Prepared in cooperation with the National Park Service, Air Resources Division

Mercury in Fishes from 21 National Parks in the Western 

United States—Inter- and Intra-Park Variation in 

Concentrations and Ecological Risk

U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2014–1051
Cover: Reflection Lake at Mount Rainier National Park. Photograph taken by Collin A. 

Eagles-Smith, U.S. Geological Survey, July 31, 2012.
Mercury in Fishes from 21 National Parks in the 

Western United States—Inter- and Intra-Park 

Variation in Concentrations and Ecological Risk

By Collin A. Eagles-Smith, James J. Willacker Jr., and Colleen M. Flanagan Pritz

Prepared in cooperation with the National Park Service, Air Resources Division

Open-File Report 2014–1051

U.S. Department of the Interior

U.S. Geological Survey. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2014

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Suggested citation:

Eagles-Smith, C.A., Willacker, J.J., and Flanagan Pritz, C.M., 2014, Mercury in fishes from 21 national parks in the 

Western United States—Inter and intra-park variation in concentrations and ecological risk: U.S. Geological Survey

Open-File Report 2014-1051, 54 p. http://dx.doi.org/10.3133/ofr20141051.

ISSN 2331-1258 (online)

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iii

Contents

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

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

Methods......................................................................................................................................................................... 4

Study Sites and Sample Collection ............................................................................................................................ 4

Sample Processing and Mercury Determination ........................................................................................................ 4

Statistical Analyses .................................................................................................................................................... 5

Risk Benchmark Values............................................................................................................................................. 6

Fish ........................................................................................................................................................................ 6

Birds ....................................................................................................................................................................... 6

Humans.................................................................................................................................................................. 7

Risk Estimation....................................................................................................................................................... 8

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

Model-Adjusted Mercury Concentrations ................................................................................................................... 9

Inter-Park Comparisons ......................................................................................................................................... 9

Intra-Park Comparisons ......................................................................................................................................... 9

Variation Across Spatial Scales ................................................................................................................................10

Inter-Annual Variation ...............................................................................................................................................10

Toxicological Risk .....................................................................................................................................................10

Fish Risk ...............................................................................................................................................................11

Avian Risk .............................................................................................................................................................12

Human Consumption Risk.....................................................................................................................................13

Discussion ....................................................................................................................................................................15

National Park Summaries .........................................................................................................................................19

Capitol Reef National Park ....................................................................................................................................19

Crater Lake National Park .....................................................................................................................................19

Denali National Park..............................................................................................................................................19

Glacier Bay National Park .....................................................................................................................................20

Glacier National Park ............................................................................................................................................20

Grand Canyon National Park.................................................................................................................................20

Grand Teton National Park....................................................................................................................................20

Great Basin National Park.....................................................................................................................................21

Great Sand Dunes National Park ..........................................................................................................................21

Lake Clark National Park.......................................................................................................................................21

Lassen Volcanic National Park..............................................................................................................................21

Mesa Verde National Park.....................................................................................................................................22

Mount Rainer National Park ..................................................................................................................................22

North Cascades National Park ..............................................................................................................................22

Olympic National Park...........................................................................................................................................22

Rocky Mountain National Park ..............................................................................................................................23

Sequoia–Kings Canyon National Park ..................................................................................................................23

Wrangell-St. Elias National Park ...........................................................................................................................23

Yellowstone National Park.....................................................................................................................................24

Yosemite National Park.........................................................................................................................................24

Zion National Park.................................................................................................................................................24
iv

Acknowledgments ........................................................................................................................................................25

References Cited..........................................................................................................................................................25

Figures

Figure 1. Spatial distribution of the 21 national parks in the Western United States sampled in this study between 

2008 and 2012............................................................................................................................................................. 29

Figure 2. Total mercury (THg) concentrations (ng/g ww) in fish muscle from 21 national parks in the 

Western United States................................................................................................................................................. 30

Figure 3. Total mercury (THg) concentrations (ng/g ww) in fish muscle from individual sites within 

21 national parks in the Western United States........................................................................................................... 31

Figure 4. Size-normalized least-square (LS) total mercury (THg) concentrations in fish from 

21 national parks in the Western United States........................................................................................................... 32

Figure 5. Least-square mean fish muscle total Hg concentrations (ng/g ww) in three size-normalized

classes from 21 national parks in the Western United States..................................................................................... 33

Figure 6. Least-square mean total mercury (THg) concentrations in fish muscle from individual sites 

in 21 national parks in the Western United States ....................................................................................................... 34

Figure 7. Inter-annual comparisons of fish total mercury concentrations (ng/g ww) in muscle tissue

from 10 sites in four national parks in the Western United States................................................................................ 35

Figure 8. Example size-risk profile to evaluate proportion of fish exceeding defined toxicological benchmarks ......... 36

Figure 9. Modeled percentage of fish across the size range sampled in each population with whole-body

total mercury concentrations that exceed benchmarks at a given size for a generic no-observed-effects 

residue (200 ng/g ww), and lowest-observed-effects-residue (300 ww) for fish health ................................................ 37

Figure 10. Modeled percentage of fish across the size range sampled in each population with whole-body

total mercury concentrations that exceed dietary toxicity benchmarks for piscivorous birds that can be 

classified as high (90 ng/g ww), medium (180 ng/g ww; common loon reproductive impairment), or low 

(270 ng/g ww) sensitivity in 21 national parks in the Western United States ............................................................... 39

Figure 11. Modeled percentages of fish across the sampled size range in each population with muscle total 

mercury concentrations exceeding the Great Lakes Advisory Group’s (GLAG) unlimited consumption threshold

(50 ng/g ww), the Environmental Protection Agency’s fish consumption criterion (300 ng/g ww), and the GLAG’s 

no-consumption threshold (950 ng/g ww) in 21 national parks in the Western United States...................................... 41
v

Tables

Table 1. Site locations and sampling information for 21 national parks in the Western United States 

sampled between 2008 and 2012................................................................................................................................ 43

Table 2. Total mercury concentrations (THg; ng/g ww) in muscle of fish from 21 national parks in the 

Western United States................................................................................................................................................. 47

Table 3. Total mercury concentrations (THg; ng/g ww) and coefficients of variation (CV) in fish muscle

from 86 sites in 21 national parks in the Western United States.................................................................................. 48

Table 4. Proportion of fish with wet weight mercury concentrations exceeding toxicity benchmarks

from 86 sites in 21 western national parks in the Western United States ................................................................... 51

Conversion Factors

SI to Inch/Pound

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

kilometer (km) 0.6214 mile (mi)

Area

acre (ac) 0.0015625 square mile (mi2) 

