 294 131 209 204

Temperature, water (°C) 220 22.5 0.0 9.8 10.0

Turbidity, unfiltered, lab (NTRU) 7 30 <2.00 1

7.2 2

Hardness, filtered (mg/L as CaCO3) 172 146 55.1 104 98.6

Calcium, filtered (mg/L) 172 37.7 14 26.6 25.5

Magnesium, filtered (mg/L) 172 13.2 4.9 9.20 8.66

Potassium, filtered (mg/L) 26 2.8 0.48 0.87 0.8

Sodium, filtered (mg/L) 26 3.41 1.17 2.46 2.5

Alkalinity, filtered, lab (mg/L) 9 148 71.5 117 131

Chloride, filtered (mg/L) 26 1.6 0.23 0.64 0.58

Fluoride, filtered (mg/L) 26 0.1 <0.10 1

0.10 <0.10

Silica, filtered (mg/L) 26 12 6.8 8.64 8.11

Sulfate, filtered (mg/L) 26 6.6 1.1 4.58 4.8

Nitrate plus nitrite, filtered (mg/L) 30 0.04 <0.005 1

0.010 0.005

Phosphorus, unfiltered (mg/L) 31 0.167 0.003 0.027 0.015

Total nitrogen, unfiltered (mg/L) 14 0.33 0.08 0.15 0.14

Cadmium, filtered (μg/L) 178 1 <0.02 1

0.02 <0.10

Cadmium, unfiltered recoverable (μg/L) 180 2 <0.01 1

0.08 <0.10

Copper, filtered (μg/L) 175 7 <0.80 1

1.20 0.7

Copper, unfiltered recoverable (μg/L) 176 34 <0.70 1

3.92 1.6

Iron, filtered (μg/L) 179 104 <3.00 1

17.5 10.2

Iron, unfiltered recoverable (μg/L) 180 3,600 13.9 378 163

Lead, filtered (μg/L) 173 8 <0.02 1

0.25 <0.50

Lead, unfiltered recoverable (μg/L) 174 25 <0.04 1

1.82 0.09

Manganese, filtered (μg/L) 179 11 <1.000 1

2.40 2

Manganese, unfiltered recoverable (μg/L) 180 180 <10.0 1

26.2 13.6

Zinc, filtered (μg/L) 178 15 <0.60 1

1.77 <3.00

Zinc, unfiltered recoverable (μg/L) 180 60 <1.00 1

4.46 <10.0

Arsenic, filtered (μg/L) 179 2 <1.00 1

0.97 0.96

Arsenic, unfiltered recoverable (μg/L) 180 4 <1.00 1

1.25 1

Sediment, suspended (percent finer than 0.062 mm) 218 98 42 80.5 82

Sediment, suspended concentration (mg/L) 220 271 1 27.0 8

Sediment, suspended discharge (ton/d) 220 7,670 1.1 485 31
Data 81

Table 21. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through September 

2017.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; lab, laboratory; NTRU, nephelometric turbidity 

ratio unit; <, less than laboratory reporting level1; mg/L, milligram per liter; CaCO3, calcium carbonate; μg/L, microgram per liter; mm, millimeter; ton/d, ton 

per day; --, no data]

Property or constituent and reporting unit Number of samples Maximum Minimum Mean Median

12340500—Clark Fork above Missoula

Period of record for water-quality data: July 1986–September 2017

Streamflow, instantaneous (ft3/s) 265 22,900 720 4,656 2,550 

pH, onsite (standard units) 223 8.8 7.9 8.3 8.3

Specific conductance, onsite (μS/cm) 243 399 142 249 255

Temperature, water (°C) 263 22.0 0.0 9.8 10.0

Turbidity, unfiltered, lab (NTRU) 40 100 <2.00 1

13.3 4.9

Hardness, filtered (mg/L as CaCO3) 223 168 60.5 116 117

Calcium, filtered (mg/L) 223 46 14 31.2 31.2

Magnesium, filtered (mg/L) 223 13.4 5.28 9.16 9.1

Potassium, filtered (mg/L) 28 4.5 0.9 1.72 1.5

Sodium, filtered (mg/L) 28 7.8 2.4 5.29 5.35

Chloride, filtered (mg/L) 28 4.2 0.9 1.93 1.8

Fluoride, filtered (mg/L) 28 0.3 <0.10 1

0.19 0.2

Silica, filtered (mg/L) 28 16 9.4 11.8 11

Sulfate, filtered (mg/L) 28 43 9.3 23.3 23

Phosphorus, unfiltered (mg/L) 2 0.102 0.066 -- --

Total nitrogen, unfiltered (mg/L) 2 0.47 0.32 -- --

Cadmium, filtered (μg/L) 222 0.2 <0.02 1

0.03 <0.10

Cadmium, unfiltered recoverable (μg/L) 223 5 <0.01 1

0.13 0.02

Copper, filtered (μg/L) 222 12.6 0.7 2.65 2

Copper, unfiltered recoverable (μg/L) 221 400 1.9 17.7 8

Iron, filtered (μg/L) 223 200 <3.00 1

22.1 14.9

Iron, unfiltered recoverable (μg/L) 223 13,000 40.9 593 250

Lead, filtered (μg/L) 216 1.2 <0.02 1

0.12 0.02

Lead, unfiltered recoverable (μg/L) 218 78 <1.00 1

3.11 1.27

Manganese, filtered (μg/L) 223 230 3.48 14.3 12.3

Manganese, unfiltered recoverable (μg/L) 223 1,100 8.8 60.9 39.8

Zinc, filtered (μg/L) 222 16 <1.00 1

3.18 2.1

Zinc, unfiltered recoverable (μg/L) 223 1,100 <3.00 1

29.8 12

Arsenic, filtered (μg/L) 223 9 1 3.39 3.1

Arsenic, unfiltered recoverable (μg/L) 223 69 1 5.18 4

Sediment, suspended (percent finer than 0.062 mm) 261 99 14 82 86

Sediment, suspended concentration (mg/L) 266 950 2 41 13

Sediment, suspended discharge (ton/d) 265 21,900 5.8 1,059 97

1

Value for the mean is estimated using a log-probability regression to predict the values of data less than the laboratory reporting level (Helsel and Cohn, 

1988).
82 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 22. Statistical summary of long-term bed-sediment data for the Clark Fork Basin, Montana, August 1986 through August 2017.

