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

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

2015 through September 2016) and Statistical Summaries of 

Data for Streams in the Clark Fork Basin, Montana

Open-File Report 2017–1136

U.S. Department of the Interior

U.S. Geological Survey
Cover. Collecting aquatic insects for tissue analysis, Blackfoot River near Bonner (12340000). 

Photograph by Michelle Hornberger, U.S. Geological Survey, taken August 6, 2017.
Water-Quality, Bed-Sediment, and 

Biological Data (October 2015 through 

September 2016) and Statistical Summaries 

of Data for Streams in the Clark Fork Basin, 

Montana

By Kent A. Dodge, Michelle I. Hornberger, and Matthew A. Turner

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

Open-File Report 2017–1136

U.S. Department of the Interior

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

RYAN K. ZINKE, Secretary

U.S. Geological Survey

William H. Werkheiser, Deputy Director 

 exercising the authority of the Director

U.S. Geological Survey, Reston, Virginia: 2018

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

resources, natural hazards, and the environment—visit https://www.usgs.gov or call 1–888–ASK–USGS.

For an overview of USGS information products, including maps, imagery, and publications, 

visit https://store.usgs.gov.

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Dodge, K.A., Hornberger, M.I., and Turner, M.A., 2018, Water-quality, bed-sediment, and biological data (October 2015 

through September 2016) and statistical summaries of data for streams in the Clark Fork Basin, Montana: U.S. Geological Survey Open-File Report 2017–1136, 118 p., https://doi.org/10.3133/ofr20171136.

ISSN 2331-1258 (online)
iii

Contents

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

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

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

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

Methods..................................................................................................................................................6

Results ....................................................................................................................................................7

Quality Assurance.................................................................................................................................7

Bed-Sediment Data .....................................................................................................................................11

Methods................................................................................................................................................11

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

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

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

Methods................................................................................................................................................13

Results ..................................................................................................................................................13

Quality Assurance...............................................................................................................................13

Statistical Summaries of Data ...................................................................................................................14

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

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

Figure

1. Map showing location of 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..........................................................................................................9

4. Water-quality data for the Clark Fork Basin, Montana, October 2015 

through September 2016............................................................................................................20

5. Daily mean streamflow and suspended-sediment data for Clark Fork at 

Turah Bridge, near Bonner, Montana (12334550), October 2015 through 

September 2016...........................................................................................................................40

6. Daily mean streamflow and suspended-sediment data for Blackfoot River 

near Bonner, Montana (12340000), October 2015 through September 2016 .....................44

7. Daily mean streamflow and suspended-sediment data for Clark Fork above 

Missoula, Montana (12340500), October 2015 through September 2016...........................48

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

statistics at Mill Creek at Opportunity, Montana (12323700), March through 

September 2016...........................................................................................................................52
iv

9. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary 

statistics at Willow Creek at Opportunity, Montana (12323720), March through 

September 2016...........................................................................................................................54

10. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary 

statistics at Warm Springs Creek at Warm Springs, Montana (12323770), 

March through September 2016...............................................................................................56

11. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary 

statistics at Lost Creek near Anaconda, Montana (12323840), March through 

August 2016..................................................................................................................................58

12. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary 

statistics at Clark Fork at Deer Lodge, Montana (12324200), March through 

September 2016...........................................................................................................................60

13. Analyses of field replicates for water samples, Clark Fork Basin, Montana ...................62

14. Precision of analyses of field replicates for water samples, Clark Fork Basin, 

Montana .......................................................................................................................................66

15. Precision of analyses of laboratory replicates for water samples, 

Clark Fork Basin, Montana........................................................................................................67

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

blank samples..............................................................................................................................67

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

Clark Fork Basin, Montana........................................................................................................68

18. Analyses of field blanks for water samples ...........................................................................69

19. Bed-sediment data for the Clark Fork Basin, Montana, August 2016................................70

20. Recovery efficiency for analyses of standard reference materials for 

bed-sediment samples...............................................................................................................71

21. Analyses of procedural blanks for bed-sediment samples.................................................72

22. Biological data for the Clark Fork Basin, Montana, August 2016 .......................................73

23. Recovery efficiency for analyses of standard reference material for 

biota samples ..............................................................................................................................74

24. Analyses of procedural blanks for biota samples.................................................................75

25. Statistical summary of long-term water-quality data for the Clark Fork 

Basin, Montana, March 1985 through September 2016 .......................................................76

26. Statistical summary of long-term bed-sediment data for the Clark Fork 

Basin, Montana, August 1986 through August 2016 .............................................................96

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

Montana, August 1986 through August 2016........................................................................101
v

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

inch (in.) 25.4 millimeter (mm)

inch (in.) 25,400 micrometer (μm)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

gallon (gal) 3,785 milliliter (mL) 

acre-foot (acre-ft) 1,233 cubic meter (m3)

Flow rate

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

Mass

ounce (oz) 28.35 gram (g) 

parts per million 1 micrograms per gram (μg/g)

parts per million 1 micrograms per milliliter (μg/mL)

ton 907.2 kilogram (kg) 

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

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

°F=(1.8×°C)+32

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).

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 2016 is the period from October 1, 

2015, through September 30, 2016.
vi

Abbreviations

CRM certified reference material

ICP–AES inductively coupled plasma-atomic emission spectrometry

ICP–MS inductively coupled plasma-mass spectrometry

LRL laboratory reporting level

MRL minimum reporting level

NIST National Institute of Standards and Technology

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 2015 through September 2016) and Statistical 

Summaries of Data for Streams in the Clark Fork Basin, 

Montana

By Kent A. Dodge, Michelle I. Hornberger, 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 upper 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, with emphasis on 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 2015 through 

September 2016. Bed-sediment and biota samples were collected once at 13 sites during August 2016.

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

samples collected at sites from October 2015 through September 2016. Water-quality data include concentrations of selected 

major ions, trace elements, and suspended sediment. Samples 

for analysis of turbidity were collected at 13 sites, whereas 

samples for analysis of dissolved organic carbon were collected at 10 sites. In addition, samples for analysis of nitrogen 

(nitrate plus nitrite) were collected at two sites. Daily values 

of mean suspended-sediment concentration and suspendedsediment discharge were determined for three sites. Seasonal 

daily values of turbidity were determined for five sites. Bedsediment data include trace-element concentrations in the finegrained (less than 0.063 millimeter) fraction. Biological data 

include trace-element concentrations in whole-body tissue of 

aquatic benthic insects. Statistical summaries of water-quality, 

bed-sediment, and biological data for sites in the upper 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) upper Clark Fork Basin 

above Missoula include irrigation, stock watering, small-scale 

industry (Cannon and Johnson, 2004), and habitat for trout 

fisheries. Primary current (2017) land uses are cattle production, logging, mining, residential development, and recreation. 

Large-scale mining and smelting were prevalent land uses in 

the upper basin for more than 100 years but are now either 

discontinued or substantially reduced in scale.

Deposits of 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 contain 

large quantities of trace elements such as arsenic, cadmium, 

copper, lead, and zinc. Eroded tailings mix with stream sediment and are deposited farther downstream in stream channels, on flood plains, in the Warm Springs Ponds, and at the 

location of the former Milltown Reservoir (fig. 1) whose dam 

(Milltown Dam, not shown in figure) was breached on March 

28, 2008 (Andrews, 1987). The presence of elevated traceelement concentrations in water and bed sediment can pose a 

potential risk to aquatic biota and human health (U.S. Environmental Protection Agency, 2004).
2 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Figure 1. Location of study area in the 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
Water-Quality Data 3

Concern about the potential 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 upper Clark Fork 

Basin to guide and monitor remedial cleanup activities. The 

development of a long-term database was considered necessary to detect trends over time to evaluate the effectiveness 

of remediation. Water-quality data have been collected by the 

U.S. Geological Survey (USGS) at selected sites in the upper 

Clark Fork Basin since 1985 (Lambing, 1987 through 1991; 

Lambing and others, 1994, 1995; Dodge and others, 1996 

through 2010, 2012, 2013, 2014a, 2014b, 2017; 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 (Axtmann 

and Luoma, 1991; Cain and others, 1992, 1995; Axtmann and 

others, 1997; Hornberger and others, 1997). In March 1993, 

an expanded monitoring program for water, bed sediment, and 

biota in the upper 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 2015 through September 2016 

(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 water-quality, bed-sediment, and biological data collected at the sites for 

the period of record.

Sampling Locations and Types of Data

Sampling sites for the monitoring program in the upper 

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 type of data are listed in 

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

upper Clark Fork into reaches of approximate uniform length 

and to have each reach encompassing either a major tributary 

or depositional environment (Warm Springs Ponds and the 

former Milltown Reservoir). Major tributaries were sampled 

to describe water-quality, bed-sediment, and biological characteristics of important hydrologic sources in the upper 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 metals entering the Clark 

Fork in an area of historical metal-processing activities near 

Anaconda, Montana. Water-quality samples were collected 

periodically at 20 sites. Daily suspended-sediment samples 

were collected at three sites, and daily turbidity values were 

computed using data measured by continuous turbidity monitors recording every 15 minutes at five sites. Bed-sediment 

and biological samples were collected annually at 13 sites, 

and one additional site (Warm Springs Creek at Warm Springs 

[USGS site number 12323770]) was sampled every third year. 

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 2016 (October 1, 2015, through September 

30, 2016) are listed in tables 4 through 24 at the back of the 

report. Statistical summaries of long-term water-quality, bedsediment, and biological data collected between March 1985 

and September 2016 are listed in tables 25 through 27 at the 

back of the report.

Quality assurance of data was maintained through the use 

of 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 in 

periodically collected stream samples. Water samples were 

collected at 20 sites in the upper Clark Fork Basin six to 

eight times per year on a schedule designed to describe seasonal and hydrologic variability. At the three daily suspendedsediment sites, suspended-sediment samples were collected 

by a contract observer two to nine times per week, depending 

on season and flow conditions. Continuous turbidity monitors 

were operated seasonally (March to September 2016) at five 

sites; turbidity data (recorded every 15 minutes) were used to 

compute daily mean turbidity values (table 1). Water-quality 

data are available in the USGS National Water Information 

System web interface (U.S. Geological Survey, 2017).
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 Biota2 12323230 Blacktail Creek at Harrison 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 Anaconda 10/2004–P 12/2004–P -- 06/2006–09/2012, D -- -- 12323700 Mill Creek at Opportunity 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 Opportunity 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 Ana- conda 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 08/1995, 08/1997, 08/1999, 08/2002, 08/2005, 08/2008, 08/2011, 08/2014 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 Anaconda 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
Water-Quality Data 

5

Site number 

(fig. 1) Site name

Continuousrecord 

streamflow

Periodic 

water quality1

Daily suspended 

sediment

Daily turbidity 

(seasonal)

Fine-grained bed 

sediment2 Biota2

461559112443301 Clark Fork at 

county bridge, near Racetrack

-- -- -- -- 08/1996–P 08/1996–P

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—P 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–P

12334550 Clark Fork at Turah 

Bridge, near Bonner

03/1985–P 03/1985–P 03/1985–03/2003, 

08/2003–P

-- 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–P

-- 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–P

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.

Table 1. Type and period of data collection at sampling sites in the Clark Fork Basin, Montana.—Continued[ --, no data; P, present; D, discontinued]
6 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

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). The use of these methods provides a vertically and laterally discharge-weighted composite sample that is intended to 

be representative of the entire flow passing through the cross 

section of a stream. Samplers consisted of isokinetic depthintegrating water-quality samplers (Davis and the Federal 

Interagency Sedimentation Project, 2005) that were 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 made during collection of periodic 

water samples. Onsite 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).

Composited water samples were analyzed for the constituents listed in table 2. Filtered (0.45-micrometer [μm] 

pore size) and unfiltered recoverable concentrations of trace 

elements (arsenic, cadmium, copper, iron, lead, manganese, 

and zinc); filtered concentrations of calcium, magnesium, 

potassium, sodium, chloride, fluoride, silica, sulfate, nitrogen (nitrate plus nitrite), and organic carbon; and unfiltered 

turbidity (selected sites) were measured by the USGS National 

Water Quality Laboratory (NWQL) in Denver, Colo. Concentrations of calcium and magnesium were used to calculate 

water hardness.

Concentrations of arsenic, cadmium, copper, lead, 

manganese, and zinc in filtered samples were measured using 

inductively coupled plasma-mass spectrometry (ICP–MS) 

(Garbarino and others, 2006). Concentrations of calcium, 

magnesium, and iron in filtered samples were measured using 

inductively coupled plasma-atomic emission spectrometry 

(ICP–AES) (Fishman and Friedman, 1989). 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 

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 Biota

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
Water-Quality Data 7

by Standard Method 3120 (American Public Health Association, 1998); sodium and silica were analyzed by ICP–AES 

(Fishman and Friedman, 1989); 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 by 

the NWQL using Standard Method 2130 (American Public 

Health Association, 1998) in selected unfiltered samples.

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 Wyoming-Montana 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).

Suspended-sediment samples for the three daily suspended-sediment sites (table 1) were collected by local contract observers using the depth-integration method at a single 

vertical transit near midstream as described by Guy (1969). 

The samples were analyzed for suspended-sediment concentration, which was used to calculate daily mean suspendedsediment concentrations according to methods described by 

Porterfield (1972).

Suspended-sediment discharge was determined according 

to the following equation (Porterfield, 1972):

Q Q C k s w = × s × (1)

where

Qs is suspended-sediment discharge, in tons per 

day;

Qw is streamflow, in cubic feet per second;

Cs is suspended-sediment concentration, in 

milligrams per liter; and

k is a units-conversion constant (0.0027) 

to convert instantaneous suspendedsediment discharge to an equivalent daily 

suspended-sediment discharge.

Turbidity was measured using turbidity monitors (Yellow Springs Instruments Company 6136 turbidity sensor) at 

five sites in the upper Clark Fork Basin (table 1). The turbidity 

sites are operated seasonally, generally from early spring (after 

ice breakup) to early fall (before stream freeze-up). Turbidity 

values are recorded at 15-minute intervals and can be viewed 

in real-time in the USGS National Water Information System 

web interface (U.S. Geological Survey, 2017). These values 

differ from the turbidity values reported from laboratory 

analyses of the discrete water-quality samples because of differences in instrumentation and sampling procedures. Continuous recordings enable determination of the minimum and 

maximum turbidity values for each day and 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).

Results

Water-quality data from samples collected periodically 

during water year 2016 (October 1, 2015, through September 

30, 2016) are listed in table 4. In water year 2016, there were 

two water-quality samples with missing dissolved iron because 

they did not pass review and could not be resolved by reruns. 

Two turbidity samples were inadvertently not collected. Daily 

mean streamflow, daily mean suspended-sediment concentration, and daily suspended-sediment discharge for water year 

2016 at the three daily suspended-sediment sites are listed 

in tables 5 through 7 along with monthly summary statistics 

and annual totals for streamflow and suspended-sediment 

discharge. Daily maximum, minimum, and mean turbidity at 

five sites are listed in tables 8 through 12 along with monthly 

summary statistics. Water-quality data are available in the 

USGS National Water Information System (U.S. Geological 

Survey, 2017).

Quality Assurance

Quality-assurance procedures used for the collection and 

field processing of water samples are 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 are described 

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

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

Wyoming-Montana Sediment Laboratory are described by 

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

calibration, measurement, and quality assurance of turbidity 

monitors are described by Anderson (2005).

The quality of analytical results reported for water 

samples was evaluated using quality-control samples that 

were submitted from the field and analyzed concurrently in the 

laboratory with routine 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 
8 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

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.

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

done 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.

Replicate data can be collected in different ways to provide an assessment of precision (reproducibility) of analytical 

results. Replicate samples are two or more samples considered 

to be almost identical in composition. Replicate samples can 

be collected in the field (field replicate) either by repeating the 

collection process to obtain two or more independent composite samples or by splitting a single composite sample into two 

or more subsamples. 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 in the field by splitting a composite stream sample. 

Replicate stream samples for suspended-sediment analysis 

were obtained in the field by collecting two independent crosssectional 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.

Precision of analytical results for laboratory replicates 

(Boughton, 2017), 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 possible variability caused by 

field sample collection and processing. Laboratory replicates 

are not obtainable for suspended-sediment samples because 

the samples are consumed during the analysis.

Spiked samples (Boughton, 2017) are used to evaluate bias, which measures the ability of an analytical method 

to accurately quantify a known amount of analyte added to 

a sample. Because some constituents in stream water potentially can interfere with the analysis of a sample for a targeted 

analyte, it is important to determine if such effects are causing biased (consistently high or low) results. Deionized-water 

blank samples and aliquots of stream samples were spiked in 

the laboratory 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 a water matrix 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.

Deionized-water blank samples were submitted for every 

field trip and analyzed to identify the presence and magnitude 

of contamination that could potentially bias analytical results. 

The type of blank sample routinely tested was a field blank. 

Field blanks are aliquots of deionized water that are certified 

as constituent free and are processed in the field through the 

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 identify if any 

detectable concentrations exist.

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 monitoring 

program.

Data-quality objectives (table 3) were established for 

water-quality data 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 quality-control 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 NWQL uses a statistically based convention for 

establishing minimum laboratory reporting levels (LRLs) 
Water-Quality Data 9

for analytical results and for reporting low-concentration 

data (Childress and others, 1999). Quality-control data are 

collected by the NWQL on a continuing basis to determine 

long-term method detection levels and LRLs. These values 

are reevaluated each year and, consequently, can change from 

year to year. The methods used to determine the LRLs are 

designed to limit the likelihood of a false positive or false 

negative error to 1 percent or less; accordingly, concentrations 

are reported as less than the LRL for samples in which the 

analyte was not detected. The LRL for organics is twice the 

long-term method detection level. A thorough description of 

these laboratory definitions can be found at the USGS NWQL 

website (http://wwwnwql.cr.usgs.gov/qas/Reporting_Limits/

Website/Abbreviations_Definitions.pdf). Estimated values are 

noted with a remark code of “E” for describing streamflow 

(for ice-affected periods) and turbidity (for periods that exceed 

the manufacturers’ threshold for the sonde).

The precision of analytical results for a constituent can be 

determined by estimating a standard deviation of the differences in concentrations between replicate analyses for several 

sets of samples. These replicate analyses may consist either 

of individual analyses of a pair of samples considered to be 

almost identical (field replicates) or of multiple analyses of an 

individual sample (laboratory replicates). The differences in 

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 mg/L 20 --

Sodium, filtered 0.06 mg/L 20 --

Alkalinity, filtered, lab 4.0–4.6 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 0.030 μg/L 20 25

Cadmium, unfiltered recoverable 0.03 μg/L 20 25

Copper, filtered 0.80 μg/L 20 25

Copper, unfiltered recoverable 0.8 μg/L 20 25

Iron, filtered 4.0 μg/L 20 25

Iron, unfiltered recoverable 4.6 μg/L 20 25

Lead, filtered 0.040 μg/L 20 25

Lead, unfiltered recoverable 0.04 μg/L 20 25

Manganese, filtered 0.40 μg/L 20 25

Manganese, unfiltered recoverable 0.4 μg/L 20 25

Zinc, filtered 2.0 μg/L 20 25

Zinc, unfiltered recoverable 2 μg/L 20 25

Arsenic, filtered 0.10 μg/L 20 25

Arsenic, unfiltered recoverable 0.01–0.2 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 --
10 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

concentration between replicate analyses can be used to estimate a standard deviation according to the following equation 

(Taylor, 1987):

S

k

d

= ∑ 2

2 (2)

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 can be expressed as a relative standard 

deviation (RSD), in percent, which is computed from the 

standard deviation and the mean concentration for all the 

replicate analyses. Expressing precision relative to a mean 

concentration standardizes the comparison of precision among 

individual constituents. The RSD is calculated according to 

the following equation (Taylor, 1987):

RSD S

x = ×100 (3)

where

RSD is the relative standard deviation,

S is the standard deviation, and

x is the mean concentration for all replicate 

analyses.

Paired analyses of field replicates are listed in table 13. 

The overall precision for each constituent estimated from 

analyses of field replicates, which include field and laboratory 

sources of variability, is listed in table 14. The data-quality 

objective used to indicate acceptable precision of results for 

field replicates was a maximum RSD of 20 percent (table 3). 

Precision estimates for the analytical results of field replicates 

were within the 20-percent RSD limit for all constituents.

The precision for each constituent estimated from laboratory replicate analyses, which include only laboratory sources 

of variability, is listed in table 15. Statistics for the precision 

of analytical results for laboratory replicates are calculated 

using unrounded values stored in laboratory data files. The 

data-quality objective used to indicate acceptable precision 

of results for laboratory replicates was a maximum RSD of 

20 percent (table 3). Precision estimates for the laboratory replicates were within the 20-percent RSD limit for all constituents (table 15). No adjustments were made to analytical data 

based on the precision of replicate analyses.

Recovery efficiency for analyses of constituents is 

determined by comparing a sample and a spiked aliquot of the 

same sample. The data-quality objective for acceptable spike 

recovery of trace elements in water samples determined by 

the NWQL was a maximum deviation of 25 percent from a 

theoretical 100-percent recovery of added constituent (table 3). 

At the laboratory, a spiked deionized-water 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 4:

R D

C = ×100 (4)

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 from 75 to 125 percent, the instrument was recalibrated and the entire sample set and all spiked samples were 

reanalyzed for that particular trace element until recoveries 

were improved to the extent possible. Recovery efficiency 

for individual trace elements in laboratory-spiked deionizedwater blank samples and in laboratory-spiked stream samples 

is listed in tables 16 and 17, respectively. The mean spike 

recovery for deionized-water blank samples spiked with trace 

elements (table 16) ranged from 95.9 to 106 percent; the 

smallest individual constituent recovery was copper, unfiltered 

recoverable, at 87.4 percent, and the largest was lead, unfiltered recoverable, at 116 percent. The 95-percent confidence 

intervals (Taylor, 1987) for the mean spike recovery for each 

constituent for which deionized-water blank samples were 

analyzed (table 16) did not exceed a 25-percent deviation from 

an expected 100-percent recovery. The mean spike recovery 

for spiked stream samples (table 17) ranged from 84.3 to 

101 percent; the smallest individual constituent recovery was 

iron, unfiltered recoverable, at 48.2 percent and the largest was arsenic, unfiltered recoverable, at 137 percent. The 

95-percent confidence intervals for the mean spike recovery 

for each constituent for which stream water samples were 

analyzed (table 17) did not exceed a 25-percent deviation 

from an expected 100-percent recovery, except for cadmium, 

unfiltered recoverable (130 percent); iron, unfiltered recoverable (48.2 percent); and arsenic, unfiltered recoverable (61.9 

and 137 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 deionized-water blank samples 

(table 16) except for cadmium, filtered (94.3–97.5 percent); 

manganese, filtered (105–107 percent); and manganese unfiltered recoverable (101–107 percent). Confidence intervals 

for percent recovery include 100 percent for all laboratoryspiked stream samples (table 17) except for cadmium, filtered 
Bed-Sediment Data 11

(95.0–99.5 percent); copper, unfiltered recoverable (79.5–

99.5 percent); and zinc, unfiltered recoverable (86.6–96.3 percent). No adjustments were made to analytical results for 

stream samples based on spike recoveries.

Analytical results for field blanks are listed in table 18. A 

field blank with constituent concentrations less than or equal 

to the LRL for the analytical method indicates 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 

collected as part of the subsequent sample set 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 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 from individual components of 

the processing sequence and were submitted for analysis to 

identify the source of contamination.

Constituent concentrations in field blanks (table 18) 

almost always were less than the LRL. Two sample concentrations of filtered silica (0.032 and 0.036 milligrams per 

liter [mg/L]) exceeded the LRL of 0.018 mg/L. One sample 

concentration of copper, unfiltered recoverable was detected at 

0.3 micrograms per liter [μg/L]); one sample concentration of 

iron, filtered (11.0 μg/L) exceeded the LRL of 4.0 μg/L; one 

sample concentration of iron, unfiltered recoverable (8.3 μg/L) 

exceeded the LRL of 4.6 μg/L; and one sample concentration 

of lead, unfiltered recoverable (0.03 μg/L) was detected. No 

adjustments were made to water-quality sample data pending 

the results of this review.

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 and table 1) during low, stable flow 

conditions at about the same time of year as previous samples 

(typically August) to facilitate data comparisons among 

years. Warm Springs Creek at Warm Springs (USGS site 

number 12323770) is sampled once every 3 years rather than 

once annually and was not sampled during water year 2016. 

Bed-sediment data are available in a machine readable data 

release (Boughton, 2017), in each annual report or by request 

in Microsoft® Excel format from the authors.

Methods

Fine-grained bed-sediment samples were collected in 

August 2016 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 National Research Program Ecology and Contaminants Project Laboratory in Menlo Park, California. Bedsediment 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 approximately 

0.5–0.6 grams (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 0.6N (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 0.6N 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 (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

Concentrations of trace elements measured in samples of 

fine-grained bed sediment collected during August 2016 are 

listed in table 19. 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:
12 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

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

dry weight = ( )(

( of sample, in grams)(dilution ratio) (5)

where

μg/g is micrograms per gram,

μg/mL is micrograms per milliliter, and

mL is milliliters.

The reported solid-phase concentrations (table 19) 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 final rinse onsite with stream water. Sampling equipment 

used at more than one site was rinsed thoroughly between sites 

with 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 metal concentrations in 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. Ten low-concentration SRMs, 10 high-concentration SRMs, and 13 procedural 

blanks were analyzed.

Standard reference materials 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 20. 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 similar to 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 

among multiple sets of analyses.

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

trace elements (table 20) illustrate analytical performance. 

Metal recoveries of sediment digests were evaluated with 

NIST 2709a San Joaquin soils and NIST 2711a Montana 

soil II. Mean recoveries in SRM 2709a ranged from 49.1 to 

91.0 percent of the certified concentrations (table 20). The 

mean recoveries were within 24 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 (between 49.1 and 67.6 percent). Mean recoveries in 

SRM 2711a ranged from 51.3 to 100 percent (table 20). The 

percent recoveries were within 16 percent of the 95-percent 

confidence interval for arsenic, cadmium, copper, iron, lead, 

nickel, and zinc and within 21 percent for manganese. Chromium had the lowest mean recovery (51.3 percent) because of 

the strong binding nature of the crystalline lattice. 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, 0.6N hydrochloric acid was added to reconstitute the 

dry residue. Analytical results of procedural blanks for bed 

sediment (table 21) are reported as a liquid-phase 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 constituents. 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 analyses 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 

and table 1), allowing for a direct comparison of biological 
Biological Data 13

data with bed-sediment data through the years. Warm Springs 

Creek at Warm Springs is sampled once every 3 years rather 

than once annually and was not sampled during water year 

2016. Biological data are available in a machine readable data 

release (Boughton, 2018), in each annual report or 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. Targeted taxa for collection 

were the order Trichoptera (caddisflies) and the order Plecoptera (stoneflies).

Two caddisfly species of the genus Hydropsyche

(Hydropsyche cockerelli and Hydropsyche occidentalis) were 

targeted for collection in this study because of their presence 

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 that are commonly 

distributed in the Clark Fork Basin.

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 there was no substantial difference 

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 National Research Program 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 0.6N hydrochloric acid, filtered through 

a 0.45-μm pore-size filter, and analyzed undiluted by 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 2016 are listed in 

table 22. The variability in the number of composite samples 

among species and among sites reflects differences in insect 

abundance, with the number of composite samples increasing 

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 5 (used earlier in this 

report to calculate solid-phase concentrations of trace elements 

in bed sediment). All tissue samples were analyzed undiluted 

(dilution ratio 1:1). As with MRLs for trace elements in bed 

sediment, MRLs for trace elements in insects may differ 

among sites as a result 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 

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

New 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 assurance 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.
14 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Recovery efficiencies for trace-element analyses of the 

TORT-3 CRM are listed in table 23. 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 85.8 to 182 percent for all constituents. The mean recoveries were within 

15 percent (based on the 95-percent confidence interval) for 

arsenic, cadmium, chromium, copper, iron, manganese, nickel, 

and zinc. Mean recovery was the highest for lead analysis 

(182 percent), likely because of the low certified concentration in the standard (0.225 μg/g). 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 24) 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 25 through 27 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 25) 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 the Milltown Reservoir, which 

might disproportionately skew the long-term statistics relative to the other sites in the network. Statistical summaries 

of bed-sediment (table 26) and biological data (table 27) 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 bed-sediment data (table 26) 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 arsenic results 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 biological data (table 27) 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 biota samples 

among species reflect differences in species abundance, within 

and among sites and among years. As a result, the statistics 

for biota 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 biota 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 

particular 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.

References Cited

American Public Health Association, 1998, Standard methods 

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

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

American Water Works Association, and Water Environment Federation, 2130, p. 2–8—2–11.

Anderson, C.W., 2005, Turbidity (version 2.0): U.S. Geological Survey Techniques of Water-Resources Investigations, 

book 9, chap. A6, section 6.7, 64 p. [Also available at 

https://water.usgs.gov/owq/FieldManual/Chapter6/

Ch6_contents.html.]

Andrews, E.D., 1987, Longitudinal dispersion of trace metals in the Clark Fork River, Montana, in Averett, R.C., 

and McKnight, D.M., eds., Chemical quality of water and 

the hydrologic cycle: Chelsea, Mich., Lewis Publishers, 

p. 179–191.

Axtmann, E.V., Cain, D.J., and Luoma, S.N., 1997, Effect 

of tributary inflows on the distribution of trace metals in 

fine-grained sediment and benthic insects of the Clark Fork 

River, Montana: Environmental Science and Technology, 

v. 31, no. 3, p. 750–758.
References Cited 15

Axtmann, E.V., and Luoma, S.N., 1991, Large scale distribution of metal contamination in the fine-grained sediment of 

the Clark Fork River, Montana: Applied Geochemistry, v. 6, 

no. 6, p. 75–88.

Brenton, R.W., and Arnett, T.L., 1993, Methods of analysis by 

the U.S. Geological Survey National Water Quality Laboratory—Determination of dissolved organic carbon by UVpromoted persulfate oxidation and infrared spectrometry: 

U.S. Geological Survey Open-File Report 92–480, 12 p.

Boughton, G.K., 2018, Water-quality, bed-sediment, and 

biological data (October 2015 through September 2016) 

and statistical summaries of data for streams in the Clark 

Fork Basin, Montana: U.S. Geological Survey data 

release, accessed March 2018 at https://doi.org/10.5066/

F79C6WDM.

Cain, D.J., Luoma, S.N., and Axtmann, E.V., 1995, Influence 

of gut content in immature aquatic insects on assessments 

of environmental metal contamination: Canadian Journal of 

Fisheries and Aquatic Sciences, v. 52, no. 12, p. 2736–2746.

Cain, D.J., Luoma, S.N., Carter, J.L., and Ferd, S.V., 1992, 

Aquatic insects as bioindicators of trace element contamination in cobble-bottom rivers and streams: Canadian Journal 

of Fisheries and Aquatic Sciences, v. 49, no. 10, p. 2141–

2154.

Cannon, M.R., and Johnson, D.R., 2004, Estimated water 

use in Montana in 2000: U.S. Geological Survey Scientific 

Investigations Report 2004–5223, 61 p. [Also available at 

https://pubs.usgs.gov/sir/2004/5223/.]

Childress, C.T., Foreman, W.T., Connor, B.F., and Maloney, 

T.J., 1999, New reporting procedures based on longterm method detection levels and some considerations 

for interpretations of water-quality data provided by the 

U.S. Geological Survey National Water Quality Laboratory: 

U.S. Geological Survey Open-File Report 99–193, 19 p.

Davis, B.E., and the Federal Interagency Sedimentation 

Project, 2005, A guide to the proper selection and use of 

federally approved sediment and water-quality samplers: 

U.S. Geological Survey Open-File Report 2005–1087, 20 p. 

[Also available at https://pubs.usgs.gov/of/2005/1087.]

Dodge, K.A., and Hornberger, M.I., 2015, Water-quality, 

bed-sediment, and biological data (October 2013 through 

September 2014) and statistical summaries of data for 

streams in the Clark Fork Basin, Montana: U.S. Geological 

Survey Open-File Report 2015–1223, 125 p. [Also available 

at https:/doi.org/10.3133/ofr20151223.]

Dodge, K.A., Hornberger, M.I., and Axtmann, E.V., 1996, 

Water-quality, bed-sediment, and biological data (October 

1994 through September 1995) and statistical summaries of 

data for streams in the upper Clark Fork Basin, Montana: 

U.S. Geological Survey Open-File Report 96–432, 109 p.

Dodge, K.A., Hornberger, M.I., and Axtmann, E.V., 1997, 

Water-quality, bed-sediment, and biological data (October 

1995 through September 1996) and statistical summaries of 

data for streams in the upper Clark Fork Basin, Montana: 

U.S. Geological Survey Open-File Report 97–552, 91 p.

Dodge, K.A., Hornberger, M.I., and Axtmann, E.V., 1998, 

Water-quality, bed-sediment, and biological data (October 

1996 through September 1997) and statistical summaries of 

data for streams in the upper Clark Fork Basin, Montana: 

U.S. Geological Survey Open-File Report 98–407, 102 p.

Dodge, K.A., Hornberger, M.I., and Bouse, R.M., 1999, 

Water-quality, bed-sediment, and biological data (October 

1997 through September 1998) and statistical summaries of 

data for streams in the upper Clark Fork Basin, Montana: 

U.S. Geological Survey Open-File Report 99–251, 102 p.

Dodge, K.A., Hornberger, M.I., and David, C.P.C., 2000, 

Water-quality, bed-sediment, and biological data (October 

1998 through September 1999) and statistical summaries of 

data for streams in the upper Clark Fork Basin, Montana: 

U.S. Geological Survey Open-File Report 00–370, 102 p.

Dodge, K.A., Hornberger, M.I., and David, C.P.C., 2001, 

Water-quality, bed-sediment, and biological data (October 

1999 through September 2000) and statistical summaries of 

data for streams in the upper Clark Fork Basin, Montana: 

U.S. Geological Survey Open-File Report 01–379, 95 p.

Dodge, K.A., Hornberger, M.I., and David, C.P.C., 2002, 

Water-quality, bed-sediment, and biological data (October 

2000 through September 2001) and statistical summaries of 

data for streams in the upper Clark Fork Basin, Montana: 

U.S. Geological Survey Open-File Report 02–358, 94 p.

Dodge, K.A., Hornberger, M.I., and Dyke, J.L., 2005, Waterquality, bed-sediment, and biological data (October 2003 

through September 2004) and statistical summaries of 

data for streams in the upper Clark Fork Basin, Montana: U.S. Geological Survey Open-File Report 2005–

1356, 124 p. [Also available at https://pubs.usgs.gov/

of/2005/1356.]

Dodge, K.A., Hornberger, M.I., and Dyke, J.L., 2006, Waterquality, bed-sediment, and biological data (October 2004 

through September 2005) and statistical summaries of 

data for streams in the upper Clark Fork Basin, Montana: U.S. Geological Survey Open-File Report 2006–

1266, 109 p. [Also available at https://pubs.usgs.gov/

of/2006/1266.]
16 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Dodge, K.A., Hornberger, M.I., and Dyke, J.L., 2007, Waterquality, bed-sediment, and biological data (October 2005 

through September 2006) and statistical summaries of 

long-term data for streams in the Clark Fork Basin, Montana: U.S. Geological Survey Open-File Report 2007–

1301, 124 p. [Also available at https://pubs.usgs.gov/

of/2007/1301.]

Dodge, K.A., Hornberger, M.I., and Dyke, J.L., 2008, Waterquality, bed-sediment, and biological data (October 2006 

through September 2007) and statistical summaries of 

long-term data for streams in the Clark Fork Basin, Montana: U.S. Geological Survey Open-File Report 2008–

1318, 132 p. [Also available at https://pubs.usgs.gov/

of/2008/1318.]

Dodge, K.A., Hornberger, M.I., and Dyke, J.L., 2009, Waterquality, bed-sediment, and biological data (October 2007 

through September 2008) and statistical summaries of 

long-term data for streams in the Clark Fork Basin, Montana: U.S. Geological Survey Open-File Report 2009–

1178, 139 p. [Also available at https://pubs.usgs.gov/

of/2009/1178.]