Mass

gram (g) 0.03527 ounce, avoirdupois (oz)

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

°F=(1.8×°C)+32
vi

Abbreviations and Acronyms

dw dry weight

ww wet weight

Hg mercury

THg total mercury

MeHg methylmercury

LSM least-square mean

NP national park

NPS National Park Service

CARE Capitol Reef National Park

CRLA Crater Lake National Park

DENA Denali National Park

GLBA Glacier Bay National Park

GLAC Glacier National Park

GRCA Grand Canyon National Park

GRTE Grand Teton National Park

GRBA Great Basin National Park

GRSA Great Sand Dunes National Park

LACL Lake Clark National Park

LAVO Lassen Volcanic National Park

MEVE Mesa Verde National Park

MORA Mount Rainer National Park

NOCA North Cascades National Park

OLYM Olympic National Park

ROMO Rocky Mountain National Park

SEKI Sequoia – Kings Canyon National Park

WRST Wrangell – St. Elias National Park

YELL Yellowstone National Park

YOSE Yosemite National Park

ZION Zion National Park
1

Mercury in Fishes from 21 National Parks in the Western 

United States—Inter- and Intra-Park Variation in 

Concentrations and Ecological Risk

By Collin A. Eagles-Smith1, James J. Willacker1, Jr., and Colleen M. Flanagan Pritz2

Abstract

Mercury (Hg) is a global contaminant and human activities have increased atmospheric Hg 

concentrations 3- to 5-fold during the past 150 years. This increased release into the atmosphere has 

resulted in elevated loadings to aquatic habitats where biogeochemical processes promote the microbial 

conversion of inorganic Hg to methylmercury, the bioavailable form of Hg. The physicochemical 

properties of Hg and its complex environmental cycle have resulted in some of the most remote and 

protected areas of the world becoming contaminated with Hg concentrations that threaten ecosystem 

and human health. The national park network in the United States is comprised of some of the most 

pristine and sensitive wilderness in North America. There is concern that via global distribution, Hg 

contamination could threaten the ecological integrity of aquatic communities in the parks and the 

wildlife that depends on them. In this study, we examined Hg concentrations in non-migratory 

freshwater fish in 86 sites across 21 national parks in the Western United States. We report Hg 

concentrations of more than 1,400 fish collected in waters extending over a 4,000 kilometer distance, 

from Alaska to the arid Southwest. Across all parks, sites, and species, fish total Hg (THg)

concentrations ranged from 9.9 to 1,109 nanograms per gram wet weight (ng/g ww) with a mean of 77.7 

ng/g ww. We found substantial variation in fish THg concentrations among and within parks, 

suggesting that patterns of Hg risk are driven by processes occurring at a combination of scales.

Additionally, variation (up to 20-fold) in site-specific fish THg concentrations within individual parks 

suggests that more intensive sampling in some parks will be required to effectively characterize Hg 

contamination in western national parks.

Across all fish sampled, only 5 percent had THg concentrations exceeding a benchmark (200 

ng/g ww) associated with toxic responses within the fish themselves. However, Hg concentrations in 35 

percent of fish sampled were above a benchmark for risk to highly sensitive avian consumers (90 ng/g 

ww), and THg concentrations in 68 percent of fish sampled were above exposure levels recommended 

by the Great Lakes Advisory Group (50 ng/g ww) for unlimited consumption by humans. Of the fish 

assessed for risk to human consumers (that is, species that are large enough to be consumed by 

recreational or subsistence anglers), only one individual fish from Yosemite National Park had a muscle 

Hg concentration exceeding the benchmark (950 ng/g ww) at which no human consumption is advised.

Zion, Capital Reef, Wrangell-St. Elias, and Lake Clark National Parks all contained sites in which most

fish exceeded benchmarks for the protection of human and wildlife health. This finding is particularly

 1 U.S. Geological Survey 2 U.S. National Park Service
2

concerning in Zion and Capitol Reef National Parks because the fish from these parks were speckled 

dace, a small, invertebrate-feeding species, yet their Hg concentrations were as high or higher than those 

in the largest, long-lived predatory species, such as lake trout. Future targeted research and monitoring

across park habitats would help identify patterns of Hg distribution across the landscape and facilitate 

management decisions aimed at reducing the ecological risk posed by Hg contamination in sensitive 

ecosystems protected by the National Park Service.

Introduction 

Mercury (Hg) is among the most widespread environmental contaminants, distributed at a global 

scale from natural sources, such as volcanic eruptions and from anthropogenic sources such as 

emissions followed by atmospheric deposition (Driscoll and others, 2013) and at local or regional scales 

from current and historic mining activities (Singer and others, 2013). When reactive forms of inorganic 

Hg are deposited or transported to aquatic habitats, microbial processes can convert the inorganic Hg to 

methylmercury (MeHg), an organic Hg form that efficiently biomagnifies through food webs (Lavoie 

and others, 2013) and is a potent neurotoxin (Clarkson and Magos, 2006; Bennett and others, 2009; 

Wiener and others, 2012). The prevalence and toxicity of Hg make it a serious threat to both wildlife 

and humans. More than 16 million lake acres and 1 million river miles are under fish consumption 

advisories due to Hg contamination in the United States, and 81 percent of all fish consumption 

advisories were issued because of Hg contamination (U.S. Environmental Protection Agency, 2013).

Mercury affects numerous physiological processes in vertebrate wildlife and humans, particularly 

neurological function, but it also can have a deleterious influence on cardiovascular, renal, and 

endocrine systems. Although the toxicological responses are particularly damaging to developing 

individuals, elevated Hg exposure also can have fitness consequences in adults through impairment of 

reproduction (Clarkson and Magos, 2006). Symptoms can occur at exposure levels commonly observed 

in the environment, and can result in reduced foraging efficiency, survival, or reproductive success 

(Burgess and Meyer, 2008; Crump and Trudeau, 2009; Wiener and others, 2012).