[Reported concentrations are in micrograms per gram dry weight. Number of samples represents the number of years that the constituent was analyzed, with 

each year represented by a single mean concentration of composite samples. Arsenic was not analyzed until 2003; therefore, the number of samples is smaller 

than that for the other trace elements. Analysis of samples for silver was discontinued in 2004; therefore, the number of samples is smaller than that for other 

trace elements. <, less than the minimum reporting level; --, indicates insufficient data (less than three samples) to compute statistic]

Constituent Number of samples Maximum Minimum Mean Median

12323600—Silver Bow Creek at Opportunity

Period of record for bed-sediment data: 1992–2017

Arsenic 15 186 16.4 84.5 58.7

Cadmium 26 43.9 5.9 24.2 25.8

Chromium 24 50.7 16.8 29.0 25.9

Copper 26 9,020 446 3,230 3,480

Iron 26 45,300 28,200 34,400 33,000

Lead 26 1,030 93.0 501 492

Manganese 26 9,220 1,160 3,270 2,840

Nickel 25 21.4 12.0 14.9 14.8

Silver 12 20.0 8.3 15.5 15.8

Zinc 26 13,400 1,350 5,770 6,140

12323750—Silver Bow Creek at Warm Springs

Period of record for bed-sediment data: 1992–2017

Arsenic 15 177 66.5 109 98

Cadmium 26 12.2 4.2 6.8 6.2

Chromium 24 46.8 <15.7 1

23.5 122.4

Copper 26 769 169 332 290

Iron 26 32,500 15,400 23,800 23,400

Lead 26 121 49.5 73.5 73.1

Manganese 26 17,700 1,470 7,220 7,210

Nickel 25 20.0 9.2 14.9 14.7

Silver 12 4.4 0.3 1

1.9 11.8

Zinc 26 2,220 554 863 681

12323770—Warm Springs Creek at Warm Springs

Period of record for bed-sediment data: 1995, 1997, 1999, 2002, 2005, 2008, 2011, 2014, 2017

Arsenic 5 66.1 34.0 55.3 59.6

Cadmium 9 5.8 1.2 3.1 2.8

Chromium 9 39.3 24.1 31.1 31.4

Copper 9 1,060 496 831 848

Iron 9 26,600 16,800 21,600 22,000

Lead 9 85.6 42.3 75.6 79.3

Manganese 9 12,100 555 6,190 6,030

Nickel 9 34.3 14.5 21.2 19.6

Silver 4 5.1 3.1 3.8 3.5

Zinc 9 453 237 386 396
Data 83

Table 22. Statistical summary of long-term bed-sediment data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of samples represents the number of years that the constituent was analyzed, with 

each year represented by a single mean concentration of composite samples. Arsenic was not analyzed until 2003; therefore, the number of samples is smaller 

than that for the other trace elements. Analysis of samples for silver was discontinued in 2004; therefore, the number of samples is smaller than that for other 

trace elements. <, less than the minimum reporting level; --, indicates insufficient data (less than three samples) to compute statistic]

Constituent Number of samples Maximum Minimum Mean Median

12323800—Clark Fork near Galen

Period of record for bed-sediment data: 1987, 1991–2017

Arsenic 15 156 73.5 108 102

Cadmium 28 20.1 3.8 7.5 6.2

Chromium 24 44.6 18.1 28.6 26.7

Copper 28 2,300 780 1,160 1,110

Iron 28 39,800 22,600 27,700 26,900

Lead 28 235 91.9 128 122

Manganese 28 17,300 1,530 8,290 6,350

Nickel 25 29.1 13.9 19.1 19.0

Silver 14 7.3 <3.2 1

4.4 14.5

Zinc 28 3,560 721 1,300 1,090

461415112450801—Clark Fork below Lost Creek, near Galen

Period of record for bed-sediment data: 1996–2017

Arsenic 15 204 90.4 123 111

Cadmium 22 10.5 4.7 6.5 6.0

Chromium 21 42.4 16.4 28.3 27.1

Copper 22 2,050 1,150 1,490 1,450

Iron 22 32,800 24,400 28,900 29,200

Lead 22 218 123 164 164

Manganese 22 9,820 1,430 5,110 4,940

Nickel 22 19.9 11.7 15.8 16.2

Silver 8 7.8 4.2 6.5 6.7

Zinc 22 1,680 930 1,240 1,190

461559112443301—Clark Fork at county bridge, near Racetrack

Period of record for bed-sediment data: 1996–2017

Arsenic 15 132 56.4 90.6 89.7

Cadmium 22 8.7 3.6 6.1 5.9

Chromium 21 45.2 13.9 27.2 24.9

Copper 22 1,810 818 1,240 1,250

Iron 22 31,700 21,200 27,000 27,400

Lead 22 186 103 140 138

Manganese 22 6,310 1,600 3,170 2,990

Nickel 22 18.4 10.3 14.0 14.3

Silver 8 6.1 <3.3 1

5.0 15.4

Zinc 22 1,550 816 1,130 1,120
84 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 22. Statistical summary of long-term bed-sediment data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of samples represents the number of years that the constituent was analyzed, with 

each year represented by a single mean concentration of composite samples. Arsenic was not analyzed until 2003; therefore, the number of samples is smaller 

than that for the other trace elements. Analysis of samples for silver was discontinued in 2004; therefore, the number of samples is smaller than that for other 

trace elements. <, less than the minimum reporting level; --, indicates insufficient data (less than three samples) to compute statistic]

Constituent Number of samples Maximum Minimum Mean Median

461903112440701—Clark Fork at Dempsey Creek diversion, near Racetrack

Period of record for bed-sediment data: 1996–2017

Arsenic 15 109 57.8 80.0 79.3

Cadmium 22 10.3 3.8 5.9 5.2

Chromium 21 39.2 13.0 25.5 24.0

Copper 22 1,580 718 1,080 1,060

Iron 22 33,700 18,800 26,500 25,700

Lead 22 155 91.9 128 131

Manganese 22 8,370 1,200 3,540 3,070

Nickel 22 16.9 8.7 12.5 12.3

Silver 8 6.2 2.7 4.9 5.0

Zinc 22 1,570 875 1,090 1,070

12324200—Clark Fork at Deer Lodge

Period of record for bed-sediment data: 1986–7, 1990–2017

Arsenic 15 102 49.1 74.3 72.2

Cadmium 30 10.0 3.5 5.7 5.0

Chromium 24 50.7 17.0 31.0 28.3

Copper 30 4,180 683 1,220 1,070

Iron 30 35,300 20,500 27,100 26,300

Lead 30 242 103 141 140

Manganese 30 6,020 1,070 2,540 2,360

Nickel 25 21.1 11.5 14.6 13.6

Silver 16 7.9 2.4 4.7 4.5

Zinc 30 1,730 844 1,140 1,050

12324400—Clark Fork above Little Blackfoot River, near Garrison

Period of record for bed-sediment data: 2009–17

Arsenic 9 90.7 49.4 67.9 59.1

Cadmium 9 5.5 3.6 4.5 4.3

Chromium 9 52.8 15.0 33.1 30.1

Copper 9 1,290 666 1,010 940

Iron 9 32,400 16,800 24,900 24,300

Lead 9 145 92.1 122 132

Manganese 9 3,560 1,150 2,450 2,660

Nickel 9 17.2 9.2 13.1 13.0

Silver 0 -- -- -- --

Zinc 9 1,240 780 1,010 977
Data 85

Table 22. Statistical summary of long-term bed-sediment data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of samples represents the number of years that the constituent was analyzed, with 

each year represented by a single mean concentration of composite samples. Arsenic was not analyzed until 2003; therefore, the number of samples is smaller 

than that for the other trace elements. Analysis of samples for silver was discontinued in 2004; therefore, the number of samples is smaller than that for other 

trace elements. <, less than the minimum reporting level; --, indicates insufficient data (less than three samples) to compute statistic]