Dodge, K.A., Hornberger, M.I., and Dyke, J.L., 2010, Waterquality, bed-sediment, and biological data (October 2008 

through September 2009) and statistical summaries of 

long-term data for streams in the Clark Fork Basin, Montana: U.S. Geological Survey Open-File Report 2010–

1267, 137 p. [Also available at https://pubs.usgs.gov/

of/2010/1267.]

Dodge, K.A., Hornberger, M.I., and Dyke, J.L., 2012, Waterquality, bed-sediment, and biological data (October 2009 

through September 2010) and statistical summaries of data 

for streams in the Clark Fork Basin, Montana: U.S. Geological Survey Open-File Report 2011–1314, 120 p. [Also 

available at https://pubs.usgs.gov/of/2011/1314.]

Dodge, K.A., Hornberger, M.I., and Dyke, J.L., 2013, Waterquality, bed-sediment, and biological data (October 2010 

through September 2011) and statistical summaries of data 

for streams in the Clark Fork Basin, Montana: U.S. Geological Survey Open-File Report 2013–1017, 132 p. [Also 

available at http://pubs.usgs.gov/of/2013/1017.]

Dodge, K.A., Hornberger, M.I., and Dyke, J.L., 2014a, Waterquality, bed-sediment, and biological data (October 2011 

through September 2012) and statistical summaries of data 

for streams in the Clark Fork Basin, Montana: U.S. Geological Survey Open-File Report 2014–1034, 121 p. [Also 

available at https://doi.org/10.3133/ofr20141034.]

Dodge, K.A., Hornberger, M.I., and Dyke, J.L., 2014b, Waterquality, bed-sediment, and biological data (October 2012 

through September 2013) and statistical summaries of data 

for streams in the Clark Fork Basin, Montana: U.S. Geological Survey Open-File Report 2014–1244, 133 p. [Also 

available at https://doi.org/10.3133/ofr20141244.]

Dodge, K.A., Hornberger, M.I., and Lavigne, I.R., 2003, 

Water-quality, bed-sediment, and biological data (October 

2001 through September 2002) and statistical summaries of 

data for streams in the upper Clark Fork Basin, Montana: 

U.S. Geological Survey Open-File Report 03–356, 95 p.

Dodge, K.A., Hornberger, M.I., and Lavigne, I.R., 2004, 

Water-quality, bed-sediment, and biological data (October 

2002 through September 2003) and statistical summaries of 

data for streams in the upper Clark Fork Basin, Montana: 

U.S. Geological Survey Open-File Report 2004–1340, 

107 p.

Dodge, K.A., Hornberger, M.I., and Turner, M.A., 2017, 

Water-quality, bed-sediment, and biological data (October 

2014 through September 2015) and statistical summaries 

of data for streams in the Clark Fork Basin, Montana: U.S. 

Geological Survey Open-File Report 2016–1201, 122 p. 

[Also available at https://doi.org/10.3133/ofr20161201.]

Dodge, K.A., and Lambing, J.H., 2006, Quality-assurance plan 

for the analysis of suspended sediment by the U.S. Geological Survey in Montana: U.S. Geological Survey Open-File 

Report 2006–1242, 25 p. [Also available at https://pubs.

usgs.gov/of/2006/1242.]

Driscoll, Alfred, and Hatcher, Jeanne, 2010, Chain of custody: 

U.S. Geological Survey National Water Quality Laboratory SOP QUAX0030.4, effective May 5, 2010, 17 p. [Also 

available at http://wwwnwql.cr.usgs.gov/USGS/htmls/

QUAX0030.4controlled.pdf.]

Edwards, T.K., and Glysson, G.D., 1999, Field methods for 

measurement of fluvial sediment: U.S. Geological Survey 

Techniques of Water-Resources Investigations, book 3, 

chap. C2, 89 p. [Also available at https://pubs.usgs.gov/

twri/twri3-c2/.]

Fishman, M.J., and Friedman, L.C., 1989, Methods for 

determination of inorganic substances in water and fluvial 

sediments: U.S. Geological Survey Techniques of WaterResources Investigations, book 5, chap. A1, 545 p.

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

practices for the chemical and biological analyses of water 

and fluvial sediments: U.S. Geological Survey Techniques 

of Water-Resources Investigations, book 5, chap. A6, 181 p. 

[Also available at https://pubs.usgs.gov/twri/twri5a6/.]
References Cited 17

Garbarino, J.R., Kanagy, L.K., and Cree, M.E., 2006, Determination of elements in natural-water, biota, sediment, and soil 

samples using collision/reaction cell inductively coupled 

plasma-mass spectrometry: U.S. Geological Survey Techniques and Methods, book 5, sec. B, chap. 1, 88 p.

Garbarino, J.R., and Struzeski, T.M., 1998, Methods of 

analysis by the U.S. Geological Survey National Water 

Quality Laboratory—Determination of elements in wholewater digests using inductively coupled plasma-optical 

emission spectrometry and inductively coupled plasmamass spectrometry: U.S. Geological Survey Open-File 

Report 98–165, 101 p.

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

analysis: U.S. Geological Survey Techniques of WaterResources Investigations, book 5, chap. C1, 58 p. [Also 

available at https://pubs.usgs.gov/twri/twri5c1/.]

Helsel, D.R., and Cohn, T.A., 1988, Estimation of descriptive 

statistics for multiply censored water quality data: Water 

Resources Research, v. 24, no. 12, p. 1997–2004.

Hoffman, G.L., Fishman, M.J., and Garbarino, J.R., 1996, 

Methods of analysis by the U.S. Geological Survey National 

Water Quality Laboratory—In-bottle acid digestion of 

whole-water samples: U.S. Geological Survey Open-File 

Report 96–225, 28 p.

Hornberger, M.I., Lambing, J.H., Luoma, S.N., and Axtmann, 

E.V., 1997, Spatial and temporal trends of trace metals in 

surface water, bed sediment, and biota of the upper Clark 

Fork Basin, Montana, 1985–95: U.S. Geological Survey 

Open-File Report 97–669, 84 p.

Horowitz, A.J., Demas, C.R., Fitzgerald, K.K., Miller, T.L., 

and Rickert, D.A., 1994, U.S. Geological Survey protocol 

for the collection and processing of surface-water samples 

for the subsequent determination of inorganic constituents in filtered water: U.S. Geological Survey Open-File 

Report 94–539, 57 p.

Jones, B.E., 1987, Quality control manual of the U.S. Geological Survey’s National Water Quality Laboratory: U.S. Geological Survey Open-File Report 87–457, 17 p.

Lambing, J.H., 1987, Water-quality data for the Clark Fork 

and selected tributaries from Deer Lodge to Milltown, 

Montana, March 1985 through June 1986: U.S. Geological 

Survey Open-File Report 87–110, 48 p.

Lambing, J.H., 1988, Water-quality data (July 1986 through 

September 1987) and statistical summaries (March 1985 

through September 1987) for the Clark Fork and selected 

tributaries from Deer Lodge to Missoula, Montana: 

U.S. Geological Survey Open-File Report 88–308, 55 p.

Lambing, J.H., 1989, Water-quality data (October 1987 

through September 1988) and statistical summaries (March 

1985 through September 1988) for the Clark Fork and 

selected tributaries from Galen to Missoula, Montana: 

U.S. Geological Survey Open-File Report 89–229, 51 p.

Lambing, J.H., 1990, Water-quality data (October 1988 

through September 1989) and statistical summaries (March 

1985 through September 1989) for the Clark Fork and 

selected tributaries from Galen to Missoula, Montana: 

U.S. Geological Survey Open-File Report 90–168, 68 p.

Lambing, J.H., 1991, Water-quality and transport characteristics of suspended sediment and trace elements in streamflow 

of the upper Clark Fork Basin from Galen to Missoula, 

Montana, 1985–90: U.S. Geological Survey WaterResources Investigations Report 91–4139, 73 p.

Lambing, J.H., comp., 2006, Quality-assurance plan for waterquality activities of the U.S. Geological Survey Montana 

Water Science Center: U.S. Geological Survey Open-File 

Report 2006–1275, 39 p. [Also available at https://pubs.

usgs.gov/of/2006/1275/.]

Lambing, J.H., Hornberger, M.I., Axtmann, E.V., and Dodge, 

K.A., 1995, Water-quality, bed-sediment, and biological 

data (October 1993 through September 1994) and statistical summaries of data for streams in the upper Clark 

Fork Basin, Montana: U.S. Geological Survey Open-File 

Report 95–429, 104 p.

Lambing, J.H., Hornberger, M.I., Axtmann, E.V., and Pope, 

D.A., 1994, Water-quality, bed-sediment, and biological data (October 1992 through September 1993) and 

statistical summaries of water-quality data (March 1985 

through September 1993) for streams in the upper Clark 

Fork Basin, Montana: U.S. Geological Survey Open-File 

Report 94–375, 85 p.

Luoma, S.N., and Bryan, G.W., 1981, A statistical assessment 

of the form of trace metals in oxidized estuarine sediments 

employing chemical extractants: Science of the Total Environment, v. 17, no. 17, p. 167–196.

Patton, C.J., and Kryskalla, J.R., 2011, Colorimetric determination of nitrate plus nitrite in water by enzymatic reduction, automated discrete analyzer methods: U.S. Geological 

Survey Techniques and Methods, book 5, chap. B8, 34 p. 

[Also available at https://pubs.usgs.gov/tm/05b08/.]

Porterfield, George, 1972, Computation of fluvial-sediment 

discharge: U.S. Geological Survey Techniques of WaterResources Investigations, book 3, chap. C3, 66 p. [Also 

available at https://pubs.usgs.gov/twri/twri3-c3/.]
18 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

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

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

35 p. [Also available at https://pubs.usgs.gov/of/1995/0443/

report.pdf.]

Rantz, S.E., and others, 1982, Measurement and computation of streamflow: U.S. Geological Survey Water-Supply 

Paper 2175, v. 2, 631 p.

Taylor, J.K., 1987, Quality assurance of chemical measurements: Chelsea, Mich., Lewis Publishers, 328 p.

U.S. Environmental Protection Agency, 2004, Clark Fork 

River Operable Unit of the Milltown Reservoir/Clark Fork 

River Superfund Site—Record of decision, part 2—Decision summary: U.S. Environmental Protection Agency, 

141 p. [Also available at http://www2.epa.gov/sites/

production/files/documents/Pt2DecisionSummary.pdf.]

U.S. Geological Survey, 2017, National Water Information System—Web interface: accessed February 2017 at 

https://doi.org/10.5066/F7P55KJN.

U.S. Geological Survey, variously dated, National field 

manual for the collection of water-quality data: U.S. Geological Survey Techniques of Water-Resources Investigations, book 9, chaps. A1–A9. [Also available at 

https://water.usgs.gov/owq/FieldManual/index.html.]

Wagner, R.J., Boulger, R.W., Jr., Oblinger, C.J., and Smith, 

B.A., 2006, Guidelines and standard procedures for continuous water-quality monitors—Station operation, record 

computation, and data reporting: U.S. Geological Survey 

Techniques and Methods, book 1, chap. D3, 51 p., 8 attachments. [Also available at https://pubs.usgs.gov/tm/2006/

tm1D3/.]

Ward, J.R., and Harr, C.A., eds., 1990, Methods for collection 

and processing of surface-water and bed-material samples 

for physical and chemical analyses: U.S. Geological Survey 

Open-File Report 90–140, 71 p.
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 2015 through September 2016.

[hh, hour; mm, minute; ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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. Unfiltered cadmium and zinc show different reporting levels because of new instrumentation at the National Water 

Quality Laboratory]

12323230—Blacktail Creek at Harrison Avenue, at Butte

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, onsite 

(standard 

units)

Specific 

conductance, 

onsite 

(μS/cm)

Water 

temperature, 

onsite 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/19/2015 0850 5.9 7.5 305 9.0 E2.2 115 33.2 7.92

03/21/2016 0905 13 7.6 264 3.5 E4.5 103 29.7 7.08

04/18/2016 0900 26 7.5 217 4.0 E6.9 83.8 24.2 5.66

05/09/2016 0915 20 7.6 212 9.0 E5.2 137 39.9 9.06

05/23/2016 0910 32 7.6 197 7.0 E7.3 83.3 23.5 5.97

06/06/2016 0905 15 7.6 227 12.5 E5.2 96.0 27.2 6.84

07/11/2016 0900 8.7 7.6 274 9.0 E4.3 116 33.6 7.89

08/08/2016 0900 4.7 7.5 315 9.0 <2.0 133 38.5 8.94

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)

10/19/2015 1.20 0.052 0.116 1.2 1.8 81.7 328 0.090 0.37

03/21/2016 0.62 <0.030 0.033 2.2 3.9 219 663 0.123 0.64

04/18/2016 0.27 0.038 0.037 5.5 8.6 282 969 0.273 1.46

05/09/2016 0.32 <0.030 <0.030 4.1 5.6 313 766 0.228 0.70

05/23/2016 0.20 0.031 0.03 4.5 7.6 310 976 0.219 1.14

06/06/2016 0.43 <0.030 0.03 3.5 4.9 390 954 0.241 0.83

07/11/2016 0.84 0.037 <0.03 2.6 3.6 163 451 0.113 0.52

08/08/2016 1.23 0.031 0.03 2.1 3.0 49.8 224 0.043 0.41

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)

10/19/2015 37.8 44.6 <2.0 2.7 2.1 3.0

03/21/2016 54.6 73.1 <2.0 4.1 2.0 2.9

04/18/2016 31.0 54.5 2.2 5.5 3.5 4.6

05/09/2016 35.2 47.6 <2.0 5.1 4.4 5.1

05/23/2016 25.9 52.9 <2.0 6 4.4 5.6

06/06/2016 41.5 60.7 <2.0 4 5.1 6.3

07/11/2016 29.9 37.8 2.5 5 3.1 3.7

08/08/2016 41.4 48.1 3.0 6 2.2 2.9

Date

Sediment, 

suspended 

(percent finer 

than 0.062 mm)

Sediment, 

suspended 

(mg/L)

Sediment 

discharge, 

suspended 

(ton/d)

10/19/2015 78 2 0.03

03/21/2016 87 9 0.32

04/18/2016 87 12 0.84

05/09/2016 95 4 0.22

05/23/2016 83 13 1.1

06/06/2016 95 7 0.28

07/11/2016 88 3 0.07

08/08/2016 84 8 0.10
Data 21

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2015 through September 2016.—Continued

[hh, hour; mm, minute; ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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. Unfiltered cadmium and zinc show different reporting levels because of new instrumentation at the National Water 

Quality Laboratory]

12323250—Silver Bow Creek below Blacktail Creek, at Butte

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, onsite 

(standard 

units)

Specific 

conductance, 

onsite 

(μS/cm)

Water 

temperature, 

onsite 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/19/2015 1025 22 7.8 536 10.0 E3.2 179 50.1 13.1

03/21/2016 1040 26 7.8 444 10.0 E3.7 157 44.4 11.2

04/18/2016 1040 40 7.6 365 6.0 E6.0 131 37.3 9.24

05/09/2016 1045 34 7.6 356 9.5 E5.2 127 36.2 8.85

05/23/2016 1040 49 7.6 324 7.5 E5.8 121 34.5 8.51

06/06/2016 1020 27 8.2 387 14.5 E5.0 141 40.1 10.0

07/11/2016 1100 26 7.6 453 10.5 E5.0 167 47.7 11.7

08/08/2016 1035 18 7.7 516 13.0 <2.0 195 55.7 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)

10/19/2015 1.19 0.069 0.142 2.7 9.9 39.2 251 0.160 1.69

03/21/2016 2.03 0.071 0.089 3.6 7.5 94.5 467 0.120 1.30

04/18/2016 1.06 0.066 0.088 5.0 10.6 160 730 0.250 2.20

05/09/2016 1.31 0.045 0.092 4.3 10.7 183 820 0.252 2.33

05/23/2016 0.91 0.057 0.08 4.7 10.7 210 804 0.243 2.29

06/06/2016 1.08 0.043 0.07 4.1 7.3 130 538 0.229 1.42

07/11/2016 1.54 0.074 0.09 4.7 8.6 55.1 311 0.176 2.00

08/08/2016 1.82 0.117 0.13 4.4 7.5 26.6 119 0.161 0.94

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)

10/19/2015 90.4 115 23.9 35.5 3.1 4.2 71 6 0.36

03/21/2016 96.6 124 27.3 36.2 2.8 3.5 79 7 0.49

04/18/2016 59.6 83.1 20.2 35.5 3.5 4.6 82 15 1.6

05/09/2016 48.9 80.6 22.3 38.3 4.1 5.2 87 11 1.0

05/23/2016 38.8 70.1 18.4 28 4.3 5.1 86 12 1.6

06/06/2016 44.7 64.6 21.8 32 4.7 5.7 91 6 0.44

07/11/2016 40.6 69.1 49.9 59 4.1 4.6 84 6 0.42

08/08/2016 58.4 74.9 53.2 62 4.9 5.6 85 3 0.15
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 2015 through September 2016.—Continued

[hh, hour; mm, minute; ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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. Unfiltered cadmium and zinc show different reporting levels because of new instrumentation at the National Water 

Quality Laboratory]

12323600—Silver Bow Creek at Opportunity

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, onsite 

(standard 

units)

Specific 

conductance, 

onsite 

(μS/cm)

Water 

temperature, 

onsite 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/19/2015 1150 34 8.5 537 10.0 E2.1 193 56.8 12.3

03/21/2016 1245 56 8.6 500 7.0 E5.1 176 52.9 10.8

04/18/2016 1215 88 8.4 363 7.0 E11 143 42.9 8.73

05/09/2016 1220 93 8.3 320 7.0 E8.9 130 40.1 7.24

05/23/2016 1220 131 8.2 301 6.0 E8.8 124 37.9 7.14

06/06/2016 1155 102 8.7 312 14.5 E5.2 127 38.9 7.31

07/11/2016 1230 48 8.2 436 11.0 E7.8 169 50.0 10.7

08/08/2016 1210 28 8.4 621 15.0 E8.4 248 75.0 14.6

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 

(mg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

10/19/2015 4.89 26.2 106 37.9 0.44 21.1 94.6 0.163 0.172

03/21/2016 4.47 28.3 111 38.4 0.45 19.9 79.9 0.198 0.315

04/18/2016 3.78 20.6 84.3 22.4 0.30 26.8 55.7 0.120 0.345

05/09/2016 2.88 14.5 85.8 15.1 0.25 20.5 47.5 0.090 0.248

05/23/2016 2.69 14.1 83.4 12.5 0.25 23.3 43.2 0.081 0.26

06/06/2016 2.69 14.4 87.5 15.0 0.23 20.0 44.3 0.066 0.17

07/11/2016 4.99 22.4 97.2 27.5 0.47 20.4 72.9 0.087 0.29

08/08/2016 6.93 32.5 106 63.9 0.54 25.7 104 0.134 0.41

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)

10/19/2015 7.8 12.1 15.7 157 0.113 0.95 25.5 55.3

03/21/2016 9.9 21.1 23.9 333 0.123 1.81 174 234

04/18/2016 9.7 25.7 99.4 878 0.344 3.81 91.3 170

05/09/2016 7.6 17.1 73.7 543 0.239 2.34 93.6 144

05/23/2016 8.0 20.1 116 659 0.325 2.92 55.6 114

06/06/2016 7.4 12.9 52.7 319 0.219 1.56 57.7 89.6

07/11/2016 8.7 20.7 37.6 463 0.287 3.17 195 314

08/08/2016 8.5 22.3 11.8 456 0.151 3.46 50.6 271

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)

10/19/2015 30.5 44.1 5.6 6.1 3.14 95 3 0.28

03/21/2016 45.8 87.7 5.5 6.8 3.43 88 12 1.8

04/18/2016 31.5 84.1 5.9 7.4 6.60 93 26 6.2

05/09/2016 25.4 56.2 6.2 6.6 6.01 94 18 4.5

05/23/2016 27.8 63 6.0 7.2 6.92 91 21 7.4

06/06/2016 13.9 33 6.9 6.7 6.16 94 10 2.8

07/11/2016 26.9 69 6.4 7.0 7.44 93 15 1.9

08/08/2016 22.9 75 8.2 9.9 6.39 84 17 1.3
Data 23

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2015 through September 2016.—Continued

[hh, hour; mm, minute; ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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. Unfiltered cadmium and zinc show different reporting levels because of new instrumentation at the National Water 

Quality Laboratory]

12323670—Mill Creek near Anaconda

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, onsite 

(standard 

units)

Specific 

conductance, 

onsite 

(μS/cm)

Water 

temperature, 

onsite 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/19/2015 1600 14 8.0 178 10.0 <2.0 76.9 21.1 5.87

03/22/2016 0815 14 7.7 173 3.0 E2.1 78.0 21.3 6.02

04/18/2016 1530 44 8.0 119 9.0 E3.1 51.0 14.3 3.70

05/09/2016 1550 139 7.5 75 3.5 E6.5 31.4 9.03 2.16

05/23/2016 1535 107 7.7 87 6.0 E2.2 37.1 10.8 2.47

06/06/2016 1505 171 7.7 69 12.5 E6.0 28.7 8.43 1.87

07/11/2016 1545 46 7.9 106 12.0 <2.0 51.5 15.0 3.41

08/08/2016 1515 17 8.1 152 14.5 <2.0 78.2 22.4 5.40

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 

(mg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

10/19/2015 0.75 3.86 83.8 0.39 0.34 11.7 8.23 0.060 0.065

03/22/2016 0.69 5.25 80.3 0.46 0.37 12.6 10.9 0.047 0.089

04/18/2016 0.71 4.91 52.5 0.36 0.30 15.5 7.48 0.053 0.064

05/09/2016 0.53 2.92 33.9 0.22 0.28 12.8 3.98 0.043 0.116

05/23/2016 0.47 3.44 39.3 0.22 0.30 14.3 4.40 0.038 0.05

06/06/2016 0.48 2.28 30.9 0.16 0.29 10.1 3.32 0.038 0.09

07/11/2016 0.49 2.64 49.5 0.20 0.30 9.89 4.66 0.038 0.04

08/08/2016 0.62 3.18 71.8 0.26 0.32 11.6 6.16 0.040 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)

10/19/2015 1.4 1.6 52.7 112 0.097 0.26 5.79 10.7

03/22/2016 1.4 2.7 35.9 128 0.076 0.51 7.31 12.9

04/18/2016 4.3 5.0 91.0 229 0.167 0.64 6.22 13.3

05/09/2016 3.0 6.3 47.5 524 0.162 1.71 7.30 29.6

05/23/2016 2.6 3.8 45.1 163 0.126 0.52 4.39 10.2

06/06/2016 3.2 5.4 40.1 420 0.118 1.21 5.32 25.0

07/11/2016 1.5 2.2 61.6 164 0.094 0.43 7.78 13.8

08/08/2016 1.3 2.1 86.2 151 0.118 0.39 9.37 16.5

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)

10/19/2015 <2.0 2.3 18.3 19.8 1.59 73 1 0.04

03/22/2016 <2.0 2.7 16.0 18.1 1.37 83 1 0.04

04/18/2016 2.4 3.4 16.8 17.3 2.73 83 5 0.59

05/09/2016 <2.0 7.1 13.0 15.1 3.18 69 18 6.8

05/23/2016 <2.0 3 13.7 13.8 2.79 79 4 1.2

06/06/2016 <2.0 6 12.4 13.7 2.68 72 14 6.5

07/11/2016 <2.0 3 12.7 13.3 1.62 83 4 0.50

08/08/2016 <2.0 <2 16.5 19.3 1.26 71 1 0.05
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 2015 through September 2016.—Continued

[hh, hour; mm, minute; ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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. Unfiltered cadmium and zinc show different reporting levels because of new instrumentation at the National Water 

Quality Laboratory]

12323700—Mill Creek at Opportunity

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, onsite 

(standard 

units)

Specific 

conductance, 

onsite 

(μS/cm)

Water 

temperature, 

onsite 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/19/2015 1650 5.2 8.0 206 11.0 <2.0 88.8 24.8 6.55

03/22/2016 0935 8.4 8.0 198 3.5 <2.0 86.3 24.0 6.40

04/18/2016 1630 25 8.1 131 10.0 E3.0 59.9 16.9 4.32

05/09/2016 1700 52 7.7 84 4.5 E9.1 35.6 10.4 2.33

05/23/2016 1625 41 7.8 95 6.5 E2.5 39.9 11.5 2.69

06/06/2016 1555 72 7.7 73 13.0 E7.1 30.7 8.93 2.04

07/11/2016 1650 26 8.0 120 10.0 <2.0 57.3 16.6 3.84

08/08/2016 1605 5.2 8.2 172 15.0 <2.0 80.1 22.8 5.66

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 

(mg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

10/19/2015 1.02 5.61 87.8 0.60 0.36 12.6 17.3 0.074 0.077

03/22/2016 0.79 6.20 83.6 0.62 0.38 12.2 20.0 0.052 0.054

04/18/2016 0.80 5.80 54.8 0.42 0.32 16.9 10.9 0.051 0.095

05/09/2016 0.61 3.26 35.9 0.25 0.29 13.4 5.66 0.054 0.299

05/23/2016 0.51 3.73 41.4 0.25 0.30 14.3 6.16 0.054 0.08

06/06/2016 0.51 2.53 32.2 0.19 0.29 10.2 4.23 0.042 0.23

07/11/2016 0.54 3.32 53.6 0.27 0.31 10.6 7.10 0.049 0.07

08/08/2016 0.83 4.57 80.1 0.41 0.34 12.0 11.6 0.053 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)

10/19/2015 2.1 2.4 73.4 116 0.098 0.15 7.88 8.8

03/22/2016 1.5 2.3 24.7 78.7 <0.040 0.19 2.20 4.6

04/18/2016 3.1 4.9 50.4 269 0.145 0.90 4.47 16.4

05/09/2016 3.5 13.1 49.6 932 0.203 4.31 8.31 58.5

05/23/2016 3.0 4.9 44.0 205 0.140 0.84 3.57 12.9

06/06/2016 3.2 10.6 41.0 736 0.187 3.21 5.95 40.0

07/11/2016 2.1 3.0 72.0 164 0.144 0.46 4.65 15.0

08/08/2016 1.9 2.3 90.3 138 0.138 0.27 4.83 6.9

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)

10/19/2015 3.5 3.9 25.9 28.8 3.04 89 1 0.01

03/22/2016 <2.0 2.7 15.9 15.9 1.41 78 1 0.02

04/18/2016 <2.0 4.6 18.4 20.6 2.84 76 6 0.41

05/09/2016 <2.0 14.2 16.6 23.3 3.45 65 35 4.9

05/23/2016 2.1 5 16.4 17.6 3.01 71 6 0.66

06/06/2016 2.1 12 15.4 20.9 2.70 58 32 6.2

07/11/2016 <2.0 3 20.4 20.1 1.60 71 2 0.14

08/08/2016 2.5 2 30.7 35.4 1.43 88 1 0.01
Data 25

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2015 through September 2016.—Continued

[hh, hour; mm, minute; ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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. Unfiltered cadmium and zinc show different reporting levels because of new instrumentation at the National Water 

Quality Laboratory]

12323710—Willow Creek near Anaconda

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, onsite 

(standard 

units)

Specific 

conductance, 

onsite 

(μS/cm)

Water 

temperature, 

onsite 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/19/2015 1410 1.7 7.7 126 9.0 <2.0 46.6 15.5 1.93

03/21/2016 1600 E2.3 7.8 126 5.0 E3.8 46.1 15.2 1.96

04/18/2016 1415 11 7.7 91 5.5 E10 34.2 11.4 1.38

05/09/2016 1420 27 7.5 70 4.0 E9.8 25.2 8.39 1.02

05/23/2016 1420 27 7.5 75 6.0 E8.5 27.5 9.29 1.05

06/06/2016 1350 18 7.8 89 12.0 E4.6 34.9 11.9 1.27

07/11/2016 1440 5.0 7.9 107 9.0 E2.6 44.3 15.0 1.69

08/08/2016 1410 1.9 8.0 110 12.0 E2.2 43.8 14.9 1.59

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 

(mg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

10/19/2015 1.09 7.20 55.4 0.57 0.07 24.5 7.97 0.031 0.030

03/21/2016 0.91 7.05 51.1 0.69 0.07 21.7 11.8 <0.030 0.035

04/18/2016 0.87 4.94 35.7 0.53 0.06 26.8 8.22 0.035 0.044

05/09/2016 0.72 4.67 29.8 0.33 0.06 23.8 4.90 0.040 0.075

05/23/2016 0.72 4.87 31.8 0.31 0.06 25.4 4.99 <0.030 0.05

06/06/2016 0.80 5.24 38.6 0.32 0.06 24.6 5.69 <0.030 0.04

07/11/2016 0.86 5.83 48.0 0.36 0.07 24.3 5.92 0.039 0.06

08/08/2016 1.09 6.63 49.0 0.47 0.07 25.9 5.89 0.044 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)

10/19/2015 1.5 1.6 123 224 0.164 0.30 11.4 18.4

03/21/2016 1.4 2.0 106 285 0.098 0.35 14.4 23.8

04/18/2016 3.4 4.3 213 584 0.373 0.89 12.8 24.0

05/09/2016 2.7 4.5 90.0 532 0.268 1.33 14.3 36.4

05/23/2016 2.5 3.8 89.5 494 0.222 0.96 8.49 22.1

06/06/2016 2.2 3.0 74.1 268 0.197 0.57 9.72 17.5

07/11/2016 4.0 4.7 108 220 0.262 0.59 11.7 20.0

08/08/2016 5.5 6.8 126 218 0.361 0.71 9.24 16.3

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)

10/19/2015 <2.0 <2.0 17.1 19.0 3.32 88 1 <0.01

03/21/2016 <2.0 <2.0 11.5 13.5 3.05 85 3 0.02

04/18/2016 3.0 4.3 16.8 17.7 6.19 86 6 0.18

05/09/2016 <2.0 6.5 14.0 15.2 4.77 79 20 1.5

05/23/2016 <2.0 4 14.0 14.7 6.24 72 12 0.87

06/06/2016 <2.0 2 14.7 15.2 4.35 87 5 0.24

07/11/2016 <2.0 5 18.1 18.0 4.07 95 4 0.05

08/08/2016 <2.0 <2 25.3 27.9 5.05 91 4 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 2015 through September 2016.—Continued

[hh, hour; mm, minute; ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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. Unfiltered cadmium and zinc show different reporting levels because of new instrumentation at the National Water 

Quality Laboratory]

12323720—Willow Creek at Opportunity

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, onsite 

(standard 

units)

Specific 

conductance, 

onsite 

(μS/cm)

Water 

temperature, 

onsite 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/19/2015 1240 5.4 8.0 293 10.0 <2.0 128 37.2 8.45

03/21/2016 1400 7.1 8.2 281 8.0 E3.2 116 34.1 7.53

04/18/2016 1255 13 8.0 221 8.0 E7.5 99.8 29.6 6.27

05/09/2016 1305 25 7.8 148 7.0 E9.3 62.9 19.3 3.56

05/23/2016 1300 41 7.8 197 7.0 E5.4 85.7 25.2 5.52

06/06/2016 1235 42 8.0 274 16.5 E5.7 133 38.3 8.96

07/11/2016 1320 27 8.1 380 11.0 E3.6 173 48.4 12.8

08/08/2016 1255 10 8.2 272 13.0 E2.8 128 38.6 7.75

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 

(mg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

10/19/2015 1.48 10.2 125 2.31 0.44 21.9 23.9 <0.030 0.035

03/21/2016 1.39 12.0 118 2.53 0.39 21.8 27.7 <0.030 0.042

04/18/2016 2.02 12.0 91.3 1.69 0.27 28.6 19.1 0.032 0.060

05/09/2016 1.03 7.36 64.2 0.85 0.17 26.6 9.6 0.031 0.107

05/23/2016 1.31 10.3 84.7 1.14 0.29 26.1 14.2 0.039 0.08

06/06/2016 2.73 10.5 133 1.61 0.48 30.8 10.2 0.057 0.11

07/11/2016 2.55 16.7 175 3.16 0.66 25.9 22.5 0.050 0.07

08/08/2016 1.68 8.91 121 2.30 0.42 21.2 19.4 <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)

10/19/2015 1.8 3.2 17.1 155 0.174 0.83 33.3 38.0

03/21/2016 2.1 4.2 36.7 191 0.105 0.79 47.8 62.5

04/18/2016 5.0 8.5 103 466 0.355 1.52 52.2 65.1

05/09/2016 6.3 11.4 112 507 0.456 2.19 35.9 55.9

05/23/2016 6.5 11.2 95.0 340 0.280 1.71 24.0 33.5

06/06/2016 8.6 13.9 109 383 0.466 2.08 38.6 51.5

07/11/2016 7.7 10.0 74.7 256 0.204 1.09 31.4 44.6

08/08/2016 2.4 3.9 28.2 204 0.208 1.00 11.5 17.8

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)

10/19/2015 2.6 4.4 13.0 13.8 2.24 94 3 0.04

03/21/2016 <2.0 4.0 19.5 23.1 2.60 94 4 0.08

04/18/2016 3.0 7.6 29.7 31.8 5.53 97 10 0.35

05/09/2016 3.2 11.7 33.0 34.5 6.02 92 15 1.0

05/23/2016 5.2 11 42.5 45.2 7.38 88 11 1.2

06/06/2016 5.4 12 132 130 10.6 90 12 1.4

07/11/2016 4.6 9 126 128 12.9 90 5 0.36

08/08/2016 <2.0 4 16.8 21.0 2.63 97 5 0.14
Data 27

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2015 through September 2016.—Continued

[hh, hour; mm, minute; ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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. Unfiltered cadmium and zinc show different reporting levels because of new instrumentation at the National Water 

Quality Laboratory]

12323750—Silver Bow Creek at Warm Springs

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, onsite 

(standard 

units)

Specific 

conductance, 

onsite 

(μS/cm)

Water 

temperature, 

onsite 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/20/2015 1015 60 8.7 524 10.0 <2.0 205 56.4 15.6

03/22/2016 1330 74 8.9 495 6.0 E4.5 194 56.0 13.2

04/19/2016 1035 147 8.4 458 8.0 E3.0 188 54.5 12.7

05/10/2016 1110 158 8.4 304 5.0 E6.9 121 35.4 7.96

05/24/2016 1020 246 8.8 352 7.0 E3.3 149 43.4 9.97

06/07/2016 0940 186 8.7 255 12.5 E8.7 110 32.0 7.23

07/12/2016 1015 69 8.8 364 11.0 E2.6 155 43.7 11.2

08/09/2016 1020 42 9.3 416 14.0 E2.8 190 53.9 13.4

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 

(mg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

10/20/2015 4.51 20.1 113 21.5 1.02 7.82 123 <0.030 <0.030

03/22/2016 3.88 21.8 104 26.2 0.71 6.37 105 0.053 0.109

04/19/2016 4.23 22.6 100 25.1 0.62 12.2 87.5 0.036 0.095

05/10/2016 2.49 13.9 75.7 12.4 0.43 16.6 53.4 0.040 0.152

05/24/2016 3.37 17.6 89.0 15.8 0.52 17.4 60.5 0.052 0.12

06/07/2016 2.14 10.0 75.5 6.85 0.44 16.6 39.9 0.045 0.21

07/12/2016 2.41 14.6 101 10.6 0.66 14.5 66.0 <0.030 0.05

08/09/2016 2.89 17.9 95.4 15.8 0.74 18.4 93.5 <0.030 0.03

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)

10/20/2015 2.6 3.0 15.0 71.8 0.049 0.21 35.5 70.3

03/22/2016 2.8 7.2 12.8 173 0.075 1.22 38.8 91.5

04/19/2016 2.8 7.2 24.8 280 0.133 1.55 104 126

05/10/2016 4.5 11.9 54.5 482 0.239 2.55 91.4 131

05/24/2016 5.0 9.7 50.2 315 0.160 1.51 118 155

06/07/2016 5.2 14.0 60.6 623 0.243 3.31 67.3 123

07/12/2016 3.5 4.6 40.2 160 0.109 0.57 66.4 100

08/09/2016 1.7 2.5 22.7 84.5 0.089 0.37 45.1 81.8

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)