The widespread transport of Hg through atmospheric and hydrologic pathways, coupled with its 

potential for environmentally induced “activation” to a highly bioaccumulative and toxic species, is 

important because it suggests that even remote and protected environments may be at risk to ecological 

harm from Hg (Lamborg and others, 2002; Schuster and others, 2002). In fact, increasing evidence 

indicates that Hg contamination of remote and protected environments is not uncommon. For example, 

total Hg (THg) concentrations in arctic char (Salvelinus alpinus) and lake trout (S. namaycush) from 

lakes in Nunavut Canada have up to 1,400 nanograms per gram wet weight (ng/g ww) (Swanson and 

Kidd, 2010), and THg concentrations in mean northern pike (Esox lucius) from remote sites in Alaska 

have been reported above 1,800 ng/g ww (Duffy and others, 1999). At some of these remote sites, THg 

concentrations are routinely above the highest benchmarks for risk to human consumers (Jewett and 

Duffy, 2007). Similarly, Hg concentrations in fish from several western national parks have previously 

been reported to exceed human and wildlife health thresholds (Landers and others, 2008). Because 

many remote and protected areas provide refuge from development and human disturbance, they often 

support high densities of rare and sensitive wildlife species. As a result, the ecological consequences of 

elevated Hg in these locations could be particularly harmful from a conservation perspective.
3

National Park Service (NPS) lands are among the most pristine natural areas in the United 

States, protecting more than 84 million acres of diverse aquatic and terrestrial habitats. This is 

particularly true for the Western United States and Alaska, which only contain about 32 percent of

national park units, yet account for approximately 89 percent of the total land area managed by the NPS. 

Because such a large proportion of NPS land is in the West, ecological stressors that are pervasive 

across the region could disproportionately affect NPS resources. Mercury contamination is among those 

stressors, because many areas of the Western United States are subject to Hg contamination at levels of 

concern for both human and ecosystem health (Peterson and others, 2007). Moreover, recent work has 

shown that some remote, high-altitude water bodies in western national parks contain fish with Hg

concentrations that exceed toxicological thresholds for both humans and wildlife (Schwindt and others, 

2008). However, the extent of contamination across western parks still lacks a systematic 

characterization and assessment of risk. Furthermore, it remains unclear whether variation in Hg 

concentrations in fish from remote national parks is more related to local, site- or park-specific 

characteristics, or broader regional characteristics. Additionally, spatially expansive baseline 

information is needed in order to evaluate the response of isolated environments to the Mercury 

and Air Toxics Standards (MATS), implemented by the U.S. Environmental Protection Agency (EPA), 

which aims to reduce Hg emissions from powerplants by 90 percent. Understanding how variation in 

fish Hg concentrations is distributed across local and regional scales will facilitate a better 

understanding of potential mitigation and management options.

As the first step toward better understanding the distribution of Hg across aquatic communities 

in western national parks, we measured Hg concentrations in fish from 21 different national parks in the

Western United States and Alaska (fig. 1). We primarily targeted fish from remote, high altitude lake 

habitats with limited hydrological connectivity to upstream watersheds in order to minimize watershed 

scale processes that may potentially confound our assessment of local fish Hg exposure and the relative

influence of local versus regional and global processes. Our primary objectives were as follows:

• Objective 1: Compare fish Hg concentrations among western national parks, and among sites 

within western national parks

• Objective 2: Determine whether variation in fish Hg concentrations in western national parks is 

more evident at local site and park scales, compared to broader regional scales;

• Objective 3: Evaluate fish Hg concentrations in western national parks with respect to a range of 

wildlife and human health exposure thresholds.

Because lakes with limited upstream connectivity were preferentially sampled, estimates of 

variability among lakes may be reduced relative to a random sampling of water available bodies, 

particularly at local and park scales. Furthermore, the hierarchical spatial design of the current study, 

combined with the gradient in landscape types, altitudes, and fish species that occur over such an 

extensive study area, preclude examination of the specific drivers of Hg variation at various scales, and 

investigating these factors was beyond the scope of the current study.
4

Methods

Study Sites and Sample Collection

This study focused on remote, fish-bearing aquatic habitats in the Western United States. We 

sampled 86 individual sites from 21 national parks in 10 Western States (fig. 1, table 1). Our primary 

target habitats were remote, high-altitude lakes containing non-migratory fish populations in order to 

reduce the likelihood that fish Hg concentrations are reflective of exposure that occurred elsewhere.

However, some parks, especially Great Basin National Park (NP) and those in the arid Southwest,

lacked similar aquatic habitats; therefore, we also sampled flowing rivers and streams in a few parks 

where lake habitats were unable to be sampled.

Fish were collected in 2008, 2009, 2011, and 2012 by NPS personnel following standardized 

protocols as described in this paragraph below. The intensive sampling at Mount Rainier in 2012 was 

conducted by U.S. Geological Survey (USGS) staff as part of a focused study in that park, examining a 

range of food web components. Whereas most of the sites were only sampled during 1 of the 4 years, 10

lakes within four parks (Lake Clark, Olympic, Rocky Mountain, Sequoia-Kings Canyon) were sampled 

in 2 separate years in order to examine temporal variation within a subset of lakes (table 1). Depending 

on the characteristics of a site, and its associated access logistics, fish were sampled using variable-mesh 

or fixed-mesh gillnets, hook and line, or beach seines. Because of ecological limits to the distribution of 

fish species across the entire western region of North America, identical species did not exist at all sites.

Instead, we focused on targeting four primary species (brook trout [S. fontinalis], cutthroat trout

[Oncorhynchus clarkii], rainbow trout [O. mykiss], and lake trout) that occurred across as many sites as 

possible. In sites where those species did not occur, we sampled the most abundant resident species that 

were found, trying where possible to match the ecological niche of at least one of our primary species.

Once fish were collected, they were immediately wrapped in chemically cleaned aluminum foil and 

sealed in individually labeled polyethylene zip bags. Fish in the field were immediately placed on wet or 

dry ice until transport to the laboratory, where they were stored at -20°C until processing and analysis.

Sample Processing and Mercury Determination

In the laboratory, we thawed each fish to room temperature, measured standard length (SL) to 

the nearest millimeter, and mass to the nearest 0.1 g. From each fish with greater than 100 mm SL, we 

dissected 5–10 g of skinless axial muscle using nitric acid and deionized-water-rinsed scalpels, scissors, 

and forceps. We then rinsed each muscle sample in deionized water to remove any surface 

contaminants, blotted them dry with clean, lint-free wipes, and weighed them on an analytical balance to 

the nearest 0.0001 g. Fish with less than 100 mm SL were processed as whole-body samples. For these, 

we removed stomach contents and thoroughly cleaned the surface of the fish with deionized water, then 

blotted dry and weighed as described above for muscle tissue. We chose to process and analyze fish less

than 100 mm SL as whole fish because they often lacked adequate muscle tissue for analysis. Moreover, 

robust conversion equations exist for translating between whole-body fish and muscle THg 

concentrations (Peterson and others, 2005, 2007); thus, the whole-body samples were still comparable to 

the muscle samples. Once muscle or whole-body samples were cleaned and weighed, we placed them in 

a drying oven at 50 °C until a constant mass was achieved, typically 48 h. We subsequently removed the 

sample from the drying oven and allowed them to cool to room temperature in a desiccator. Once cool, 

we measured the dry mass of each sample to the nearest 0.0001 g, and homogenized each to a fine 

powder with scissors and a ceramic mortar and pestle. The homogenized samples were stored in a 

desiccator until chemical analysis.
5

We determined THg concentrations of each sample following EPA method 7473 (U.S. 