Constituent Number of samples Maximum Minimum Mean Median

12324680—Clark Fork at Goldcreek

Period of record for bed-sediment data: 1992–2017

Arsenic 15 62.1 23.4 39.9 35.9

Cadmium 26 8.1 2.0 4.2 3.8

Chromium 24 55.3 9.9 31.0 28.8

Copper 26 1,080 281 643 664

Iron 26 32,100 11,500 22,700 23,200

Lead 26 152 45.4 90.6 92.2

Manganese 26 2,730 977 1,820 1,810

Nickel 25 18.6 7.6 13.3 13.3

Silver 12 4.8 2.3 3.2 3.2

Zinc 26 1,320 427 856 842

12331800—Clark Fork near Drummond

Period of record for bed-sediment data: 1986–7, 1991–2017

Arsenic 15 66.2 17.2 37.1 32.8

Cadmium 29 7.7 1.7 4.1 4.1

Chromium 24 41.9 9.2 26.5 26.1

Copper 29 747 183 459 443

Iron 29 44,000 14,800 24,200 20,400

Lead 29 135 26.8 83.0 82.0

Manganese 29 4,820 832 1,990 1,810

Nickel 25 16.8 4.8 12.6 13.0

Silver 15 4.7 <3.2 1

3.0 12.9

Zinc 29 1,230 380 900 947

12334550—Clark Fork at Turah Bridge, near Bonner

Period of record for bed-sediment data: 1986, 1991–2017

Arsenic 15 43.1 17.3 26.0 24.8

Cadmium 28 7.3 1.2 3.1 3.1

Chromium 24 42.5 13.6 25.8 25.4

Copper 28 635 211 334 320

Iron 28 25,900 12,600 19,000 17,300

Lead 28 115 37.4 63.9 60.4

Manganese 28 2,340 383 1,200 1,180

Nickel 25 19.1 6.9 12.2 11.5

Silver 14 3.9 <1.9 1

2.1 11.9

Zinc 28 1,160 448 747 742
86 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 22. Statistical summary of long-term bed-sediment data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of samples represents the number of years that the constituent was analyzed, with 

each year represented by a single mean concentration of composite samples. Arsenic was not analyzed until 2003; therefore, the number of samples is smaller 

than that for the other trace elements. Analysis of samples for silver was discontinued in 2004; therefore, the number of samples is smaller than that for other 

trace elements. <, less than the minimum reporting level; --, indicates insufficient data (less than three samples) to compute statistic]

Constituent Number of samples Maximum Minimum Mean Median

12340000—Blackfoot River near Bonner

Period of record for bed-sediment data: 1986–7, 1991, 1993–6, 1998–2001, 2003, 2006–17

Arsenic 13 6.2 <0.2 1

3.9 14.3

Cadmium 24 2.0 <0.04 1

0.4 10.2

Chromium 20 35.2 13.3 21.3 21.8

Copper 24 27.0 11.3 19.8 20.7

Iron 24 23,000 12,400 17,500 18,000

Lead 24 20.5 <13.0 1

12.4 111.1

Manganese 24 746 298 515 538

Nickel 21 14.3 6.0 11.1 11.1

Silver 12 <1.9 <0.3 1

0.5 10.3

Zinc 24 81.5 35.2 59.7 59.8

12340500—Clark Fork above Missoula

Period of record for bed-sediment data: 1997–2017

Arsenic 15 53.9 12.4 26.4 23.3

Cadmium 21 5.8 1.0 2.6 2.6

Chromium 20 40.7 12.8 25.1 26.0

Copper 21 551 125 306 281

Iron 21 27,000 13,800 19,900 19,500

Lead 21 78.2 24.7 48.8 47.3

Manganese 21 2,250 477 1,020 914

Nickel 21 15.8 7.6 12.2 12.0

Silver 7 2.9 0.8 1

2.0 12.1

Zinc 21 1,090 343 635 590

1

Value determined by substituting one-half of the minimum reporting level for censored (<) values when both uncensored and censored values were used to 

determine the mean and median.
Data 87

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

12323600—Silver Bow Creek at Opportunity

Period of record for biological data: 1992, 1994–5, 1997–2017

Brachycentrus spp.

Arsenic 0 -- -- -- --

Cadmium 5 12.5 5.8 10.1 11.6

Chromium 5 5.9 0.7 2.1 0.9

Copper 5 846 235 587 592

Iron 5 1,190 335 617 469

Lead 5 21.5 7.4 13.7 13.8

Manganese 5 817 231 515 503

Nickel 5 2.1 <0.1 1

1.3 11.6

Zinc 5 995 629 803 815

Hydropsyche cockerelli

Arsenic 30 33.3 4.3 10.4 7.3

Cadmium 36 9.7 2.4 4.8 4.5

Chromium 36 25.5 1.0 4.1 3.9

Copper 36 1,090 78.6 290 271

Iron 36 6,160 689 2,680 2,440

Lead 36 74.3 11.2 29.3 20.9

Manganese 36 4,000 180 1,400 1,190

Nickel 36 4.3 0.7 2.8 3.1

Zinc 36 1,590 432 756 739

Hydropsyche spp.

Arsenic 15 23.1 3.5 10.8 9.8

Cadmium 20 11.0 1.0 5.2 4.8

Chromium 20 9.7 0.6 3.2 3.0

Copper 20 930 71.0 410 342

Iron 20 3,630 1,050 2,210 2,170

Lead 20 237 9.4 43.7 36.0

Manganese 20 2,750 612 1,130 1,050

Nickel 20 4.1 0.7 2.2 2.4

Zinc 20 1,290 380 850 855
88 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

12323600—Silver Bow Creek at Opportunity—Continued

Period of record for biological data: 1992, 1994–5, 1997–2017

Hydropsyche tana

Arsenic 0 -- -- -- --

Cadmium 6 9.2 4.8 6.8 6.9

Chromium 6 11.5 0.9 4.5 1.8

Copper 6 456 10.5 236 298

Iron 6 1,520 875 1,100 1,050

Lead 6 21.0 15.6 18.6 18.3

Manganese 6 969 307 634 675

Nickel 6 1.8 0.7 1.4 1.6

Zinc 6 1,070 760 961 1,020

12323750—Silver Bow Creek at Warm Springs

Period of record for biological data: 1992–2017

Claassenia sabulosa

Arsenic 2 5.0 1.8 3.4 --

Cadmium 2 1.1 0.5 0.8 --

Chromium 2 2.8 0.6 1.7 --

Copper 2 66.4 47.6 57.0 --

Iron 2 300 151 226 --

Lead 2 1.5 0.6 1.0 --

Manganese 2 922 98 510 --

Nickel 2 0.6 0.5 0.6 --

Zinc 2 400 340 370 --

Hydropsyche cockerelli

Arsenic 27 23.6 7.9 12.1 11.7

Cadmium 53 2.1 0.2 0.6 0.5

Chromium 53 4.3 0.1 1.2 1.0

Copper 53 97.0 16.7 35.7 31.1

Iron 53 1,660 351 830 793

Lead 53 6.0 0.3 3.2 2.9

Manganese 53 3,890 491 1,230 1,020

Nickel 53 1.8 0.3 1.0 0.9

Zinc 53 276 115 174 168
Data 89

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

12323750—Silver Bow Creek at Warm Springs—Continued

Period of record for biological data: 1992–2017

Hydropsyche occidentalis

Arsenic 11 31.0 10.5 18.6 15.6

Cadmium 26 1.6 0.2 0.7 0.4

Chromium 26 6.8 0.3 2.0 1.0

Copper 26 48.9 11.0 34.0 33.0

Iron 26 2,960 372 1,280 1,020

Lead 26 8.2 <1.7 1

4.1 13.8

Manganese 26 6,940 996 2,400 2,040

Nickel 26 3.2 0.7 1.6 1.5

Zinc 26 220 140 182 184

Hydropsyche spp.