10/20/2015 <2.0 2.3 23.2 24.5 5.17 93 1 0.16

03/22/2016 2.8 14.2 8.5 9.9 2.88 95 5 1.0

04/19/2016 4.3 16.1 11.2 13.6 3.73 88 7 2.8

05/10/2016 2.8 15.9 21.7 23.8 5.42 88 15 6.4

05/24/2016 3.7 16 19.8 23.8 5.95 86 8 5.3

06/07/2016 2.7 16 41.7 44.9 5.77 87 20 10

07/12/2016 <2.0 4 38.8 39.3 5.87 89 3 0.56

08/09/2016 <2.0 2 28.5 34.5 4.61 81 3 0.34
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 2015 through September 2016.—Continued

[hh, hour; mm, minute; ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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. Unfiltered cadmium and zinc show different reporting levels because of new instrumentation at the National Water 

Quality Laboratory]

12323760—Warm Springs Creek near Anaconda

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, onsite 

(standard 

units)

Specific 

conductance, 

onsite 

(μS/cm)

Water 

temperature, 

onsite 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/20/2015 0840 73 8.3 270 8.0 <2.0 126 37.4 8.01

04/19/2016 0845 68 8.4 251 4.5 <2.0 134 40.1 8.17

05/10/2016 0910 221 8.1 157 3.0 E3.3 77.8 23.9 4.39

05/24/2016 0835 185 8.0 175 4.5 <2.0 88.0 26.8 5.12

07/12/2016 0825 150 8.2 195 7.0 <2.0 102 31.0 6.03

08/09/2016 0830 70 8.3 248 8.0 <2.0 125 37.7 7.60

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 

(mg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

10/20/2015 1.37 2.83 127 1.26 0.41 10.3 14.4 <0.030 <0.030

04/19/2016 1.30 3.41 118 1.24 0.37 11.7 13.9 0.030 <0.030

05/10/2016 0.82 1.80 68.0 0.59 0.29 9.76 11.6 0.041 0.042

05/24/2016 0.89 2.13 77.2 0.71 0.33 10.4 11.3 0.037 0.04

07/12/2016 0.97 2.20 84.6 0.90 0.40 9.72 14.6 0.047 0.04

08/09/2016 1.25 3.04 114 1.15 0.40 10.1 15.1 <0.030 0.03

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)

10/20/2015 <0.80 1.7 8.0 196 <0.040 0.26 0.44 5.1

04/19/2016 0.88 2.5 8.2 106 <0.040 0.34 0.62 4.2

05/10/2016 1.1 4.8 11.2 250 <0.040 0.56 4.20 14.4

05/24/2016 1.3 2.6 10.0 102 0.021 0.27 2.80 8.1

07/12/2016 1.1 2.2 11.1 84.7 <0.040 0.20 3.10 9.0

08/09/2016 0.81 1.8 8.4 57.0 <0.040 0.21 0.95 5.0

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)

10/20/2015 <2.0 2.4 2.5 3.0 1.43 71 3 0.59

04/19/2016 <2.0 3.1 2.1 2.2 1.15 71 5 0.92

05/10/2016 2.7 8.4 1.4 2.0 2.10 61 12 7.2

05/24/2016 4.6 7 2.8 2.9 1.95 60 5 2.5

07/12/2016 4.8 11 1.6 1.9 1.28 70 3 1.2

08/09/2016 <2.0 5 2.2 2.8 0.77 81 4 0.76
Data 29

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2015 through September 2016.—Continued

[hh, hour; mm, minute; ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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. Unfiltered cadmium and zinc show different reporting levels because of new instrumentation at the National Water 

Quality Laboratory]

12323770—Warm Springs Creek at Warm Springs

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, onsite 

(standard 

units)

Specific 

conductance, 

onsite 

(μS/cm)

Water 

temperature, 

onsite 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/20/2015 0935 29 8.1 379 8.5 <2.0 185 55.8 11.1

03/22/2016 1245 30 8.3 371 5.5 E2.9 185 56.1 10.9

04/19/2016 0955 50 8.2 325 5.0 E2.1 174 52.3 10.6

05/10/2016 1020 151 7.9 188 3.5 E5.7 94.0 29.0 5.23

05/24/2016 0940 130 7.9 213 5.5 E2.4 108 32.8 6.25

06/07/2016 0850 195 7.8 158 10.0 E9.3 76.7 23.7 4.28

07/12/2016 0935 75 8.2 240 8.0 E2.0 124 38.1 6.98

08/09/2016 0935 14 8.2 328 10.5 <2.0 175 53.1 10.2

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 

(mg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

10/20/2015 1.79 4.11 148 1.85 0.44 11.4 48.8 <0.030 <0.030

03/22/2016 1.55 4.40 149 1.89 0.45 9.90 49.4 0.031 0.040

04/19/2016 1.50 4.12 133 1.56 0.40 11.9 35.8 0.044 0.050

05/10/2016 0.93 2.12 75.8 0.73 0.31 10.1 19.2 0.037 0.080

05/24/2016 1.01 2.37 85.6 0.89 0.36 10.6 21.5 0.043 0.06

06/07/2016 0.90 1.83 60.1 0.55 0.36 9.27 17.3 0.031 0.13

07/12/2016 1.13 2.61 97.1 1.11 0.42 10.3 24.3 0.044 0.05

08/09/2016 1.51 3.82 131 1.54 0.43 10.5 39.1 0.036 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)

10/20/2015 2.9 5.7 23.5 104 0.049 0.24 31.7 55.5

03/22/2016 1.9 4.6 9.2 62.0 <0.040 0.28 51.6 100

04/19/2016 2.5 8.5 11.6 138 <0.040 0.71 39.1 103

05/10/2016 2.7 18.1 13.2 349 0.059 1.98 21.7 89.6

05/24/2016 2.3 10.0 12.2 164 <0.040 0.97 23.1 56.1

06/07/2016 3.7 38.5 16.6 668 0.073 4.09 26.4 137

07/12/2016 2.2 7.9 15.5 127 0.050 0.73 27.6 47.7

08/09/2016 2.5 5.0 15.9 58.8 0.050 0.27 31.5 53.3

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)

10/20/2015 <2.0 2.3 7.1 7.8 1.69 71 1 0.08

03/22/2016 <2.0 2.1 4.5 4.6 0.88 73 3 0.24

04/19/2016 <2.0 3.7 4.7 5.4 1.28 78 5 0.68

05/10/2016 <2.0 10.9 3.8 5.4 2.31 74 15 6.1

05/24/2016 2.2 6 3.4 3.9 2.27 73 7 2.5

06/07/2016 2.0 19 4.8 8.9 2.28 69 32 17

07/12/2016 <2.0 7 4.1 4.5 1.47 72 3 0.61

08/09/2016 <2.0 3 6.2 7.5 0.91 81 1 0.04
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 2015 through September 2016.—Continued

[hh, hour; mm, minute; ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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. Unfiltered cadmium and zinc show different reporting levels because of new instrumentation at the National Water 

Quality Laboratory]

12323800—Clark Fork near Galen

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, onsite 

(standard 

units)

Specific 

conductance, 

onsite 

(μS/cm)

Water 

temperature, 

onsite 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/20/2015 1145 89 8.3 482 10.0 204 58.3 14.1

03/23/2016 0750 126 8.3 470 4.0 207 60.9 13.3

04/19/2016 1210 206 8.4 427 9.5 176 51.6 11.4

05/10/2016 1315 313 8.3 249 7.0 109 32.6 6.67

05/24/2016 1205 387 8.6 301 8.0 128 37.6 8.18

06/07/2016 1110 398 8.3 206 13.0 93.9 28.1 5.76

07/12/2016 1155 147 8.6 307 12.0 142 41.9 9.14

08/09/2016 1230 60 8.9 400 16.0 183 52.7 12.5

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)

10/20/2015 0.036 0.035 4.3 6.4 24.5 73.7 0.162 0.48

03/23/2016 0.069 0.140 3.0 12.8 11.0 268 0.059 1.75

04/19/2016 0.049 0.139 4.3 14.6 20.7 410 0.110 2.29

05/10/2016 0.038 0.156 4.0 23.2 32.3 598 0.165 3.37

05/24/2016 0.049 0.16 4.8 24.5 29.6 510 0.115 3.40

06/07/2016 0.044 0.23 5.4 38.6 29.6 813 0.193 5.18

07/12/2016 0.079 0.10 3.9 7.8 25.5 147 0.087 0.71

08/09/2016 0.033 0.05 3.2 6.0 16.3 101 0.080 0.61

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)

10/20/2015 27.9 41.4 2.8 4.4 16.3 17.6 87 2 0.48

03/23/2016 56.1 137 4.6 17.9 6.8 9.2 73 11 3.7

04/19/2016 75.2 145 4.6 20.2 10.2 12.6 70 14 7.8

05/10/2016 50.8 129 2.2 19.1 12.6 16.6 67 26 22

05/24/2016 67.0 124 3.0 23 14.6 19.7 72 35 37

06/07/2016 38.2 140 2.3 26 22.4 27.1 82 35 38

07/12/2016 26.7 60.1 2.9 8 22.3 22.9 87 4 1.6

08/09/2016 25.9 65.9 <2.0 5 21.1 24.6 82 3 0.49
Data 31

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2015 through September 2016.—Continued

[hh, hour; mm, minute; ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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. Unfiltered cadmium and zinc show different reporting levels because of new instrumentation at the National Water 

Quality Laboratory]

12323840—Lost Creek near Anaconda

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, onsite 

(standard 

units)

Specific 

conductance, 

onsite 

(μS/cm)

Water 

temperature, 

onsite 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/20/2015 0750 1.6 8.0 241 8.0 <2.0 112 33.7 6.78

03/22/2016 1115 5.5 8.3 231 4.5 <2.0 115 34.4 7.13

04/19/2016 0745 7.3 7.9 216 4.5 <2.0 111 33.6 6.65

05/10/2016 0800 14 7.8 151 3.5 E4.5 78.0 23.7 4.57

05/24/2016 0740 13 7.9 165 5.0 E3.3 85.2 26.1 4.88

06/07/2016 0750 9.8 7.9 182 9.5 E3.0 95.0 29.1 5.40

07/12/2016 0740 5.7 8.0 219 7.5 <2.0 112 34.6 6.25

08/09/2016 0735 7.4 8.0 218 9.0 <2.0 112 34.3 6.28

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 

(mg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

10/20/2015 1.51 3.34 116 0.94 0.44 11.7 9.77 0.036 <0.030

03/22/2016 1.27 3.32 112 0.96 0.50 10.8 11.5 <0.030 0.031

04/19/2016 1.35 3.08 102 0.77 0.42 12.8 9.89 0.031 0.034

05/10/2016 0.96 2.31 71.8 0.51 0.31 11.6 6.22 <0.030 0.06

05/24/2016 1.05 2.40 77.5 0.53 0.32 11.8 6.82 <0.030 0.05

06/07/2016 1.18 2.87 86.4 0.64 0.32 11.7 7.21 0.031 0.04

07/12/2016 1.16 3.14 107 0.71 0.40 11.5 7.38 <0.030 <0.03

08/09/2016 1.31 3.10 106 0.66 0.40 12.1 7.80 <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)

10/20/2015 1.8 2.3 13.6 39.6 <0.040 0.10 1.32 2.4

03/22/2016 1.6 3.5 5.7 71.3 <0.040 0.32 0.87 3.5

04/19/2016 1.8 5.7 14.9 128 0.058 0.58 1.61 6.3

05/10/2016 1.7 7.8 17.7 276 0.100 1.09 1.83 10.8

05/24/2016 1.7 6.7 18.7 210 <0.040 0.86 1.52 8.3

06/07/2016 2.0 5.7 14.4 158 0.041 0.62 2.22 8.6

07/12/2016 1.7 2.6 9.9 36.6 <0.040 0.16 0.78 2.2

08/09/2016 1.6 4.3 16.4 159 0.040 0.50 1.51 7.9

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)

10/20/2015 <2.0 <2.0 5.2 5.5 1.83 50 1 <0.01

03/22/2016 <2.0 <2.0 3.3 3.4 0.87 86 2 0.03

04/19/2016 <2.0 2.6 3.9 4.3 1.34 73 6 0.12

05/10/2016 <2.0 4.3 3.4 3.9 2.37 73 17 0.64

05/24/2016 <2.0 3 3.8 3.9 2.15 72 10 0.35

06/07/2016 <2.0 4 5.5 6.0 2.03 67 8 0.21

07/12/2016 <2.0 2 6.6 6.4 1.51 78 1 0.02

08/09/2016 <2.0 4 7.7 9.2 1.13 68 5 0.10
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 2015 through September 2016.—Continued

[hh, hour; mm, minute; ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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. Unfiltered cadmium and zinc show different reporting levels because of new instrumentation at the National Water 

Quality Laboratory]

12323850—Lost Creek near Galen

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, onsite 

(standard 

units)

Specific 

conductance, 

onsite 

(μS/cm)

Water 

temperature, 

onsite 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/20/2015 1105 41 8.1 613 9.0 <2.0 294 85.6 19.4

03/22/2016 1510 51 8.4 588 7.0 E4.1 292 85.0 19.3

04/19/2016 1135 51 8.3 577 8.0 E2.9 301 87.4 20.2

05/10/2016 1215 26 8.3 554 6.0 E2.2 285 83.5 18.6

05/24/2016 1120 23 8.3 659 8.0 <2.0 337 97.0 23.1

06/07/2016 1030 6.0 8.2 645 15.5 <2.0 335 95.3 23.5

07/12/2016 1120 5.0 8.4 654 11.5 <2.0 326 92.0 23.5

08/09/2016 1145 1.9 8.2 661 13.5 <2.0 306 82.9 24.0

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 

(mg/L)

Cadmium, 

filtered 

(μg/L)

Cadmium, 

unfiltered 

recoverable 

(μg/L)

10/20/2015 2.62 11.6 190 5.30 0.49 15.2 134 <0.030 <0.030

03/22/2016 2.16 12.4 189 4.52 0.52 15.9 125 <0.030 0.046

04/19/2016 2.18 12.8 182 4.50 0.46 16.7 123 -- 0.050

05/10/2016 1.89 11.5 170 4.04 0.43 16.6 122 <0.030 <0.030

05/24/2016 2.28 14.0 193 4.79 0.55 17.9 159 0.033 <0.03

06/07/2016 2.57 16.7 187 4.58 0.50 17.7 153 <0.030 <0.03

07/12/2016 2.71 20.2 199 4.84 0.64 18.5 152 0.031 <0.03

08/09/2016 3.39 30.2 223 5.27 0.82 23.9 132 0.046 0.08

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)

10/20/2015 1.4 2.4 13.0 134 <0.040 0.17 5.94 9.3

03/22/2016 1.2 6.8 9.9 183 0.043 0.83 14.4 22.7

04/19/2016 1.6 6.1 11.5 179 0.055 0.74 15.6 22.5

05/10/2016 1.2 4.3 17.1 123 0.054 0.45 21.4 26.6

05/24/2016 1.8 4.4 15.1 95.1 <0.040 0.37 16.0 20.6

06/07/2016 1.7 3.3 11.3 61.6 0.045 0.19 24.8 26.7

07/12/2016 1.5 2.7 10.7 55.7 <0.040 0.18 7.81 11.9

08/09/2016 2.3 4.5 30.9 255 0.049 0.22 16.3 23.1

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)

10/20/2015 <2.0 2.1 9.2 10.0 2.15 84 13 1.4

03/22/2016 <2.0 4.6 10.4 12.0 1.28 84 8 1.1

04/19/2016 <2.0 3.9 10.4 11.1 1.44 73 18 2.5

05/10/2016 <2.0 3.1 9.0 9.5 1.84 86 15 1.1

05/24/2016 <2.0 3 16.0 16.3 2.86 54 22 1.4

06/07/2016 <2.0 <2 13.2 12.9 2.07 33 25 0.41

07/12/2016 <2.0 2 8.1 8.6 1.70 62 23 0.31

08/09/2016 <2.0 4 13.7 17.5 2.30 67 22 0.11
Data 33

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2015 through September 2016.—Continued

[hh, hour; mm, minute; ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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. Unfiltered cadmium and zinc show different reporting levels because of new instrumentation at the National Water 

Quality Laboratory]

12324200—Clark Fork at Deer Lodge

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, onsite 

(standard 

units)

Specific 

conductance, 

onsite 

(μS/cm)

Water 

temperature, 

onsite 

(°C)

Turbidity, 

unfiltered, lab 

(NTRU)

Hardness, 

filtered 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/20/2015 1310 172 8.4 530 10.0 -- 235 68.2 15.6

03/23/2016 0915 241 8.2 501 4.0 E7.6 220 64.7 14.1

04/19/2016 1335 311 8.2 468 10.5 -- 209 62.2 13.2

05/10/2016 1455 425 8.1 300 7.0 E13 132 39.5 8.07

05/24/2016 1335 477 8.2 366 10.0 E11 163 47.6 10.8

06/07/2016 1235 386 8.3 278 17.0 E10 126 37.5 7.75

07/12/2016 1315 168 8.6 407 15.5 E3.2 193 57.4 12.1

08/09/2016 1350 76 8.6 490 17.0 <2.0 218 63.7 14.4

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)

10/20/2015 0.039 0.061 5.4 15.1 10.7 184 0.066 1.39

03/23/2016 0.071 0.175 4.9 29.8 6.6 458 0.052 3.62

04/19/2016 0.077 0.270 6.5 54.0 13.4 942 0.137 7.27

05/10/2016 0.078 0.276 12.5 57.7 120 1,090 1.24 7.77

05/24/2016 0.072 0.30 7.8 66.6 21.1 1,210 0.171 9.58

06/07/2016 0.049 0.23 9.5 57.3 19.9 862 0.188 7.21

07/12/2016 0.053 0.06 7.6 15.5 20.1 160 0.117 1.34

08/09/2016 0.031 0.03 6.0 8.4 9.6 36.3 0.050 0.23

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)

10/20/2015 25.8 51.5 3.8 11.7 12.2 13.7 87 10 4.6

03/23/2016 38.1 114 7.3 28.7 8.3 11.5 83 16 10

04/19/2016 25.5 142 5.9 46.9 11.5 17.5 78 39 33

05/10/2016 38.2 141 9.4 49.3 12.1 18.2 71 44 50

05/24/2016 23.3 132 7.1 56 15.1 22.5 61 55 71

06/07/2016 17.4 110 3.4 41 19.6 26.6 81 32 33

07/12/2016 18.9 42.5 2.2 11 16.0 16.7 91 4 1.8

08/09/2016 2.54 6.8 <2.0 3 13.0 15.0 75 8 1.6
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 2015 through September 2016.—Continued

[hh, hour; mm, minute; ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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. Unfiltered cadmium and zinc show different reporting levels because of new instrumentation at the National Water 

Quality Laboratory]

12324400—Clark Fork above Little Blackfoot River, near Garrison

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, onsite 

(standard 

units)

Specific 

conductance, 

onsite 

(μS/cm)

Water 

temperature, 

onsite 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/20/2015 1435 221 8.5 530 10.0 234 67.8 15.7

03/23/2016 1120 274 8.4 503 5.0 236 69.4 15.2

04/19/2016 1450 325 8.4 472 12.0 207 60.4 13.7

05/10/2016 1650 457 8.3 308 7.5 143 43.2 8.63

05/24/2016 1530 544 8.4 394 11.0 176 50.7 12.0

06/07/2016 1405 429 8.5 316 19.0 141 41.5 9.16

07/12/2016 1440 189 8.6 443 16.0 212 62.1 13.9

08/09/2016 1500 66 8.6 482 18.0 216 60.4 15.8

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)

10/20/2015 0.032 0.052 5.0 14.5 7.0 174 0.048 1.24

03/23/2016 0.069 0.153 5.4 27.4 8.0 397 0.080 3.17

04/19/2016 0.072 0.297 7.7 63.9 12.4 1,050 0.168 8.20

05/10/2016 0.050 0.332 8.8 74.5 24.8 1,290 0.226 10.9

05/24/2016 0.135 0.33 10.9 84.9 21.0 1,320 0.273 11.2

06/07/2016 0.046 0.18 10.5 41.8 -- 555 0.190 4.83

07/12/2016 0.044 0.05 7.9 12.9 11.1 103 0.082 0.79

08/09/2016 <0.030 0.03 7.4 9.7 7.7 21.5 0.044 0.15

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)

10/20/2015 24.5 66.3 2.2 10.9 12.4 13.8 76 9 5.4

03/23/2016 44.4 107 6.2 26.5 9.2 11.9 77 20 15

04/19/2016 22.3 160 4.6 53.9 13.2 20.2 79 44 39

05/10/2016 20.6 161 5.6 62.6 12.4 20.2 76 53 65

05/24/2016 21.6 147 6.0 67 17.3 27.1 69 60 88

06/07/2016 19.5 81.0 2.7 30 19.2 23.5 84 21 24

07/12/2016 9.22 28.8 <2.0 8 15.3 15.7 82 3 1.5

08/09/2016 4.68 10.3 <2.0 3 15.3 17.8 59 3 0.53
Data 35

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2015 through September 2016.—Continued

[hh, hour; mm, minute; ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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. Unfiltered cadmium and zinc show different reporting levels because of new instrumentation at the National Water 

Quality Laboratory]

12324680—Clark Fork at Goldcreek

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, onsite 

(standard 

units)

Specific 

conductance, 

onsite 

(μS/cm)

Water 

temperature, 

onsite 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/20/2015 1535 280 8.6 455 10.5 203 59.5 13.3

03/23/2016 1245 415 8.7 428 6.0 194 57.1 12.4

04/19/2016 1545 591 8.5 350 11.5 155 45.9 9.87

05/11/2016 1130 776 8.3 271 6.5 120 35.7 7.47

05/25/2016 1120 1,120 8.2 306 9.5 138 40.5 8.97

06/07/2016 1520 776 8.5 285 18.5 129 38.5 8.00

07/12/2016 1540 325 8.7 402 17.0 197 58.7 12.3

08/10/2016 0705 129 8.1 445 11.5 198 57.5 13.2

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)

10/20/2015 <0.030 0.034 4.0 7.9 6.3 91.3 0.042 0.69

03/23/2016 0.044 0.087 4.0 16.4 6.2 249 0.057 1.92

04/19/2016 0.040 0.202 5.2 39.1 37.2 890 0.199 5.66

05/11/2016 0.035 0.168 5.2 36.3 30.6 738 0.189 4.79

05/25/2016 0.044 0.22 6.5 47.3 27.9 999 0.183 7.13

06/07/2016 0.055 0.10 11.0 20.6 -- 326 -- 2.31

07/12/2016 0.035 0.05 6.1 9.5 8.7 102 0.061 0.62

08/10/2016 <0.030 0.04 3.8 6.2 9.4 45.5 <0.040 0.26

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)

10/20/2015 9.84 40.1 <2.0 5.9 8.9 9.7 91 4 3.0

03/23/2016 23.2 64.4 2.4 15.5 7.3 9.1 86 12 13

04/19/2016 14.3 113 3.0 37.2 9.0 13.3 82 38 61

05/11/2016 12.1 93.5 3.1 31.7 8.2 12.3 78 31 65

05/25/2016 12.3 108 4.5 43 10.8 15.2 71 46 139

06/07/2016 24.2 51.2 6.0 16 13.3 14.1 90 12 25

07/12/2016 6.52 27.6 <2.0 5 10.6 10.2 90 4 3.5

08/10/2016 15.7 36.8 <2.0 5 8.6 10.2 78 3 1.0
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 2015 through September 2016.—Continued

[hh, hour; mm, minute; ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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. Unfiltered cadmium and zinc show different reporting levels because of new instrumentation at the National Water 

Quality Laboratory]

12331800—Clark Fork near Drummond

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, onsite 

(standard 

units)

Specific 

conductance, 

onsite 

(μS/cm)

Water 

temperature, 

onsite 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/21/2015 0805 461 8.2 494 9.5 220 62.0 15.7

03/23/2016 1425 586 8.4 452 8.0 212 61.0 14.4

04/20/2016 0805 778 8.1 381 10.0 178 51.6 12.0

05/11/2016 1000 1,030 8.1 290 7.0 88.8 21.1 8.76

05/25/2016 0955 1,290 8.1 333 10.0 150 43.7 10.0

06/08/2016 0810 878 8.1 333 17.5 159 46.3 10.6

07/13/2016 0805 495 8.1 469 14.5 230 65.9 15.9

08/10/2016 0815 212 8.1 563 14.0 261 72.2 19.5

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)

10/21/2015 <0.030 0.067 2.7 10.0 6.4 216 0.059 1.57

03/23/2016 0.034 0.088 3.9 14.9 6.3 288 0.073 2.22

04/20/2016 0.037 0.249 4.7 41.6 24.8 1,100 0.189 7.80

05/11/2016 0.031 0.212 5.1 42.7 30.7 994 0.239 7.33

05/25/2016 0.042 0.33 6.4 57.4 25.4 1,410 0.217 9.78

06/08/2016 0.042 0.12 6.7 22.2 13.8 397 0.169 3.15

07/13/2016 0.033 0.05 4.9 8.0 13.7 109 0.098 0.85

08/10/2016 <0.030 0.09 2.8 10.6 6.6 206 0.060 1.55

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)

10/21/2015 11.5 62.1 3.3 13.5 8.7 9.5 79 14 17

03/23/2016 17.6 62.4 3.0 17.9 7.7 9.5 77 16 25

04/20/2016 8.06 144 3.9 51.0 9.5 14.2 73 57 120

05/11/2016 8.69 123 3.8 46.7 8.3 13.6 63 54 150

05/25/2016 10.4 146 5.0 66 10.4 17.1 58 86 300

06/08/2016 9.64 68.2 3.2 23 12.8 14.2 89 17 40

07/13/2016 6.83 33.7 2.8 9 10.6 10.9 87 5 6.7

08/10/2016 26.2 126 2.8 16 10.2 12.3 59 26 15
Data 37

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2015 through September 2016.—Continued

[hh, hour; mm, minute; ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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. Unfiltered cadmium and zinc show different reporting levels because of new instrumentation at the National Water 

Quality Laboratory]

12334550—Clark Fork at Turah Bridge, near Bonner

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, onsite 

(standard 

units)

Specific 

conductance, 

onsite 

(μS/cm)

Water 

temperature, 

onsite 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/21/2015 0930 703 8.2 396 9.0 179 50.2 13.1

03/24/2016 0845 999 8.2 350 6.0 144 39.0 11.2

04/20/2016 0945 1,770 8.2 243 9.0 109 31.0 7.70

05/11/2016 0800 2,860 8.0 170 6.5 82.5 21.5 7.02

05/25/2016 0755 2,890 8.0 208 8.5 92.6 26.2 6.60

06/08/2016 1040 2,200 8.1 204 15.0 97.1 27.6 6.85

07/13/2016 0950 1,120 8.2 285 13.0 139 38.6 10.2

08/10/2016 0945 487 8.2 336 12.0 177 51.3 11.8

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)

10/21/2015 <0.030 0.037 1.8 7.2 5.9 156 <0.040 1.05

03/24/2016 <0.030 0.079 2.3 12.0 9.7 272 0.056 1.82

04/20/2016 <0.030 0.128 3.0 21.0 31.0 632 0.151 3.83

05/11/2016 0.036 0.105 2.8 18.6 11.5 597 0.165 3.45

05/25/2016 <0.030 0.14 3.4 23.5 35.3 643 0.163 4.02

06/08/2016 <0.030 0.05 3.5 9.0 21.2 276 0.166 1.34

07/13/2016 <0.030 <0.03 2.7 3.5 14.5 70.4 <0.040 0.25

08/10/2016 <0.030 0.07 1.5 6.6 9.6 603 <0.040 1.53

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)

10/21/2015 3.46 39.2 2.4 10.5 5.9 6.7 84 10 19

03/24/2016 7.13 45.1 2.7 15.9 4.9 6.2 81 16 43

04/20/2016 5.43 73.5 3.0 28.5 5.1 7.2 74 34 162

05/11/2016 4.73 71.1 2.5 25.9 3.9 5.8 52 45 347

05/25/2016 5.13 65.2 3.5 29 5.2 7.5 61 42 328

06/08/2016 5.78 33.8 2.1 14 5.6 6.0 73 14 83

07/13/2016 2.93 8.8 <2.0 4 4.8 5.3 77 3 9.1

08/10/2016 4.56 76.7 <2.0 13 4.7 6.0 96 37 49
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 2015 through September 2016.—Continued

[hh, hour; mm, minute; ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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. Unfiltered cadmium and zinc show different reporting levels because of new instrumentation at the National Water 

Quality Laboratory]

12340000—Blackfoot River near Bonner

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, onsite 

(standard 

units)

Specific 

conductance, 

onsite 

(μS/cm)

Water 

temperature, 

onsite 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/21/2015 1100 430 8.4 281 8.0 142 35.3 13.0

04/20/2016 1215 2,360 8.2 164 9.0 82.9 21.9 6.85

05/11/2016 1410 3,710 8.2 160 8.0 82.3 21.6 6.87

05/25/2016 1345 3,180 8.3 178 10.5 92.2 23.8 7.97

07/13/2016 1200 1,040 8.5 235 15.5 129 32.8 11.3

08/10/2016 1100 579 8.4 246 14.5 128 30.5 12.6

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)

10/21/2015 <0.030 <0.030 <0.80 <0.80 5.0 43.8 <0.040 <0.04

04/20/2016 <0.030 <0.030 <0.80 <0.80 15.7 135 <0.040 0.12

05/11/2016 <0.030 <0.030 <0.80 1.4 17.4 289 <0.040 0.37

05/25/2016 <0.030 <0.03 <0.80 0.80 10.8 159 <0.040 0.20

07/13/2016 <0.030 <0.03 <0.80 <0.80 7.0 39.6 <0.040 0.05

08/10/2016 <0.030 <0.03 <0.80 0.60 <4.0 41.6 <0.040 0.07

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)

10/21/2015 1.14 4.9 <2.0 <2.0 1.1 1.4 83 2 2.3

04/20/2016 2.26 14.3 <2.0 <2.0 1.0 1.1 81 8 51

05/11/2016 1.87 21.7 <2.0 2.2 0.69 0.82 90 19 190

05/25/2016 2.08 13.6 <2.0 <2 0.76 0.80 86 11 94

07/13/2016 1.58 5.2 <2.0 <2 1.1 1.5 85 2 5.6

08/10/2016 2.04 8.8 <2.0 <2 1.1 1.3 73 4 6.3
Data 39

Table 4. Water-quality data for the Clark Fork Basin, Montana, October 2015 through September 2016.—Continued

[hh, hour; mm, minute; ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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. Unfiltered cadmium and zinc show different reporting levels because of new instrumentation at the National Water 

Quality Laboratory]

12340500—Clark Fork above Missoula

Date Time

(hhmm)

Streamflow, 

instantaneous 

(ft3/s)

pH, onsite 

(standard 

units)

Specific 

conductance, 

onsite 

(μS/cm)

Water 

temperature, 

onsite 

(°C)

Hardness, 

filtered 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

10/21/2015 1255 1,160 8.4 345 9.0 158 42.7 12.6

03/24/2016 1120 2,000 8.3 279 6.0 129 35.5 9.71

04/20/2016 1415 4,320 8.3 198 10.0 95.4 26.3 7.20

05/11/2016 1545 6,790 8.2 166 8.5 125 39.7 6.29

05/25/2016 1515 6,360 8.3 194 11.0 90.6 24.5 7.13

06/08/2016 1245 5,380 8.3 186 16.5 93.2 25.3 7.28

07/13/2016 1355 2,190 8.5 261 15.0 136 36.5 10.8

08/10/2016 1305 1,040 8.3 286 14.0 141 36.8 11.9

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)

10/16/2014 <0.030 <0.030 1.3 3.7 5.7 109 <0.040 0.51

03/25/2015 <0.030 0.041 1.7 6.0 14.1 191 0.047 0.92

04/22/2015 <0.030 0.054 1.6 9.0 20.1 326 0.071 1.56

05/13/2015 <0.030 0.040 1.6 7.9 23.8 425 0.080 1.59

05/28/2015 <0.030 0.07 2.1 11.0 20.0 408 0.088 1.93

06/10/2015 <0.030 0.04 2.6 4.5 11.8 214 0.043 0.70

07/15/2015 <0.030 <0.03 1.7 2.2 9.6 56.4 <0.040 0.18

08/12/2015 <0.030 0.04 1.1 3.7 6.4 342 <0.040 0.82

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)

10/16/2014 5.78 23.0 <2.0 5.8 4.0 4.6 88 6 19

03/25/2015 6.62 28.7 <2.0 8.6 3.1 3.5 85 11 59

04/22/2015 4.82 38.4 <2.0 12.0 2.6 3.4 76 19 222

05/13/2015 4.70 38.6 <2.0 12.4 2.3 3.1 77 24 440

05/28/2015 5.17 39.2 <2.0 16 3.0 3.9 72 23 395

06/10/2015 4.71 23.5 <2.0 6 2.8 3.1 80 13 189

07/15/2015 3.66 9.8 <2.0 3 3.2 3.5 74 2 12

08/12/2015 5.78 45.8 <2.0 8 2.8 3.7 95 19 53
40 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 5. Daily mean streamflow and suspended-sediment data for Clark Fork at Turah Bridge, near Bonner, Montana (12334550), 

October 2015 through September 2016.