Environmental Protection Agency, 2000) on a Milestone tri-cell DMA-80 Direct Mercury Analyzer 

(Milestone, Inc., Monroe, Connecticut, U.S.A.). Briefly, we used an integrated sequence of drying (250

°C for 30 s), thermal decomposition (650 °C for 90s), catalytic conversion, and then amalgamation in a 

gold trap, followed by cold vapor atomic absorption spectroscopy. Quality-assurance measures included 

analysis of two certified reference materials (either dogfish muscle tissue [DORM-4; National Research 

Council of Canada, Ottawa, Canada], or dogfish liver [DOLT-3; National Research Council of Canada, 

Ottawa, Canada]), two system and method blanks, and two duplicates-per-batch of 30 samples.

Recoveries (± standard error) averaged 102.8 ± 0.6 percent (n = 88) and 97.83 ± 1.06 percent (n = 128) 

for certified reference materials and calibration checks, respectively. Absolute relative percent 

difference for all duplicates averaged 3.31 ± 0.40 percent.

Statistical Analyses

Unless otherwise noted, all statistical analyses were conducted on dry-weight THg 

concentrations to minimize inconsistencies resulting from variable moisture contents of individual fish.

However, to facilitate comparisons with other work, we present wet weight THg concentrations in the 

text and figures. Fish length is often positively correlated with Hg concentrations, which can confound 

direct comparisons of fish Hg concentrations among locations with different sized fish. In order to make 

spatial comparisons among and within parks, we first evaluated whether size adjusting THg 

concentrations was necessary for each species of fish at each sampling site. To make this determination,

we developed decision rules based on a combination of the strength of regression coefficients (R2

) and 

the small sample-size corrected Akaike’s Information Criterion (AICc) for length versus THg 

concentration (dry weight, log10-transformed) regression models from each species-site combination. No 

size adjustment was made for models with R2 less than 0.20. For regression models with R2 greater than 

0.20, we compared the regression model with a null model using AIC to assess whether including fish 

length as a variable improved the likelihood of predicting fish THg concentrations. If the difference 

between the regression and null AICc values (∆AICc) was less than 2, we proceeded with size adjusting 

individual THg concentrations using linear regression. We also used AIC-based model assessment to 

determine whether sampling year (where available) influenced the relationship between size and Hg 

concentrations by including a year-by-size interaction. The year-by-size interaction failed to improve 

the plausibility of the size-Hg relationship in all cases; thus for size adjustment, we lumped all fish from 

a population regardless of year sampled.

The variation in sizes and species of fish collected across sites complicated direct comparisons 

of size-adjusted THg concentrations for all fish simultaneously. Therefore, using length-frequency 

histograms, we classified fish species into three different size categories (50, 200, and 400 mm SL), thus 

minimizing extrapolation of THg concentrations outside the range of sizes observed for each species.

Mercury concentrations in smallest size category of fishes (speckled dace [Rhinichthys osculus], 

threespine stickleback [Gasteristeus aculeatus], and torrent sculpin [Cottus rhotheus]) were adjusted to 

the concentration predicted at 50 mm SL for each individual. Mercury concentrations in the 

intermediate size category of fishes (arctic grayling [Thymallus arcticus], brook trout, brown trout 

[Salmo trutta], cutthroat trout, Dolly Varden [S. malma malma], golden trout [O. mykiss aquabonita], 

kokanee [O. nerka], rainbow trout), were adjusted to the concentration predicted at 200 mm SL for each 

individual. Mercury concentrations in the largest size category of fishes (bull trout [S. confluentus], lake 

trout, lake whitefish [Coregonus clupeaformis], and northern pike) were adjusted to the concentration 

predicted at 400 mm SL for each individual. To standardize THg concentrations to the appropriate sizes, 

we used the linear regression equations for each site-species combination, then added the residuals from 
6

each individual fish to its predicted concentration in order to incorporate the unexplained variation back 

into the estimate. For those fish sampled from sites where there was no meaningful Hg-size relationship, 

we used the un-adjusted Hg concentrations for each individual.

To compare Hg concentrations among parks and sites within parks, we constructed separate 

mixed effects, nested general linear models for each of the three size classes (50, 200, and 400 mm SL) 

with park and site (nested within park) included as fixed effects, and species included as a random effect 

in each model to statistically account for variation due to different species being collected across sites.

In addition to comparing model-adjusted fish THg concentrations among parks and sites within parks, 

we used the model-adjusted THg concentrations at sites and parks to examine how variation in THg 

concentrations was partitioned across a gradient of spatial scales. To do this, we evaluated the 

coefficient of variation (CV) for (1) all fish within a site using individual fish THg concentrations, (2) 

all sites within a park using model-generated least-square mean (LSM) THg concentrations for each 

site, and (3) all parks using model-generated LSM Hg concentrations for each park. By comparing the 

CVs from each of these scales with t-tests (two-sample in comparison 1 and 2, one-sample in 

comparison 3), we evaluated whether within-lake processes, within-catchment processes, or withinregion processes accounted for the most variation in THg concentrations.

In order to evaluate temporal variation in the subset of 10 sites that were sampled in more than 1 

year, we used analysis of covariance (ANCOVA), which tested whether fish Hg concentrations were 

different between years for each lake, while statistically controlling for fish length. Therefore, we

included standard length as a covariate in the models. The initial sampling event for each site varied 

between 2008, 2009, and 2011 depending on the park. The final sampling for all sites was 2012.

Because of this, our goal was not to test whether there were consistent year effects, but simply to 

evaluate how Hg concentrations within a site might differ between two distinct years regardless of 

which years those were.

Risk Benchmark Values

In addition to examining spatial and temporal variation in fish THg concentrations across parks, 

we also evaluated the threat Hg might pose at each site to the health of fish, piscivorous wildlife, and 

humans by comparing measured and modeled THg concentrations to a range of established benchmarks

of toxicity to different taxonomic groups.

Fish

We compared whole-body Hg concentrations in fish to a no-observed-effects-residue (NOER) of 

200 ng/g ww (Beckvar and others, 2005) and a lowest-observed-effects-residue (LOER) of 300 ng/g ww 

(Sandheinrich and others, 2011) to assess potential risks of Hg exposure to fish themselves. The NOER 

threshold identifies the Hg concentration in fish tissues below which fish should not experience 

deleterious effects of Hg exposure on reproduction, growth, or survival. In contrast, the LOER threshold 

indicates the concentration above which sublethal endpoints of Hg exposure, including alterations to 

reproductive health, have been documented in laboratory and field studies of fish.