Arsenic 1 -- -- 14.0 --

Cadmium 5 2.3 0.4 1.0 0.6

Chromium 5 2.5 0.5 1.4 1.3

Copper 5 47.6 34.9 39.9 40.4

Iron 5 1,100 561 763 767

Lead 5 5.1 1.9 4.0 4.5

Manganese 5 1,190 443 817 804

Nickel 5 1.9 <0.4 1

1.0 10.8

Zinc 5 284 141 188 162

12323770—Warm Springs Creek at Warm Springs

Period of record for biological data: 1995, 1997, 1999, 2002, 2005, 2008, 2011, 2014, 2017

Arctopsyche grandis

Arsenic 7 9.8 7.6 8.7 8.4

Cadmium 11 3.6 0.4 2.5 2.6

Chromium 11 5.0 0.8 2.7 2.8

Copper 11 133 53.2 104 102

Iron 11 1,490 684 1,080 1,050

Lead 11 8.7 3.0 1

6.0 16.3

Manganese 11 3,560 738 2,120 1,800

Nickel 11 7.5 1.1 1

3.7 12.8

Zinc 11 331 181 228 200
90 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

12323770—Warm Springs Creek at Warm Springs—Continued

Period of record for biological data: 1995, 1997, 1999, 2002, 2005, 2008, 2011, 2014, 2017

Hesperoperla spp.

Arsenic 4 2.9 1.2 2.2 2.4

Cadmium 4 2.6 0.5 1.3 1.1

Chromium 4 7.6 0.5 2.8 1.4

Copper 4 64.9 44.2 56.4 58.2

Iron 4 456 375 409 403

Lead 4 1.9 1.4 1.6 1.6

Manganese 4 356 202 284 289

Nickel 4 2.1 0.6 1.2 1.1

Zinc 4 573 394 479 474

Hydropsyche occidentalis

Arsenic 4 13.6 9.8 12.4 13.0

Cadmium 6 1.4 0.7 1.1 1.2

Chromium 6 8.6 0.3 3.7 3.2

Copper 6 183 116 151 150

Iron 6 2,360 1,520 1,870 1,840

Lead 6 12.6 6.7 8.2 7.4

Manganese 6 3,190 1,440 2,580 2,680

Nickel 6 4.5 2.0 3.1 3.2

Zinc 6 204 148 169 168

Hydropsyche spp.

Arsenic 1 -- -- 13.1 --

Cadmium 3 1.3 0.6 1.0 1.1

Chromium 3 3.5 1.4 2.2 1.6

Copper 3 155 94.8 115 95.9

Iron 3 2,260 1,150 1,540 1,220 

Lead 3 11.3 5.2 7.5 5.9

Manganese 3 3,390 956 2,120 2,030 

Nickel 3 8.8 1.8 4.2 2.0

Zinc 3 214 125 156 129
Data 91

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

12323800—Clark Fork near Galen

Period of record for biological data: 1987, 1991–2017

Claassenia sabulosa

Arsenic 1 -- -- 2.0 --

Cadmium 1 -- -- 0.2 --

Chromium 1 -- -- 1.5 --

Copper 1 -- -- 54.7 --

Iron 1 -- -- 242 --

Lead 1 -- -- 1.0 --

Manganese 1 -- -- 323 --

Nickel 1 -- -- 0.5 --

Zinc 1 -- -- 237 --

Hydropsyche cockerelli

Arsenic 21 20.5 10.0 14.9 14.1

Cadmium 46 2.7 0.7 1.6 1.5

Chromium 46 9.6 0.7 2.4 2.3

Copper 46 181 48.7 108 111

Iron 46 2,660 816 1,600 1,510

Lead 46 17.1 1.2 9.1 8.8

Manganese 46 3,620 1,070 2,260 2,220

Nickel 46 6.5 0.9 2.2 1.9

Zinc 46 536 136 229 220

Hydropsyche morosa group

Arsenic 0 -- -- -- --

Cadmium 5 3.2 2.4 2.5 2.4

Chromium 5 4.6 1.8 2.6 2.2

Copper 5 185 156 173 175

Iron 5 1,890 1,360 1,510 1,430

Lead 5 12.4 7.1 8.5 7.9

Manganese 5 3,960 2,360 3,500 3,860

Nickel 5 3.6 1.9 2.3 2.1

Zinc 5 349 292 309 303
92 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

12323800—Clark Fork near Galen—Continued

Period of record for biological data: 1987, 1991–2017

Hydropsyche occidentalis

Arsenic 23 17.7 9.1 14.3 14.6

Cadmium 55 1.6 0.6 1.1 1.2

Chromium 55 6.6 0.4 2.2 2.0

Copper 55 151 49.2 95.1 93.1

Iron 55 2,590 642 1,520 1,450

Lead 55 13.5 1.6 8.3 8.4

Manganese 55 6,170 653 2,490 2,230

Nickel 55 3.8 0.8 1.9 1.8

Zinc 55 286 168 209 203

Hydropsyche tana

Arsenic 0 -- -- -- --

Cadmium 1 -- -- 1.5 --

Chromium 1 -- -- 1.4 --

Copper 1 -- -- 92.9 --

Iron 1 -- -- 1,340 --

Lead 1 -- -- 9.0 --

Manganese 1 -- -- 2,160 --

Nickel 1 -- -- 2.1 --

Zinc 1 -- -- 206 --

Hydropsyche spp.

Arsenic 6 15.7 5.5 10.5 10.7

Cadmium 10 3.5 0.7 1.8 1.3

Chromium 6 2.4 0.6 1.6 1.6

Copper 10 154 55.3 105 105

Iron 10 2,110 914 1,320 1,260

Lead 10 13.5 3.8 8.7 9.2

Manganese 6 4,760 668 2,330 1,720

Nickel 6 3.9 0.9 2.0 1.6

Zinc 10 329 132 236 223
Data 93

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

461415112450801—Clark Fork below Lost Creek, near Galen

Period of record for biological data: 1996–2017

Claassenia sabulosa

Arsenic 1 -- -- 1.5 --

Cadmium 2 0.4 0.3 0.4 --

Chromium 2 1.9 0.4 1.2 --

Copper 2 70.1 67.1 68.6 --

Iron 2 209 189 199 --

Lead 2 1.2 0.7 1.0 --

Manganese 2 238 90.4 164 --

Nickel 2 0.2 <0.2 1

0.2 --

Zinc 2 245 208 226 --

Hydropsyche cockerelli

Arsenic 24 27.8 8.8 16.4 16.1

Cadmium 35 3.7 1.1 1.9 1.8

Chromium 35 5.5 0.8 2.4 2.5

Copper 35 338 48.8 155 144

Iron 35 4,080 691 1,860 1,900

Lead 35 28.6 3.0 14.0 14.3

Manganese 35 3,160 1,230 1,810 1,670

Nickel 35 4.5 0.9 1.9 1.9

Zinc 35 339 151 244 248

Hydropsyche occidentalis

Arsenic 13 20.9 12.7 16.1 15.6

Cadmium 27 2.1 0.5 1.4 1.5

Chromium 27 6.5 1.2 2.7 2.1

Copper 27 219 52.1 125 121

Iron 27 2,830 963 1,690 1,620

Lead 27 20.4 6.6 11.9 11.5

Manganese 27 4,150 1,220 2,510 2,190

Nickel 27 6.4 0.5 1.9 1.5

Zinc 27 330 174 252 252
94 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

461415112450801—Clark Fork below Lost Creek, near Galen—Continued

Period of record for biological data: 1996–2017

Hydropsyche spp.