[ft3/s, cubic foot per second; mg/L, milligram per liter; ton/d, ton per day; e, estimated; --, no data or value not computed; max, maximum; min, minimum]

Day

Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

October November December

1 625 11 19 865 20 47 e410 2 2.2

2 635 11 19 986 25 67 e450 4 4.9

3 654 10 18 984 25 66 e540 7 10

4 663 10 18 960 21 54 e620 11 18

5 668 10 18 934 16 40 e700 14 26

6 673 10 18 914 12 30 e760 17 35

7 681 10 18 886 10 24 e820 19 42

8 708 12 23 869 9 21 863 21 49

9 706 16 30 874 9 21 971 23 60

10 697 16 30 891 10 24 1,010 20 55

11 688 13 24 872 9 21 940 16 41

12 691 11 21 852 8 18 898 12 29

13 693 10 19 851 8 18 886 10 24

14 685 10 18 852 8 18 886 10 24

15 680 9 17 859 8 19 866 10 23

16 682 9 17 843 8 18 850 11 25

17 681 9 17 830 8 18 800 9 19

18 677 10 18 836 8 18 701 8 15

19 677 10 18 857 8 19 782 8 17

20 695 10 19 828 6 13 834 10 23

21 704 10 19 741 4 8.0 754 9 18

22 715 10 19 687 4 7.4 743 8 16

23 727 10 20 716 4 7.7 806 8 17

24 735 10 20 e740 4 8.0 706 7 13

25 740 10 20 e740 6 12 e660 6 11

26 735 10 20 e620 5 8.4 e620 4 6.7

27 735 10 20 e500 4 5.4 e580 3 4.7

28 742 10 20 e400 3 3.2 e560 3 4.5

29 745 10 20 e380 2 2.1 599 3 4.9

30 750 11 22 e400 2 2.2 621 4 6.7

31 782 15 32 -- -- -- 604 3 4.9

Total1 21,669 -- 631 23,567 -- 638.4 22,840 -- 649.5

Mean 699 11 20 786 9 21 737 10 21

Max 782 16 32 986 25 67 1,010 23 60

Min 625 9 17 380 2 2.1 410 2 2.2
Data 41

Table 5. Daily mean streamflow and suspended-sediment data for Clark Fork at Turah Bridge, near Bonner, Montana (12334550), 

October 2015 through September 2016.—Continued

[ft3/s, cubic foot per second; mg/L, milligram per liter; ton/d, ton per day; e, estimated; --, no data or value not computed; max, maximum; min, minimum]

Day

Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

January February March

1 e580 2 3.1 788 16 34 978 16 42

2 e500 2 2.7 752 14 28 940 14 36

3 e420 1 1.1 695 13 24 928 14 35

4 e450 4 4.9 666 12 22 915 12 30

5 e560 8 12 751 11 22 909 13 32

6 e590 8 13 771 12 25 934 14 35

7 699 9 17 754 13 26 973 14 37

8 716 9 17 744 15 30 962 14 36

9 713 9 17 770 16 33 934 15 38

10 e690 8 15 776 19 40 915 16 40

11 e640 7 12 783 23 49 960 21 54

12 e580 6 9.4 832 31 70 1,000 24 65

13 e660 6 11 926 44 110 1,030 23 64

14 772 7 15 1,000 49 132 1,080 21 61

15 833 8 18 1,080 57 166 1,070 20 58

16 776 6 13 1,450 207 810 1,030 16 44

17 764 6 12 1,470 133 528 1,000 14 38

18 791 7 15 1,320 68 242 985 14 37

19 805 7 15 1,210 38 124 927 14 35

20 796 8 17 1,160 33 103 930 15 38

21 801 8 17 1,080 26 76 969 20 52

22 784 9 19 1,010 22 60 1,010 23 63

23 782 9 19 989 19 51 1,010 19 52

24 803 11 24 918 16 40 997 16 43

25 795 11 24 905 14 34 996 15 40

26 774 9 19 916 14 35 980 13 34

27 759 8 16 926 14 35 961 13 34

28 817 12 26 946 16 41 965 12 31

29 843 20 46 977 18 47 952 12 31

30 861 21 49 -- -- -- 939 14 35

31 821 18 40 -- -- -- 925 16 40

Total1 22,175 -- 539.2 27,365 -- 3,037 30,104 -- 1,310

Mean 715 9 17 944 34 105 971 16 42

Max 861 21 49 1,470 207 810 1,080 24 65

Min 420 1 1.1 666 11 22 909 12 30
42 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 5. Daily mean streamflow and suspended-sediment data for Clark Fork at Turah Bridge, near Bonner, Montana (12334550), 

October 2015 through September 2016.—Continued

[ft3/s, cubic foot per second; mg/L, milligram per liter; ton/d, ton per day; e, estimated; --, no data or value not computed; max, maximum; min, minimum]

Day

Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

April May June

1 938 17 43 2,160 32 187 2,300 23 143

2 944 19 48 2,100 32 181 2,200 20 119

3 983 22 58 2,100 31 176 2,160 18 105

4 1,070 24 69 2,180 29 171 2,140 19 110

5 1,160 26 81 2,340 32 202 2,100 18 102

6 1,190 26 84 2,500 38 256 2,130 18 104

7 1,180 26 83 2,660 47 338 2,190 18 106

8 1,210 28 91 2,820 54 411 2,230 16 96

9 1,330 44 158 3,020 65 530 2,200 16 95

10 1,530 67 277 3,060 63 521 2,140 15 87

11 1,680 67 304 2,790 39 294 2,030 12 66

12 1,750 68 321 2,570 29 201 1,920 10 52

13 1,890 75 383 2,450 26 172 1,740 8 38

14 2,060 89 495 2,360 21 134 1,610 7 30

15 2,070 81 453 2,310 20 125 1,580 6 26

16 1,960 61 323 2,340 20 126 1,640 5 22

17 1,850 50 250 2,250 20 122 1,740 5 23

18 1,800 46 224 2,160 18 105 1,640 4 18

19 1,780 42 202 2,260 24 146 1,500 4 16

20 1,780 37 178 2,690 39 283 1,400 3 11

21 1,910 44 227 2,760 42 313 1,300 4 14

22 2,140 56 324 2,970 52 417 1,200 3 9.7

23 2,470 91 607 2,950 51 406 1,140 3 9.2

24 2,740 101 747 2,870 39 302 1,090 2 5.9

25 2,830 104 795 2,900 42 329 1,050 1 2.8

26 2,680 79 572 2,790 42 316 1,010 2 5.5

27 2,550 62 427 2,710 38 278 959 2 5.2

28 2,450 50 331 2,800 37 280 899 2 4.9

29 2,340 38 240 2,710 36 263 821 2 4.4

30 2,270 34 208 2,550 28 193 768 2 4.1

31 -- -- -- 2,430 25 164 -- -- --

Total1 54,535 -- 8,603 79,560 -- 7,942 48,827 -- 1,434.7

Mean 1,818 52 287 2,566 36 256 1,628 9 48

Max 2,830 104 795 3,060 65 530 2,300 23 143

Min 938 17 43 2,100 18 105 768 1 2.8
Data 43

Table 5. Daily mean streamflow and suspended-sediment data for Clark Fork at Turah Bridge, near Bonner, Montana (12334550), 

October 2015 through September 2016.—Continued

[ft3/s, cubic foot per second; mg/L, milligram per liter; ton/d, ton per day; e, estimated; --, no data or value not computed; max, maximum; min, minimum]

Day

Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

July August September

1 741 2 4.0 464 6 7.5 342 6 5.5

2 743 1 2.0 436 5 5.9 346 5 4.7

3 719 1 1.9 417 5 5.6 352 5 4.8

4 697 2 3.8 407 5 5.5 349 5 4.7

5 675 2 3.6 397 5 5.4 368 5 5.0

6 680 2 3.7 354 5 4.8 434 9 11

7 671 1 1.8 366 5 4.9 488 13 17

8 655 1 1.8 382 6 6.2 485 13 17

9 637 1 1.7 427 13 15 483 12 16

10 683 1 1.8 476 32 41 469 11 14

11 978 6 16 478 24 31 458 10 12

12 1,210 5 16 467 21 26 452 8 9.8

13 1,100 3 8.9 453 19 23 451 6 7.3

14 1,020 2 5.5 433 17 20 446 5 6.0

15 915 2 4.9 415 15 17 447 5 6.0

16 880 2 4.8 403 13 14 448 5 6.0

17 865 2 4.7 389 12 13 442 6 7.2

18 827 3 6.7 383 11 11 451 8 9.7

19 788 4 8.5 400 11 12 458 9 11

20 750 4 8.1 399 10 11 459 9 11

21 706 3 5.7 395 9 9.6 501 12 16

22 668 5 9.0 389 8 8.4 603 15 24

23 631 6 10 388 8 8.4 607 16 26

24 598 5 8.1 387 8 8.4 622 15 25

25 572 4 6.2 386 8 8.3 625 12 20

26 547 4 5.9 375 7 7.1 603 12 20

27 537 5 7.2 356 7 6.7 623 12 20

28 533 6 8.6 350 8 7.6 623 14 24

29 514 6 8.3 351 8 7.6 615 14 23

30 490 7 9.3 348 8 7.5 602 14 23

31 481 8 10 347 7 6.6 -- -- --

Total1 22,511 -- 198.5 12,418 -- 366 14,652 -- 406.7

Mean 726 3 6 401 11 12 488 10 14

Max 1,210 8 16 478 32 41 625 16 26

Min 481 1 1.7 347 5 4.8 342 5 4.7

1

Total for water year 2016 (unrounded sum of daily values): streamflow=380,223 ft3/s (annual runoff=754,200 acre-feet); suspended-sediment discharge=25,756.0 tons.
44 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 6. Daily mean streamflow and suspended-sediment data for Blackfoot River near Bonner, Montana (12340000), October 2015 

through September 2016.

[ft3/s, cubic foot per second; mg/L, milligram per liter; ton/d, ton per day; e, estimated; --, no data or value not computed; max, maximum; min, minimum]

Day

Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

October November December

1 411 2 2.2 533 5 7.2 e340 2 1.8

2 410 2 2.2 559 9 14 e400 2 2.2

3 411 2 2.2 550 8 12 e430 2 2.3

4 409 2 2.2 527 6 8.5 e450 2 2.4

5 410 2 2.2 511 4 5.5 e520 2 2.8

6 412 3 3.3 517 2 2.8 e500 2 2.7

7 416 3 3.4 519 2 2.8 e450 2 2.4

8 424 4 4.6 522 3 4.2 e520 2 2.8

9 424 4 4.6 524 3 4.2 e640 3 5.2

10 421 4 4.5 543 4 5.9 e600 4 6.5

11 419 3 3.4 546 4 5.9 e560 4 6.0

12 410 2 2.2 534 3 4.3 e540 3 4.4

13 411 2 2.2 524 2 2.8 e520 3 4.2

14 415 2 2.2 525 2 2.8 e520 3 4.2

15 414 2 2.2 518 2 2.8 521 2 2.8

16 414 2 2.2 512 2 2.8 504 2 2.7

17 415 2 2.2 505 2 2.7 e480 2 2.6

18 416 2 2.2 531 3 4.3 e470 1 1.3

19 419 4 4.5 520 2 2.8 e460 1 1.2

20 428 3 3.5 505 1 1.4 e480 1 1.3

21 428 2 2.3 456 1 1.2 e470 1 1.3

22 425 4 4.6 e480 1 1.3 e470 1 1.3

23 421 3 3.4 e490 1 1.3 e480 1 1.3

24 420 2 2.3 e480 1 1.3 e460 1 1.2

25 419 2 2.3 e480 2 2.6 e440 2 2.4

26 418 2 2.3 e400 2 2.2 e400 2 2.2

27 416 2 2.2 e350 2 1.9 e380 3 3.1

28 414 2 2.2 e320 1 0.86 e360 3 2.9

29 415 2 2.2 e320 1 0.86 e410 2 2.2

30 418 3 3.4 e330 2 1.8 e440 2 2.4

31 454 5 6.1 -- -- -- e440 2 2.4

Total1 12,957 -- 91.5 14,631 -- 115.02 14,655 -- 84.5

Mean 418 3 3.0 488 3 3.8 473 2 2.7

Max 454 5 6.1 559 9 14 640 4 6.5

Min 409 2 2.2 320 1 0.86 340 1 1.2
Data 45

Table 6. Daily mean streamflow and suspended-sediment data for Blackfoot River near Bonner, Montana (12340000), October 2015 

through September 2016.—Continued

[ft3/s, cubic foot per second; mg/L, milligram per liter; ton/d, ton per day; e, estimated; --, no data or value not computed; max, maximum; min, minimum]

Day

Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

January February March

1 e380 2 2.1 451 3 3.7 709 5 9.6

2 e360 2 1.9 e420 3 3.4 707 5 9.5

3 e310 1 0.84 e410 2 2.2 701 4 7.6

4 e330 1 0.89 e430 2 2.3 688 5 9.3

5 e430 1 1.2 e440 2 2.4 681 4 7.4

6 e480 1 1.3 450 2 2.4 692 4 7.5

7 e520 1 1.4 441 2 2.4 705 4 7.6

8 e500 1 1.4 443 2 2.4 716 5 9.7

9 e500 1 1.4 447 2 2.4 718 6 12

10 e470 1 1.3 444 3 3.6 723 5 9.8

11 e420 2 2.3 451 4 4.9 747 6 12

12 e390 2 2.1 478 5 6.5 770 7 15

13 e410 3 3.3 519 6 8.4 805 7 15

14 e430 3 3.5 555 6 9.0 895 11 27

15 e440 2 2.4 635 11 19 918 9 22

16 e440 2 2.4 960 35 91 920 7 17

17 e440 2 2.4 1,020 40 110 921 6 15

18 e460 2 2.5 899 26 63 900 5 12

19 e450 2 2.4 823 16 36 878 4 9.5

20 e450 2 2.4 798 12 26 868 4 9.4

21 e450 2 2.4 760 10 21 880 5 12

22 e450 2 2.4 727 7 14 911 6 15

23 e440 2 2.4 700 6 11 933 7 18

24 e440 2 2.4 670 5 9.0 953 6 15

25 e440 2 2.4 657 4 7.1 966 7 18

26 e430 2 2.3 647 4 7.0 963 6 16

27 458 2 2.5 655 5 8.8 958 6 16

28 467 3 3.8 690 6 11 955 6 15

29 475 3 3.8 711 6 12 940 5 13

30 470 3 3.8 -- -- -- 935 4 10

31 464 3 3.8 -- -- -- 950 7 18

Total1 13,594 -- 71.43 17,731 -- 501.9 26,006 -- 409.9

Mean 439 2 2.3 611 8 17 839 6 13

Max 520 3 3.8 1,020 40 110 966 11 27

Min 310 1 0.84 410 2 2.2 681 4 7.4
46 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 6. Daily mean streamflow and suspended-sediment data for Blackfoot River near Bonner, Montana (12340000), October 2015 

through September 2016.—Continued

[ft3/s, cubic foot per second; mg/L, milligram per liter; ton/d, ton per day; e, estimated; --, no data or value not computed; max, maximum; min, minimum]

Day

Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

April May June

1 954 9 23 2,740 10 74 2,690 8 58

2 969 6 16 2,590 9 63 2,640 10 71

3 1,020 7 19 2,580 8 56 2,650 10 72

4 1,170 10 32 2,760 10 75 2,690 10 73

5 1,300 13 46 3,150 14 119 2,770 11 82

6 1,380 12 45 3,620 20 195 2,840 11 84

7 1,430 12 46 3,910 21 222 2,930 13 103

8 1,530 12 50 4,060 23 252 2,980 13 105

9 1,790 17 82 4,330 27 316 2,950 13 104

10 2,210 27 161 4,220 25 285 2,870 13 101

11 2,450 26 172 3,750 20 202 2,700 10 73

12 2,560 20 138 3,300 16 143 2,490 9 61

13 2,760 21 156 2,980 12 97 2,260 7 43

14 2,860 20 154 2,730 9 66 2,110 8 46

15 2,740 13 96 2,550 8 55 1,990 6 32

16 2,500 9 61 2,480 8 54 1,880 6 30

17 2,310 8 50 2,370 7 45 1,840 5 25

18 2,240 8 48 2,300 7 43 1,730 4 19

19 2,260 8 49 2,440 8 53 1,640 4 18

20 2,360 8 51 2,790 10 75 1,570 4 17

21 2,660 14 101 2,870 10 77 1,470 2 7.9

22 3,230 27 235 2,950 12 96 1,410 3 11

23 3,860 40 417 3,060 12 99 1,360 2 7.3

24 4,330 45 526 3,180 12 103 1,320 2 7.1

25 4,430 41 490 3,160 11 94 1,300 2 7.0

26 4,160 30 337 3,090 12 100 1,280 2 6.9

27 3,850 22 229 3,100 12 100 1,220 2 6.6

28 3,520 16 152 3,070 10 83 1,170 2 6.3

29 3,210 14 121 2,940 8 64 1,110 2 6.0

30 2,980 11 89 2,840 8 61 1,060 2 5.7

31 -- -- -- 2,760 9 67 -- -- --

Total1 75,023 -- 4,192 94,670 -- 3,434 60,920 -- 1,288.8

Mean 2,501 18 140 3,054 13 111 2,031 7 43

Max 4,430 45 526 4,330 27 316 2,980 13 105

Min 954 6 16 2,300 7 43 1,060 2 5.7
Data 47

Table 6. Daily mean streamflow and suspended-sediment data for Blackfoot River near Bonner, Montana (12340000), October 2015 

through September 2016.—Continued

[ft3/s, cubic foot per second; mg/L, milligram per liter; ton/d, ton per day; e, estimated; --, no data or value not computed; max, maximum; min, minimum]

Day

Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

July August September

1 1,030 2 5.6 545 2 2.9 404 2 2.2

2 1,010 1 2.7 541 2 2.9 400 2 2.2

3 989 1 2.7 530 2 2.9 403 2 2.2

4 956 1 2.6 526 2 2.8 403 3 3.3

5 913 1 2.5 521 2 2.8 415 4 4.5

6 911 1 2.5 510 2 2.8 428 3 3.5

7 929 1 2.5 507 2 2.7 439 3 3.6

8 895 2 4.8 532 2 2.9 440 4 4.8

9 873 2 4.7 551 3 4.5 442 3 3.6

10 890 2 4.8 566 3 4.6 428 2 2.3

11 1,000 2 5.4 549 2 3.0 414 2 2.2

12 1,070 2 5.8 524 4 5.7 417 2 2.3

13 1,040 2 5.6 503 3 4.1 411 2 2.2

14 984 2 5.3 491 2 2.7 420 2 2.3

15 932 2 5.0 477 2 2.6 418 2 2.3

16 894 2 4.8 460 2 2.5 406 2 2.2

17 874 2 4.7 449 3 3.6 407 2 2.2

18 850 2 4.6 444 3 3.6 428 3 3.5

19 831 3 6.7 468 4 5.1 426 4 4.6

20 800 3 6.5 473 4 5.1 423 2 2.3

21 758 2 4.1 464 4 5.0 428 2 2.3

22 728 3 5.9 446 2 2.4 475 4 5.1

23 690 4 7.5 431 2 2.3 468 3 3.8

24 678 3 5.5 424 2 2.3 457 4 4.9

25 657 2 3.5 422 2 2.3 445 2 2.4

26 638 2 3.4 423 3 3.4 436 4 4.7

27 627 2 3.4 420 4 4.5 431 5 5.8

28 613 3 5.0 411 2 2.2 425 3 3.4

29 599 4 6.5 406 2 2.2 408 2 2.2

30 583 3 4.7 409 2 2.2 403 2 2.2

31 564 2 3.0 408 3 3.3 -- -- --

Total1 25,806 -- 142.3 14,831 -- 101.9 12,748 -- 95.1

Mean 832 2 4.6 478 3 3.3 425 3 3.2

Max 1,070 4 7.5 566 4 5.7 475 5 5.8

Min 564 1 2.5 406 2 2.2 400 2 2.2

1

Total for water year 2016 (unrounded sum of daily values): streamflow=443,729 ft3/s (annual runoff=880,100 acre-feet); suspended-sediment discharge=10,528.35 tons.
48 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 7. Daily mean streamflow and suspended-sediment data for Clark Fork above Missoula, Montana (12340500), October 2015 

through September 2016.

[ft3/s, cubic foot per second; mg/L, milligram per liter; ton/d, ton per day; e, estimated; --, no data or value not computed; max, maximum; min, minimum]

Day

Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

October November December

1 1,060 5 14 1,410 12 46 e740 18 36

2 1,070 5 14 1,570 12 51 e840 22 50

3 1,080 5 15 1,580 11 47 e960 31 80

4 1,090 5 15 1,530 11 45 e1,050 40 113

5 1,100 5 15 1,480 9 36 e1,200 49 159

6 1,110 5 15 1,460 7 28 e1,250 58 196

7 1,120 5 15 1,440 5 19 e1,250 58 196

8 1,150 6 19 1,420 5 19 e1,350 38 139

9 1,150 6 19 1,430 5 19 e1,600 16 69

10 1,140 7 22 1,470 5 20 1,590 9 39

11 1,130 7 21 1,450 5 20 1,490 8 32

12 1,120 6 18 1,420 4 15 1,430 7 27

13 1,130 6 18 1,400 4 15 1,400 6 23

14 1,120 6 18 1,400 4 15 1,390 6 23

15 1,120 6 18 1,400 4 15 1,370 5 18

16 1,120 6 18 1,390 4 15 1,340 5 18

17 1,120 6 18 1,360 4 15 1,270 5 17

18 1,120 6 18 1,380 4 15 1,160 4 13

19 1,120 6 18 1,390 4 15 1,230 4 13

20 1,140 6 18 1,350 4 15 1,300 4 14

21 1,160 5 16 1,220 4 13 1,210 4 13

22 1,160 6 19 1,180 5 16 1,200 4 13

23 1,170 6 19 1,220 4 13 1,280 4 14

24 1,170 6 19 1,240 5 17 1,190 4 13

25 1,180 6 19 1,240 5 17 1,120 4 12

26 1,170 6 19 1,040 6 17 1,030 4 11

27 1,170 5 16 850 17 39 e960 3 7.8

28 1,170 5 16 e720 44 86 e920 3 7.5

29 1,180 6 19 e700 51 96 e1,000 3 8.1

30 1,190 8 26 e720 31 60 e1,050 2 5.7

31 1,250 9 30 -- -- -- e1,050 2 5.7

Total1 35,280 -- 564 38,860 -- 859 37,220 -- 1,385.8

Mean 1,138 6 18 1,295 10 29 1,201 14 45

Max 1,250 9 30 1,580 51 96 1,600 58 196

Min 1,060 5 14 700 4 13 740 2 5.7
Data 49

Day

Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

January February March

1 e950 2 5.1 1,220 7 23 1,710 9 42

2 e850 2 4.6 1,170 7 22 1,670 7 32

3 e720 4 7.8 1,090 6 18 1,650 7 31

4 e770 5 10 1,090 6 18 1,620 8 35

5 e980 6 16 1,170 6 19 1,610 8 35

6 e1,050 7 20 1,200 6 19 1,640 8 35

7 e1,200 8 26 1,170 7 22 1,690 8 37

8 e1,200 9 29 1,160 7 22 1,700 8 37

9 e1,200 9 29 1,190 7 22 1,680 8 36

10 e1,150 8 25 1,190 9 29 1,660 8 36

11 e1,050 7 20 1,210 12 39 1,720 10 46

12 e980 6 16 1,290 17 59 1,790 11 53

13 1,050 4 11 1,420 22 84 1,860 12 60

14 1,190 4 13 1,540 26 108 2,020 14 76

15 1,260 4 14 1,690 33 151 2,040 13 72

16 1,200 4 13 2,390 95 613 2,010 10 54

17 1,190 4 13 2,590 79 552 1,980 8 43

18 1,230 4 13 2,310 42 262 1,940 8 42

19 1,240 4 13 2,100 26 147 1,860 8 40

20 1,230 3 10 2,020 21 115 1,840 8 40

21 1,230 3 10 1,900 16 82 1,890 10 51

22 1,220 3 9.9 1,770 13 62 1,960 11 58

23 1,200 4 13 1,730 10 47 2,000 11 59

24 1,220 4 13 1,620 10 44 2,010 10 54

25 1,220 4 13 1,580 9 38 2,020 10 55

26 1,180 5 16 1,580 8 34 2,000 8 43

27 1,200 7 23 1,600 9 39 1,980 8 43

28 1,250 8 27 1,650 10 45 1,980 8 43

29 1,300 10 35 1,700 10 46 1,950 7 37

30 1,310 9 32 -- -- -- 1,930 7 36

31 1,270 8 27 -- -- -- 1,920 9 47

Total1 35,290 -- 527.4 45,340 -- 2,781 57,330 -- 1,408

Mean 1,138 5 17 1,563 18 96 1,849 9 45

Max 1,310 10 35 2,590 95 613 2,040 14 76

Min 720 2 4.6 1,090 6 18 1,610 7 31

Table 7. Daily mean streamflow and suspended-sediment data for Clark Fork above Missoula, Montana (12340500), October 2015 

through September 2016.—Continued

[ft3/s, cubic foot per second; mg/L, milligram per liter; ton/d, ton per day; e, estimated; --, no data or value not computed; max, maximum; min, minimum]
50 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 7. Daily mean streamflow and suspended-sediment data for Clark Fork above Missoula, Montana (12340500), October 2015 

through September 2016.—Continued

[ft3/s, cubic foot per second; mg/L, milligram per liter; ton/d, ton per day; e, estimated; --, no data or value not computed; max, maximum; min, minimum]

Day

Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

April May June

1 1,940 9 47 5,190 16 224 5,210 13 183

2 1,950 10 53 4,950 15 200 5,020 12 163

3 2,050 13 72 4,910 14 186 4,990 11 148

4 2,280 16 98 5,160 15 209 5,000 12 162

5 2,530 18 123 5,720 18 278 5,050 11 150

6 2,650 17 122 6,340 24 411 5,140 11 153

7 2,700 18 131 6,870 27 501 5,280 12 171

8 2,810 19 144 7,180 29 562 5,390 13 189

9 3,170 28 240 7,620 44 905 5,340 12 173

10 3,830 40 414 7,660 46 951 5,230 11 155

11 4,300 40 464 6,880 25 464 4,930 10 133

12 4,470 35 422 6,180 18 300 4,610 8 100

13 4,820 37 482 5,690 16 246 4,200 7 79

14 5,170 40 558 5,330 14 201 3,890 8 84

15 5,090 36 495 5,090 12 165 3,730 5 50

16 4,720 26 331 5,040 10 136 3,660 4 40

17 4,390 22 261 4,840 10 131 3,720 5 50

18 4,250 20 230 4,670 10 126 3,520 4 38

19 4,230 18 206 4,850 12 157 3,280 4 35

20 4,330 18 210 5,670 20 306 3,110 4 34

21 4,740 21 269 5,890 20 318 2,910 3 24

22 5,540 31 464 6,190 25 418 2,720 3 22

23 6,530 53 934 6,280 27 458 2,610 3 21

24 7,350 70 1,390 6,320 22 375 2,520 2 14

25 7,600 66 1,350 6,330 22 376 2,450 2 13

26 7,210 42 818 6,170 25 416 2,380 2 13

27 6,750 34 620 6,050 20 327 2,280 2 12

28 6,310 26 443 6,110 18 297 2,150 2 12

29 5,870 20 317 5,910 18 287 2,010 2 11

30 5,550 19 285 5,640 16 244 1,900 2 10

31 -- -- -- 5,430 14 205 -- -- --

Total1 135,130 -- 11,993 182,160 -- 10,380 114,230 -- 2,442

Mean 4,504 29 400 5,876 20 335 3,808 7 81

Max 7,600 70 1,390 7,660 46 951 5,390 13 189

Min 1,940 9 47 4,670 10 126 1,900 2 10
Data 51

Table 7. Daily mean streamflow and suspended-sediment data for Clark Fork above Missoula, Montana (12340500), October 2015 

through September 2016.—Continued

[ft3/s, cubic foot per second; mg/L, milligram per liter; ton/d, ton per day; e, estimated; --, no data or value not computed; max, maximum; min, minimum]

Day

Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment Mean 

streamflow 

(ft3/s)

Suspended sediment

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

Mean 

concentration 

(mg/L)

Discharge 

(ton/d)

July August September

1 1,820 1 4.9 992 5 13 776 4 8.4

2 1,790 1 4.8 965 5 13 768 4 8.3

3 1,750 1 4.7 939 5 13 781 4 8.4

4 1,690 1 4.6 917 4 9.9 782 6 13

5 1,630 1 4.4 904 3 7.3 809 7 15

6 1,620 1 4.4 860 4 9.3 880 5 12

7 1,620 1 4.4 863 4 9.3 951 7 18

8 1,580 2 8.5 901 5 12 958 6 16

9 1,540 2 8.3 949 6 15 964 6 16

10 1,590 2 8.6 1,020 17 47 926 5 13

11 2,000 4 22 1,020 13 36 897 5 12

12 2,350 5 32 991 10 27 891 4 9.6

13 2,210 3 18 952 9 23 888 3 7.2

14 2,070 3 17 919 8 20 895 4 9.7

15 1,900 2 10 890 7 17 895 5 12

16 1,810 2 9.8 861 6 14 885 4 9.6

17 1,770 2 9.6 844 5 11 874 4 9.4

18 1,710 4 18 834 6 14 911 5 12

19 1,640 4 18 866 6 14 913 5 12

20 1,560 4 17 889 5 12 906 4 9.8

21 1,480 5 20 878 5 12 935 5 13

22 1,400 4 15 857 4 9.3 1,100 7 21

23 1,320 4 14 849 4 9.2 1,110 8 24

24 1,260 4 14 844 4 9.1 1,110 7 21

25 1,220 4 13 838 4 9.1 1,110 6 18

26 1,180 4 13 832 4 9.0 1,080 5 15

27 1,140 4 12 811 4 8.8 1,080 5 15

28 1,120 4 12 794 4 8.6 1,090 7 21

29 1,090 4 12 789 4 8.5 1,060 7 20

30 1,050 4 11 787 4 8.5 1,030 7 19

31 1,030 4 11 779 4 8.4 -- -- --

Total1 48,940 -- 376 27,434 -- 437.3 28,255 -- 418.4

Mean 1,579 3 12 885 6 14 942 5 14

Max 2,350 5 32 1,020 17 47 1,110 8 24

Min 1,030 1 4.4 779 3 7.3 768 3 7.2

1

Total for water year 2016 (unrounded sum of daily values): streamflow=785,469 ft3/s (annual runoff=1,558,000 acre-feet); suspended-sediment discharge=33,571.9 tons.
52 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 Mill Creek at Opportunity, Montana 

(12323700), March through September 2016.

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 90 ± 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 -- -- -- 2.0 1.0 1.5 5.0 3.0 4.0 5.5 3.0 4.0

2 -- -- -- 2.0 1.0 1.5 4.5 3.0 3.5 5.5 4.0 4.5

3 -- -- -- 2.5 1.5 1.5 4.5 2.5 3.0 8.5 5.0 6.5

4 -- -- -- 3.5 2.0 2.5 4.0 2.5 3.0 -- -- --

5 -- -- -- 3.5 2.0 2.5 5.5 3.0 4.0 -- -- --

6 -- -- -- 3.5 1.5 2.0 10 5.0 7.0 -- -- --

7 -- -- -- 3.5 1.5 2.5 12 6.0 8.0 -- -- --

8 -- -- -- 8.0 3.0 4.0 25 7.5 12 -- -- --

9 -- -- -- 14 5.5 8.5 32 10 17 18 7.5 12

10 -- -- -- 16 7.0 11 11 5.5 7.0 9.0 5.0 6.5

11 -- -- -- 12 5.5 8.0 5.5 4.0 4.5 6.5 3.5 5.0

12 -- -- -- 12 6.0 8.5 5.0 3.5 4.0 5.5 3.0 4.0

13 -- -- -- 42 10 21 5.0 3.0 3.5 5.0 2.5 3.0

14 -- -- -- 19 8.0 12 4.5 3.0 3.5 3.5 2.0 2.5

15 -- -- -- 11 5.5 7.5 4.5 3.0 3.5 -- -- --

16 -- -- -- 23 5.0 7.0 3.5 2.5 3.0 5.0 2.0 3.0

17 -- -- -- 7.0 3.5 5.0 4.0 2.5 3.0 4.0 2.0 2.5

18 -- -- -- -- -- -- 4.5 2.5 3.0 3.5 2.0 2.5

19 -- -- -- -- -- -- 7.0 3.5 4.5 3.0 1.5 2.5

20 -- -- -- -- -- -- 7.0 3.5 5.0 3.0 1.5 2.0

21 -- -- -- 6.5 4.0 5.0 9.0 4.0 6.0 3.0 1.5 2.5

22 -- -- -- 9.5 5.0 6.5 -- -- -- 3.0 1.5 2.0

23 -- -- -- 14 7.0 9.5 -- -- -- 3.0 1.0 2.0

24 -- -- -- 17 8.0 11 -- -- -- 3.0 1.5 2.0

25 -- -- -- 9.5 6.0 7.0 -- -- -- 2.5 1.0 1.5

26 -- -- -- 7.5 5.0 6.0 -- -- -- 2.5 1.0 1.5

27 -- -- -- 7.0 4.5 5.5 -- -- -- 2.5 1.0 1.5

28 -- -- -- 5.5 4.0 4.5 -- -- -- 3.0 1.0 1.5

29 2.5 1.5 1.5 5.0 3.5 4.0 -- -- -- 2.5 1.0 2.0

30 1.5 1.0 1.5 5.5 3.5 4.0 -- -- -- 3.0 1.0 2.0

31 2.0 1.0 1.5 -- -- -- 5.0 3.5 4.0 -- -- --

Month1 2.5 1.0 1.5 42 1.0 6.3 32 2.5 5.3 18 1.0 3.3
Data 53

Table 8. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics at Mill Creek at Opportunity, Montana 

(12323700), March through September 2016.—Continued

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 90 ± 2.5 degrees to 

incident beam, reported in formazin nephelometric units (FNU). --, no data]

1

For months with missing daily values, the means are calculated using available values.

Day

Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean

July August September

1 3.0 1.0 1.5 -- -- -- 1.5 1.0 1.0

2 2.5 1.0 1.5 -- -- -- 1.5 1.0 1.0

3 2.5 1.0 1.5 -- -- -- 1.5 1.0 1.5

4 2.5 1.0 1.5 -- -- -- 1.5 1.0 1.5

5 2.0 1.0 1.5 -- -- -- -- -- --

6 2.0 1.0 1.5 -- -- -- -- -- --

7 2.0 0.5 1.0 -- -- -- -- -- --

8 2.0 1.0 1.5 -- -- -- -- -- --

9 2.5 1.5 1.5 1.5 1.0 1.0 -- -- --

10 4.5 1.5 2.5 1.5 1.0 1.0 1.0 1.0 1.0

11 4.0 1.5 2.5 1.5 0.5 1.0 1.0 0.5 1.0

12 3.0 1.5 2.0 1.5 1.0 1.0 1.5 1.0 1.0

13 2.5 1.5 2.0 1.5 1.0 1.0 1.0 1.0 1.0

14 3.0 2.0 2.5 1.0 1.0 1.0 1.5 1.0 1.0

15 3.0 2.0 2.5 1.5 0.5 1.0 1.5 1.0 1.0

16 3.0 1.5 2.0 1.5 1.0 1.0 1.5 0.5 1.0

17 3.0 1.5 2.0 1.5 1.0 1.0 0.5 0.5 0.5

18 3.0 1.5 2.0 1.5 0.5 1.0 1.0 0.5 0.5

19 3.5 1.0 2.0 1.5 0.5 1.0 0.5 0.5 0.5

20 2.0 1.0 1.5 1.0 1.0 1.0 1.5 0.5 0.5

21 2.0 1.0 1.0 1.0 0.5 1.0 1.0 0.5 0.5

22 2.0 1.0 1.0 1.5 0.5 1.0 1.0 0.5 0.5

23 1.5 0.5 1.0 1.0 0.5 1.0 1.0 0.5 0.5

24 1.5 0.5 1.0 1.0 0.5 1.0 1.0 0.5 0.5

25 1.5 0.5 1.0 1.5 0.5 1.0 1.0 0.5 0.5

26 2.0 1.0 1.0 1.5 0.5 1.0 0.5 0.5 0.5

27 2.5 1.0 1.0 1.0 0.5 0.5 1.0 0.5 0.5

28 1.5 1.0 1.0 1.5 0.5 1.0 1.0 0.5 0.5

29 1.5 1.0 1.0 1.5 0.5 1.0 1.0 0.5 0.5

30 -- -- -- 2.0 1.0 1.0 1.5 0.5 1.0

31 -- -- -- 2.0 1.0 1.5 -- -- --

Month1 4.5 0.5 1.6 2.0 0.5 1.0 1.5 0.5 0.8
54 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 9. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics at Willow Creek at Opportunity, 

Montana (12323720), March through September 2016.

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 90 ± 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 -- -- -- 4.5 2.5 3.5 11 7.5 8.5 10 6.0 8.0

2 -- -- -- 4.5 2.0 3.0 12 8.0 9.0 9.0 5.0 7.0

3 -- -- -- -- -- -- 10 7.0 8.0 8.5 5.0 6.5

4 -- -- -- -- -- -- 9.5 8.0 8.5 7.5 5.0 6.0

5 -- -- -- 8.5 4.5 5.5 10 8.0 9.0 7.0 4.5 5.5

6 -- -- -- 7.5 5.5 6.0 18 9.0 12 12 4.5 7.0

7 -- -- -- 8.0 5.5 6.5 15 12 13 -- -- --

8 -- -- -- 9.5 7.0 8.0 15 12 13 -- -- --

9 -- -- -- 19 8.5 12 17 11 13 14 4.0 5.0

10 -- -- -- 19 13 15 17 11 13 6.0 3.5 4.5

11 -- -- -- 19 15 17 13 9.5 11 6.5 3.5 4.5

12 -- -- -- 18 15 16 11 9.0 10 6.5 3.5 5.0

13 -- -- -- 36 15 20 11 8.0 9.0 7.0 3.5 5.0

14 -- -- -- 110 14 35 9.0 7.0 8.0 6.5 3.5 4.5

15 -- -- -- 14 10 12 11 8.0 9.5 6.5 3.0 4.0

16 -- -- -- 12 10 11 10 6.5 8.0 7.5 3.5 5.0

17 -- -- -- 14 10 12 11 8.0 9.5 5.5 2.5 3.5

18 -- -- -- -- -- -- 13 8.5 10 9.5 2.5 4.5

19 -- -- -- -- -- -- 18 9.5 12 7.0 3.0 4.0

20 -- -- -- -- -- -- 14 8.5 10 5.0 3.0 3.5

21 -- -- -- 15 10 12 15 7.5 10 5.5 3.0 3.5

22 -- -- -- 15 10 12 11 7.5 8.5 8.0 3.0 4.0

23 -- -- -- 24 14 16 11 7.0 8.0 8.5 2.5 4.0

24 -- -- -- 29 17 21 9.5 7.0 8.0 6.0 3.5 4.5

25 -- -- -- 19 16 17 8.0 5.5 6.5 4.5 2.0 3.0

26 -- -- -- 19 14 16 -- -- -- -- -- --

27 -- -- -- 18 14 15 9.5 7.5 8.5 -- -- --

28 -- -- -- -- -- -- 9.0 5.5 7.0 -- -- --

29 4.5 2.5 3.5 14 12 13 8.5 5.0 6.5 -- -- --

30 5.0 3.0 4.0 15 8.5 13 10 5.5 7.0 -- -- --

31 4.5 2.5 3.0 -- -- -- 8.0 5.5 6.5 -- -- --

Month1 5.0 2.5 3.5 110 2.0 13 18 5.0 9.4 14 2.0 4.9
Data 55

Table 9. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics at Willow Creek at Opportunity, 

Montana (12323720), March through September 2016.—Continued

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 90 ± 2.5 degrees to 

incident beam, reported in formazin nephelometric units (FNU). --, no data]

1

For months with missing daily values, the means are calculated using available values.