Birds

Birds are sensitive to the toxicological effects of MeHg exposure, and piscivorous birds are 

among the taxa most commonly at risk because of their high trophic position. However, robust data on 

the dietary Hg exposure thresholds that result in deleterious effects exist for very few bird species.

Moreover, there is considerable evidence of substantial variability in the sensitivity of different bird 
7

species to Hg exposure (Heinz and others, 2009). Therefore, accurately extrapolating risk across a range 

of unique species can be difficult and may result in low confidence estimates. This is particularly 

problematic in studies such as this one, where no single piscivorous bird species with well-documented 

toxicological responses to Hg exposure extends across such an expansive spatial extent, nor over such a 

range of habitats. Therefore, our approach was to establish a baseline of risk in a well-studied avian 

piscivore, then evaluate the likely range of risk for arbitrary taxa that are more and less sensitive to Hg 

than the baseline species. Arguably the most robust information on avian piscivore toxicological 

responses to Hg exposure across a range of scales of ecological organization exists for the common loon 

(Gavia immer), which has been intensively studied in field and laboratory settings for several decades 

(Kenow and others, 2008; Mitro and others, 2008; Scheuhammer and others, 2008; Kenow and others, 

2011). This extensive research on the behavioral and reproductive impacts of Hg contamination has 

resulted in the development of robust dietary benchmarks for identifying ecological risk of Hg to 

common loons at a range of deleterious endpoints. These studies, coupled with other work on 

interspecific sensitivity to Hg exposure (Heinz and others, 2009), suggest that loons are moderately 

sensitive to Hg exposure in comparison to some other taxa. Therefore, we utilized the common loon 

dietary screening benchmark of 180 ng Hg/g ww in whole-body prey-fish (Depew and others, 2012b) as 

our baseline indicator of Hg risk to moderately sensitive avian consumers. Without solid quantitative 

comparisons of relative sensitivity among species, we chose a conservative approach of scaling the loon 

screening value down and up by 50 percent in order to estimate potential risk to bird species that are 

more or less sensitive to Hg exposure than the common loon. Thus, we assessed risk to avian consumers 

by comparing Hg concentrations in whole-body fish to 90 (high sensitivity), 180 (moderate sensitivity), 

and 270 ng Hg/g ww (low sensitivity) benchmarks. We recognize that this scaling is somewhat arbitrary 

in that it is not calibrated to specific avian species responses, but we chose this approach to better 

encompass the range of potential risk depending on the species that might occur at any given area. Much 

work is still needed to refine the scientific understanding of interspecies differences in sensitivity, but 

we use Heinz and others (2009) as the baseline for identifying some taxonomic groups that may fall into 

each classification. Based on that study of 27 bird species, piscivorous taxa that can be categorized as 

high sensitivity and that are found in some of the parks studied include osprey (Pandion haliaetus), 

white ibis (Eudocimus albus), and snowy egret (Egretta thula). Species that can be categorized as low 

sensitivity include hooded merganser (Lophodytes cucullatus) and double-crested cormorant 

(Phalacrocorax auritus). Besides common loon, other species with probable moderate sensitivity 

include common tern (Sterna hirundo), royal tern (Sterna maxima), and great egret (Ardea alba).

Humans

We assessed risk of Hg exposure to human consumers of fish by comparing Hg concentrations 

in fish muscle to the EPA’s tissue residue criterion for Hg (300 ng/g ww) and two benchmarks 

recommended by the Great Lakes Advisory Group (GLAG) for limiting the risk of Hg exposure to 

anglers (Great Lakes Advisory Group, 2007). The lower benchmark (50 ng/g ww) represents the 

concentration of Hg in fish muscle below which unrestricted consumption of fish poses no risk to 

consumers. The higher benchmark (950 ng/g ww) represents the concentration of Hg in fish muscle 

above which GLAG recommends that no consumption occur.
8

Risk Estimation

We assessed risk to fish, avian consumers, and humans using two approaches. First, we 

compared whole-body (fish and avian risk assessments) or muscle (human risk assessment) Hg 

concentrations in fish to each of the reference values discussed above (two fish, three avian, and three

human benchmarks) and enumerated the proportion of individuals exceeding each benchmark at each 

site, park, and across parks. This analysis provides an overview of Hg risk in all parks and sites 

sampled, but does not account for other factors that influence Hg risk. In particular, because Hg 

concentrations can be strongly influenced by fish size, it is important to understand how risk varies 

across the size spectra of the fish communities. Therefore, in the populations (that is, species-site 

combinations) where size was correlated with Hg concentrations, we used a second approach utilizing

the size-Hg relationships to model the Hg concentration of each fish sampled from a population at 1 mm 

increments over the range of sizes observed in that population. We then compared these modeled fish 

Hg concentrations to each of the eight benchmarks at 1 mm increments to determine the proportion of 

individuals exceeding each benchmark at a given size. Uncertainty in these size-specific risk estimates 

was preserved by comparing the bounds of a 95 percent prediction interval for each fitted value to the 

benchmarks. The resulting size-specific risk profiles present changes in the risk of Hg across the size of 

individuals sampled from a population and can be used to identify the size at which a given proportion 

of individuals in a population likely exceed a specified threshold, or conversely, the proportion of 

individuals in a population that exceed a threshold at a given size. Because Hg concentrations in fish, 

and thus the risk of Hg to fish, wildlife, and humans, varies with fish size, these size-specific risk 

profiles better approximate the range of risks present in a population and provide important insights into 

how risks can be managed.