Arsenic 5 14.5 7.0 11.1 12.0

Cadmium 9 1.8 1.0 1.4 1.3

Chromium 9 3.0 0.9 1.6 1.3

Copper 9 153 45.1 101 103

Iron 9 2,040 533 1,260 1,200

Lead 9 20.5 4.1 10.2 8.7

Manganese 9 2,800 775 1,440 1,230

Nickel 9 4.4 0.9 1.9 1.4

Zinc 9 276 143 192 179

Rhyacophila spp.

Arsenic 2 5.2 3.5 4.4 --

Cadmium 2 4.3 3.9 4.1 --

Chromium 2 1.1 1.0 1.0 --

Copper 2 93.1 73.7 83.4 --

Iron 2 346 324 335 --

Lead 2 5.9 4.8 5.4 --

Manganese 2 320 192 256 --

Nickel 2 0.3 0.3 0.3 --

Zinc 2 411 301 356 --

461559112443301—Clark Fork at county bridge, near Racetrack

Period of record for biological data: 1996–2017

Arctopsyche grandis

Arsenic 3 13.0 5.2 9.2 9.3

Cadmium 3 3.5 1.2 2.3 2.4

Chromium 3 4.5 1.9 3.2 3.3

Copper 3 101 81.0 90.9 90.9

Iron 3 1,410 803 1,030 889

Lead 3 13.2 9.1 10.5 9.1

Manganese 3 3,140 1,430 2,350 2,480

Nickel 3 6.4 1.4 3.2 1.9

Zinc 3 572 243 358 260
Data 95

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

461559112443301—Clark Fork at county bridge, near Racetrack—Continued

Period of record for biological data: 1996–2017

Claassenia sabulosa

Arsenic 0 -- -- -- --

Cadmium 1 -- -- 0.4 --

Chromium 1 -- -- 0.3 --

Copper 1 -- -- 40.3 --

Iron 1 -- -- 113 --

Lead 1 -- -- 0.8 --

Manganese 1 -- -- 172 --

Nickel 1 -- -- 0.2 --

Zinc 1 -- -- 213 --

Hydropsyche cockerelli

Arsenic 21 20.2 11.0 14.1 13.6

Cadmium 32 2.8 0.8 1.7 1.5

Chromium 32 3.0 0.6 2.0 2.3

Copper 32 197 50.0 110 108

Iron 32 3,330 657 1,450 1,260

Lead 32 18.7 3.7 9.9 9.7

Manganese 32 2,360 646 1,670 1,780

Nickel 32 2.0 0.7 1.7 1.5

Zinc 32 302 139 211 198

Hydropsyche occidentalis

Arsenic 18 16.8 9.2 13.1 12.9

Cadmium 31 2.3 0.7 1.4 1.4

Chromium 31 3.7 1.1 2.1 2.0

Copper 31 168 59.5 116 121

Iron 31 3,690 1,030 1,660 1,580

Lead 31 15.7 4.3 11.0 10.7

Manganese 31 3,770 660 2,030 2,020

Nickel 31 5.7 1.1 1.7 1.4

Zinc 31 361 181 236 230
96 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

461559112443301—Clark Fork at county bridge, near Racetrack—Continued

Period of record for biological data: 1996–2017

Hydropsyche spp.

Arsenic 6 12.8 5.7 9.6 9.8

Cadmium 8 2.4 1.0 1.6 1.5

Chromium 8 3.9 0.7 1.6 1.0

Copper 8 144 68.1 97 84.0

Iron 8 1,880 787 1,220 1,170

Lead 8 15.0 5.7 8.8 7.1

Manganese 8 2,370 886 1,320 1,150

Nickel 8 2.0 0.7 1.3 1.2

Zinc 8 229 151 193 194

461903112440701—Clark Fork at Dempsey Creek diversion, near Racetrack

Period of record for biological data: 1996–2017

Arctopsyche grandis

Arsenic 12 17.5 4.4 7.2 5.9

Cadmium 13 7.1 0.9 2.6 2.2

Chromium 13 12.9 0.5 1

2.1 10.9

Copper 13 196 30.8 70.1 52.6

Iron 13 2,800 333 735 505

Lead 13 17.6 2.1 1

6.7 15.1

Manganese 13 2,060 510 1,060 956

Nickel 13 2.5 0.5 1.1 1.0

Zinc 13 489 86.8 241 216

Claassenia sabulosa

Arsenic 8 3.8 1.2 2.2 2.0

Cadmium 8 2.4 0.4 1.0 0.8

Chromium 8 1.7 0.2 0.7 0.5

Copper 8 87.2 47.5 62.4 58.8

Iron 8 485 94 215 180

Lead 8 3.4 0.4 1.3 1.0

Manganese 8 1,260 98 329 208

Nickel 8 1.0 0.2 0.4 0.3

Zinc 8 394 168 279 266
Data 97

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

461903112440701—Clark Fork at Dempsey Creek diversion, near Racetrack—Continued

Period of record for biological data: 1996–2017

Hydropsyche cockerelli

Arsenic 21 18.8 8.0 12.0 10.2

Cadmium 30 2.1 0.7 1.5 1.5

Chromium 30 4.6 0.5 1.9 1.7

Copper 30 247 60.7 110 94.3

Iron 30 3,010 552 1,330 1,130

Lead 30 21.9 3.5 9.1 8.5

Manganese 30 2,650 487 1,380 1,230

Nickel 30 2.5 0.5 1.3 1.4

Zinc 30 285 162 217 217

Hydropsyche occidentalis

Arsenic 22 24.0 7.2 14.0 13.9

Cadmium 39 2.4 0.7 1.3 1.3

Chromium 39 6.2 0.3 2.1 1.9

Copper 39 345 57.1 124 106

Iron 39 3,390 630 1,690 1,520

Lead 39 21.8 4.4 12.1 11.4

Manganese 39 4,460 826 2,230 2,150

Nickel 39 2.4 1.0 1.6 1.5

Zinc 39 386 189 259 241

Hydropsyche spp.