Day

Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean

July August September

1 -- -- -- 4.0 2.5 3.0 3.0 2.0 2.5

2 -- -- -- 4.0 2.0 3.0 3.0 2.0 2.5

3 -- -- -- 5.0 2.0 3.0 3.0 2.0 2.5

4 -- -- -- 4.0 2.0 3.0 3.5 2.0 2.5

5 -- -- -- 5.5 2.5 3.5 3.5 2.5 3.0

6 -- -- -- 6.0 3.5 4.5 4.0 2.5 3.0

7 6.5 3.5 5.0 12 4.0 5.5 3.0 2.5 2.5

8 6.5 3.0 4.5 11 4.0 5.5 3.5 2.5 2.5

9 6.5 2.5 4.0 5.5 3.5 4.0 3.0 2.0 2.5

10 6.5 3.0 4.0 5.5 3.5 4.5 2.5 2.0 2.5

11 8.0 2.5 4.5 5.0 3.0 4.0 2.5 2.0 2.5

12 4.5 1.5 2.5 5.0 3.0 4.0 3.0 2.0 2.5

13 3.0 1.5 2.0 4.5 3.0 3.5 3.0 2.0 2.5

14 3.5 1.5 2.0 4.0 3.0 3.5 3.0 2.0 2.5

15 3.5 1.5 2.5 4.0 3.0 3.5 3.5 2.5 2.5

16 4.0 2.0 2.5 4.0 3.0 3.5 3.5 2.0 3.0

17 4.0 2.0 2.5 4.0 3.0 3.0 3.0 2.0 2.5

18 5.5 2.0 3.0 4.0 2.5 3.0 3.0 2.0 2.5

19 4.5 2.0 3.0 3.5 2.5 3.0 3.5 2.0 2.5

20 5.0 3.0 4.0 3.5 2.5 2.5 4.0 2.5 3.0

21 4.5 2.0 3.0 3.5 2.5 3.0 4.0 3.0 3.0

22 5.0 2.0 3.0 3.5 2.5 2.5 4.0 3.0 3.5

23 4.5 2.0 3.0 3.0 2.0 2.5 5.0 3.0 3.5

24 4.0 2.0 3.0 3.5 2.0 2.5 5.5 3.5 4.5

25 4.5 2.0 3.0 3.0 2.5 2.5 4.5 3.0 3.5

26 5.5 2.0 3.0 3.5 2.5 2.5 4.0 3.0 3.0

27 4.5 2.0 3.0 3.0 2.0 2.5 4.0 2.5 3.0

28 4.5 2.0 3.0 3.0 2.0 2.5 4.5 3.0 3.5

29 5.5 2.5 3.5 3.0 2.0 2.5 4.5 2.5 3.5

30 4.0 2.5 3.5 2.5 2.0 2.5 5.0 3.0 3.5

31 4.5 2.5 3.0 3.0 2.0 2.5 -- -- --

Month1 8.0 1.5 3.2 12 2.0 3.3 5.5 2.0 2.9
56 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 10. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics at Warm Springs Creek at Warm 

Springs, Montana (12323770), March through September 2016.

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 90 ± 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 -- -- -- 3.0 1.5 2.0 5.0 2.5 3.5 5.0 2.5 3.5

2 -- -- -- 3.0 1.5 2.0 5.0 2.5 3.5 5.5 3.0 4.0

3 -- -- -- 3.0 1.5 2.0 4.5 2.5 3.5 6.0 3.0 4.0

4 -- -- -- 3.0 1.5 2.0 5.5 3.0 4.0 7.5 3.5 5.0

5 -- -- -- 3.5 1.5 2.5 9.0 4.0 6.5 10 4.5 6.5

6 -- -- -- 3.0 1.5 2.0 14 5.5 11 14 5.5 9.5

7 -- -- -- 3.5 1.5 2.0 16 7.5 11 23 6.5 9.5

8 -- -- -- 3.0 1.5 2.0 30 7.5 17 19 8.0 11

9 -- -- -- 3.5 2.0 2.5 18 8.5 13 13 6.0 8.0

10 -- -- -- 4.0 2.0 2.5 9.5 4.5 6.0 8.5 4.5 6.0

11 -- -- -- 3.5 1.5 2.0 5.5 3.5 4.5 6.5 3.5 5.0

12 -- -- -- 3.5 1.5 2.0 5.0 3.0 4.0 6.0 3.0 4.0

13 -- -- -- 10 2.0 7.0 5.0 2.5 3.5 6.0 2.5 3.5

14 -- -- -- 8.5 4.0 5.5 5.5 2.5 3.5 6.0 2.5 4.0

15 -- -- -- 6.0 3.0 4.0 5.0 3.0 4.0 6.0 3.0 4.5

16 -- -- -- 4.5 2.0 3.0 5.0 2.5 3.5 7.5 4.0 5.5

17 -- -- -- 7.0 2.0 3.0 4.5 2.5 3.0 6.0 2.5 4.0

18 -- -- -- 4.0 1.5 2.5 5.0 2.5 3.5 5.5 2.5 4.0

19 -- -- -- 4.5 1.5 3.0 9.0 3.5 5.0 5.0 2.5 3.5

20 -- -- -- 4.0 2.0 3.0 9.5 4.0 6.0 5.0 2.5 3.0

21 -- -- -- 5.5 3.0 4.0 6.5 3.5 5.0 4.5 1.5 2.5

22 -- -- -- -- -- -- 6.0 3.5 4.5 4.0 1.5 2.5

23 -- -- -- -- -- -- 5.5 2.5 4.0 4.0 1.0 2.5

24 -- -- -- -- -- -- 5.0 3.0 3.5 3.5 2.0 2.5

25 -- -- -- -- -- -- 5.0 3.0 3.5 3.5 1.5 2.0

26 -- -- -- -- -- -- 5.0 3.0 3.5 3.5 1.5 2.0

27 -- -- -- 7.5 3.5 4.5 8.0 3.5 5.0 3.5 1.0 2.0

28 -- -- -- 5.5 3.0 4.0 6.0 3.0 4.5 3.5 1.0 2.0

29 -- -- -- 5.0 2.5 3.5 5.5 3.0 4.0 3.5 1.0 2.0

30 3.0 1.5 2.0 6.0 3.0 4.0 5.0 3.0 3.5 3.0 1.0 2.0

31 3.0 1.5 2.0 -- -- -- 5.5 3.0 4.0 -- -- --

Month1 3.0 1.5 4.0 10 1.5 3.1 30 2.5 5.3 23 1.0 4.3
Data 57

Table 10. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics at Warm Springs Creek at Warm 

Springs, Montana (12323770), March through September 2016.—Continued

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 90 ± 2.5 degrees to 

incident beam, reported in formazin nephelometric units (FNU). --, no data]

1

For months with missing daily values, the means are calculated using available values.

Day

Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean

July August September

1 2.5 1.0 2.0 -- -- -- 7.0 3.0 4.5

2 2.5 0.5 1.5 -- -- -- 17 6.0 11

3 2.5 0.5 1.0 -- -- -- -- -- --

4 -- -- -- -- -- -- 14 9.0 11

5 -- -- -- -- -- -- 19 12 15

6 2.0 0.5 1.0 -- -- -- -- -- --

7 2.5 0.5 1.0 -- -- -- 8.5 5.5 6.5

8 2.5 0.5 1.0 -- -- -- 9.0 5.0 6.5

9 2.5 0.5 1.0 7.5 6.5 7.0 7.5 4.5 5.5

10 3.0 1.0 1.5 7.5 6.0 6.5 6.0 4.5 5.0

11 6.5 1.5 3.0 6.5 5.5 6.0 7.0 5.0 6.0

12 3.0 1.0 2.0 7.5 5.5 6.5 6.5 5.5 6.0

13 2.5 0.5 1.5 6.5 5.0 5.5 7.5 4.5 6.0

14 2.5 0.5 1.0 6.0 4.5 5.0 -- -- --

15 2.0 0.5 1.0 5.5 4.0 4.5 4.5 2.5 3.5

16 2.5 0.5 1.0 -- -- -- 4.5 1.5 2.5

17 2.0 0.5 1.0 4.0 1.5 2.5 4.0 1.5 2.5

18 -- -- -- 11 3.5 5.5 5.0 1.5 3.0

19 -- -- -- 10 4.5 5.5 4.0 1.5 2.5

20 -- -- -- 11 4.5 7.0 4.0 2.0 2.5

21 -- -- -- 15 2.5 7.5 -- -- --

22 -- -- -- 10 2.5 5.0 -- -- --

23 -- -- -- -- -- -- -- -- --

24 -- -- -- -- -- -- -- -- --

25 -- -- -- -- -- -- 2.0 1.0 1.0

26 -- -- -- 8.0 6.5 7.5 2.5 1.0 1.5

27 -- -- -- 11 6.0 7.0 1.5 1.0 1.0

28 -- -- -- 8.5 5.0 6.5 2.0 1.0 1.5

29 -- -- -- 7.5 4.5 6.0 -- -- --

30 -- -- -- 7.0 4.0 5.5 -- -- --

31 -- -- -- 8.0 3.5 5.5 -- -- --

Month1 6.5 0.5 1.4 15 1.5 5.9 19 1.0 5.0
58 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 11. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics at Lost Creek near Anaconda, 

Montana (12323840), March through August 2016.

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 90 ± 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 -- -- -- 5.0 3.5 4.0 11 4.5 7.0 9.0 5.0 5.5

2 -- -- -- 5.0 3.5 4.0 12 6.0 7.5 7.0 4.5 5.5

3 -- -- -- 6.0 3.5 4.0 12 6.0 8.0 9.5 4.0 6.0

4 -- -- -- 9.0 3.5 4.5 14 6.5 9.0 8.0 4.5 5.5

5 -- -- -- 5.5 3.5 4.0 18 6.5 10 27 5.0 7.0

6 -- -- -- 4.5 3.0 3.5 22 7.5 9.5 9.5 5.5 6.5

7 -- -- -- 5.0 3.0 3.5 21 7.5 10 10 5.0 6.0

8 -- -- -- 6.0 3.5 4.5 24 8.0 13 11 5.5 6.5

9 -- -- -- 6.5 4.0 5.0 19 9.5 13 9.0 6.0 7.0

10 -- -- -- 6.5 4.5 5.5 24 7.0 9.5 15 5.5 7.0

11 -- -- -- 7.5 4.0 5.0 11 6.5 8.0 7.0 5.0 5.5

12 -- -- -- 8.5 5.0 5.5 8.0 5.5 7.0 8.5 4.5 5.5

13 -- -- -- 21 5.0 11 9.0 5.0 6.5 5.5 4.0 4.5

14 -- -- -- 8.5 3.5 5.0 10 4.5 6.0 8.0 3.0 4.5

15 -- -- -- 6.5 2.5 4.0 7.5 4.5 5.5 7.0 4.5 5.5

16 -- -- -- 6.0 3.0 3.5 8.0 5.0 6.0 6.5 4.0 5.0

17 -- -- -- 8.0 2.5 4.0 12 5.5 6.5 5.0 3.5 4.0

18 -- -- -- 6.5 2.5 3.5 9.0 5.5 7.0 5.0 3.0 3.5

19 -- -- -- 6.0 2.5 4.0 18 6.5 9.5 4.5 3.0 3.5

20 -- -- -- 6.0 2.5 4.0 18 8.0 10 5.5 3.5 4.0

21 -- -- -- 9.0 3.5 5.5 18 8.0 11 4.5 3.0 3.5

22 -- -- -- 12 3.5 6.0 12 7.0 8.5 5.5 3.0 4.0

23 -- -- -- 16 4.5 9.5 13 7.0 8.5 11 3.0 4.5

24 -- -- -- 26 4.0 8.0 18 7.5 9.0 7.0 4.0 4.5

25 -- -- -- 8.5 3.5 5.5 11 7.0 8.5 8.5 4.0 5.0

26 -- -- -- 9.5 4.0 6.5 10 5.0 7.0 19 4.5 6.0

27 -- -- -- 10 6.0 7.0 14 6.0 8.5 8.0 4.0 5.0

28 -- -- -- 9.5 5.5 7.0 -- -- -- 8.0 4.5 5.5

29 -- -- -- 9.5 5.5 6.5 10 5.0 6.0 11 4.0 6.0

30 5.0 3.5 4.0 13 5.5 8.0 8.0 4.5 6.0 8.0 4.0 5.5

31 7.0 3.5 4.5 -- -- -- 9.0 4.5 5.5 -- -- --

Month1 7.0 3.5 4.2 26 2.5 5.4 24 4.5 8.2 27 3.0 5.2
Data 59

Table 11. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics at Lost 

Creek near Anaconda, Montana (12323840), March through August 2016.—Continued

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection 

angle of 90 ± 2.5 degrees to incident beam, reported in formazin nephelometric units (FNU). --, no data]

Day

Maximum Minimum Mean Maximum Minimum Mean

July August

1 6.5 3.5 4.5 -- -- --

2 4.5 3.0 4.0 5.5 3.0 4.0

3 4.5 4.0 4.0 29 2.5 4.5

4 5.0 3.0 4.5 6.5 3.5 4.5

5 5.5 4.0 4.5 4.0 2.5 3.0

6 5.0 4.0 4.0 3.0 1.5 2.0

7 5.0 3.5 4.0 68 1.0 6.0

8 4.5 1.0 3.5 14 7.0 8.5

9 4.0 1.0 1.5 13 6.5 7.5

10 7.0 2.0 4.5 9.0 6.5 7.5

11 4.0 3.5 4.0 8.5 3.0 6.5

12 5.0 3.5 3.5 8.5 6.0 7.0

13 4.5 3.0 3.5 10 6.0 7.5

14 3.5 2.5 3.5 8.5 4.0 6.5

15 3.5 2.0 3.0 7.5 6.0 6.5

16 4.0 2.0 2.5 6.5 5.0 5.5

17 3.5 1.5 2.0 7.0 3.0 5.5

18 1.5 1.0 1.5 7.0 4.0 6.0

19 -- -- -- 6.5 5.0 5.5

20 -- -- -- 6.5 5.5 6.0

21 -- -- -- 6.5 5.5 6.0

22 -- -- -- 7.0 5.5 6.0

23 -- -- -- 7.5 6.5 6.5

24 -- -- -- 9.0 6.0 6.5

25 -- -- -- 6.5 4.0 5.0

26 -- -- -- 6.5 5.0 6.0

27 -- -- -- 6.5 5.0 5.5

28 -- -- -- 6.0 4.5 5.0

29 -- -- -- 6.0 4.5 5.0

30 -- -- -- -- -- --

31 -- -- -- -- -- --

Month1 7.0 1.0 3.5 68 1.0 5.8

1

For months with missing daily values, the means are calculated using available values.
60 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 12. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics at Clark Fork at Deer Lodge, Montana 

(12324200), March through September 2016.

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 90 ± 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 -- -- -- 11 8.0 9.5 16 11 13 12 7.5 10

2 -- -- -- 27 8.5 13 16 10 12 11 7.5 9.5

3 -- -- -- 12 7.0 9.0 18 11 13 11 7.5 9.0

4 -- -- -- 17 8.5 10 28 11 14 11 7.0 8.5

5 -- -- -- 15 8.0 10 -- -- -- 11 8.0 9.5

6 -- -- -- 16 8.5 12 -- -- -- 11 8.5 9.5

7 -- -- -- 17 9.0 12 -- -- -- 17 11 13

8 -- -- -- 18 10 12 38 14 19 19 14 16

9 -- -- -- 29 15 19 31 16 21 22 15 18

10 -- -- -- 50 13 21 23 15 18 23 12 16

11 -- -- -- 18 12 15 16 11 13 15 9.5 12

12 -- -- -- 18 13 15 13 9.5 11 12 8.0 10

13 -- -- -- -- -- -- 16 9.0 11 -- -- --

14 -- -- -- -- -- -- 11 8.0 9.5 -- -- --

15 -- -- -- -- -- -- 10 8.5 9.5 -- -- --

16 -- -- -- -- -- -- 11 9.5 10 -- -- --

17 -- -- -- -- -- -- 15 8.0 10 -- -- --

18 -- -- -- -- -- -- 11 7.5 9.0 7.0 5.5 6.0

19 -- -- -- 21 14 17 14 9.0 11 7.0 5.0 6.0

20 -- -- -- 21 13 15 21 13 17 7.0 5.5 6.0

21 -- -- -- 23 14 17 41 18 24 6.5 5.5 6.0

22 -- -- -- 20 15 17 44 23 34 6.5 5.0 5.5

23 -- -- -- 22 17 20 24 14 18 7.0 5.0 5.5

24 -- -- -- 31 20 27 19 15 16 6.0 5.0 5.0

25 11 7.5 8.5 31 19 24 21 15 18 5.5 4.5 5.0

26 10 7.5 8.0 25 16 20 50 12 17 5.5 4.5 5.0

27 9.0 6.5 7.5 22 14 18 20 15 17 5.5 4.0 5.0

28 9.5 6.5 7.5 18 12 15 19 15 17 5.0 4.0 4.5

29 8.0 6.0 7.0 16 12 13 17 11 14 6.0 4.0 4.5

30 9.5 7.0 8.0 16 12 13 14 9.5 12 9.0 4.0 5.0

31 11 8.0 9.0 -- -- -- 13 9.0 11 -- -- --

Month1 11 6.0 7.9 50 7.0 16 50 7.5 15 23 4.0 8.4
Data 61

Table 12. Seasonal daily maximum, minimum, and mean turbidity, with monthly summary statistics at Clark Fork at Deer Lodge, 

Montana (12324200), March through September 2016.—Continued

[Turbidity values are based on near-infrared monochrome light emitted at wavelengths of 780 to 900 nanometers with a detection angle of 90 ± 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 8.5 5.5 6.0 2.0 1.5 1.5 3.5 2.0 2.5

2 -- -- -- 3.5 1.5 2.0 3.0 2.0 2.5

3 -- -- -- 4.0 1.5 2.0 2.5 2.0 2.5

4 -- -- -- 3.5 1.5 2.0 3.0 2.5 2.5

5 -- -- -- 4.0 1.5 2.0 12 2.5 3.5

6 -- -- -- 16 2.0 3.0 4.5 3.0 3.5

7 3.5 2.5 2.5 8.5 2.0 3.0 4.5 3.0 3.5

8 3.0 2.0 2.5 -- -- -- 4.0 3.0 3.5

9 2.5 2.0 2.5 16 1.5 2.0 -- -- --

10 4.5 2.5 2.5 -- -- -- -- -- --

11 4.0 2.0 2.5 -- -- -- -- -- --

12 4.5 1.5 2.5 -- -- -- -- -- --

13 4.5 1.5 2.0 -- -- -- -- -- --

14 2.0 1.5 1.5 -- -- -- 3.5 2.0 2.5

15 3.0 1.5 1.5 -- -- -- 3.5 2.5 3.0

16 2.0 1.5 1.5 -- -- -- 4.0 2.5 3.0

17 2.0 1.5 1.5 -- -- -- 4.0 3.0 3.5

18 3.0 1.5 2.0 -- -- -- -- -- --

19 3.0 1.5 2.0 -- -- -- 5.0 3.5 4.0

20 3.5 2.0 2.5 -- -- -- 5.5 4.5 4.5

21 3.0 1.5 2.0 -- -- -- -- -- --

22 3.0 1.5 2.0 -- -- -- -- -- --

23 2.5 1.5 2.0 -- -- -- -- -- --

24 2.0 1.5 2.0 -- -- -- -- -- --

25 29 1.5 3.5 -- -- -- -- -- --

26 7.0 1.5 2.0 2.5 2.0 2.0 -- -- --

27 2.5 1.5 2.0 3.0 2.0 2.0 -- -- --

28 2.0 1.5 1.5 3.0 2.0 2.0 5.0 3.0 4.0

29 2.5 1.5 1.5 3.0 2.0 2.0 5.5 3.0 3.5

30 2.0 1.0 1.5 3.0 2.0 2.0 5.5 3.0 3.5

31 2.0 1.0 1.5 3.0 2.0 2.5 -- -- --

Month1 29 1.0 2.2 16 1.5 2.1 12 2.0 3.3

1

For months with missing daily values, the means are calculated using available values.
62 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana Table 13. Analyses of field replicates for water samples, Clark Fork Basin, Montana. [hh, hour; mm, minute; 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 10/20/2015 1535 -- 203 59.5 13.3 -- -- --

10/20/2015 1540 -- 202 58.7 13.4 -- -- --

12323250 Silver Bow Creek below 

Blacktail Creek, at Butte

03/21/2016 1040 E3.7 157 44.4 11.2 -- -- --03/21/2016 1045 E3.7 154 43.5 11.1 -- -- --

12324400 Clark Fork above Little 

Blackfoot River, near Garrison

03/23/2016 1120 -- 236 69.4 15.2 -- -- --03/23/2016 1125 -- 231 67.6 15.1 -- -- --

12323840 Lost Creek near Anaconda 04/19/2016 0745 <2.0 111 33.6 6.65 1.35 3.08 102

04/19/2016 0750 E2.2 109 32.6 6.81 1.34 3.04 102

12324200 Clark Fork at Deer Lodge 05/10/2016 1455 E13 132 39.5 8.07 -- -- --

05/10/2016 1500 E12 129 38.3 8.23 -- -- --

12334550 Clark Fork at Turah Bridge, 

near Bonner

05/25/2016 0755 -- 92.6 26.2 6.60 -- -- --05/25/2016 0800 -- 93.9 26.8 6.58 -- -- --

12340500 Clark Fork above Missoula 06/08/2016 1245 -- 93.2 25.3 7.28 -- -- --

06/08/2016 1250 -- 89.9 24.6 6.94 -- -- --

12323750 Silver Bow Creek at Warm 

Springs

07/12/2016 1015 E2.6 155 43.7 11.2 2.41 14.6 10107/12/2016 1020 E2.7 156 44.0 11.2 2.48 14.6 101

12323700 Mill Creek at Opportunity 08/08/2016 1605 <2.0 80.1 22.8 5.66 0.83 4.57 80.1

08/08/2016 1610 <2.0 81.9 22.9 5.98 0.83 4.61 75.5
Data 63

Table 13. Analyses of field replicates for water samples, Clark Fork Basin, Montana.—Continued[hh, hour; mm, minute; 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)

12324680 Clark Fork at Goldcreek 10/20/2015 1535 -- -- -- -- -- <0.030 0.034

10/20/2015 1540 -- -- -- -- -- <0.030 <0.030

12323250 Silver Bow Creek below 

Blacktail Creek, at Butte

03/21/2016 1040 -- -- -- -- 2.03 0.071 0.08903/21/2016 1045 -- -- -- -- 2.04 0.070 0.101

12324400 Clark Fork above Little 

Blackfoot River, near Garrison

03/23/2016 1120 -- -- -- -- -- 0.069 0.15303/23/2016 1125 -- -- -- -- -- 0.067 0.173

12323840 Lost Creek near Anaconda 04/19/2016 0745 0.77 0.42 12.8 9.89 -- 0.031 0.034

04/19/2016 0750 0.76 0.42 12.2 9.89 -- 0.033 0.043

12324200 Clark Fork at Deer Lodge 05/10/2016 1455 -- -- -- -- -- 0.078 0.276

05/10/2016 1500 -- -- -- -- -- 0.081 0.266

12334550 Clark Fork at Turah Bridge, 

near Bonner

05/25/2016 0755 -- -- -- -- -- <0.030 0.1405/25/2016 0800 -- -- -- -- -- 0.031 0.13

12340500 Clark Fork above Missoula 06/08/2016 1245 -- -- -- -- -- <0.030 0.04

06/08/2016 1250 -- -- -- -- -- <0.030 0.03

12323750 Silver Bow Creek at Warm 

Springs

07/12/2016 1015 10.6 0.66 14.5 66.0 -- <0.030 0.0507/12/2016 1020 10.6 0.67 14.4 66.0 -- <0.030 0.05

12323700 Mill Creek at Opportunity 08/08/2016 1605 0.41 0.34 12.0 11.6 -- 0.053 0.06

08/08/2016 1610 0.41 0.34 11.8 11.6 -- 0.044 0.06
64 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana Table 13. Analyses of field replicates for water samples, Clark Fork Basin, Montana.—Continued [hh, hour; mm, minute; 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) 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) 12324680 Clark Fork at Goldcreek 10/20/2015 1535 4.0 7.9 6.3 91.3 0.042 0.69 9.84 40.1 10/20/2015 1540 3.8 8.2 6.8 88.8 <0.040 0.62 9.71 39.7 12323250 Silver Bow Creek below Blacktail Creek, at Butte 03/21/2016 1040 3.6 7.5 94.5 467 0.120 1.30 96.6 124 03/21/2016 1045 3.4 7.5 92.0 470 0.117 1.28 96.2 128 12324400 Clark Fork above Little Blackfoot River, near Garrison 03/23/2016 1120 5.4 27.4 8.0 397 0.080 3.17 44.4 107 03/23/2016 1125 5.3 26.9 8.5 417 0.075 3.40 44.2 103 12323840 Lost Creek near Anaconda 04/19/2016 0745 1.8 5.7 14.9 128 0.058 0.58 1.61 6.3 04/19/2016 0750 2.0 5.2 13.2 130 0.057 0.55 1.63 6.0 12324200 Clark Fork at Deer Lodge 05/10/2016 1455 12.5 57.7 120 1,090 1.24 7.77 38.2 141 05/10/2016 1500 13.1 59.8 132 1,010 1.10 8.10 37.3 138 12334550 Clark Fork at Turah Bridge, near Bonner 05/25/2016 0755 3.4 23.5 35.3 643 0.163 4.02 5.13 65.2 05/25/2016 0800 3.8 24.7 33.8 626 0.168 3.99 5.35 67.6 12340500 Clark Fork above Missoula 06/08/2016 1245 2.6 4.5 11.8 214 0.043 0.70 4.71 23.5 06/08/2016 1250 1.7 4.5 8.3 214 0.044 0.68 4.73 24.5 12323750 Silver Bow Creek at Warm Springs 07/12/2016 1015 3.5 4.6 40.2 160 0.109 0.57 66.4 100 07/12/2016 1020 3.5 5.0 40.4 151 0.109 0.56 66.5 100 12323700 Mill Creek at Opportunity 08/08/2016 1605 1.9 2.3 90.3 138 0.138 0.27 4.83 6.9 08/08/2016 1610 1.9 2.3 91.7 147 0.139 0.27 4.72 7.2
Data 65

Table 13. Analyses of field replicates for water samples, Clark Fork Basin, Montana.—Continued[hh, hour; mm, minute; 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) 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)

12324680 Clark Fork at Goldcreek 10/20/2015 1535 <2.0 5.9 8.9 9.7 -- 91 4

10/20/2015 1540 <2.0 6.5 8.8 9.5 -- 84 4

12323250 Silver Bow Creek below 

Blacktail Creek, at Butte

03/21/2016 1040 27.3 36.2 2.8 3.5 -- 79 703/21/2016 1045 27.2 36.3 2.7 3.4 -- 76 8

12324400 Clark Fork above Little 

Blackfoot River, near Garrison

03/23/2016 1120 6.2 26.5 9.2 11.9 -- 77 2003/23/2016 1125 6.1 26.5 9.1 12.2 -- 77 19

12323840 Lost Creek near Anaconda 04/19/2016 0745 <2.0 2.6 3.9 4.3 1.34 73 6

04/19/2016 0750 <2.0 3.0 3.9 4.3 1.68 68 5

12324200 Clark Fork at Deer Lodge 05/10/2016 1455 9.4 49.3 12.1 18.2 -- 71 44

05/10/2016 1500 10.4 51.1 12.3 18.3 -- 73 42

12334550 Clark Fork at Turah Bridge, 

near Bonner

05/25/2016 0755 3.5 29 5.2 7.5 -- 61 4205/25/2016 0800 3.7 31 5.4 7.7 -- 64 40

12340500 Clark Fork above Missoula 06/08/2016 1245 <2.0 6 2.8 3.1 -- 80 13

06/08/2016 1250 <2.0 6 2.9 3.3 -- 78 12

12323750 Silver Bow Creek at Warm 

Springs

07/12/2016 1015 <2.0 4 38.8 39.3 5.87 89 307/12/2016 1020 <2.0 5 38.9 41.1 5.90 92 3

12323700 Mill Creek at Opportunity 08/08/2016 1605 2.5 2 30.7 35.4 1.43 88 1

08/08/2016 1610 <2.0 <2 30.7 35.5 1.41 70 1
66 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 14. Precision of analyses of field replicates for water samples, Clark Fork Basin, Montana.

[lab, laboratory; NTRU, nephelometric turbidity ratio unit; mg/L, milligram per liter; CaCO3, calcium carbonate; 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) 5 0.49 12 Yes

Calcium, filtered (mg/L) 9 0.67 1.7 Yes

Magnesium, filtered (mg/L) 9 0.13 1.4 Yes

Potassium, filtered (mg/L) 3 0.03 1.9 Yes

Sodium, filtered (mg/L) 3 0.02 0.31 Yes

Alkalinity, filtered, lab (mg/L as CaCO3) 3 1.9 2.0 Yes

Chloride, filtered (mg/L) 3 0.00 0.10 Yes

Fluoride, filtered (mg/L) 3 0.00 0.86 Yes

Silica, filtered (mg/L) 3 0.26 2.0 Yes

Sulfate, filtered (mg/L) 3 0.00 0.00 Yes

Cadmium, filtered (μg/L) 9 0.00 11 Yes

Cadmium, unfiltered recoverable (μg/L) 9 0.01 8.7 Yes

Copper, filtered (μg/L) 9 0.28 6.6 Yes

Copper, unfiltered recoverable (μg/L) 9 0.61 3.8 Yes

Iron, filtered (μg/L) 9 3.1 6.5 Yes

Iron, unfiltered recoverable (μg/L) 9 20 5.5 Yes

Lead, filtered (μg/L) 9 0.03 16 Yes

Lead, unfiltered recoverable (μg/L) 9 0.01 4.5 Yes

Manganese, filtered (μg/L) 9 0.25 0.82 Yes

Manganese, unfiltered recoverable (μg/L) 9 1.6 2.4 Yes

Zinc, filtered (μg/L) 9 0.43 7.3 Yes

Zinc, unfiltered recoverable (μg/L) 9 0.74 4.0 Yes

Arsenic, filtered (μg/L) 9 0.08 0.67 Yes

Arsenic, unfiltered recoverable (μg/L) 9 0.44 3.0 Yes

Organic carbon, filtered (mg/L) 3 0.14 4.8 Yes

Sediment, suspended (percent finer than 0.062 mm) 9 4.9 6.3 Yes

Sediment, suspended (mg/L) 9 0.82 5.4 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).
Data 67

Table 15. Precision of analyses of laboratory replicates for 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 

(listed units)

Relative standard 

deviation 

(percent)

Within limits1

of data-quality objective

Calcium, filtered (mg/L) 8 0.39 1.0 Yes

Magnesium, filtered (mg/L) 8 0.14 1.5 Yes

Cadmium, filtered (μg/L) 8 0.00 7.0 Yes

Cadmium, unfiltered recoverable (μg/L) 8 0.00 4.5 Yes

Copper, filtered (μg/L) 8 0.07 1.5 Yes

Copper, unfiltered recoverable (μg/L) 8 0.21 2.2 Yes

Iron, filtered (μg/L) 8 0.99 2.4 Yes

Iron, unfiltered recoverable (μg/L) 8 5.7 1.6 Yes

Lead, filtered (μg/L) 8 0.01 3.7 Yes

Lead, unfiltered recoverable (μg/L) 8 0.01 0.94 Yes

Manganese, filtered (μg/L) 8 0.18 1.0 Yes

Manganese, unfiltered recoverable (μg/L) 8 0.24 0.52 Yes

Zinc, filtered (μg/L) 8 0.10 3.1 Yes

Zinc, unfiltered recoverable (μg/L) 8 0.34 3.1 Yes

Arsenic, filtered (μg/L) 8 0.10 0.68 Yes

Arsenic, unfiltered recoverable (μg/L) 8 0.67 4.2 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 16. 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) 3 94.3–97.5 95.9 Yes

Cadmium, unfiltered recoverable (μg/L) 3 96.5–102 99.1 Yes

Copper, filtered (μg/L) 3 90.2–104 97.1 Yes

Copper, unfiltered recoverable (μg/L) 3 87.4–109 98.2 Yes

Iron, filtered (μg/L) 3 93.2–108 100 Yes

Iron, unfiltered recoverable (μg/L) 4 99.0–108 104 Yes

Lead, filtered (μg/L) 3 96.3–105 100 Yes

Lead, unfiltered recoverable (μg/L) 3 89.1–116 103 Yes

Manganese, filtered (μg/L) 4 105–107 106 Yes

Manganese, unfiltered recoverable (μg/L) 5 101–107 104 Yes

Zinc, filtered (μg/L) 3 89.1–104 96.6 Yes

Zinc, unfiltered recoverable (μg/L) 4 97.8–105 102 Yes

Arsenic, filtered (μg/L) 3 96.0–104 100 Yes

Arsenic, unfiltered recoverable (μg/L) 3 95.5–109 102 Yes

1

The data-quality objective for acceptable bias is a maximum deviation of 25 percent from a theoretical 100-percent recovery (table 3).
68 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 17. 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 dataquality objective

Cadmium, filtered (μg/L) 3 95.0–99.5 97.2 Yes

Cadmium, unfiltered recoverable (μg/L) 3 64.7–130 97.3 No2

Copper, filtered (μg/L) 3 79.9–107 93.2 Yes

Copper, unfiltered recoverable, μg/L) 3 79.5–99.5 89.5 Yes

Iron, filtered (μg/L) 3 79.8–117 98.4 Yes

Iron, unfiltered recoverable (μg/L) 4 48.2–120 84.3 No3

Lead, filtered (μg/L) 3 87.4–115 101 Yes

Lead, unfiltered recoverable (μg/L) 3 79.7–118 99.0 Yes

Manganese, filtered (μg/L) 4 95.0–102 98.4 Yes

Manganese, unfiltered recoverable (μg/L) 5 81.5–103 92.2 Yes

Zinc, filtered (μg/L) 3 76.8–108 92.2 Yes

Zinc, unfiltered recoverable (μg/L) 4 86.6–96.3 91.4 Yes

Arsenic, filtered (μg/L) 3 96.7–102 99.1 Yes

Arsenic, unfiltered recoverable (μg/L) 3 61.9–137 99.5 No4

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 data-quality objective is an artifact of a small sample size with a recovery percent range from 86.6 to 112.

3

Exceedance of data-quality objective is an artifact of a small sample size with a recovery percent range from 64.1 to 109.

4

Exceedance of data-quality objective is an artifact of a small sample size with a recovery percent range from 85.2 to 115.
Data 69

Table 18. Analyses of field blanks for water samples.