Results

Over a 4 year time span (2008, 2009, 2011, and 2012), we sampled 1,486 fish representing 16 

different species from 86 individual sites across 21 national parks (table 1). Throughout all parks and 

species, fish muscle THg concentrations ranged over two orders of magnitude from 9.9 to 1,109 ng/g 

ww. The overall geometric mean (95-percent confidence interval in parentheses) of all fish sampled was 

77.7 (73.6–80.8) ng/g ww. However, fish THg concentrations varied substantially among individual 

parks, with park-specific geometric mean values ranging from 32.6 (28.3–37.6) ng/g ww in Grand Teton

NP to 325.6 (281.4–376.9) ng/g ww in Capitol Reef NP (table 2; fig. 2). Furthermore, within parks there 

was considerable variation in geometric mean fish THg concentrations among sites (table 3, figs. 2 and

3). The greatest range in site-specific geometric mean fish THg concentrations within parks occurred in

Mount Rainier and Rocky Mountain NPs, where we measured approximately 11- and 8-fold differences, 

respectively, between the sites within each park with the lowest and highest THg concentrations (table 

2, fig. 3). Importantly, the species and size distribution of fishes differed among parks and lakes, 

confounding direct comparisons across locations because of the influence that these factors have on 

THg concentrations (fig. 3). Therefore, we subsequently normalized the THg concentrations to account 

for the effects of size and species on fish THg concentrations, thus allowing for more meaningful spatial 

comparisons.
9

Model-Adjusted Mercury Concentrations

Inter-Park Comparisons

In order to control for the influence of size and species on fish Hg concentrations, we first 

assessed the relationships between fish length and THg concentrations on a site and species-specific 

basis as described in section, “Methods.” Size was correlated with THg concentrations in 61 of the 104 

site-species combinations (table 1; Significant Size Regression). For those 61 combinations, we 

normalized each individual THg concentration to a standardized length (50, 200, or 400 mm SL), which 

was dependent on the taxonomic grouping to which it was assigned (see section, “Methods”). For the 

site-species combinations where there were no relationships between length and Hg concentrations, we 

used unadjusted Hg values for each fish as it was assigned to its respective size category (table 1).

After accounting for the effects of size and species, LSM THg concentrations of each fish size 

class differed among parks (50 mm SL: F3,107 = 100.15, p < 0.001; 200 mm SL: F14,56.7 = 79.60, p < 

0.001; 400 mm SL: F4,124 = 79.08, p < 0.001; fig. 4). Fish species assigned to the 400 mm SL size class

only occurred in 5 of the 21 parks, primarily the northernmost parks—Denali, Wrangell-St. Elias, Lake 

Clark, Glacier, and Yellowstone NPs. Among those five parks, LSM THg concentrations in fish ranged 

from 47.4 ± 1.6 to 278.9 ± 7.4 ng/g ww. Fish THg concentrations were highest at Wrangell-St. Elias NP 

followed by Glacier, Lake Clark, Yellowstone, and Denali NPs (table 2, figs. 4 and 5).

Fish assigned to the 200 mm SL size class were collected from the greatest number of parks, and 

representatives of this size class are absent only from Denali, Lake Clark, Glacier, Capitol Reef, Zion, 

and Mesa Verde NPs. Mercury concentrations in fish from the 200 mm SL size class had a much 

narrower range of LSMs across parks than the 400 mm SL fish with concentrations ranging from 26.6 ±

2.6 to 119.9 ± 10.2 ng/g ww. Within this size class, Yellowstone NP had the highest fish THg 

concentrations, followed by Olympic, Glacier Bay, Grand Canyon, Wrangell-St. Elias, North Cascades, 

Yosemite, Sequoia-Kings Canyon, Lassen Volcanic, Great Sand Dunes, Mount Rainier, Rocky 

Mountain, Great Basin, Grand Teton, and Crater Lake NPs (fig 4, table 2).

Similar to the largest size class of fishes, we only collected samples falling into our smallest size 

class of fishes (50 mm SL) from a limited subset of four parks, mostly in the Southwestern region. 

Least-square mean THg concentrations in this size class ranged from 74.9 ± 2.9 to 242.5 ± 5.4 among 

parks. Among the 50 mm SL size class, fish Hg concentrations were highest at Zion NP, followed by 

Capitol Reef, Mount Rainier, and Mesa Verde NPs. The LSM values of 50 mm SL fish from Zion and 

Capitol Reef NPs are comparable to those in parks with the highest 400 mm SL fish (figs. 4 and 5).

Intra-Park Comparisons

In addition to regional differences in THg concentrations across parks, we also found differences 

in fish THg concentrations among sites nested within parks for each of the three size classes (50 mm

SL: F5, 107 = 12.22, p < 0.001; 200 mm SL: F57, 679.9 = 41.72, p < 0.001; 400 mm SL: F3, 124 = 31.56, p < 

0.001; fig 6, table 3). The magnitude of site differences within a park varied among parks and size 

classes. For the 400 mm SL size class, there were only two parks with multiple sites containing fish 

assigned to this size class. The sites with the highest THg concentrations were 1.33- and 3.35-fold 

higher than the sites with the lowest THg concentrations for Wrangell-St. Elias and Lake Clark NPs, 

respectively. For the 200 mm SL size class, the highest site within a park averaged 4.4 times higher than 

the lowest site within a park. The differences between the highest and lowest sites within parks ranged 
10

from 1.27- to 22.61-fold in Great Basin and Mount Rainier NPs, respectively. For the 50 mm SL size 

class, the highest site within a park was on average 1.7 times higher than the lowest site within a park, 

and this difference between highest and lowest sites within a park ranged from 1.05- to 2.25-fold in 

Zion and Mount Rainier NPs, respectively. The values above provide insight into the overall range in 

concentrations within and among NPs, but do not adequately address the overall variance that was 

measured at each scale.

Variation Across Spatial Scales

To evaluate whether variation in fish THg concentration was most prevalent at the site, park, or 

regional level, we examined the CV at three scales: (1) CV among fish within individual sites, (2) CV 

among lakes within individual parks, and (3) CV among parks across the .Western United States,

including Alaska. The CV among fish within individual sites ranged from 0.097 at Death Canyon Creek 

in Grand Teton NP to 0.819 at The Loch in Rocky Mountain NP, and averaged 0.303 across all sites

(table 3). The CV among lakes within individual parks ranged from 0.121 in Great Basin NP to 0.865 on 

Yosemite NP (table 3). The mean CV among sites within parks (0.493) was greater than the average CV 

among fish within sites (t = 3.87, df = 18, p = 0.001). The CV among parks was 0.673 (table 3); 

significantly higher than the mean CV among sites within parks (t = -3.798, df = 16, p = 0.002). These 

data suggest that variation in THg concentrations increases at progressively larger landscape scales, with 

the greatest variation resulting from regional factors, followed by local and within-lake biological 

factors.