Arsenic 4 9.1 6.5 7.6 7.4

Cadmium 6 1.7 0.9 1.3 1.4

Chromium 6 2.3 0.8 1.7 1.8

Copper 6 140 65.5 101 108

Iron 6 1,610 875 1,220 1,200

Lead 6 13.2 7.1 9.0 8.0

Manganese 6 1,150 638 877 848

Nickel 6 1.6 0.6 1.2 1.5

Zinc 6 212 162 185 186
98 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

12324200—Clark Fork at Deer Lodge

Period of record for biological data: 1986–7, 1990–2017

Arctopsyche grandis

Arsenic 7 13.3 5.8 8.8 8.3

Cadmium 9 4.7 2.6 1

3.5 13.4

Chromium 9 4.7 1.0 1

2.3 12.0

Copper 9 183 34.9 96.8 88.6

Iron 9 2,320 537 1,180 1,090

Lead 9 17.4 3.8 1

10.7 111.2

Manganese 9 1,620 380 1,150 1,320

Nickel 9 1.9 <1.3 1

1.4 11.3

Zinc 9 370 140 268 269

Hydropsyche cockerelli

Arsenic 21 17.1 5.8 9.8 9.8

Cadmium 44 4.9 0.6 1.9 1.9

Chromium 44 4.5 0.4 2.0 2.0

Copper 44 241 54.7 110 103

Iron 44 3,340 490 1,320 1,160

Lead 44 24.9 3.8 10.9 10.2

Manganese 41 1,580 396 1,050 1,030

Nickel 44 3.3 0.3 1.4 1.3

Zinc 44 391 132 207 198

Hydropsyche occidentalis

Arsenic 25 21.1 6.6 11.1 9.7

Cadmium 62 3.4 0.6 1.5 1.3

Chromium 62 3.7 0.6 2.0 1.9

Copper 62 222 49.4 123 121

Iron 62 3,240 557 1,510 1,490

Lead 62 20.1 3.5 11.8 11.8

Manganese 62 2,840 649 1,600 1,640

Nickel 62 12.9 1.0 1.7 1.5

Zinc 62 346 166 246 239
Data 99

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

12324200—Clark Fork at Deer Lodge—Continued

Period of record for biological data: 1986–7, 1990–2017

Hydropsyche spp.

Arsenic 1 -- -- 6.0 --

Cadmium 4 2.6 1.6 2.2 2.3

Chromium 1 -- -- 0.8 --

Copper 4 222 91 166 176

Iron 4 2,220 1,070 1,770 1,900

Lead 4 16.7 9.0 14.4 15.9

Manganese 1 -- -- 837 --

Nickel 1 -- -- 0.9 --

Zinc 4 298 196 242 237

12324400—Clark Fork above Little Blackfoot River, near Garrison

Period of record for biological data: 2009–17

Arctopsyche grandis

Arsenic 17 16.6 3.2 5.8 4.3

Cadmium 17 4.9 0.9 2.5 2.0

Chromium 17 4.6 0.6 1

1.5 11.3

Copper 17 209 35.4 74.2 54.6

Iron 17 2,580 257 711 453

Lead 17 18.0 2.8 6.5 4.7

Manganese 17 1,940 578 1,000 940

Nickel 17 2.2 0.5 1.0 0.8

Zinc 17 378 179 247 238

Claassenia sabulosa

Arsenic 4 2.9 2.0 2.3 2.2

Cadmium 4 1.3 0.3 0.8 0.7

Chromium 4 0.6 0.3 0.5 0.6

Copper 4 73.1 58.3 67.7 69.7

Iron 4 284 173 254 279

Lead 4 2.3 1.7 2.0 2.1

Manganese 4 226 149 194 202

Nickel 4 0.8 0.6 0.7 0.7

Zinc 4 297 231 265 266
100 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

12324400—Clark Fork above Little Blackfoot River, near Garrison—Continued

Period of record for biological data: 2009–17

Hydropsyche cockerelli

Arsenic 7 11.1 6.1 8.2 7.8

Cadmium 7 4.0 0.9 1.9 1.4

Chromium 7 3.4 1.1 2.0 1.9

Copper 7 158 81.5 112 108

Iron 7 2,150 746 1,170 1,050

Lead 7 18.8 8.5 11.7 10.8

Manganese 7 1,880 984 1,280 1,130

Nickel 7 1.8 1.4 1.6 1.5

Zinc 7 284 205 226 213

Hydropsyche occidentalis

Arsenic 13 14.7 6.4 9.5 8.4

Cadmium 13 2.5 1.0 1.8 1.7

Chromium 13 3.6 0.7 2.1 2.0

Copper 13 182 78.1 123 120

Iron 13 2,390 908 1,450 1,240

Lead 13 17.9 8.8 12.6 11.5

Manganese 13 2,100 975 1,460 1,340

Nickel 13 1.9 1.0 1.5 1.6

Zinc 13 299 223 251 248

Hydropsyche spp.

Arsenic 1 -- -- 13.6 --

Cadmium 1 -- -- 1.7 --

Chromium 1 -- -- 4.3 --

Copper 1 -- -- 187 --

Iron 1 -- -- 2,570 --

Lead 1 -- -- 18.5 --

Manganese 1 -- -- 919 --

Nickel 1 -- -- 1.8 --

Zinc 1 -- -- 296 --
Data 101

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

12324680—Clark Fork at Goldcreek

Period of record for biological data: 1992–2017

Arctopsyche grandis

Arsenic 48 17.0 1.8 5.0 4.1

Cadmium 77 6.6 0.6 2.0 1.8

Chromium 77 5.3 0.1 1.3 1.1

Copper 77 232 19.9 50.3 39

Iron 77 3,070 195 729 516

Lead 77 16.9 1.0 4.0 3.4

Manganese 77 1,580 436 887 871

Nickel 77 3.1 0.2 0.8 0.7

Zinc 77 326 146 204 189

Claassenia sabulosa

Arsenic 34 2.9 0.4 1.4 1.4

Cadmium 54 3.5 0.1 1.0 0.7

Chromium 54 1.6 0.2 0.7 0.6

Copper 54 84.9 29.7 58.9 58.2

Iron 54 640 63.0 203 171

Lead 54 2.8 0.4 1.0 0.9

Manganese 54 325 50.6 164 155

Nickel 54 1.0 0.1 0.4 0.3

Zinc 54 364 166 267 261

Hydropsyche cockerelli

Arsenic 22 11.1 4.1 6.6 6.0

Cadmium 41 4.2 0.5 1.4 1.3

Chromium 41 4.7 0.5 2.5 2.0

Copper 41 188 17.1 76.1 61.4

Iron 41 3,250 522 1,180 1,010

Lead 41 17.6 2.4 6.9 5.5

Manganese 41 1,710 538 1,030 1,000

Nickel 41 3.5 0.3 1.3 1.2

Zinc 41 359 106 193 188
102 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

12324680—Clark Fork at Goldcreek—Continued

Period of record for biological data: 1992–2017

Hydropsyche morosa group

Arsenic 0 -- -- -- --

Cadmium 4 1.7 1.1 1.4 1.4

Chromium 4 1.4 1.3 1.4 1.4

Copper 4 72.9 43.8 60.5 62.7

Iron 4 1,320 612 1,050 1,130

Lead 4 6.9 2.4 4.6 4.6

Manganese 4 1,030 538 804 822

Nickel 4 1.4 0.9 1.2 1.2

Zinc 4 190 137 167 170

Hydropsyche occidentalis

Arsenic 18 11.5 4.4 6.9 6.5

Cadmium 33 2.3 0.4 1.3 1.3

Chromium 33 3.9 0.4 1.9 1.7

Copper 33 169 26.4 73.1 64.8

Iron 33 2,720 466 1,230 1,120

Lead 33 15.7 2.9 7.5 6.0

Manganese 33 2,900 530 1,300 1,180

Nickel 33 2.5 0.8 1.3 1.1

Zinc 33 328 97.0 206 203

Hydropsyche spp.