[hh, hour; mm, minute; μS/cm, microsiemen per centimeter at 25 degrees Celsius; lab, laboratory; NTRU, nephelometric turbidity ratio unit; mg/L, milligram 

per liter; CaCO3, calcium carbonate; <, less than laboratory reporting level; --, no data; μg/L, microgram per liter]

Date Time 

(hhmm)

pH, 

onsite 

(standard 

units)

Specific 

conductance, 

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 as 

CaCO3)

Chloride, 

filtered 

(mg/L)

10/19/2015 1405 5.3 2 <2.0 <0.022 <0.011 <0.03 <0.06 <4.6 <0.02

1

04/13/2016 1000 5.6 2 <2.0 <0.022 <0.011 <0.03 <0.06 <4.0 <0.02

04/20/2016 1410 5.2 2 -- <0.022 <0.011 -- -- -- --

05/10/2016 0755 5.4 2 <2.0 <0.022 <0.011 <0.03 <0.06 <4.0 <0.02

05/24/2016 1330 5.4 2 <2.0 <0.022 <0.011 -- -- -- --

06/08/2016 0805 5.4 2 -- <0.022 <0.011 -- -- -- --

07/12/2016 1150 5.2 2 -- <0.022 <0.011 -- -- -- --

08/09/2016 1015 5.3 2 <2.0 <0.022 <0.011 <0.03 <0.06 <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)

10/19/2015 <0.01 0.018 <0.02 -- <0.030 <0.030 <0.80 <0.80 <4.0 8.3

1

04/13/2016 <0.01 0.032 <0.02 <0.01 <0.030 <0.030 <0.80 <0.80 <4.0 <4.6

04/20/2016 -- -- -- -- <0.030 <0.030 <0.80 <0.80 <4.0 <4.6

05/10/2016 <0.01 <0.018 <0.02 -- <0.030 <0.030 <0.80 <0.80 <4.0 <4.6

05/24/2016 -- -- -- -- <0.030 <0.03 <0.80 <0.8 <4.0 <4.6

06/08/2016 -- -- -- -- <0.030 <0.03 <0.80 <0.8 <4.0 <4.6

07/12/2016 -- -- -- -- <0.030 <0.03 <0.80 <0.8 <4.0 <4.6

08/09/2016 <0.01 0.036 <0.02 -- <0.030 <0.03 <0.80 0.3 11.0 <4.6

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)

10/19/2015 <0.040 <0.04 <0.40 <0.4 <2.0 <2.0 <0.10 <0.20 <0.23

1

04/13/2016 <0.040 <0.04 <0.40 <0.4 <2.0 <2.0 <0.10 <0.20 <0.23

04/20/2016 <0.040 <0.04 <0.40 <0.4 <2.0 <2.0 <0.10 <0.20 --

05/10/2016 <0.040 <0.04 <0.40 <0.4 <2.0 <2.0 <0.10 <0.20 <0.23

05/24/2016 <0.040 <0.04 <0.40 <0.4 <2.0 <2 <0.10 <0.2 --

06/08/2016 <0.040 <0.04 <0.40 <0.4 <2.0 <2 <0.10 <0.2 --

07/12/2016 <0.040 <0.04 <0.40 <0.4 <2.0 <2 <0.10 <0.2 --

08/09/2016 <0.040 0.03 <0.40 <0.4 <2.0 <2 <0.10 <0.01 <0.23

1

Annual office equipment blank collected before any equipment was used in the field.
70 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana Table 19. Bed-sediment data for the Clark Fork Basin, Montana, August 2016. [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 analy- ses 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 20.4 9.4 21.3 446 30,000 93.0 5,800 15.4 1,810 12323750 Silver Bow Creek at Warm Springs

3 96.3 5.0 17.0 238 26,300 121 3,460 15.0 639

12323800 Clark Fork near Galen 3 102 4.2 18.1 791 25,500 96.3 6,380 22.5 837461415112450801 Clark Fork below Lost Creek, 

near Galen 

3 158 5.5 16.4 1,430 27,500 158 6,480 17.2 1,210

461559112443301 Clark Fork at county bridge, near 

Racetrack 

3 80.4 3.6 13.9 818 23,400 108 2,700 11.5 816

461903112440701 Clark Fork at Dempsey Creek 

diversion, near Racetrack 

3 68.7 4.4 14.5 815 24,500 126 2,850 11.8 935

12324200 Clark Fork at Deer Lodge 3 62.6 4.6 17.0 819 20,500 104 4,220 12.4 86212324400 Clark Fork above Little Blackfoot River, near Garrison

3 55.4 4.2 26.3 822 24,200 107 2,260 12.5 947

12324680 Clark Fork at Goldcreek 3 43.4 3.5 24.7 510 22,600 91.5 2,120 11.8 81512331800 Clark Fork near Drummond 3 30.1 2.9 16.9 334 17,700 66.9 2,810 10.7 75012334550 Clark Fork at Turah Bridge, near 

Bonner 

3 18.8 1.7 20.9 236 17,100 49.6 674 10.8 507

12340000 Blackfoot River near Bonner 3 5.1 <0.1 17.8 17.0 18,700 9.8 363 11.8 49.312340500 Clark Fork above Missoula 3 13.4 1.1 18.7 125 16,300 27.1 802 10.1 343
Data 71

Table 20. 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 60.5 58.5–62.4

Cadmium 10 1:10 0.371 66.8 64.6–69.0

Chromium 10 1:10 130 67.6 66.6–68.7

Copper 10 1:10 33.9 77.0 76.0–78.1

Iron 10 1:10 33,600 91.0 90.1–91.8

Lead 10 1:10 17.3 49.1 47.8–50.5

Manganese 10 1:10 529 87.5 86.8–88.2

Nickel 10 1:10 85 89.7 88.7–90.7

Zinc 10 1:10 103 79.4 78.4–80.5

SRM sample 2711a

Arsenic 10 1:10 107 86.5 84.4–88.7

Cadmium 10 1:10 54.1 100 99.0–101

Chromium 10 1:10 52.3 51.3 50.2–52.5

Copper 10 1:10 140 90.5 89.4–91.5

Iron 10 1:10 28,200 85.4 84.3–86.5

Lead 10 1:10 1,400 98.7 97.5–99.9

Manganese 10 1:10 675 80.0 79.0–81.0

Nickel 10 1:10 21.7 91.0 89.9–92.2

Zinc 10 1:10 414 93.6 92.5–94.7
72 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana Table 21. 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 μg/mL] Site number (fig. 1) Site name Dilution ratio Concentration (μg/mL) Arsenic Cadmium Chromium Copper Iron Lead Manga- nese Nickel Zinc 12323600 Silver Bow Creek at Opportunity 1:10 <0.003 <0.0005 <0.007 <0.005 <0.02 <0.004 <0.001 <0.004 <0.0005 12323750 Silver Bow Creek at Warm Springs 1:10 <0.003 <0.0005 <0.007 <0.005 <0.02 <0.004 <0.001 <0.004 <0.0005 12323800 Clark Fork near Galen 1:10 <0.003 <0.0005 <0.007 <0.005 <0.02 <0.004 <0.001 <0.004 <0.0005 461415112450801 Clark Fork below Lost Creek, near Galen 1:10 <0.003 <0.0005 <0.007 <0.005 <0.02 <0.004 <0.001 <0.004 <0.0005 461559112443301 Clark Fork at county bridge, near Racetrack 1:10 <0.003 <0.0005 <0.007 <0.005 <0.02 <0.004 <0.001 <0.004 <0.0005 461903112440701 Clark Fork at Dempsey Creek diversion, near Racetrack 1:10 <0.003 <0.0005 <0.007 <0.005 <0.02 <0.004 <0.001 <0.004 <0.0005 12324200 Clark Fork at Deer Lodge 1:10 <0.003 <0.0005 <0.007 <0.005 <0.02 <0.004 <0.001 <0.004 <0.0005 12324400 Clark Fork above Little Blackfoot River, near Garrison 1:10 <0.003 <0.0005 <0.007 <0.005 <0.02 <0.004 <0.001 <0.004 <0.0005 12324680 Clark Fork at Goldcreek 1:10 <0.003 <0.0005 <0.007 <0.005 <0.02 <0.004 <0.001 <0.004 <0.0005 12331800 Clark Fork near Drummond 1:10 <0.003 <0.0005 <0.007 <0.005 <0.02 <0.004 <0.001 <0.004 <0.0005 12334550 Clark Fork at Turah Bridge, near Bonner 1:10 <0.003 <0.0005 <0.007 <0.005 <0.02 <0.004 <0.001 <0.004 <0.0005 12340000 Blackfoot River near Bonner 1:10 <0.003 <0.0005 <0.007 <0.005 <0.02 <0.004 <0.001 <0.004 <0.0005 12340500 Clark Fork above Missoula 1:10 <0.003 <0.0005 <0.007 <0.005 <0.02 <0.004 <0.001 <0.004 <0.0005
Data 73

Table 22. Biological data for the Clark Fork Basin, Montana, August 2016.

[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 ManganeseNickel Zinc

12323600–Silver Bow Creek at Opportunity

Hydropsyche cockerelli 3 5.2 5.1 4.6 157 2,470 12.8 3,690 3.8 566

12323750–Silver Bow Creek at Warm Springs

Hydropsyche cockerelli 2 12.6 0.6 1.4 31.1 815 3.2 1,500 1.7 176

Hydropsyche occidentalis 1 21.6 1.1 3.2 43.6 1,720 7.3 3,020 3.2 210

12323800–Clark Fork near Galen

Hydropsyche cockerelli 3 17.6 2.5 4.4 134 2,290 13.1 2,400 4.5 381

Hydropsyche occidentalis 2 14.5 1.5 3.5 102 1,840 10.0 2,560 3.8 277

461415112450801–Clark Fork below Lost Creek, near Galen

Hydropsyche cockerelli 1 20.2 3.7 5.5 247 3,040 21.4 2,170 4.5 336

Hydropsyche occidentalis 2 18.2 1.9 3.6 164 1,900 14.8 2,740 3.7 313

Hydropsyche species 1 14.4 1.5 3.0 138 2,040 16.0 2,790 4.4 276

461559112443301–Clark Fork at county bridge, near Racetrack

Arctopsyche grandis 1 9.3 3.5 4.5 90.9 803 9.1 3,140 6.4 572

Hydropsyche cockerelli 2 13.3 2.7 2.7 110 1,550 9.3 2,000 2.2 242

Hydropsyche occidentalis 1 12.9 1.5 2.0 72.4 1,200 9.4 2,880 2.5 237

461903112440701–Clark Fork at Dempsey Creek diversion, near Racetrack

Arctopsyche grandis 3 5.1 1.8 0.8 45.3 391 3.6 948 0.8 223

Claassenia sabulosa 1 1.9 0.8 0.3 54.4 188 0.9 187 0.4 277

Hydropsyche cockerelli 4 9.7 2.0 2.1 92.3 1,120 8.0 1,330 1.4 220

Hydropsyche occidentalis 2 9.2 1.0 2.0 74.5 949 7.2 1,410 1.5 236

12324200–Clark Fork at Deer Lodge

Hydropsyche cockerelli 4 7.0 2.3 1.8 84.7 863 7.7 977 1.3 212

Hydropsyche occidentalis 1 8.0 1.2 1.9 80.7 975 8.5 1,280 1.5 240

12324400–Clark Fork above Little Blackfoot River, near Garrison

Arctopsyche grandis 3 5.2 1.6 1.1 42.2 328 3.7 811 1.1 242

Claassenia sabulosa 2 2.0 0.4 0.5 64.1 225 2.0 179 0.7 266

Hydropsyche cockerelli 1 7.4 1.6 1.4 92.7 808 8.5 1,110 1.5 213

Hydropsyche occidentalis 1 7.3 1.1 1.8 78.1 908 9.6 1,800 1.7 230

12324680–Clark Fork at Goldcreek

Arctopsyche grandis 3 3.5 2.1 0.6 34.8 294 2.6 942 0.7 213

Claassenia sabulosa 3 2.1 0.6 0.8 51.8 235 1.7 266 0.9 325

Hydropsyche cockerelli 1 5.1 1.5 2.0 49.2 535 5.1 1,250 1.3 205

Hydropsyche occidentalis 1 7.4 1.3 2.6 77.4 1,100 9.8 2,820 2.0 279

12331800–Clark Fork near Drummond

Arctopsyche grandis 3 2.8 0.8 0.6 23.5 306 3.5 1,240 0.8 195

Claassenia sabulosa 3 1.6 0.4 0.5 53.7 192 1.5 218 0.7 280

Hydropsyche cockerelli 2 4.9 0.9 1.6 43.1 819 7.7 1,720 1.4 210

Hydropsyche occidentalis 2 7.5 1.3 3.8 72.5 1,700 14.0 2,750 3.9 296
74 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Taxon

Number of 

composite 

samples

Concentration (μg/g)

Arsenic Cadmium Chromium Copper Iron Lead ManganeseNickel Zinc

12334550–Clark Fork at Turah Bridge, near Bonner

Arctopsyche grandis 2 4.2 0.9 1.0 20.0 440 7.0 677 1.1 227

Claassenia sabulosa 1 1.1 0.5 0.2 81.1 99 0.4 109 0.4 361

Hydropsyche cockerelli 1 4.9 1.0 1.5 30.4 777 5.1 684 1.3 212

Hydropsyche occidentalis 3 4.6 0.7 2.7 29.7 1,290 5.0 704 1.7 188

12340000–Blackfoot River near Bonner

Arctopsyche grandis 2 2.7 0.2 1.3 11.9 576 0.6 420 0.8 151

Hydropsyche cockerelli 2 3.6 0.2 3.2 14.5 1,340 1.7 542 1.7 146

Hydropsyche occidentalis 1 4.0 0.2 2.8 18.3 1,180 1.8 693 2.7 211

12340500–Clark Fork above Missoula

Arctopsyche grandis 2 3.6 1.0 1.3 24.6 622 2.5 1,170 1.0 228

Claassenia sabulosa 2 1.0 0.3 0.6 44.2 232 0.9 110 0.9 327

Hydropsyche cockerelli 2 6.9 0.7 2.3 28.0 1,050 4.4 1,160 1.3 231

Hydropsyche occidentalis 2 4.5 0.7 2.4 31.4 1,080 4.5 1,580 1.6 244

Table 22. Biological data for the Clark Fork Basin, Montana, August 2016.—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]

Table 23. Recovery efficiency for analyses of standard 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 59.5 112 111–112

Cadmium 12 42.3 91.0 90.1–91.8

Chromium 12 1.95 85.8 83.9–87.7

Copper 12 497 88.3 88.0–88.7

Iron 12 179 92.5 91.9–93.2

Lead 12 0.225 182 170–192

Manganese 12 15.6 89.5 88.4–90.5

Nickel 12 5.3 88.7 87.2–90.3

Zinc 12 136 91.9 90.4–93.3
Data 75

Table 24. 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 μg/mL]

Site number 

(fig. 1) Site name Dilution ratio Concentration (μg/mL) Arsenic Cadmium Chromium Copper Iron Lead Manga- nese Nickel Zinc

12323600 Silver Bow Creek at 

Opportunity

1:1 <0.002 <0.0003 <0.007 <0.006 <0.05 <0.003 <0.001 <0.001 <0.02

12323750 Silver Bow Creek at 

Warm Springs

1:1 <0.002 <0.0003 <0.007 <0.006 <0.05 <0.003 <0.001 <0.001 <0.02

12323800 Clark Fork near 

Galen

1:1 <0.002 <0.0003 <0.007 <0.006 <0.05 <0.003 <0.001 <0.001 <0.10

461415112450801 Clark Fork below 

Lost Creek, near Galen

1:1 <0.002 <0.0003 <0.007 <0.006 <0.05 <0.003 <0.001 <0.001 <0.02

461559112443301 Clark Fork at county 

bridge, near Racetrack

1:1 <0.002 <0.0003 <0.007 <0.006 <0.05 <0.003 <0.001 <0.001 <0.02

461903112440701 Clark Fork at 

Dempsey Creek diversion, near Racetrack

1:1 <0.002 <0.0003 <0.007 <0.006 <0.05 <0.003 <0.001 <0.001 <0.02

12324200 Clark Fork at Deer 

Lodge

1:1 <0.002 <0.0003 <0.007 <0.006 <0.05 <0.003 <0.001 <0.001 <0.02

12324400 Clark Fork above 

Little Blackfoot River, near Garrison

1:1 <0.002 <0.0003 <0.007 <0.006 <0.05 <0.003 <0.001 <0.001 <0.02

12324680 Clark Fork at Goldcreek 1:1 <0.002 <0.0003 <0.007 <0.006 <0.05 <0.003 <0.001 <0.001 <0.0212331800 Clark Fork near 

Drummond

1:1 <0.002 <0.0003 <0.007 <0.006 <0.05 <0.003 <0.001 <0.001 <0.10

12334550 Clark Fork at Turah 

Bridge, near Bonner

1:1 <0.002 <0.0003 <0.007 <0.006 <0.05 <0.003 <0.001 <0.001 <0.02

12340000 Blackfoot River near 

Bonner

1:1 <0.002 <0.0003 <0.007 <0.006 <0.05 <0.003 <0.001 <0.001 <0.10

12340500 Clark Fork above 

Missoula

1:1 <0.002 <0.0003 <0.007 <0.006 <0.05 <0.003 <0.001 <0.001 <0.02
76 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 25. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through September 2016.

[ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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; --, indicates 

either too few samples (less than three) or insufficient data to compute statistic]

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 2016

Streamflow, instantaneous (ft3/s) 179 156 1.9 16 9.3

pH, onsite (standard units) 179 8.4 7.3 7.7 7.7

Specific conductance, onsite (μS/cm) 179 412 116 262 262

Temperature, water (°C) 179 17.5 1.0 7.9 8.5

Turbidity, unfiltered, lab (NTRU) 23 7.5 <2.0 23.9 3.5

Hardness, filtered (mg/L as CaCO3) 179 153 37.7 104 105

Calcium, filtered (mg/L) 179 42.9 10.6 29.7 29.8

Magnesium, filtered (mg/L) 179 11.1 2.71 7.23 7.20

Potassium, filtered (mg/L) 49 6.40 2.00 2.75 2.57

Sodium, filtered (mg/L) 49 18.0 6.40 10.6 10.2

Alkalinity, filtered, lab (mg/L as CaCO3) 21 124 54.5 85.5 78.4

Chloride, filtered (mg/L) 49 18.0 2.80 8.53 8.00

Fluoride, filtered (mg/L) 49 0.60 0.18 0.28 0.30

Silica, filtered (mg/L) 49 32.0 14.0 24.3 24.4

Sulfate, filtered (mg/L) 49 40.2 14.7 26.2 26.0

Nitrate plus nitrite, filtered (mg/L) 23 1.24 0.16 0.63 0.52

Cadmium, filtered (μg/L) 177 0.50 <0.03 20.04 0.02

Cadmium, unfiltered recoverable (μg/L) 179 0.12 <0.01 20.04 <1.0

Copper, filtered (μg/L) 178 10.0 <1.0 23.5 3.0

Copper, unfiltered recoverable (μg/L) 179 52.0 0.91 6.2 4.9

Iron, filtered (μg/L) 179 739 15.2 197 175

Iron, unfiltered recoverable (μg/L) 179 4,220 123 659 590

Lead, filtered (μg/L) 179 2.80 <0.02 20.18 0.06

Lead, unfiltered recoverable (μg/L) 179 47.0 <1.00 21.52 0.64

Manganese, filtered (μg/L) 179 144 14.2 44.1 39.4

Manganese, unfiltered recoverable (μg/L) 179 240 23.5 61.0 52.7

Zinc, filtered (μg/L) 177 11 <1.0 23.2 2.4

Zinc, unfiltered recoverable (μg/L) 179 130 <3.0 27.4 4.0

Arsenic, filtered (μg/L) 178 13.0 1.0 4.0 3.4

Arsenic, unfiltered recoverable (μg/L) 179 18.0 1.0 25.3 4.5

Organic carbon, filtered (mg/L) 21 9.52 1.40 4.73 4.29

Sediment, suspended (percent finer than 

0.062 mm)

179 97 50 83 85

Sediment, suspended concentration (mg/L) 179 139 1 11 7

Sediment, suspended discharge (ton/d) 179 59 0.01 0.90 0.17
Data 77

Table 25. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through 

September 2016.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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; --, indicates 

either too few samples (less than three) or insufficient data to compute statistic]

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 2016

Streamflow, instantaneous (ft3/s) 187 202 13 31 25

pH, onsite (standard units) 187 8.2 7.2 7.6 7.6

Specific conductance, onsite (μS/cm) 187 691 209 457 460

Temperature, water (°C) 187 20.0 1.0 10.3 10.0

Turbidity, unflitered, lab (NTRU) 23 8.6 <2.0 24.0 3.7

Hardness, filtered (mg/L as CaCO3) 187 217 66.0 147 150

Calcium, filtered (mg/L) 187 62.7 19.0 41.9 42.2

Magnesium, filtered (mg/L) 187 16.1 4.51 10.4 10.7

Potassium, filtered (mg/L) 49 35.0 3.64 7.50 5.70

Sodium, filtered (mg/L) 49 66.0 12.0 24.9 24.7

Alkalinity, filtered, lab (mg/L as CaCO3) 21 119 66.9 87.7 88.6

Chloride, filtered (mg/L) 48 88.0 6.70 23.8 21.2

Fluoride, filtered (mg/L) 48 0.80 0.26 0.41 0.40

Silica, filtered (mg/L) 48 28.0 17.0 22.1 22.0

Sulfate, filtered (mg/L) 48 96.0 35.0 71.1 73.8

Nitrate plus nitrite, filtered (mg/L) 23 4.40 0.34 1.10 0.91

Cadmium, filtered (μg/L) 187 6.2 0.04 0.76 0.15

Cadmium, unfiltered recoverable (μg/L) 187 6.0 0.06 1.03 0.24

Copper, filtered (μg/L) 187 303 2.6 26.3 11.3

Copper, unfiltered recoverable (μg/L) 187 550 7.3 60.8 21.3

Iron, filtered (μg/L) 187 392 9.6 101 81.2

Iron, unfiltered recoverable (μg/L) 187 7,400 85.4 752 535

Lead, filtered (μg/L) 187 2.4 <0.5 20.41 0.24

Lead, unfiltered recoverable (μg/L) 187 250 0.61 9.41 2.29

Manganese, filtered (μg/L) 187 1,700 20.7 264 121

Manganese, unfiltered recoverable (μg/L) 187 1,600 25.9 301 148

Zinc, filtered (μg/L) 187 2,200 5.3 250 58.6

Zinc, unfiltered recoverable (μg/L) 187 2,200 20.5 304 75.0

Arsenic, filtered (μg/L) 187 13.4 2.3 5.8 5.3

Arsenic, unfiltered recoverable (μg/L) 187 45.0 3.0 9.1 8.0

Organic carbon, filtered (mg/L) 21 9.97 4.93 7.16 7.21

Sediment, suspended (percent finer than 

0.062 mm)

186 98 42 83 85

Sediment, suspended concentration (mg/L) 186 405 2 18 9

Sediment, suspended discharge (ton/d) 186 70 0.08 2.1 0.59
78 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 25. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through 

September 2016.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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; --, indicates 

either too few samples (less than three) or insufficient data to compute statistic]

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 2016

Streamflow, instantaneous (ft3/s) 187 648 13 78 56

pH, onsite (standard units) 189 9.5 7.2 8.4 8.3

Specific conductance, onsite (μS/cm) 189 633 202 414 403

Temperature, water (°C) 189 24.0 −1.0 9.5 9.5

Turbidity, unfiltered, lab (NTRU) 23 12 2.1 5.7 5.2

Hardness, filtered (mg/L as CaCO3) 189 248 60.2 150 148

Calcium, filtered (mg/L) 189 75.0 18.5 44.4 44.0

Magnesium, filtered (mg/L) 189 15.0 3.42 9.45 9.10

Potassium, filtered (mg/L) 60 16.0 1.79 4.54 4.10

Sodium, filtered (mg/L) 60 33.5 5.06 18.5 17.6

Alkalinity, filtered, lab (mg/L as CaCO3) 31 111 71.6 93.1 91.5

Chloride, filtered (mg/L) 59 63.9 3.20 17.7 14.1

Fluoride, filtered (mg/L) 59 0.80 0.16 0.39 0.40

Silica, filtered (mg/L) 59 28.0 9.56 20.2 21.0

Sulfate, filtered (mg/L) 59 190 32.0 65.9 62.0

Cadmium, filtered (μg/L) 188 41.0 <0.1 20.87 0.44

Cadmium, unfiltered recoverable (μg/L) 189 49.0 0.17 21.58 0.94

Copper, filtered (μg/L) 187 450 6.5 36.2 27.6

Copper, unfiltered recoverable (μg/L) 189 3,900 12.1 154 84.2

Iron, filtered (μg/L) 189 397 <3 251.0 30.0

Iron, unfiltered recoverable (μg/L) 188 24,100 114 1,340 664

Lead, filtered (μg/L) 189 5.1 <0.5 20.62 0.31

Lead, unfiltered recoverable (μg/L) 189 650 0.67 28.9 12.7

Manganese, filtered (μg/L) 189 9,300 25.5 331 240

Manganese, unfiltered recoverable (μg/L) 189 10,000 55.3 439 330

Zinc, filtered (μg/L) 188 13,000 11.2 223 102

Zinc, unfiltered recoverable (μg/L) 189 15,000 26.8 394 221

Arsenic, filtered (μg/L) 189 34.0 1.0 10.1 9.5

Arsenic, unfiltered recoverable (μg/L) 189 235 5.5 21.2 15.9

Organic carbon, filtered (mg/L) 28 8.35 3.06 5.54 5.44

Sediment, suspended (percent finer than 

0.062 mm)

190 95 37 78 84

Sediment, suspended concentration (mg/L) 190 801 3 44 18

Sediment, suspended discharge (ton/d) 187 781 0.18 19 2.6
Data 79

Table 25. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through 

September 2016.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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; --, indicates 

either too few samples (less than three) or insufficient data to compute statistic]

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 2016

Streamflow, instantaneous (ft3/s) 95 309 7.4 64 38

pH, onsite (standard units) 96 8.6 7.5 8.0 8.0

Specific conductance, onsite (μS/cm) 96 213 56 129 129

Temperature, water (°C) 96 17.0 0.0 8.6 9.0

Turbidity, unfiltered, lab (NTRU) 89 21 <2.0 22.4 <2.0

Hardness, filtered (mg/L as CaCO3) 96 98.0 23.7 56.6 52.9

Calcium, filtered (mg/L) 96 26.7 7.00 15.7 14.9

Magnesium, filtered (mg/L) 96 8.01 1.45 4.21 3.92

Potassium, filtered (mg/L) 23 0.82 0.47 0.62 0.62

Sodium, filtered (mg/L) 23 6.04 2.14 3.82 3.45

Alkalinity, filtered, lab (mg/L as CaCO3) 23 85.1 30.8 54.5 52.5

Chloride, filtered (mg/L) 23 0.54 0.16 0.30 0.26

Fluoride, filtered (mg/L) 23 0.37 0.28 0.31 0.30

Silica, filtered (mg/L) 23 15.5 9.27 12.3 12.1

Sulfate, filtered (mg/L) 23 13.9 3.12 6.18 5.37

Cadmium, filtered (μg/L) 95 0.11 0.02 20.04 0.04

Cadmium, unfiltered recoverable (μg/L) 96 0.19 0.03 0.07 0.07

Copper, filtered (μg/L) 96 5.1 0.72 2.2 2.1

Copper, unfiltered recoverable (μg/L) 96 10.6 1.3 3.7 3.1

Iron, filtered (μg/L) 96 125 21.2 48.4 42.6

Iron, unfiltered recoverable (μg/L) 96 730 64.9 194 154

Lead, filtered (μg/L) 96 0.36 0.02 20.12 0.11

Lead, unfiltered recoverable (μg/L) 96 3.12 0.15 0.70 0.52

Manganese, filtered (μg/L) 96 12.0 3.1 5.9 5.7

Manganese, unfiltered recoverable (μg/L) 96 36.6 6.2 13.4 11.5

Zinc, filtered (μg/L) 96 4.3 <1.4 21.6 1.3

Zinc, unfiltered recoverable (μg/L) 96 9.2 <2.0 23.0 2.6

Arsenic, filtered (μg/L) 96 32.9 7.3 16.0 14.9

Arsenic, unfiltered recoverable (μg/L) 96 34.8 7.8 17.2 15.6

Organic carbon, filtered (mg/L) 23 3.48 1.26 2.24 2.27

Sediment, suspended (percent finer than 

0.062 mm)

96 96 14 64 67

Sediment, suspended concentration (mg/L) 96 42 1 6 4

Sediment, suspended discharge (ton/d) 95 28 0.02 2.0 0.36
80 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 25. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through 

September 2016.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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; --, indicates 

either too few samples (less than three) or insufficient data to compute statistic]

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 2016

Streamflow, instantaneous (ft3/s) 110 261 0.43 37 15

pH, onsite (standard units) 112 8.3 7.5 8.0 8.0

Specific conductance, onsite (μS/cm) 112 242 59 146 144

Temperature, water (°C) 112 20.0 −1.0 9.3 9.5

Turbidity, unfiltered, lab (NTRU) 30 9.1 <2.0 22.4 <2.0

Hardness, filtered (mg/L as CaCO3) 112 112 24.0 62.6 60.2

Calcium, filtered (mg/L) 112 31.0 7.01 17.6 17.0

Magnesium, filtered (mg/L) 112 8.44 1.56 4.54 4.42

Potassium, filtered (mg/L) 30 1.02 0.48 0.70 0.72

Sodium, filtered (mg/L) 30 8.15 2.29 4.40 4.12

Alkalinity, filtered, lab (mg/L as CaCO3) 30 88.2 31.9 57.2 56.0

Chloride, filtered (mg/L) 30 0.82 0.18 0.38 0.32

Fluoride, filtered (mg/L) 30 0.40 0.29 0.33 0.32

Silica, filtered (mg/L) 30 16.9 9.47 12.3 12.0

Sulfate, filtered (mg/L) 30 27.7 4.11 10.4 9.40

Cadmium, filtered (μg/L) 112 0.13 0.02 0.06 0.06

Cadmium, unfiltered recoverable (μg/L) 112 0.86 0.03 0.13 0.09

Copper, filtered (μg/L) 112 6.1 1.0 2.8 2.4

Copper, unfiltered recoverable (μg/L) 112 38.8 1.5 5.9 3.8

Iron, filtered (μg/L) 112 108 15.9 48.1 42.4

Iron, unfiltered recoverable (μg/L) 112 1,960 44.3 284 160

Lead, filtered (μg/L) 112 0.35 <0.04 20.13 0.12

Lead, unfiltered recoverable (μg/L) 112 12.7 0.07 1.30 0.52

Manganese, filtered (μg/L) 112 32.8 2.1 6.5 5.0

Manganese, unfiltered recoverable (μg/L) 112 113 2.9 17.5 12.0

Zinc, filtered (μg/L) 111 7.7 <1.4 22.7 2.5

Zinc, unfiltered recoverable (μg/L) 112 41 <2.0 25.9 4.0

Arsenic, filtered (μg/L) 112 55.1 9.0 20.8 18.6

Arsenic, unfiltered recoverable (μg/L) 112 53.5 10.0 23.4 21.2

Organic carbon, filtered (mg/L) 30 4.10 1.33 2.34 2.28

Sediment, suspended (percent finer than 

0.062 mm)

112 91 26 70 71

Sediment, suspended concentration (mg/L) 112 107 1 11 4

Sediment, suspended discharge (ton/d) 110 55 <0.01 23.0 0.14
Data 81

Table 25. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through 

September 2016.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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; --, indicates 

either too few samples (less than three) or insufficient data to compute statistic]

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 2016

Streamflow, instantaneous (ft3/s) 86 114 1.0 15 8.3

pH, onsite (standard units) 89 8.2 7.5 7.7 7.7

Specific conductance, onsite (μS/cm) 89 151 65 103 107

Temperature, water (°C) 89 16.0 0.0 7.4 7.5

Turbidity, unfiltered, lab (NTRU) 82 39 <2.0 25.2 3.2

Hardness, filtered (mg/L as CaCO3) 89 56.3 21.5 37.6 38.5

Calcium, filtered (mg/L) 89 18.3 7.22 12.6 13.0

Magnesium, filtered (mg/L) 89 2.60 0.78 1.50 1.48

Potassium, filtered (mg/L) 23 1.13 0.70 0.92 0.91

Sodium, filtered (mg/L) 23 7.94 4.39 5.93 5.99

Alkalinity, filtered, lab (mg/L as CaCO3) 23 55.4 26.3 41.7 38.9

Chloride, filtered (mg/L) 23 0.83 0.30 0.46 0.38

Fluoride, filtered (mg/L) 23 0.08 0.06 0.07 0.07

Silica, filtered (mg/L) 23 26.9 20.9 24.5 24.7

Sulfate, filtered (mg/L) 23 15.7 4.90 7.4 6.36

Cadmium, filtered (μg/L) 87 0.05 <0.02 20.03 0.03

Cadmium, unfiltered recoverable (μg/L) 89 0.33 <0.03 20.06 0.05

Copper, filtered (μg/L) 89 5.5 0.82 2.2 2.1

Copper, unfiltered recoverable (μg/L) 89 16.8 1.0 3.6 3.0

Iron, filtered (μg/L) 89 277 28 91.9 81.8

Iron, unfiltered recoverable (μg/L) 89 2,380 85.7 347 231

Lead, filtered (μg/L) 89 0.39 0.03 20.17 0.16

Lead, unfiltered recoverable (μg/L) 89 7.96 0.10 0.82 0.53

Manganese, filtered (μg/L) 89 34.5 6.0 13.4 11.9

Manganese, unfiltered recoverable (μg/L) 89 99.9 12.8 24.6 21.7

Zinc, filtered (μg/L) 89 3.3 0.65 21.7 1.4

Zinc, unfiltered recoverable (μg/L) 89 17.8 <2.0 23.0 2.0

Arsenic, filtered (μg/L) 89 25.7 7.7 15.9 14.9

Arsenic, unfiltered recoverable (μg/L) 89 27.9 9.8 17.0 15.4

Organic carbon, filtered (mg/L) 23 7.07 3.05 4.77 4.44

Sediment, suspended (percent finer than 

0.062 mm)

89 97 25 78 83

Sediment, suspended concentration (mg/L) 89 195 1 13 4

Sediment, suspended discharge (ton/d) 86 50 <0.01 21.8 0.10
82 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 25. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through 

September 2016.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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; --, indicates 

either too few samples (less than three) or insufficient data to compute statistic]

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 2016

Streamflow, instantaneous (ft3/s) 112 116 4.5 17 9.8

pH, onsite (standard units) 112 9.0 7.6 8.1 8.1

Specific conductance, onsite (μS/cm) 112 380 116 262 279

Temperature, water (°C) 112 24.0 0.0 11.0 11.0

Turbidity, unfiltered, lab (NTRU) 30 9.3 <2.0 24.0 3.6

Hardness, filtered (mg/L as CaCO3) 112 173 54.2 114 122

Calcium, filtered (mg/L) 112 48.4 16.5 33.3 35.8

Magnesium, filtered (mg/L) 112 12.8 2.99 7.52 7.99

Potassium, filtered (mg/L) 30 2.73 0.94 1.48 1.39

Sodium, filtered (mg/L) 30 16.7 6.12 9.63 9.25

Alkalinity, filtered, lab (mg/L as CaCO3) 30 175 53.3 103 110

Chloride, filtered (mg/L) 30 3.28 0.79 1.82 1.67

Fluoride, filtered (mg/L) 30 0.66 0.15 0.36 0.40

Silica, filtered (mg/L) 30 30.8 18.4 23.3 22.8

Sulfate, filtered (mg/L) 30 36.5 9.21 19.1 19.2

Cadmium, filtered (μg/L) 112 0.12 <0.03 20.04 0.04

Cadmium, unfiltered recoverable (μg/L) 111 0.52 0.02 0.10 0.07

Copper, filtered (μg/L) 112 21.4 0.87 5.1 3.6

Copper, unfiltered recoverable (μg/L) 111 48.8 2.6 10.4 7.7

Iron, filtered (μg/L) 112 274 6.1 53.2 47.4

Iron, unfiltered recoverable (μg/L) 111 1,670 27.4 284 228

Lead, filtered (μg/L) 112 0.89 0.04 20.23 0.20

Lead, unfiltered recoverable (μg/L) 111 14.4 0.27 2.08 1.43

Manganese, filtered (μg/L) 112 200 3.3 32.3 25.7

Manganese, unfiltered recoverable (μg/L) 111 228 4.7 45.3 38.0

Zinc, filtered (μg/L) 112 19.8 <1.4 24.8 3.8

Zinc, unfiltered recoverable (μg/L) 111 68 1.2 11.4 9.0

Arsenic, filtered (μg/L) 112 164 9.3 37.8 26.2

Arsenic, unfiltered recoverable (μg/L) 112 164 11.4 40.2 27.4

Organic carbon, filtered (mg/L) 30 12.9 1.60 4.90 4.20

Sediment, suspended (percent finer than 

0.062 mm)