Inter-Annual Variation

There were no consistent patterns in inter-annual variability across the 10 sites sampled over 

separate years. Significant differences in mean Hg concentrations were observed at 5 of 10 sites. Fish 

THg concentrations increased from the first sampling year to the second at two sites: Sun Up Lake 

(Olympic NP; F1,27 = 6.35, p = 0.018; fig. 7) and Center Basin Lake (Sequoia-Kings Canyon NP; F1,42 = 

22.87, p < 0.0001; fig. 7). Conversely, fish THg concentrations decreased from the first sampling event 

to the second in three sites—Upper Lena Lake (Olympic NP; F1,24 = 7.12, p = 0.014, fig. 7), Poudre 

Lake (Rocky Mountain NP; F1,27 = 4.77, p = 0.038, fig. 7), and Ypsilon Lake (Rocky Mountain NP; 

F1,27 = 4.36, p = 0.046, fig. 7). Finally, we found no differences among years at the remaining five

sites—Gladys Lake (Olympic NP; F1,26 = 1.13, p = 0.30), Lake Nanita (Rocky Mountain NP; F1,20 = 

0.004, p = 0.89), Mirror Lake (Rocky Mountain NP; F1,27 = 0.21, p = 0.65), Kern Point (Sequoia-Kings 

Canyon NP; F1,27 = 1.47, p = 0.23), and Lake Clark (Lake Clark NP; F1,24 = 0.037, p = 0.85). The 

magnitude of differences between years was 19.6 percent in Sun Up Lake (Olympic NP), 24.4 percent 

in Ypsilon Lake (Rocky Mountain NP), 24.8 percent in Upper Lena Lake (Olympic NP), 26.5 percent in 

Poudre Lake (Rocky Mountain NP), and 43.6 percent in Center Basin Lake (Sequoia-Kings Canyon 

NP).

Toxicological Risk

Estimating toxicological risk of Hg within ecosystems can be subjective and dependent on the 

endpoints selected, the uncertainty surrounding individual- and species-specific sensitivity estimates, 

and whether risk is based on dietary exposure or tissue-based Hg concentrations. Because of the 

geographic scale of this study, the wide range of species sampled, and the somewhat limited sample 

sizes within sites, we evaluated ecological and human health risk at a relatively coarse scale, by 

comparing measured, unadjusted fish THg concentrations to a gradient of pre-established benchmarks
11

individually for fish health, avian (piscivorous bird) health, and human health. However, in addition to 

simply comparing the proportion of sampled fish to these thresholds, we modeled Hg risk to each group 

across the range of fish sizes for each site in order to evaluate how risk to these groups varies with fish 

size (fig. 8; see section, “Methods”).

Fish Risk

Across all parks, species, and sizes of fish, 5 percent of individuals had whole-body THg 

concentrations above which Hg exposure may affect fish health (NOER; 200 ng/g ww; table 4). Fewer

than 2 percent of individuals had whole-body THg concentrations above which deleterious effects are 

likely (LOER; 300 ng/g ww; table 4).

The distribution of risk was not evenly distributed across all parks. Thirteen of the 21 parks 

sampled contained no fish exceeding the 200 ng/g NOER benchmark. In the eight parks (38 percent) 

with fish exceeding 200 ng/g THg, the proportion of individual fish exceeding this benchmark was 

highest in Capitol Reef NP, where 49 percent of fish sampled had concentrations above 200 ng/g ww, 

followed by Lake Clark, Zion, Wrangell-St. Elias, Yosemite, Lassen Volcanic, Rocky Mountain, and 

Mount Rainier NPs (table 4). Of the 21 parks sampled, only 6 (Capitol Reef, Lake Clark, Wrangell-St. 

Elias, Zion, Yosemite, and Rocky Mountain NPs; 29 percent) contained fish with THg concentrations 

exceeding the 300 ng/g ww LOER benchmark (table 4), the value above which deleterious effects to 

fish are likely. Twenty-two percent of fish from Capitol Reef NP exceeded this concentration, whereas 

Lake Clark, Wrangell-St. Elias, Zion, Yosemite, and Rocky Mountain NPs had progressively lower 

proportions fish exceeding this benchmark (table 4).

When examined on a site-specific basis, fish THg concentrations exceeded 200 ng/g ww in 13 

sites (15 percent) across the 8 parks containing fish with values above this benchmark. More than onehalf of the individual fish exceeded the NOER threshold at Tanada Lake (85 percent) in Wrangell-St. 

Elias NP, Fremont River site 1 (67 percent) and site 7 (60 percent) in Capitol Reef NP, and Lake Clark 

(54 percent) in Lake Clark NP (table 4). Other sites with fish exceeding the NOER benchmark include

East Fork Virgin River (Zion NP), MORA_1614 (Mount Rainier NP), Fremont River site 4 (Capitol 

Reef NP), Lake Kontrashibuna (Lake Clark), Mildred Lake (Yosemite NP), Fall River (Rocky Mountain 

NP), Mirror Lake (Rocky Mountain NP), North Fork Virgin River (Zion NP), Horseshoe Lake (Lassen 

Volcanic NP). The 300 ng/g LOER was exceeded in only 8 individual sites (9 percent). Two sites in 

Capitol Reef NP (Fremont River sites 1 and 7) had the highest proportions of individuals exceeding this 

benchmark, 33 and 27 percent, respectively (table 4). Other sites with fish exceeding the LOER 

benchmark include Tanada Lake (Wrangell-St. Elias NP), Lake Clark (Lake Clark NP), Fremont River 

site 4 (Capitol Reef NP), Mildred Lake (Yosemite NP), North Fork Virgin River (Zion NP), and Fall 

River (Rocky Mountain NP).

Size-Specific Risk

We modeled risk across the observed size range for all 61 populations with size-Hg 

relationships. This approach was implemented so that instead of simply calculating the proportion of 

fish exceeding benchmarks from the sampled size range (which is not necessarily representative of the 

size distribution of fish within the lake), we could estimate specific lengths at which most fish exceed 

each benchmark. Taking this approach, our models estimated that fish would exceed the 200 ng/g ww 

NOER benchmark in 21 (34 percent) of the populations modeled (fig. 9). In eight of those populations,

at least one-half of all individuals are predicted to exceed the NOER at some length along their size 

spectra (fig. 9). Four of these populations were speckled dace from three sites in Capitol Reef NP and 

one site in Zion NP. In these four populations, the mean size at which 50 percent of the individuals were 
12

modeled to exceed the benchmark was 61 mm SL, ranging from 52 mm SL in Capitol Reef’s Fremont 

River site 1, to 67 mm SL in Fremont River sites 4 and 7 (fig. 9). For the other four populations, our 

models predict that 50 percent of the individuals will exceed the NOER at 264 and 302 mm in brook 

trout from Mildred Lake in Yosemite NP and Horseshoe Lake in Lassen Volcanic NP, respectively, 323 

mm SL in suckers from Fall River in Rocky Mountain NP, and 412 mm SL in lake trout from Tanada 

Lake in Wrangell-St. Elias NP (fig. 9).