Arsenic 2 5.9 5.7 5.8 --

Cadmium 2 1.8 1.7 1.8 --

Chromium 2 1.6 1.6 1.6 --

Copper 2 83.5 73.6 78.6 --

Iron 2 1,150 1,110 1,130 --

Lead 2 9.2 8.0 8.6 --

Manganese 2 1,180 1,130 1,160 --

Nickel 2 0.8 0.8 0.8 --

Zinc 2 210 196 203 --
Data 103

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

12331800—Clark Fork near Drummond

Period of record for biological data: 1986, 1991–2017

Arctopsyche grandis

Arsenic 38 9.9 1.8 4.0 3.7

Cadmium 70 3.8 0.4 1.4 1.2

Chromium 70 4.2 0.1 1.1 1.0

Copper 70 103 16.9 34.9 28.2

Iron 70 2,400 193 611 486

Lead 70 12.4 1.6 4.7 3.9

Manganese 70 2,010 456 859 764

Nickel 70 2.6 0.1 0.7 0.6

Zinc 70 314 137 201 192

Claassenia sabulosa

Arsenic 32 1.9 0.6 1.3 1.3

Cadmium 68 2.8 0.1 1.0 0.8

Chromium 68 3.3 0.1 0.6 0.5

Copper 68 165 18.0 63.7 60.3

Iron 68 449 45.4 178 148

Lead 68 2.9 0.2 1.0 0.9

Manganese 68 748 33.1 182 149

Nickel 68 1.1 0.1 1

0.3 10.3

Zinc 68 567 103 279 269

Hydropsyche cockerelli

Arsenic 21 7.6 3.9 5.6 5.3

Cadmium 50 4.5 0.3 1.2 0.9

Chromium 50 3.5 0.4 1.6 1.6

Copper 50 156 30.0 58.4 51.7

Iron 50 2,500 506 1,160 940

Lead 50 15.0 4.7 8.1 7.4

Manganese 50 1,840 549 1,040 975

Nickel 50 2.0 0.5 1.2 1.1

Zinc 50 322 134 197 194
104 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

12331800—Clark Fork near Drummond—Continued

Period of record for biological data: 1986, 1991–2017

Hydropsyche morosa group

Arsenic 0 -- -- -- --

Cadmium 6 1.3 1.1 1.2 1.2

Chromium 6 2.8 1.9 2.3 2.2

Copper 6 57.4 50.2 55.2 55.8

Iron 6 1,730 1,370 1,570 1,600

Lead 6 10.8 7.0 8.9 9.0

Manganese 6 1,940 1,260 1,610 1,610

Nickel 6 1.7 1.3 1.5 1.5

Zinc 6 250 227 239 240

Hydropsyche occidentalis

Arsenic 22 9.2 4.3 5.8 5.8

Cadmium 38 2.9 0.4 1.1 1.0

Chromium 38 8.1 0.4 2.3 2.1

Copper 38 118 13.3 59.3 56.6

Iron 38 2,400 424 1,260 1,230

Lead 38 17.1 2.9 8.7 8.9

Manganese 38 2,920 477 1,480 1,260

Nickel 38 6.0 0.5 1.5 1.2

Zinc 38 344 153 226 222

Hydropsyche spp.

Arsenic 2 7.9 7.8 7.8 --

Cadmium 3 2.6 1.2 1.7 1.3

Chromium 2 3.5 2.7 3.1 3.1

Copper 3 94.4 85.0 90.1 90.9

Iron 3 2,220 913 1,800 2,150

Lead 3 10.8 9.1 9.9 9.9

Manganese 2 1,390 1,370 1,380 1,380

Nickel 2 2.4 2.4 2.4 2.4

Zinc 3 260 238 246 239
Data 105

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

12334550—Clark Fork at Turah Bridge, near Bonner

Period of record for biological data: 1986, 1991–2017

Arctopsyche grandis

Arsenic 39 7.2 2.8 4.4 4.3

Cadmium 81 2.7 0.3 1.2 1.0

Chromium 81 4.1 0.2 1.5 1.4

Copper 81 125 15.9 36.7 31.7

Iron 81 2,870 321 893 788

Lead 81 13.2 1.6 4.3 3.7

Manganese 81 1,050 324 656 662

Nickel 81 2.7 0.4 1.1 0.9

Zinc 81 282 111 204 204

Claassenia sabulosa

Arsenic 27 3.1 0.2 1.1 1.0

Cadmium 53 2.5 0.05 1.1 0.8

Chromium 53 2.0 0.2 0.7 0.6

Copper 53 97.8 37.5 59.8 55.0

Iron 53 378 58.6 133 114

Lead 53 1.6 0.2 0.6 0.6

Manganese 53 229 37.2 102 90.6

Nickel 53 0.6 0.04 0.2 0.2

Zinc 53 429 144 239 243

Hydropsyche cockerelli

Arsenic 30 9.8 3.7 4.9 4.8

Cadmium 58 2.2 0.3 0.9 0.7

Chromium 58 14.2 0.1 2.2 1.7

Copper 58 126 26.4 49.0 44.1

Iron 58 3,180 566 1,240 1,120

Lead 58 19.7 2.2 5.7 5.2

Manganese 58 957 426 656 666

Nickel 58 2.7 0.6 1.3 1.3

Zinc 58 332 119 192 195
106 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

12334550—Clark Fork at Turah Bridge, near Bonner—Continued

Period of record for biological data: 1986, 1991–2017

Hydropsyche morosa group

Arsenic 0 -- -- -- --

Cadmium 2 1.3 1.1 1.2 --

Chromium 2 4.6 2.4 3.5 --

Copper 2 84.1 26.8 55.4 --

Iron 2 1,800 986 1,390 --

Lead 2 6.6 <7.8 1

5.2 --

Manganese 2 1,320 537 928 --

Nickel 2 1.7 1.3 1.5 --

Zinc 2 231 171 201 --

Hydropsyche occidentalis

Arsenic 24 7.3 2.9 4.7 4.3

Cadmium 44 1.8 0.3 0.9 0.9

Chromium 44 5.0 0.6 2.0 1.8

Copper 44 102 20.1 48.2 44.8

Iron 44 2,590 472 1,280 1,150

Lead 44 14.2 2.8 6.4 5.6

Manganese 44 1,600 454 845 807

Nickel 44 3.2 0.6 1.3 1.2

Zinc 44 416 126 214 220

Hydropsyche spp.