112 99 54 87 90

Sediment, suspended concentration (mg/L) 112 87 1 10 6

Sediment, suspended discharge (ton/d) 112 11 0.01 0.83 0.17
Data 83

Table 25. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through 

September 2016.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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; --, indicates 

either too few samples (less than three) or insufficient data to compute statistic]

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 2016

Streamflow, instantaneous (ft3/s) 196 1,030 16 138 89

pH, onsite (standard units) 194 9.6 8.0 8.8 8.8

Specific conductance, onsite (μS/cm) 194 783 182 453 460

Temperature, water (°C) 195 25.0 0.0 10.4 10.0

Turbidity, unfiltered, lab (NTRU) 23 11 <2.0 23.7 3.0

Hardness, filtered (mg/L as CaCO3) 194 314 74.9 188 190

Calcium, filtered (mg/L) 194 90.4 22.5 54.5 55.0

Magnesium, filtered (mg/L) 194 21.4 4.52 12.5 12.8

Potassium, filtered (mg/L) 54 8.30 1.72 3.89 3.84

Sodium, filtered (mg/L) 54 23.0 8.20 16.1 17.0

Alkalinity, filtered, lab (mg/L as CaCO3) 26 113 69.2 90.6 94.0

Chloride, filtered (mg/L) 54 26.2 1.30 10.9 10.00

Fluoride, filtered (mg/L) 54 1.20 0.41 0.67 0.66

Silica, filtered (mg/L) 54 20.0 6.30 12.6 12.2

Sulfate, filtered (mg/L) 54 210 39.2 101 93.6

Cadmium, filtered (μg/L) 194 0.31 <0.03 20.06 0.03

Cadmium, unfiltered recoverable (μg/L) 194 0.57 <0.03 20.12 0.07

Copper, filtered (μg/L) 194 40.0 1.6 7.0 5.0

Copper, unfiltered recoverable (μg/L) 194 96.8 2.4 14.3 10.0

Iron, filtered (μg/L) 194 93 <5 221.1 17

Iron, unfiltered recoverable (μg/L) 194 3,000 35.8 308 235

Lead, filtered (μg/L) 194 1.0 <0.08 20.13 0.05

Lead, unfiltered recoverable (μg/L) 194 41.8 <1.00 22.20 1.23

Manganese, filtered (μg/L) 194 875 11.8 109 72.9

Manganese, unfiltered recoverable (μg/L) 194 899 24.0 165 127

Zinc, filtered (μg/L) 194 73 <1.0 26.3 3.5

Zinc, unfiltered recoverable (μg/L) 194 180 2.0 226.5 14.2

Arsenic, filtered (μg/L) 194 60.0 6.8 22.6 22.1

Arsenic, unfiltered recoverable (μg/L) 194 94.0 9.9 26.1 24.4

Organic carbon, filtered (mg/L) 23 5.95 2.88 4.78 4.86

Sediment, suspended (percent finer than 

0.062 mm)

195 98 43 83 86

Sediment, suspended concentration (mg/L) 196 229 1 9 6

Sediment, suspended discharge (ton/d) 196 279 0.05 5.6 1.4
84 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 25. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through 

September 2016.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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; --, indicates 

either too few samples (less than three) or insufficient data to compute statistic]

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 2016

Streamflow, instantaneous (ft3/s) 66 573 41 137 92

pH, onsite (standard units) 66 8.8 7.8 8.4 8.4

Specific conductance, onsite (μS/cm) 66 278 125 221 236

Temperature, water (°C) 66 16.0 0.5 8.2 8.0

Turbidity, unfiltered, lab (NTRU) 60 18 <2.0 22.0 <2.0

Hardness, filtered (mg/L as CaCO3) 66 145 58.5 109 114

Calcium, filtered (mg/L) 66 42.8 18.5 32.6 34.2

Magnesium, filtered (mg/L) 66 9.34 2.96 6.63 6.99

Potassium, filtered (mg/L) 17 1.37 0.80 1.11 1.17

Sodium, filtered (mg/L) 17 3.44 1.54 2.62 2.83

Alkalinity, filtered, lab (mg/L as CaCO3) 17 127 60.3 101 111

Chloride, filtered (mg/L) 17 1.53 0.49 1.00 1.06

Fluoride, filtered (mg/L) 17 0.42 0.29 0.37 0.37

Silica, filtered (mg/L) 17 11.7 8.25 10 9.92

Sulfate, filtered (mg/L) 17 15.9 7.98 12.5 13.0

Cadmium, filtered (μg/L) 66 0.05 <0.02 20.02 0.02

Cadmium, unfiltered recoverable (μg/L) 66 0.14 <0.02 20.03 0.02

Copper, filtered (μg/L) 65 6.4 <0.80 21.1 0.88

Copper, unfiltered recoverable (μg/L) 66 28.0 <0.80 23.2 2.1

Iron, filtered (μg/L) 66 37.0 <4 27.9 6.7

Iron, unfiltered recoverable (μg/L) 66 1,000 19.1 123 75.8

Lead, filtered (μg/L) 66 0.11 <0.02 20.03 <0.08

Lead, unfiltered recoverable (μg/L) 66 3.51 0.07 0.41 0.25

Manganese, filtered (μg/L) 66 4.2 0.13 21.3 1.1

Manganese, unfiltered recoverable (μg/L) 66 45.2 0.90 6.0 4.2

Zinc, filtered (μg/L) 66 5.6 <1.4 21.1 <2.0

Zinc, unfiltered recoverable (μg/L) 66 20.1 <2.0 23.5 2

Arsenic, filtered (μg/L) 66 3.9 1.3 2.2 2.1

Arsenic, unfiltered recoverable (μg/L) 66 5.6 1.5 2.6 2.5

Organic carbon, filtered (mg/L) 17 2.92 0.77 1.42 1.28

Sediment, suspended (percent finer than 

0.062 mm)

66 84 32 66 66

Sediment, suspended concentration (mg/L) 66 65 1 7 4

Sediment, suspended discharge (ton/d) 66 68 0.13 4.2 0.94
Data 85

Table 25. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through 

September 2016.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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; --, indicates 

either too few samples (less than three) or insufficient data to compute statistic]

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 2016

Streamflow, instantaneous (ft3/s) 152 420 2.8 95 57

pH, onsite (standard units) 151 8.7 7.4 8.2 8.2

Specific conductance, onsite (μS/cm) 151 795 139 291 299

Temperature, water (°C) 152 20.0 0.0 8.3 8.0

Turbidity, unfiltered, lab (NTRU) 30 11 <2.0 22.4 <2.0

Hardness, filtered (mg/L as CaCO3) 151 415 39.8 142 146

Calcium, filtered (mg/L) 151 130 10.5 43.3 44.1

Magnesium, filtered (mg/L) 151 22.0 3.29 8.26 8.38

Potassium, filtered (mg/L) 49 4.70 0.83 1.47 1.37

Sodium, filtered (mg/L) 49 19.2 1.78 3.72 3.31

Alkalinity, filtered, lab (mg/L as CaCO3) 32 149 60.1 114 126

Chloride, filtered (mg/L) 49 3.60 0.50 1.28 1.11

Fluoride, filtered (mg/L) 49 0.60 0.30 0.42 0.40

Silica, filtered (mg/L) 49 13.0 8.40 10.4 10.1

Sulfate, filtered (mg/L) 49 270 15.3 46.9 35.8

Cadmium, filtered (μg/L) 150 0.10 <0.03 20.04 0.03

Cadmium, unfiltered recoverable (μg/L) 150 0.41 <0.03 20.08 0.04

Copper, filtered (μg/L) 150 16.0 1.0 3.1 2.7

Copper, unfiltered recoverable (μg/L) 150 147 2.3 17.9 8.6

Iron, filtered (μg/L) 151 36.8 <5.0 212.4 10.8

Iron, unfiltered recoverable (μg/L) 151 2,110 17.2 289 120

Lead, filtered (μg/L) 150 1.8 <0.025 20.07 <1.0

Lead, unfiltered recoverable (μg/L) 150 14.0 <1.00 21.76 0.66

Manganese, filtered (μg/L) 150 570 18.8 102 73.4

Manganese, unfiltered recoverable (μg/L) 150 1,400 37.1 178 131

Zinc, filtered (μg/L) 150 10 <1.0 22.0 1.1

Zinc, unfiltered recoverable (μg/L) 151 60 <2.0 28.4 3.1

Arsenic, filtered (μg/L) 150 14.0 2.0 5.0 4.4

Arsenic, unfiltered recoverable (μg/L) 150 27.0 3.0 7.1 5.9

Organic carbon, filtered (mg/L) 30 3.27 0.88 1.60 1.50

Sediment, suspended (percent finer than 

0.062 mm)

152 95 43 71 71

Sediment, suspended concentration (mg/L) 152 127 1 16 7

Sediment, suspended discharge (ton/d) 152 87 0.03 7.6 1.0
86 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

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 2016

Streamflow, instantaneous (ft3/s) 236 1,380 14 222 144

pH, onsite (standard units) 224 9.2 7.5 8.5 8.6

Specific conductance, onsite (μS/cm) 225 720 182 405 414

Temperature, water (°C) 236 23.5 0.0 9.8 10.0

Hardness, filtered (mg/L as CaCO3) 223 365 76.4 176 182

Calcium, filtered (mg/L) 223 110 23.2 52.2 53.1

Magnesium, filtered (mg/L) 223 22.0 4.44 11.2 11.6

Potassium, filtered (mg/L) 32 5.90 2.00 3.51 3.30

Sodium, filtered (mg/L) 32 19.0 3.60 12.0 12.5

Alkalinity, filtered, lab (mg/L as CaCO3) 3 117 84.4 96.3 87.4

Chloride, filtered (mg/L) 32 11.0 2.00 6.47 6.22

Fluoride, filtered (mg/L) 32 1.10 0.40 0.62 0.60

Silica, filtered (mg/L) 32 17.0 8.10 11.7 11.8

Sulfate, filtered (mg/L) 32 220 34.0 97.2 98.5

Cadmium, filtered (μg/L) 223 1.0 <0.03 20.06 0.03

Cadmium, unfiltered recoverable (μg/L) 223 3.0 <0.10 20.17 0.06

Copper, filtered (μg/L) 223 50.0 1.4 7.1 5.1

Copper, unfiltered recoverable (μg/L) 222 240 4.1 25.0 14.6

Iron, filtered (μg/L) 223 110 <3.0 216.7 13.0

Iron, unfiltered recoverable (μg/L) 223 9,200 56.2 444 265

Lead, filtered (μg/L) 223 3.00 <0.08 20.14 <5.00

Lead, unfiltered recoverable (μg/L) 223 31.0 <1.00 23.15 1.75

Manganese, filtered (μg/L) 223 460 13.1 96.1 69.9

Manganese, unfiltered recoverable (μg/L) 223 1,400 40.9 200 152

Zinc, filtered (μg/L) 223 110 <1.0 27.8 3.4

Zinc, unfiltered recoverable (μg/L) 223 360 2.7 232.8 19.8

Arsenic, filtered (μg/L) 223 53.0 4.0 15.0 14.0

Arsenic, unfiltered recoverable (μg/L) 223 78.0 3.0 18.8 16.9

Sediment, suspended (percent finer than 

0.062 mm)

236 97 32 76 77

Sediment, suspended concentration (mg/L) 237 338 1 17 8

Sediment, suspended discharge (ton/d) 236 459 0.12 19 2.9

Table 25. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through 

September 2016.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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; --, indicates 

either too few samples (less than three) or insufficient data to compute statistic]
Data 87

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 2016

Streamflow, instantaneous (ft3/s) 95 73 0.37 12 9.1

pH, onsite (standard units) 95 8.6 7.4 8.1 8.2

Specific conductance, onsite (μS/cm) 95 253 121 199 212

Temperature, water (°C) 95 17.0 0.0 7.7 8.0

Turbidity, unfiltered, lab (NTRU) 95 24,200 <2.0 2257 <2.0

Hardness, filtered (mg/L as CaCO3) 95 122 50.4 96.2 102

Calcium, filtered (mg/L) 95 37.1 15.7 29.2 30.6

Magnesium, filtered (mg/L) 95 7.47 2.71 5.67 5.96

Potassium, filtered (mg/L) 30 1.51 0.88 1.23 1.26

Sodium, filtered (mg/L) 30 3.68 1.87 2.88 2.86

Alkalinity, filtered, lab (mg/L as CaCO3) 30 118 59.5 96.2 102

Chloride, filtered (mg/L) 30 2.13 0.51 0.78 0.71

Fluoride, filtered (mg/L) 30 0.50 0.28 0.39 0.40

Silica, filtered (mg/L) 30 12.8 9.65 11.4 11.3

Sulfate, filtered (mg/L) 30 13.8 5.89 8.72 8.10

Cadmium, filtered (μg/L) 93 0.90 <0.02 20.04 0.02

Cadmium, unfiltered recoverable (μg/L) 94 147 <0.02 21.6 0.04

Copper, filtered (μg/L) 94 90.5 0.80 2.8 1.7

Copper, unfiltered recoverable (μg/L) 94 29,100 1.3 316 4.5

Iron, filtered (μg/L) 94 26.5 <6.0 210.5 9.4

Iron, unfiltered recoverable (μg/L) 94 99,700 22.3 1,250 115

Lead, filtered (μg/L) 94 0.18 <0.02 20.04 <0.12

Lead, unfiltered recoverable (μg/L) 94 1,290 0.08 14.5 0.49

Manganese, filtered (μg/L) 94 42.4 <0.2 21.8 1.4

Manganese, unfiltered recoverable (μg/L) 94 8,830 1.2 101 5.0

Zinc, filtered (μg/L) 93 30.0 <1.4 21.6 <2.8

Zinc, unfiltered recoverable (μg/L) 93 7,780 <2 287.0 2.2

Arsenic, filtered (μg/L) 94 156 1.8 5.8 3.4

Arsenic, unfiltered recoverable (μg/L) 94 3,860 2.0 45.8 4.0

Organic carbon, filtered (mg/L) 30 3.84 0.87 1.74 1.66

Sediment, suspended (percent finer than 

0.062 mm)

95 97 22 58 61

Sediment, suspended concentration (mg/L) 95 58,900 1 632 6

Sediment, suspended discharge (ton/d) 95 1,320 <0.01 215 0.13

Table 25. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through 

September 2016.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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; --, indicates 

either too few samples (less than three) or insufficient data to compute statistic]
88 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

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 2016

Streamflow, instantaneous (ft3/s) 110 71 1.3 24 18

pH, onsite (standard units) 112 8.7 7.9 8.3 8.3

Specific conductance, onsite (μS/cm) 112 934 540 638 627

Temperature, water (°C) 112 26.5 0.0 10.2 10.0

Turbidity, unfiltered, lab (NTRU) 23 5.4 <2.0 21.8 <2.0

Hardness, filtered (mg/L as CaCO3) 112 451 203 304 301

Calcium, filtered (mg/L) 112 122 48.5 86.2 86.1

Magnesium, filtered (mg/L) 112 35.7 17.3 21.5 20.9

Potassium, filtered (mg/L) 23 3.68 1.89 2.54 2.40

Sodium, filtered (mg/L) 23 31.5 10.1 16.1 12.9

Alkalinity, filtered, lab (mg/L as CaCO3) 23 224 166 191 188

Chloride, filtered (mg/L) 23 5.62 3.90 4.74 4.71

Fluoride, filtered (mg/L) 23 0.82 0.43 0.55 0.50

Silica, filtered (mg/L) 23 23.9 11.7 16.7 16.6

Sulfate, filtered (mg/L) 23 200 95.3 137 134

Cadmium, filtered (μg/L) 110 0.05 <0.02 20.03 0.02

Cadmium, unfiltered recoverable (μg/L) 112 0.12 <0.02 20.04 0.03

Copper, filtered (μg/L) 112 6.7 0.80 2.1 1.8

Copper, unfiltered recoverable (μg/L) 112 22.5 1.5 5.1 4.2

Iron, filtered (μg/L) 112 84.5 4.0 214.7 11.6

Iron, unfiltered recoverable (μg/L) 112 392 14.0 108 83.4

Lead, filtered (μg/L) 111 0.33 <0.025 20.05 0.03

Lead, unfiltered recoverable (μg/L) 112 1.90 0.04 0.40 0.28

Manganese, filtered (μg/L) 112 54.0 1.91 15.9 15.0

Manganese, unfiltered recoverable (μg/L) 112 56.5 2.20 21.0 20.3

Zinc, filtered (μg/L) 111 3.8 <1.0 21.5 1

Zinc, unfiltered recoverable (μg/L) 112 10.3 <2.0 22.9 2.1

Arsenic, filtered (μg/L) 112 41.8 6.0 13.9 12.6

Arsenic, unfiltered recoverable (μg/L) 112 43.0 6.0 14.8 13.0

Organic carbon, filtered (mg/L) 23 4.33 1.28 2.20 2.07

Sediment, suspended (percent finer than 

0.062 mm)

112 94 18 62 64

Sediment, suspended concentration (mg/L) 112 79 2 16 15

Sediment, suspended discharge (ton/d) 110 4.2 0.01 1.0 0.74

Table 25. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through 

September 2016.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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; --, indicates 

either too few samples (less than three) or insufficient data to compute statistic]
Data 89

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 2016

Streamflow, instantaneous (ft3/s) 289 2,000 23 305 229

pH, onsite (standard units) 237 8.9 7.4 8.3 8.3

Specific conductance, onsite (μS/cm) 272 642 228 464 488

Temperature, water (°C) 288 23.0 0.0 10.2 10.5

Turbidity, unfiltered, lab (NTRU) 6 13.0 <2.0 27.8 7.6

Hardness, filtered (mg/L as CaCO3) 229 282 94.9 197 206

Calcium, filtered (mg/L) 229 82.0 28.2 58.2 60.7

Magnesium, filtered (mg/L) 229 18.7 5.53 12.5 13.2

Potassium, filtered (mg/L) 31 6.30 2.40 3.62 3.60

Sodium, filtered (mg/L) 31 25.0 8.60 14.9 14.0

Alkalinity, filtered, lab (mg/L as CaCO3) 3 142 105 119 109

Chloride, filtered (mg/L) 31 12.0 1.20 7.00 7.10

Fluoride, filtered (mg/L) 31 0.70 0.10 0.61 0.60

Silica, filtered (mg/L) 31 34.0 11.0 16.6 16.0

Sulfate, filtered (mg/L) 31 140 44.0 96.2 98.0

Cadmium, filtered (μg/L) 238 2.0 <0.10 20.08 0.04

Cadmium, unfiltered recoverable (μg/L) 238 5.0 <0.10 20.36 0.10

Copper, filtered (μg/L) 239 120 3.2 10.3 7.8

Copper, unfiltered recoverable (μg/L) 237 1,500 8.2 73.4 34.0

Iron, filtered (μg/L) 239 190 <3 215.7 10.0

Iron, unfiltered recoverable (μg/L) 239 29,000 27.2 1,310 494

Lead, filtered (μg/L) 239 6.00 <0.04 20.29 0.04

Lead, unfiltered recoverable (μg/L) 239 200 0.23 29.67 4.08

Manganese, filtered (μg/L) 239 400 1.0 39.6 31.3

Manganese, unfiltered recoverable (μg/L) 239 4,600 6.8 208 120

Zinc, filtered (μg/L) 239 230 <2.0 210.6 7.0

Zinc, unfiltered recoverable (μg/L) 237 1,700 3.0 75.0 35.8

Arsenic, filtered (μg/L) 239 39.0 6.0 14.3 13.2

Arsenic, unfiltered recoverable (μg/L) 238 215 4.8 22.9 17.0

Sediment, suspended (percent finer than 

0.062 mm)

280 99 31 72 74

Sediment, suspended concentration (mg/L) 289 2,250 1 63 21

Sediment, suspended discharge (ton/d) 289 8,690 0.18 130 12

Table 25. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through 

September 2016.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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; --, indicates 

either too few samples (less than three) or insufficient data to compute statistic]
90 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 25. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through 

September 2016.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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; --, indicates 

either too few samples (less than three) or insufficient data to compute statistic]

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 2016

Streamflow, instantaneous (ft3/s) 62 2,310 66 427 306

pH, onsite (standard units) 62 8.9 7.9 8.4 8.4

Specific conductance, onsite (μS/cm) 62 530 249 416 444

Temperature, water (°C) 62 22.0 1.0 12.0 12.8

Hardness, filtered (mg/L as CaCO3) 62 236 104 184 198

Calcium, filtered (mg/L) 62 69.4 31.8 53.6 57.2

Magnesium, filtered (mg/L) 62 15.8 5.93 12.1 13.2

Cadmium, filtered (μg/L) 62 0.23 0.02 0.07 0.06

Cadmium, unfiltered recoverable (μg/L) 62 0.84 0.03 0.24 0.18

Copper, filtered (μg/L) 62 40.6 2.8 9.3 7.9

Copper, unfiltered recoverable (μg/L) 62 222 9.7 55.8 33.8

Iron, filtered (μg/L) 61 64.4 4.5 17.6 13.5

Iron, unfiltered recoverable (μg/L) 61 3,860 21.5 850 541

Lead, filtered (μg/L) 62 0.72 0.04 0.17 0.13

Lead, unfiltered recoverable (μg/L) 62 32.3 0.15 7.2 4.08

Manganese, filtered (μg/L) 62 65.1 4.68 27.5 23.4

Manganese, unfiltered recoverable (μg/L) 62 344 10.3 115 100

Zinc, filtered (μg/L) 62 37.1 <2.0 25.6 4.9

Zinc, unfiltered recoverable (μg/L) 62 181 3.0 45.2 28.8

Arsenic, filtered (μg/L) 62 36.7 7.8 15.0 15.2

Arsenic, unfiltered recoverable (μg/L) 62 46.0 10.5 20.9 17.9

Sediment, suspended (percent finer than 

0.062 mm)

62 92 42 73 76

Sediment, suspended concentration (mg/L) 62 205 1 41 22

Sediment, suspended discharge (ton/d) 62 550 0.31 75 22
Data 91

Table 25. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through 

September 2016.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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; --, indicates 

either too few samples (less than three) or insufficient data to compute statistic]

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 2016

Streamflow, instantaneous (ft3/s) 195 4,450 87 757 513

pH, onsite (standard units) 194 9.1 7.9 8.4 8.3

Specific conductance, onsite (μS/cm) 194 510 206 366 376

Temperature, water (°C) 195 23.0 0.0 10.4 10.5

Hardness, filtered (mg/L as CaCO3) 194 232 85.8 161 169

Calcium, filtered (mg/L) 194 68.0 25.9 47.6 49.4

Magnesium, filtered (mg/L) 194 15.0 5.15 10.3 10.7

Potassium, filtered (mg/L) 28 6.90 2.00 3.11 3.00

Sodium, filtered (mg/L) 28 19.0 6.90 11.5 12.0

Chloride, filtered (mg/L) 28 7.20 2.50 4.73 4.40

Fluoride, filtered (mg/L) 28 0.60 0.10 0.43 0.40

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) 194 0.2 <0.02 20.04 0.03

Cadmium, unfiltered recoverable (μg/L) 194 2.0 <0.10 20.17 0.08

Copper, filtered (μg/L) 193 36.0 2.1 6.5 5.2

Copper, unfiltered recoverable (μg/L) 193 440 5.2 37.5 21.4

Iron, filtered (μg/L) 193 100 <3 219.9 12.9

Iron, unfiltered recoverable (μg/L) 194 12,000 27.3 801 410

Lead, filtered (μg/L) 191 0.68 <0.04 20.12 <1.00

Lead, unfiltered recoverable (μg/L) 193 73.0 0.14 25.20 2.76

Manganese, filtered (μg/L) 194 57.3 4.0 18.5 16.4

Manganese, unfiltered recoverable (μg/L) 194 1,100 9.3 111 80.2

Zinc, filtered (μg/L) 194 26 <1.0 25.1 3.5

Zinc, unfiltered recoverable (μg/L) 194 510 2.0 39.4 26.2

Arsenic, filtered (μg/L) 194 22.5 5.6 10.0 9.8

Arsenic, unfiltered recoverable (μg/L) 194 75.0 7.0 14.3 12.0

Sediment, suspended (percent finer than 

0.062 mm)

195 94 43 76 78

Sediment, suspended concentration (mg/L) 195 752 1 44 19

Sediment, suspended discharge (ton/d) 195 7,960 0.55 185 27
92 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 25. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through 

September 2016.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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; --, indicates 

either too few samples (less than three) or insufficient data to compute statistic]

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 2016

Streamflow, instantaneous (ft3/s) 195 5,540 149 1,030 768

pH, onsite (standard units) 194 8.7 7.8 8.3 8.2

Specific conductance, onsite (μS/cm) 194 630 189 407 418

Temperature, water (°C) 195 22.5 0.5 11.1 11.0

Hardness, filtered (mg/L as CaCO3) 194 298 73.9 184 190

Calcium, filtered (mg/L) 194 83.0 21.0 52.6 54.4

Magnesium, filtered (mg/L) 194 22.0 5.2 12.7 13.0

Potassium, filtered (mg/L) 28 10.0 2.10 3.67 3.40

Sodium, filtered (mg/L) 28 20.0 5.60 11.5 12.0

Chloride, filtered (mg/L) 28 7.80 2.70 4.83 4.65

Fluoride, filtered (mg/L) 28 0.50 0.20 0.39 0.40

Silica, filtered (mg/L) 28 24.0 10.0 18.7 18.5

Sulfate, filtered (mg/L) 28 130 25.0 64.8 64.5

Cadmium, filtered (μg/L) 193 0.30 <0.03 20.05 0.03

Cadmium, unfiltered recoverable (μg/L) 194 2.0 <0.03 20.21 0.09

Copper, filtered (μg/L) 191 21.0 1.0 6.2 4.9

Copper, unfiltered recoverable (μg/L) 192 360 4.6 39.5 21.8

Iron, filtered (μg/L) 194 150 <3 218.6 10.0

Iron, unfiltered recoverable (μg/L) 193 8,800 19.7 923 457

Lead, filtered (μg/L) 190 1.2 <0.04 20.16 0.05

Lead, unfiltered recoverable (μg/L) 190 56.0 0.17 26.96 3.38

Manganese, filtered (μg/L) 193 60.7 3.3 16.4 14.6

Manganese, unfiltered recoverable (μg/L) 194 880 8.0 134 88.4

Zinc, filtered (μg/L) 194 21.0 <1.4 25.5 4.2

Zinc, unfiltered recoverable (μg/L) 194 490 2.9 53.4 30.0

Arsenic, filtered (μg/L) 194 23.9 3.2 10.4 10.0

Arsenic, unfiltered recoverable (μg/L) 194 62 7.7 15.5 12.8

Sediment, suspended (percent finer than 

0.062 mm)

195 93 38 74 75

Sediment, suspended concentration (mg/L) 195 530 2 57 25

Sediment, suspended discharge (ton/d) 195 4,720 1.7 284 46
Data 93

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 2016

Streamflow, instantaneous (ft3/s) 292 10,600 296 1,950 1,190

pH, onsite (standard units) 238 8.8 7.4 8.2 8.2

Specific conductance, onsite (μS/cm) 267 483 139 296 308

Temperature, water (°C) 291 22.0 0.0 9.6 10.0

Hardness, filtered (mg/L as CaCO3) 228 205 53.6 130 132

Calcium, filtered (mg/L) 228 59.0 14.9 36.6 37.0

Magnesium, filtered (mg/L) 228 14.0 3.95 9.38 9.40

Potassium, filtered (mg/L) 32 5.70 1.51 2.45 2.45

Sodium, filtered (mg/L) 32 12.0 3.34 7.95 8.45

Alkalinity, filtered, lab (mg/L as CaCO3) 4 155 52.5 108 111

Chloride, filtered (mg/L) 32 5.60 1.50 3.13 2.95

Fluoride, filtered (mg/L) 32 0.40 0.17 0.29 0.30

Silica, filtered (mg/L) 32 19.0 12.0 14.9 15.0

Sulfate, filtered (mg/L) 32 68.0 12.6 41.8 41.0

Nitrate plus nitrite, filtered (mg/L) 8 0.069 <0.013 20.027 0.012

Phosphorus, unfiltered (mg/L) 10 0.240 0.014 0.080 0.068

Total nitrogen, unfiltered (mg/L) 2 0.49 0.38 0.44 --

Cadmium, filtered (μg/L) 236 0.10 <0.02 20.03 <1

Cadmium, unfiltered recoverable (μg/L) 237 4.00 <0.01 20.22 0.04

Copper, filtered (μg/L) 236 25.0 1.1 4.5 3.4

Copper, unfiltered recoverable (μg/L) 235 500 2.7 30.2 14.0

Iron, filtered (μg/L) 237 359 <3 224.5 14.3

Iron, unfiltered recoverable (μg/L) 237 19,000 32.6 898 356

Lead, filtered (μg/L) 233 7.00 <.02 20.25 <1.00

Lead, unfiltered recoverable (μg/L) 233 100 <1.00 26.04 2.30

Manganese, filtered (μg/L) 237 48.6 <1.0 28.3 7.0

Manganese, unfiltered recoverable (μg/L) 237 2,000 8.8 108 57.3

Zinc, filtered (μg/L) 235 39 <2.0 25.4 3.8

Zinc, unfiltered recoverable (μg/L) 237 1,100 2.9 250.9 22.0

Arsenic, filtered (μg/L) 237 17.0 2.7 6.0 5.5

Arsenic, unfiltered recoverable (μg/L) 237 110 3.0 9.2 7.0

Sediment, suspended (percent finer than 

0.062 mm)

281 98 27 74 76

Sediment, suspended concentration (mg/L) 292 1,370 2 52 18

Sediment, suspended discharge (ton/d) 292 34,700 3.0 575 60

Table 25. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through 

September 2016.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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; --, indicates 

either too few samples (less than three) or insufficient data to compute statistic]
94 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 25. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through 

September 2016.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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; --, indicates 

either too few samples (less than three) or insufficient data to compute statistic]

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 2016

Streamflow, instantaneous (ft3/s) 214 13,400 344 2,750 1,380

pH, onsite (standard units) 174 8.7 7.5 8.3 8.3

Specific conductance, onsite (μS/cm) 191 294 131 209 204

Temperature, water (°C) 214 22.5 0.0 9.7 10.0

Turbidity, unfiltered, lab (NTRU) 7 30 <2.0 27.2 2.0

Hardness, filtered (mg/L as CaCO3) 166 146 55.1 104 98.6

Calcium, filtered (mg/L) 166 37.7 14.0 26.6 25.4

Magnesium, filtered (mg/L) 166 13.2 4.90 9.19 8.66

Potassium, filtered (mg/L) 26 2.80 0.48 0.87 0.80

Sodium, filtered (mg/L) 26 3.41 1.17 2.46 2.50

Alkalinity, filtered, lab (mg/L as CaCO3) 9 148 71.5 117 131

Chloride, filtered (mg/L) 26 1.60 0.23 0.64 0.58

Fluoride, filtered (mg/L) 26 0.10 <0.10 20.10 <0.10

Silica, filtered (mg/L) 26 12.0 6.80 8.64 8.10

Sulfate, filtered (mg/L) 26 6.60 1.10 4.58 4.80

Nitrate plus nitrite, filtered (mg/L) 30 0.040 <0.005 20.010 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) 172 1.00 <0.02 20.02 <0.10

Cadmium, unfiltered recoverable (μg/L) 174 2.00 <0.01 20.08 <0.10

Copper, filtered (μg/L) 170 7.0 <0.80 21.2 0.60

Copper, unfiltered recoverable (μg/L) 171 34.0 <0.70 24.0 1.6

Iron, filtered (μg/L) 173 104 <3 217.5 10.2

Iron, unfiltered recoverable (μg/L) 174 3,600 13.9 380 163

Lead, filtered (μg/L) 168 8.00 <0.02 20.25 <0.50

Lead, unfiltered recoverable (μg/L) 169 25.0 <0.04 21.86 0.09

Manganese, filtered (μg/L) 173 11.0 <1.0 22.4 2.0

Manganese, unfiltered recoverable (μg/L) 174 180 <10.0 226.4 13.6

Zinc, filtered (μg/L) 172 15.0 <0.60 21.8 <3.0

Zinc, unfiltered recoverable (μg/L) 174 60.0 <1.0 24.6 <10.0

Arsenic, filtered (μg/L) 173 2.0 <1.0 20.96 0.96

Arsenic, unfiltered recoverable (μg/L) 174 4.0 <1.0 21.3 1.0

Sediment, suspended (percent finer than 

0.062 mm)

212 98 42 80 82

Sediment, suspended concentration (mg/L) 214 271 1 27 8

Sediment, suspended discharge (ton/d) 214 7,670 1.1 486 31
Data 95

Table 25. Statistical summary of long-term water-quality data for the Clark Fork Basin, Montana, March 1985 through 

September 2016.—Continued

[ft3/s, cubic foot per second; μS/cm, microsiemen per centimeter at 25 °C; °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; --, indicates 

either too few samples (less than three) or insufficient data to compute statistic]

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 2016

Streamflow, instantaneous (ft3/s) 257 22,900 720 4,600 2,520

pH, onsite (standard units) 215 8.8 7.9 8.3 8.3

Specific conductance, onsite (μS/cm) 235 399 142 250 259

Temperature, water (°C) 255 22.0 0.0 9.8 10.0

Turbidity, unfiltered, lab (NTRU) 40 100 <2.0 213.0 4.9

Hardness, filtered (mg/L as CaCO3) 215 168 60.5 116 117

Calcium, filtered (mg/L) 215 46.0 14.0 31.4 31.5

Magnesium, filtered (mg/L) 215 13.4 5.28 9.19 9.15

Potassium, filtered (mg/L) 28 4.50 0.90 1.72 1.50

Sodium, filtered (mg/L) 28 7.80 2.40 5.29 5.35

Chloride, filtered (mg/L) 28 4.20 0.90 1.92 1.80

Fluoride, filtered (mg/L) 28 0.30 <0.10 20.19 0.20

Silica, filtered (mg/L) 28 16.0 9.40 11.8 11.0

Sulfate, filtered (mg/L) 28 43.0 9.30 23.3 23.0

Phosphorus, unfiltered (mg/L) 2 0.102 0.066 0.084 --

Total nitrogen, unfiltered (mg/L) 2 0.470 0.320 0.395 --

Cadmium, filtered (μg/L) 214 0.20 <0.02 20.03 <0.10

Cadmium, unfiltered recoverable (μg/L) 215 5.0 <0.01 20.13 <1.0

Copper, filtered (μg/L) 214 12.6 0.7 2.7 2.0

Copper, unfiltered recoverable (μg/L) 213 400 1.9 17.4 8.0

Iron, filtered (μg/L) 215 200 <3 221.2 14.9

Iron, unfiltered recoverable (μg/L) 215 13,000 40.9 575 247

Lead, filtered (μg/L) 208 1.20 <0.02 20.12 <1.00

Lead, unfiltered recoverable (μg/L) 210 78.0 <1.00 23.06 1.27

Manganese, filtered (μg/L) 215 230 3.5 14.4 12.5

Manganese, unfiltered recoverable (μg/L) 215 1,100 8.8 59.9 39.8

Zinc, filtered (μg/L) 214 16.0 <1.0 23.2 2.1

Zinc, unfiltered recoverable (μg/L) 215 1,100 <3.0 229.4 12.0

Arsenic, filtered (μg/L) 215 9.0 1.0 3.4 3.1

Arsenic, unfiltered recoverable (μg/L) 215 69.0 1.0 5.1 4.0

Sediment, suspended (percent finer than 

0.062 mm)

253 99 14 82 87

Sediment, suspended concentration (mg/L) 258 950 2 41 12

Sediment, suspended discharge (ton/d) 257 21,900 5.8 1,020 85

1

Differing less-than (<) values for an individual constituent are the result of changes in the laboratory reporting level during the period of record.

2

Value for the mean is estimated by using a log-probability regression to predict the values of data less than the laboratory reporting level (Helsel and Cohn, 

1988). Minimum values that are not censored when the mean indicates that a censored value was used in the mean calculation are a result of changes in the 

laboratory reporting level during the period of record.
96 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Table 26. Statistical summary of long-term bed-sediment data for the Clark Fork Basin, Montana, August 1986 through August 2016.

[Reported concentrations are in microgram per gram dry weight (μg/g). 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. <, 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: 1992–2016

Arsenic 14 186 20 89 66

Cadmium 25 43.9 5.9 24.9 26.0

Chromium 23 50.7 16.8 29.2 25.9

Copper 25 9,020 446 3,340 3,570

Iron 25 45,300 28,200 34,500 33,200

Lead 25 1,030 93 517 503

Manganese 25 9,220 1,160 3,270 2,770

Nickel 24 21.4 12.0 14.9 14.8

Silver 12 20.0 8.3 15.5 15.8

Zinc 25 13,400 1,490 5,950 6,660

12323750—Silver Bow Creek at Warm Springs

Period of record for bed-sediment data: 1992–2016

Arsenic 14 177 66 111 101

Cadmium 25 12.2 4.2 6.8 6.4

Chromium 23 46.8 <15.7 123.6 122.9

Copper 25 769 169 335 294

Iron 25 32,500 15,400 23,900 23,800

Lead 25 121 49 73 73

Manganese 25 17,700 1,470 7,300 7,230

Nickel 24 20.0 9.2 14.9 14.7

Silver 12 4.4 0.3 11.9 11.8

Zinc 25 2,220 554 873 686

12323770—Warm Springs Creek at Warm Springs

Period of record for bed-sediment data: 1995, 1997, 1999, 2002, 2005, 2008, 2011, 2014

Arsenic 4 66 34 54 58

Cadmium 8 5.8 1.2 3.2 3.1

Chromium 8 39.3 24.1 31.1 31.1

Copper 8 1,060 496 839 864

Iron 8 26,600 16,800 21,500 21,900

Lead 8 86 42 75 81

Manganese 8 12,100 555 6,620 6,900

Nickel 8 25.5 14.5 19.6 19.4

Silver 4 5.1 3.1 3.8 3.5

Zinc 8 453 237 379 385
Data 97

Constituent Number of samples Maximum Minimum Mean Median

12323800—Clark Fork near Galen

Period of record for bed-sediment data: 1987, 1991–2016

Arsenic 14 156 73 108 105

Cadmium 27 20.1 3.8 7.6 6.4

Chromium 23 44.6 18.1 28.5 26.4

Copper 27 2,300 791 1,170 1,110

Iron 27 39,800 22,600 27,800 27,000

Lead 27 235 92 128 126

Manganese 27 17,300 1,530 8,420 6,380

Nickel 24 23.2 13.9 18.7 18.6

Silver 14 7.3 <3.2 14.4 14.5

Zinc 27 3,560 721 1,320 1,090

461415112450801—Clark Fork below Lost Creek, near Galen

Period of record for bed-sediment data: 1996–2016

Arsenic 14 204 90 124 110

Cadmium 21 10.5 4.8 6.6 6.2

Chromium 20 42.4 16.4 28.5 27.3

Copper 21 2,050 1,150 1,490 1,450

Iron 21 32,800 24,400 28,900 28,800

Lead 21 218 123 162 161

Manganese 21 9,820 1,430 5,250 5,000

Nickel 21 19.9 11.7 15.8 16.3

Silver 8 7.8 4.2 6.5 6.7

Zinc 21 1,680 930 1,250 1,210

461559112443301—Clark Fork at county bridge, near Racetrack

Period of record for bed-sediment data: 1996–2016

Arsenic 14 132 56 92 90

Cadmium 21 8.7 3.6 6.2 5.9

Chromium 20 45.2 13.9 27.6 26.3

Copper 21 1,810 818 1,250 1,270

Iron 21 31,700 21,200 27,100 28,100

Lead 21 186 103 140 137

Manganese 21 6,310 1,600 3,220 3,060

Nickel 21 18.4 10.3 14.1 14.5

Silver 8 6.1 <3.3 15.0 15.4

Zinc 21 1,550 816 1,140 1,130

Table 26. Statistical summary of long-term bed-sediment data for the Clark Fork Basin, Montana, August 1986 through August 2016.—

Continued

[Reported concentrations are in microgram per gram dry weight (μg/g). 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. <, less than the minimum reporting level; --, indicates insufficient data (less than three samples) to compute statistic]
98 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Constituent Number of samples Maximum Minimum Mean Median

461903112440701—Clark Fork at Dempsey Creek diversion, near Racetrack

Period of record for bed-sediment data: 1996–2016

Arsenic 14 109 58 81 80

Cadmium 21 10.3 4.1 6.0 5.2

Chromium 20 39.2 14.5 26.1 24.8

Copper 21 1,580 721 1,100 1,090

Iron 21 33,700 20,600 26,900 26,100

Lead 21 155 92 129 132

Manganese 21 8,370 1,200 3,640 3,080

Nickel 21 16.9 8.7 12.7 12.4

Silver 8 6.2 2.7 4.9 5.0

Zinc 21 1,570 900 1,100 1,080

12324200—Clark Fork at Deer Lodge

Period of record for bed-sediment data: 1986–87, 1990–2016

Arsenic 14 102 49 74 71

Cadmium 29 10.0 3.5 5.8 5.0

Chromium 23 50.7 17.0 31.0 28.2

Copper 29 4,180 683 1,220 1,060

Iron 29 35,300 20,500 27,100 26,100

Lead 29 242 103 141 138

Manganese 29 6,020 1,070 2,580 2,410

Nickel 24 21.1 11.5 14.6 13.9

Silver 16 7.9 2.4 4.7 4.5

Zinc 29 1,730 844 1,150 1,050

12324400—Clark Fork above Little Blackfoot River, near Garrison

Period of record for bed-sediment data: 2009–2016

Arsenic 8 91 49 69 69

Cadmium 8 5.5 4.1 4.6 4.4

Chromium 8 52.8 15.0 33.4 32.6

Copper 8 1,290 666 1,020 1,030

Iron 8 32,400 16,800 25,000 25,400

Lead 8 145 92 120 120

Manganese 8 3,560 1,150 2,530 2,660

Nickel 8 17.2 9.2 13.1 13.2

Silver 0 -- -- -- --

Zinc 8 1,240 780 1,010 1,040

Table 26. Statistical summary of long-term bed-sediment data for the Clark Fork Basin, Montana, August 1986 through August 2016.—

Continued

[Reported concentrations are in microgram per gram dry weight (μg/g). 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. <, less than the minimum reporting level; --, indicates insufficient data (less than three samples) to compute statistic]
Data 99

Constituent Number of samples Maximum Minimum Mean Median

12324680—Clark Fork at Goldcreek

Period of record for bed-sediment data: 1992–2016

Arsenic 14 62 23 40 37

Cadmium 25 8.1 2.0 4.3 3.8

Chromium 23 55.3 9.9 31.3 29.4

Copper 25 1,080 281 652 675

Iron 25 32,100 11,500 22,900 23,700

Lead 25 152 45 91 93

Manganese 25 2,730 977 1,830 1,840

Nickel 24 18.6 7.6 13.4 13.7

Silver 12 4.8 2.3 3.2 3.2

Zinc 25 1,320 427 867 869

12331800—Clark Fork near Drummond

Period of record for bed-sediment data: 1986–87, 1991–2016

Arsenic 14 66 17 37 32

Cadmium 28 7.7 1.7 4.0 4.0

Chromium 23 41.9 9.2 26.7 27.0

Copper 28 747 183 459 452

Iron 28 44,000 14,800 24,300 21,800

Lead 28 135 27 83 82

Manganese 28 4,820 832 2,010 1,840

Nickel 24 16.8 4.8 12.6 13.1

Silver 15 4.7 <3.2 13.0 12.9

Zinc 28 1,230 380 893 943

12334550—Clark Fork at Turah Bridge, near Bonner

Period of record for bed-sediment data: 1986, 1991–2016

Arsenic 14 43 17 26 23

Cadmium 27 7.3 1.2 3.2 3.1

Chromium 23 42.5 13.6 25.8 26.7

Copper 27 635 211 336 322

Iron 27 25,900 12,600 19,000 17,300

Lead 27 115 37 64 62

Manganese 27 2,340 383 1,200 1,130

Nickel 24 19.1 6.9 12.1 11.4

Silver 14 3.9 <1.9 12.1 11.9

Zinc 27 1,160 448 751 759

Table 26. Statistical summary of long-term bed-sediment data for the Clark Fork Basin, Montana, August 1986 through August 2016.—

Continued

[Reported concentrations are in microgram per gram dry weight (μg/g). 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. <, less than the minimum reporting level; --, indicates insufficient data (less than three samples) to compute statistic]
100 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Constituent Number of samples Maximum Minimum Mean Median

12340000—Blackfoot River near Bonner

Period of record for bed-sediment data: 1986–87, 1991, 1993–96, 1998–2001, 2003, 2006–16

Arsenic 12 6 <0.2 14 14

Cadmium 23 2.0 <0.1 10.4 10.2

Chromium 19 35.2 13.3 21.5 22.0

Copper 23 27 11 20 21

Iron 23 23,000 12,400 17,500 18,100

Lead 23 20 <13 112 111

Manganese 23 746 298 520 542

Nickel 20 14.3 6.0 11.2 11.4

Silver 12 <1.9 <0.3 10.5 10.3

Zinc 23 82 35 60 60

12340500—Clark Fork above Missoula

Period of record for bed-sediment data: 1997–2016

Arsenic 14 54 12 27 26

Cadmium 20 5.8 1.0 2.6 2.6

Chromium 19 40.7 12.8 25.3 26.2

Copper 20 551 125 313 281

Iron 20 27,000 13,800 19,900 19,900

Lead 20 78 25 49 49

Manganese 20 2,250 477 1,050 942

Nickel 20 15.8 7.6 12.2 12.1

Silver 7 2.9 0.8 12.0 12.1

Zinc 20 1,090 343 646 611

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.

Table 26. Statistical summary of long-term bed-sediment data for the Clark Fork Basin, Montana, August 1986 through August 2016.—

Continued

[Reported concentrations are in microgram per gram dry weight (μg/g). 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. <, less than the minimum reporting level; --, indicates insufficient data (less than three samples) to compute statistic]
Data 101

Table 27. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2016.

[Reported concentrations are in microgram per gram dry weight (μg/g). 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 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche species combined. At some sites, statistics of 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, 1994–95, 1997–2016

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 11.3 11.6

Zinc 5 995 629 803 815

Hydropsyche cockerelli

Arsenic 28 33.3 4.3 10.7 8.6

Cadmium 34 9.7 2.4 4.9 4.7

Chromium 34 25.5 1.0 4.2 3.9

Copper 34 1,090 78.6 299 298

Iron 34 6,150 689 2,710 2,470

Lead 34 74.3 11.8 30.4 21.3

Manganese 34 4,000 180 1,300 1,150

Nickel 34 4.3 0.7 2.8 2.9

Zinc 34 1,590 432 772 745

Hydropsyche spp.

Arsenic 14 23.1 6.1 12.1 10.7

Cadmium 19 11.0 2.0 5.4 5.0

Chromium 19 4.7 0.6 2.6 3.0

Copper 19 930 80.7 428 352

Iron 19 3,630 1,050 2,260 2,210

Lead 19 237 19.3 45.5 36.5

Manganese 19 1,790 612 1,040 1,040

Nickel 19 4.1 0.7 2.2 2.3

Zinc 19 1,290 388 875 876

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

Constituent Number of composite 

samples Maximum Minimum Mean Median

12323750—Silver Bow Creek at Warm Springs

Period of record for biological data: 1992–2016

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 25 23.6 7.9 12.4 11.8

Cadmium 51 2.1 0.2 0.6 0.5

Chromium 51 4.3 0.4 1.2 1.0

Copper 51 97.0 16.7 35.9 31.1

Iron 51 1,650 351 835 799

Lead 51 6.0 0.3 3.2 3.0

Manganese 51 3,890 491 1,240 1,010

Nickel 51 1.8 0.3 1.0 0.9

Zinc 51 276 115 175 169

Hydropsyche occidentalis

Arsenic 10 31.0 10.5 18.6 16.8

Cadmium 25 1.6 0.2 0.7 0.4

Chromium 25 6.8 0.3 2.0 1.0

Copper 25 48.9 11.0 33.7 32.8

Iron 25 2,960 372 1,260 1,010

Lead 25 8.2 <1.7 14.0 13.7

Manganese 25 6,940 996 2,400 1,940

Nickel 25 3.2 0.7 1.5 1.5

Zinc 25 220 140 182 183

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 11.0 10.8

Zinc 5 284 141 188 162

Table 27. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2016.—

Continued

[Reported concentrations are in microgram per gram dry weight (μg/g). 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 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche species combined. At some sites, statistics of 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]
Data 103

Constituent Number of composite 

samples Maximum Minimum Mean Median

12323770—Warm Springs Creek at Warm Springs

Period of record for biological data: 1995, 1997, 1999, 2002, 2005, 2008, 2011, 2014

Arctopsyche grandis

Arsenic 5 9.8 7.6 8.9 9.5

Cadmium 9 3.6 0.4 2.5 2.5

Chromium 9 5.0 0.8 2.7 2.8

Copper 9 132 53.2 102 102

Iron 9 1,490 684 1,030 1,040

Lead 9 7.7 3.0 15.6 15.3

Manganese 9 3,560 738 2,230 2,280

Nickel 9 4.0 1.1 12.5 12.3

Zinc 9 267 181 206 197

Hesperoperla spp.

Arsenic 2 2.9 1.2 2.0 --

Cadmium 2 2.6 1.0 1.8 --

Chromium 2 2.0 0.9 1.4 --

Copper 2 64.9 55.9 60.4 --

Iron 2 456 375 416 --

Lead 2 1.9 1.4 1.6 --

Manganese 2 270 202 236 --

Nickel 2 1.1 0.6 0.8 --

Zinc 2 573 427 500 --

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 0 -- -- -- --

Cadmium 2 1.1 0.6 0.8 --

Chromium 2 1.6 1.4 1.5 --

Copper 2 95.9 94.8 95.4 --

Iron 2 1,220 1,150 1,180 --

Lead 2 5.9 5.2 5.6 --

Manganese 2 3,390 956 2,170 --

Nickel 2 2.0 1.8 1.9 --

Zinc 2 129 125 127 --

Table 27. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2016.—

Continued

[Reported concentrations are in microgram per gram dry weight (μg/g). 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 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche species combined. At some sites, statistics of 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]
104 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Constituent Number of composite 

samples Maximum Minimum Mean Median

12323800—Clark Fork near Galen

Period of record for biological data: 1987, 1991–2016

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 19 20.5 13.2 15.3 14.2

Cadmium 44 2.7 0.7 1.6 1.5

Chromium 44 9.6 0.7 2.4 2.2

Copper 44 181 48.7 109 116

Iron 44 2,660 816 1,610 1,520

Lead 44 17.1 1.2 9.2 8.8

Manganese 44 3,620 1,070 2,270 2,270

Nickel 44 6.5 0.9 2.2 1.8

Zinc 44 536 136 230 224

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

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

Table 27. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2016.—

Continued

[Reported concentrations are in microgram per gram dry weight (μg/g). 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 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche species combined. At some sites, statistics of 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]
Data 105

Constituent Number of composite 

samples Maximum Minimum Mean Median

12323800—Clark Fork near Galen—Continued

Period of record for biological data: 1987, 1991–2016

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 5 15.7 5.5 11.1 14.2

Cadmium 9 3.5 0.7 1.8 1.3

Chromium 5 2.4 1.1 1.8 1.9

Copper 9 154 55.3 110 126

Iron 9 2,110 914 1,350 1,300

Lead 9 13.5 3.8 9.0 10.5

Manganese 5 4,760 668 2,410 1,520

Nickel 5 2.7 0.9 1.6 1.5

Zinc 9 329 132 239 228

461415112450801—Clark Fork below Lost Creek, near Galen

Period of record for biological data: 1996–2016

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 10.2 --

Zinc 2 245 208 226 --

Hydropsyche cockerelli

Arsenic 22 27.8 8.8 16.6 17.1

Cadmium 33 3.7 1.1 1.9 1.8

Chromium 33 5.5 0.8 2.4 2.5

Copper 33 338 48.8 155 141

Iron 33 4,080 691 1,850 1,840

Lead 33 28.6 3.0 13.8 13.3

Manganese 33 3,160 1,230 1,820 1,720

Nickel 33 4.5 0.9 1.8 1.7

Zinc 33 339 151 244 248

Table 27. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2016.—

Continued

[Reported concentrations are in microgram per gram dry weight (μg/g). 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 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche species combined. At some sites, statistics of 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]
106 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Constituent Number of composite 

samples Maximum Minimum Mean Median

461415112450801—Clark Fork below Lost Creek, near Galen—Continued

Period of record for biological data: 1996–2016

Hydropsyche occidentalis

Arsenic 12 20.9 12.7 16.3 15.8

Cadmium 26 2.1 0.5 1.4 1.4

Chromium 26 6.5 1.2 2.4 2.1

Copper 26 219 52.1 123 121

Iron 26 2,830 963 1,680 1,580

Lead 26 20.4 6.6 11.7 11.1

Manganese 26 4,150 1,220 2,520 2,240

Nickel 26 3.9 0.5 1.7 1.5

Zinc 26 330 174 252 251

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 --

Table 27. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2016.—

Continued

[Reported concentrations are in microgram per gram dry weight (μg/g). 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 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche species combined. At some sites, statistics of 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]
Data 107

Constituent Number of composite 

samples Maximum Minimum Mean Median

461559112443301—Clark Fork at county bridge, near Racetrack

Period of record for biological data: 1996–2016

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

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 19 20.2 11.1 14.3 13.8

Cadmium 30 2.8 0.8 1.7 1.6

Chromium 30 3.0 0.6 1.9 2.2

Copper 30 198 50.0 108 104

Iron 30 3,330 657 1,430 1,180

Lead 30 18.7 3.7 9.8 9.0

Manganese 30 2,360 646 1,680 1,860

Nickel 30 2.0 0.7 1.6 1.3

Zinc 30 302 139 210 196

Hydropsyche occidentalis

Arsenic 17 16.8 9.2 13.0 12.8

Cadmium 30 2.3 0.7 1.4 1.4

Chromium 30 3.7 1.1 2.1 2.0

Copper 30 164 59.5 114 116

Iron 30 3,690 1,030 1,650 1,550

Lead 30 15.7 4.3 10.8 10.7

Manganese 30 3,770 660 2,010 1,910

Nickel 30 2.5 1.1 1.5 1.4

Zinc 30 361 181 234 229

Table 27. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2016.—

Continued

[Reported concentrations are in microgram per gram dry weight (μg/g). 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 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche species combined. At some sites, statistics of 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]
108 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Constituent Number of composite 

samples Maximum Minimum Mean Median

461559112443301—Clark Fork at county bridge, near Racetrack—Continued

Period of record for biological data: 1996–2016

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: 1996–2016

Arctopsyche grandis

Arsenic 11 17.5 4.4 7.3 5.9

Cadmium 12 7.1 0.9 2.6 2.1

Chromium 12 12.9 0.7 12.2 10.9

Copper 12 196 30.8 69.2 49.0

Iron 12 2,800 333 742 456

Lead 12 17.6 2.1 16.8 15.2

Manganese 12 2,060 510 1,070 1,010

Nickel 12 2.5 0.5 1.1 0.9

Zinc 12 489 87 244 236

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

Hydropsyche cockerelli

Arsenic 19 18.8 8.0 12.3 10.4

Cadmium 28 2.1 0.7 1.5 1.5

Chromium 28 4.6 0.5 1.8 1.6

Copper 28 247 60.7 109 92.7

Iron 28 3,010 552 1,300 1,130

Lead 28 21.9 3.5 9.0 8.2

Manganese 28 2,650 487 1,410 1,290

Nickel 28 2.5 0.5 1.3 1.3

Zinc 28 285 162 218 218

Table 27. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2016.—

Continued

[Reported concentrations are in microgram per gram dry weight (μg/g). 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 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche species combined. At some sites, statistics of 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]
Data 109

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: 1996–2016

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 2 6.5 6.4 6.4 --

Cadmium 4 1.7 0.9 1.3 1.3

Chromium 4 2.1 0.8 1.4 1.2

Copper 4 140 65.5 94.1 85.4

Iron 4 1,610 875 1,120 987

Lead 4 13.2 7.3 9.7 9.1

Manganese 4 1,150 638 824 756

Nickel 4 1.6 0.6 1.1 1.1

Zinc 4 212 162 184 180

12324200—Clark Fork at Deer Lodge

Period of record for biological data: 1986–87, 1990–2016

Arctopsyche grandis

Arsenic 7 13.3 5.8 8.8 8.3

Cadmium 9 4.7 2.6 13.5 13.4

Chromium 9 4.7 1.0 12.3 12.0

Copper 9 183 34.9 96.8 88.6

Iron 9 2,320 537 1,180 1,090

Lead 9 17.4 3.8 110.7 111.2

Manganese 9 1,620 380 1,150 1,320

Nickel 9 1.9 <1.3 11.4 11.3

Zinc 9 370 140 268 269

Hydropsyche cockerelli

Arsenic 19 17.1 5.8 9.5 9.6

Cadmium 42 4.9 0.6 1.9 1.8

Chromium 42 4.3 0.4 1.9 1.9

Copper 42 241 54.7 107 101

Iron 42 3,340 490 1,290 1,090

Lead 42 24.9 3.8 10.6 9.6

Manganese 42 1,580 396 1,030 1,030

Nickel 42 3.3 0.3 1.4 1.2

Zinc 42 391 132 205 196

Table 27. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2016.—

Continued

[Reported concentrations are in microgram per gram dry weight (μg/g). 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 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche species combined. At some sites, statistics of 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]
110 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Constituent Number of composite 

samples Maximum Minimum Mean Median

12324200—Clark Fork at Deer Lodge—Continued

Period of record for biological data: 1986–87, 1990–2016

Hydropsyche occidentalis

Arsenic 24 21.1 6.6 11.1 9.7

Cadmium 61 3.4 0.6 1.4 1.3

Chromium 61 3.7 0.6 2.0 1.9

Copper 61 222 49.4 123 121

Iron 61 3,240 558 1,510 1,480

Lead 61 20.1 3.5 11.8 11.8

Manganese 61 2,850 649 1,600 1,650

Nickel 61 12.9 1.0 1.7 1.5

Zinc 61 346 166 246 238

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: 2009–16

Arctopsyche grandis

Arsenic 15 16.6 3.2 6.1 5.2

Cadmium 15 4.9 0.9 2.7 3.2

Chromium 15 4.6 0.6 11.6 11.3

Copper 15 209 35.4 78.5 55.4

Iron 15 2,580 257 758 529

Lead 15 18.0 2.8 6.8 5.3

Manganese 15 1,940 578 1,050 954

Nickel 15 2.2 0.5 1.1 0.8

Zinc 15 378 184 256 238

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

Table 27. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2016.—

Continued

[Reported concentrations are in microgram per gram dry weight (μg/g). 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 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche species combined. At some sites, statistics of 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]
Data 111

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: 2009–16

Hydropsyche cockerelli

Arsenic 5 11.1 7.4 8.9 8.8

Cadmium 5 4.0 0.9 2.2 1.6

Chromium 5 3.4 1.4 2.2 2.0

Copper 5 158 81.5 112 101

Iron 5 2,150 746 1,230 1,050

Lead 5 18.8 8.5 12.1 10.1

Manganese 5 1,870 1,110 1,370 1,270

Nickel 5 1.8 1.4 1.6 1.5

Zinc 5 284 212 233 216

Hydropsyche occidentalis

Arsenic 12 14.7 6.4 9.6 8.6

Cadmium 12 2.5 1.0 1.8 1.8

Chromium 12 3.6 0.7 2.1 2.0

Copper 12 182 78.1 124 125

Iron 12 2,390 908 1,470 1,270

Lead 12 17.9 8.8 12.6 11.4

Manganese 12 2,100 975 1,480 1,390

Nickel 12 1.9 1.0 1.5 1.6

Zinc 12 299 223 252 250

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 --

12324680—Clark Fork at Goldcreek

Period of record for biological data: 1992–2016

Arctopsyche grandis

Arsenic 46 17.0 1.8 4.9 4.1

Cadmium 75 6.6 0.6 2.0 1.8

Chromium 75 5.3 0.1 1.4 1.1

Copper 75 232 19.9 50.0 38.4

Iron 75 3,070 195 727 508

Lead 75 16.9 1.0 4.0 3.3

Manganese 75 1,580 436 885 871

Nickel 75 3.1 0.2 0.8 0.7

Zinc 75 326 146 205 190

Table 27. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2016.—

Continued

[Reported concentrations are in microgram per gram dry weight (μg/g). 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 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche species combined. At some sites, statistics of 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]
112 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Constituent Number of composite 

samples Maximum Minimum Mean Median

12324680—Clark Fork at Goldcreek—Continued

Period of record for biological data: 1992–2016

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 19 9.8 4.1 6.0 5.7

Cadmium 38 4.2 0.5 1.4 1.3

Chromium 38 4.7 0.5 2.5 1.9

Copper 38 188 17.1 73.1 58.5

Iron 38 3,250 522 1,140 942

Lead 38 17.6 2.4 6.7 5.3

Manganese 38 1,710 538 1,010 981

Nickel 38 3.5 0.3 1.3 1.2

Zinc 38 359 106 193 187

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 17 11.5 4.4 6.8 6.5

Cadmium 32 2.3 0.4 1.3 1.3

Chromium 32 3.9 0.4 1.9 1.7

Copper 32 170 26.4 72.9 63.7

Iron 32 2,720 466 1,230 1,110

Lead 32 15.7 2.9 7.5 6.0

Manganese 32 2,900 530 1,300 1,160

Nickel 32 2.5 0.8 1.3 1.1

Zinc 32 328 97.0 207 203

Table 27. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2016.—

Continued

[Reported concentrations are in microgram per gram dry weight (μg/g). 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 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche species combined. At some sites, statistics of 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]
Data 113

Constituent Number of composite 

samples Maximum Minimum Mean Median

12324680—Clark Fork at Goldcreek—Continued

Period of record for biological data: 1992–2016

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 --

12331800—Clark Fork near Drummond

Period of record for biological data: 1986, 1991–2016

Arctopsyche grandis

Arsenic 37 9.9 1.8 4.0 3.8

Cadmium 69 3.8 0.4 1.4 1.2

Chromium 69 4.2 0.2 1.1 1.0

Copper 69 103 16.9 34.8 28.2

Iron 69 2,400 193 615 490

Lead 69 12.4 1.6 4.7 3.9

Manganese 69 2,010 456 861 775

Nickel 69 2.6 0.1 0.7 0.6

Zinc 69 314 137 201 194

Claassenia sabulosa

Arsenic 31 1.9 0.6 1.3 1.3

Cadmium 67 2.8 0.1 1.0 0.7

Chromium 67 3.3 0.1 0.6 0.6

Copper 67 165 18.0 63.8 60.0

Iron 67 449 45.4 177 148

Lead 67 2.9 0.2 1.0 0.9

Manganese 67 748 33.1 183 150

Nickel 67 1.1 0.1 10.3 10.3

Zinc 67 567 103 280 269

Hydropsyche cockerelli

Arsenic 20 7.2 3.9 5.5 5.3

Cadmium 49 4.5 0.3 1.2 0.9

Chromium 49 3.5 0.4 1.6 1.6

Copper 49 156 30.0 57.9 51.1

Iron 49 2,500 506 1,140 912

Lead 49 15.0 4.7 8.1 7.4

Manganese 49 1,840 549 1,040 975

Nickel 49 2.0 0.5 1.2 1.1

Zinc 49 322 134 197 194

Table 27. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2016.—

Continued

[Reported concentrations are in microgram per gram dry weight (μg/g). 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 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche species combined. At some sites, statistics of 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]
114 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Constituent Number of composite 

samples Maximum Minimum Mean Median

12331800—Clark Fork near Drummond—Continued

Period of record for biological data: 1986, 1991–2016

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 21 9.2 4.3 5.8 5.7

Cadmium 37 2.8 0.4 1.1 1.0

Chromium 37 8.1 0.4 2.3 2.1

Copper 37 118 13.3 59.0 56.3

Iron 37 2,410 424 1,260 1,190

Lead 37 17.1 3.0 8.8 9.1

Manganese 37 2,920 477 1,480 1,270

Nickel 37 6.0 0.5 1.4 1.2

Zinc 37 344 153 226 222

Hydropsyche spp.

Arsenic 0 -- -- -- --

Cadmium 1 -- -- 2.6 --

Chromium 0 -- -- -- --

Copper 1 -- -- 85.0 --

Iron 1 -- -- 913 --

Lead 1 -- -- 9.1 --

Manganese 0 -- -- -- --

Nickel 0 -- -- -- --

Zinc 1 -- -- 260 --

12334550—Clark Fork at Turah Bridge, near Bonner

Period of record for biological data: 1986, 1991–2016

Arctopsyche grandis

Arsenic 37 7.2 2.8 4.4 4.3

Cadmium 79 2.7 0.4 1.2 0.9

Chromium 79 4.1 0.5 1.6 1.4

Copper 79 125 15.9 36.7 31.7

Iron 79 2,870 321 896 788

Lead 79 13.2 1.6 4.4 3.7

Manganese 79 1,050 324 656 662

Nickel 79 2.6 0.4 1.1 0.9

Zinc 79 282 111 204 203

Table 27. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2016.—

Continued

[Reported concentrations are in microgram per gram dry weight (μg/g). 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 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche species combined. At some sites, statistics of 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]
Data 115

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, 1991–2016

Claassenia sabulosa

Arsenic 26 3.1 0.2 1.1 1.0

Cadmium 52 2.5 0.05 1.1 0.8

Chromium 52 2.0 0.2 0.7 0.6

Copper 52 97.8 37.5 60.2 55.9

Iron 52 378 58.6 133 114

Lead 52 1.6 0.2 0.6 0.6

Manganese 52 229 37.2 102 90.4

Nickel 52 0.6 0.04 0.2 0.2

Zinc 52 429 144 239 244

Hydropsyche cockerelli

Arsenic 28 9.8 3.7 4.8 4.8

Cadmium 56 2.2 0.3 0.9 0.7

Chromium 56 14.2 0.2 2.2 1.7

Copper 56 126 26.4 48.4 43.9

Iron 56 3,180 566 1,210 1,100

Lead 56 19.7 2.2 5.6 5.1

Manganese 56 957 426 654 664

Nickel 56 2.7 0.6 1.3 1.2

Zinc 56 332 119 191 194

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 15.2 --

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

Table 27. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2016.—

Continued

[Reported concentrations are in microgram per gram dry weight (μg/g). 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 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche species combined. At some sites, statistics of 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]
116 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

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, 1991–2016

Hydropsyche spp.

Arsenic 0 -- -- -- --

Cadmium 1 -- -- 1.3 --

Chromium 1 -- -- 2.4 --

Copper 1 -- -- 84.1 --

Iron 1 -- -- 1,800 --

Lead 1 -- -- <7.8 --

Manganese 1 -- -- 537 --

Nickel 1 -- -- 1.3 --

Zinc 1 -- -- 171 --

12340000—Blackfoot River near Bonner

Period of record for biological data: 1986–87, 1991, 1993, 1996, 1998, 2000, 2003, 2006–16

Arctopsyche grandis

Arsenic 16 4.6 1.6 2.7 2.6

Cadmium 26 0.5 0.1 0.3 0.2

Chromium 21 6.9 0.5 2.0 1.5

Copper 26 19.3 9.9 13.5 12.6

Iron 26 1,880 108 744 761

Lead 26 2.3 0.5 1.1 0.9

Manganese 21 633 286 442 422

Nickel 21 3.7 0.7 1.4 1.2

Zinc 26 170 106 144 145

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 11 4.2 2.1 3.1 3.1

Cadmium 11 0.6 <0.1 10.3 10.3

Chromium 11 5.7 1.6 3.2 3.5

Copper 11 17.5 5.6 14.6 14.8

Iron 11 2,390 1,120 1,660 1,550

Lead 11 2.6 1.5 2.0 1.9

Manganese 11 814 409 555 538

Nickel 11 4.6 1.4 2.0 1.8

Zinc 11 165 132 148 147

Table 27. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2016.—

Continued

[Reported concentrations are in microgram per gram dry weight (μg/g). 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 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche species combined. At some sites, statistics of 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]
Data 117

Constituent Number of composite 

samples Maximum Minimum Mean Median

12340000—Blackfoot River near Bonner—Continued

Period of record for biological data: 1986–87, 1991, 1993, 1996, 1998, 2000, 2003, 2006–16

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 1 -- -- 4.0 --

Cadmium 2 0.6 0.2 0.4 --

Chromium 2 2.8 1.6 2.2 --

Copper 2 18.3 13.9 16.1 --

Iron 2 1,180 1,140 1,160 --

Lead 2 2.9 1.8 2.3 --

Manganese 2 693 525 609 --

Nickel 2 2.8 2.7 2.8 --

Zinc 2 211 132 171 --

12340500—Clark Fork above Missoula

Period of record for biological data: 1997–2016

Arctopsyche grandis

Arsenic 37 7.2 1.2 3.6 3.5

Cadmium 56 2.3 0.1 1.0 0.8

Chromium 56 4.2 0.4 1.6 1.4

Copper 56 81.2 13.7 36.7 29.8

Iron 56 2,340 302 960 830

Lead 56 8.8 1.1 3.9 3.3

Manganese 56 1,410 476 902 890

Nickel 56 2.1 0.3 1.1 1.1

Zinc 56 272 133 199 198

Claassenia sabulosa

Arsenic 26 1.9 0.1 1.1 1.0

Cadmium 35 2.0 0.2 0.7 0.6

Chromium 35 1.4 0.1 0.8 0.7

Copper 35 81.1 25.8 50.8 48.6

Iron 35 424 82.0 218 226

Lead 35 3.1 0.2 0.9 0.8

Manganese 35 683 57.8 182 136

Nickel 35 0.7 0.2 10.4 1

0.4

Zinc 35 384 191 278 271

Table 27. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2016.—

Continued

[Reported concentrations are in microgram per gram dry weight (μg/g). 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 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche species combined. At some sites, statistics of 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]
118 Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries of Data, Clark Fork Basin, Montana

Constituent Number of composite 

samples Maximum Minimum Mean Median

12340500—Clark Fork above Missoula—Continued

Period of record for biological data: 1997–2016

Hydropsyche cockerelli

Arsenic 27 9.3 2.4 5.6 5.4

Cadmium 36 2.0 0.4 0.8 0.8

Chromium 36 6.0 1.0 2.7 2.3

Copper 36 99.7 24.4 57.2 52.9

Iron 36 3,590 830 1,860 1,810

Lead 36 12.1 2.5 6.7 6.0

Manganese 36 1,910 764 1,160 1,170

Nickel 36 2.4 0.9 1.8 1.7

Zinc 36 266 156 217 219

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

Table 27. Statistical summary of long-term biological data for the Clark Fork Basin, Montana, August 1986 through August 2016.—

Continued

[Reported concentrations are in microgram per gram dry weight (μg/g). 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 1986–89, Hydropsyche species statistics for stations sampled during those years are based on the results of all Hydropsyche species combined. At some sites, statistics of 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]

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://wy-mt.water.usgs.gov

Publishing support provided by the 

Rolla Publishing Service Center

Dodge and others—Water-Quality, Bed-Sediment, and Biological Data and Statistical Summaries, Clark Fork Basin, Montana—Open-File Report 2017–1136

ISSN 2331-1258 (online)

https://doi.org/10.3133/ofr20171136