Arsenic 1 -- -- 4.4 --

Cadmium 2 1.3 1.1 1.2 --

Chromium 2 2.6 2.4 2.5 --

Copper 2 84.1 50.5 67.3 --

Iron 2 1,800 1,430 1,610 --

Lead 2 7.8 5.9 1

6.8 --

Manganese 2 980 537 759 --

Nickel 2 1.7 1.3 1.5 --

Zinc 2 231 171 201 --
Data 107

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

12340000—Blackfoot River near Bonner

Period of record for biological data: 1986–7, 1991, 1993, 1996, 1998, 2000, 2003, 2006–17

Arctopsyche grandis

Arsenic 17 4.6 1.6 2.7 2.6

Cadmium 27 0.5 0.1 0.3 0.2

Chromium 22 6.9 0.5 2.0 1.5

Copper 27 19.3 9.9 13.7 12.8

Iron 27 1,880 108 763 765

Lead 27 2.3 0.5 1.1 0.9

Manganese 22 633 286 446 422

Nickel 22 3.7 0.7 1.4 1.2

Zinc 27 170 106 144 147

Claassenia sabulosa

Arsenic 13 3.0 0.1 1.0 0.7

Cadmium 24 0.2 0.1 0.1 0.2

Chromium 19 5.2 0.3 1.0 0.7

Copper 24 88.5 19.0 43.3 44.0

Iron 24 317 46.2 144 137

Lead 24 0.8 0.1 0.3 0.2

Manganese 19 133 26.3 79.3 73.4

Nickel 19 1.1 0.1 0.3 0.3

Zinc 24 399 117 229 207

Hydropsyche cockerelli

Arsenic 12 4.2 2.1 3.2 3.1

Cadmium 12 0.6 <0.1 1

0.3 10.3

Chromium 12 5.7 1.6 3.4 3.5

Copper 12 17.5 5.6 14.7 15.2

Iron 12 2,400 1,120 1,720 1,600

Lead 12 2.6 1.5 2.0 1.9

Manganese 12 814 409 556 542

Nickel 12 4.5 1.4 2.0 1.8

Zinc 12 165 132 148 148
108 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

12340000—Blackfoot River near Bonner—Continued

Period of record for biological data: 1986–7, 1991, 1993, 1996, 1998, 2000, 2003, 2006–17

Hydropsyche occidentalis

Arsenic 16 3.8 1.2 2.2 2.1

Cadmium 28 0.5 0.1 0.2 0.2

Chromium 28 5.8 0.8 2.2 1.9

Copper 28 20.9 12.0 15.9 15.8

Iron 28 2,090 927 1,470 1,480

Lead 28 2.0 0.8 1.5 1.6

Manganese 28 798 412 520 461

Nickel 28 4.9 0.9 1.6 1.4

Zinc 28 202 116 145 145

Hydropsyche spp.

Arsenic 2 4.0 3.1 3.5 --

Cadmium 3 0.6 0.2 0.3 0.2

Chromium 3 4.4 1.6 2.9 2.8

Copper 3 19.9 13.9 17.4 18.3

Iron 3 2,100 1,140 1,480 1,180

Lead 3 2.9 1.8 2.2 2.0

Manganese 3 693 525 613 623

Nickel 3 2.8 2.4 2.7 2.7

Zinc 3 211 132 167 160

12340500—Clark Fork above Missoula

Period of record for biological data: 1997–2017

Arctopsyche grandis

Arsenic 39 7.2 1.2 3.6 3.5

Cadmium 58 2.3 0.1 1.0 0.8

Chromium 58 4.2 0.3 1.6 1.4

Copper 58 81.2 13.7 36.1 29.1

Iron 58 2,340 302 944 824

Lead 58 8.9 1.1 3.8 3.2

Manganese 58 1,400 476 898 868

Nickel 58 2.1 0.3 1.1 1.1

Zinc 58 272 133 199 197
Data 109

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

12340500—Clark Fork above Missoula—Continued

Period of record for biological data: 1997–2017

Claassenia sabulosa

Arsenic 27 1.9 0.1 1.1 1.1

Cadmium 36 2.0 0.2 0.8 0.6

Chromium 36 2.9 0.1 0.9 0.7

Copper 36 81.1 25.8 50.4 48.6

Iron 36 424 82.0 220 227

Lead 36 3.1 0.2 0.9 0.8

Manganese 36 683 57.8 184 139

Nickel 36 1.5 0.2 1

0.5 10.4

Zinc 36 384 191 280 272

Hydropsyche cockerelli

Arsenic 29 9.3 2.4 5.5 5.2

Cadmium 38 2.0 0.1 0.9 0.8

Chromium 38 6.0 1.0 2.8 2.4

Copper 38 99.7 24.4 56.4 47.8

Iron 38 3,590 830 1,850 1,810

Lead 38 12.1 2.5 6.7 5.9

Manganese 38 1,910 764 1,150 1,150

Nickel 38 2.5 0.9 1.8 1.7

Zinc 38 266 156 217 219

Hydropsyche spp.

Arsenic 1 -- -- 3.3 --

Cadmium 1 -- -- 1.0 --

Chromium 1 -- -- <3.4 --

Copper 1 -- -- 45.4 --

Iron 1 -- -- 1,140 --

Lead 1 -- -- 4.6 --

Manganese 1 -- -- 1,180 --

Nickel 1 -- -- 2.8 --

Zinc 1 -- -- 223 --
110 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 23. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2017.—

Continued

[Reported concentrations are in micrograms per gram dry weight. Number of composite samples represents the total of all individual composite samples collected for every year that the constituent was analyzed. Values for a single sample are arbitrarily listed in the “Mean” column. Because Hydropsyche insects were 

not sorted to the species level during 1986–9, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche

species combined. At some sites, statistics of the Hydropsyche morosa group are based on the combined results of two or more species. Insects collected during 

1986–98 were depurated before analysis; depuration was discontinued in 1999. Arsenic was not analyzed until 2003; therefore, the number of samples may be 

small or zero for some taxa. spp., one or more similar species; --, indicates either too few samples (less than three) or insufficient data to compute statistic, or 

element not analyzed; <, less than minimum reporting level]

Constituent Number of composite 

samples Maximum Minimum Mean Median

12340500—Clark Fork above Missoula—Continued

Period of record for biological data: 1997–2017

Hydropsyche occidentalis

Arsenic 14 7.4 2.2 5.0 5.1

Cadmium 20 1.5 0.4 0.8 0.7

Chromium 20 5.5 0.7 2.9 3.0

Copper 20 80.7 25.3 51.6 57.3

Iron 20 2,540 690 1,820 1,990

Lead 20 11.4 2.1 6.5 6.3

Manganese 20 2,470 717 1,510 1,560

Nickel 20 2.4 0.7 1.8 1.7

Zinc 20 278 183 230 230

1

Values determined by substituting one-half of the minimum reporting level for censored (<) values when both uncensored and censored values were used in 

determining the mean and median.
For more information about this publication, contact:

Director, USGS Wyoming-Montana Water Science Center 

3162 Bozeman Avenue

Helena, MT 59601

406–457–5900

For additional information, visit: https://www.usgs.gov/centers/wy-mt-water/

Publishing support provided by the 

Rolla Publishing Service Center
Cleasby and others—Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana—Open-File Report 2019–1060

ISSN 2331-1258 (online)

https://doi.org/10.3133/ofr20191060