Model predictions estimate that fewer fish populations (12 of 61 populations modeled; 20 

percent) are expected to contain individuals exceeding the 300 ng/g LOER over the range of fish sizes 

sampled in each population than estimated for the NOER (fig. 9). At least 50 percent of the individuals 

in five of the populations were predicted to exceed this benchmark at some point within their measured 

size spectra. Four of those populations were specked dace from Capitol Reef and Zion NPs, where the 

estimated size at which 50 percent exceeded the benchmark was 71 mm SL (fig. 9). Additionally, at 

least one-half of the lake trout population greater than 526 mm SL from Tanada Lake in Wrangell-St. 

Elias NP are projected to exceed the LOER (fig. 9).

Avian Risk 

When examining the unadjusted whole-body THg concentrations, 35 percent of all fishes

sampled had THg concentrations above our benchmark for risk to birds with high sensitivity to Hg 

exposure (90 ng/g ww; table 4). Tissue concentrations in 12 percent of individual fish exceeded the 180 

ng/g ww benchmark for reproductive impairment in species with moderate sensitivity, and 5 percent of 

individual fish exceeded 270 ng/g ww, our benchmark for risk to birds with low sensitivity to Hg 

exposure (table 4).

Among the 21 parks, the potential risk to piscivorous birds varied substantially. In 7 parks (33 

percent), none of the fish analyzed exceeded the 90 ng/g ww benchmark for highly sensitive bird 

species. In the remaining 14 parks (67 percent), more than one-half of sampled fish were above this 

concentration, and more than three-quarters of sampled fish exceeded this value in Lake Clark, Zion, 

Capitol Reef, and Glacier NPs (76, 90, 98, and 100 percent, respectively). The benchmark for 

reproductive impairment in moderately sensitive avian species was exceeded in nine (43 percent) parks.

The proportion of fish within these nine parks that exceeded this benchmark, ranged from 1 percent of 

individual fish at Yellowstone NP to 56 percent of individual fish at Capitol Reef NP, which was the 

only park from which more than one-half of the fish sampled exceeded the moderate sensitivity

benchmark (table 4). Fourteen of the 21 parks had no fish with THg concentrations above the 

benchmark for birds with low Hg sensitivity (table 4), and the proportion of fish exceeding this 

threshold was less than 10 percent in all remaining seven parks (33 percent) except Capitol Reef, where 

33 percent of fish sampled exceeded the threshold (table 4).

On a site-specific level, 41 of the 86 sites sampled had no fish with THg concentrations above

the benchmark for the most sensitive avian species (table 4). However, at the remaining 45 sites (52 

percent), 63 percent of fish exceeded this benchmark, and at 7 sites, 100 percent of fish sampled were 

above the high sensitivity avian benchmark. At an additional seven sites, between 50 and 93 percent of 

fish had THg concentrations greater than the high sensitivity avian threshold (table 4). The loon 

reproductive impairment threshold was exceeded at 18 sites (21 percent), with more than one-half of the 

fish surpassing this benchmark at four sites (table 4). Nine individual sites (representing seven parks) 

contained fish with THg concentrations above the benchmark for birds with low sensitivity to Hg (table 

4).
13

Size-Specific Risk

Size-specific Hg risk to piscivorous birds was modeled for 61 populations. Of these, whole-body 

Hg concentrations in fish from 14 populations (23 percent) did not exceed the 90 ng/g ww benchmark 

for risk to the most sensitive avian species, while the remaining 47 populations (77 percent) were 

modeled to exceed this threshold at some size (fig. 10). However, 100 percent of lake trout from Tanada 

and Copper Lakes in Wrangell-St. Elias NP and lake whitefish from Lake McDonald in Glacier NP 

were predicted to exceed this benchmark over the entire range of fish sizes (fig. 10). The size at which 

50 percent of the fish in a population were predicted to exceed the benchmark for risk to highly sensitive 

piscivorous birds ranged from less than 40 mm SL in speckled dace from Fremont River site 1 in 

Capitol Reef NP to 414 mm SL in brown trout from the Colorado River in Rocky Mountain NP. Among 

the smaller “forage fish” (that is, speckled dace, torrent sculpin, and threespine stickleback), the mean 

size at which 50 percent of the individuals within a population exceeded the threshold was 59 mm SL (n 

= 6 populations). For brook trout, cutthroat trout, and rainbow trout, the mean size at which 50 percent

of the individuals within a population exceeded the threshold was 223 mm SL (n = 15 populations).

The majority of individual populations modeled (36 of 61 populations, 59 percent) were 

predicted to have no individual fish with THg concentrations exceeding the benchmark for reproductive 

impairment in moderately sensitive avian consumers across the range of fish lengths, whereas in 25 

parks (41 percent), some fish were modeled to exceed this benchmark (fig. 10). However, in 10 

populations, more than one-half of the individual fish in each population were predicted to have THg 

concentrations above the common loon reproductive impairment benchmark, and lake trout from 

Tanada Lake in Wrangell-St. Elias NP were modeled to exceed this threshold over the entire range of 

sizes sampled (fig. 10). Four of the 10 populations with greater than 50 percent of fish predicted to 

exceed the loon risk concentration at some length within the population were speckled dace. The mean 

size at which 50 percent of these speckled dace populations was predicted to exceed the loon risk 

benchmark is 58 mm SL. The mean size at which 50 percent of the individuals in a population was 

modeled to exceed the loon risk threshold was 261 mm SL for three brook trout populations (Horseshoe 

Lake in Lassen Volcanic NP, Mirror Lake in Rocky Mountain NP, and Mildred Lake in Yosemite NP).

Our models predicted that fish from 12 populations sampled (20 percent) would exceed the 270 

ng/g ww threshold for birds with the lowest Hg sensitivity at some point along their size spectrum (fig. 

10). In six of the populations, 50 percent or more of the individuals were modeled to exceed this 

threshold at some size. Four of these six populations were speckled dace from Capitol Reef and Zion 

NPs, and the mean length at which 50 percent of the population was predicted to exceed the threshold 

was 68 mm SL, only 10 mm greater than the same exceedance level for loon risk. The other two 

populations were suckers from the Fall River in Rocky Mountain NP and lake trout from Tanada Lake

in Wrangell-St. Elias NP. In those populations, the model-predicted size at which 50 percent of the 

population exceeded the threshold was 353 and 496 mm SL, respectively.

Human Consumption Risk

As mentioned in section, “Methods,” human health risk was assessed using fish muscle THg 

concentrations, not whole-body concentrations as was done for wildlife risk. In the unadjusted data 

across all parks, species and sizes of fish, 32 percent of fish sampled had THg concentrations in their 

muscle below the 50 ng/g ww threshold established by the GLAG for unlimited consumption of fish, 

indicating that some human consumption guidance would apply to 68 percent of the individuals 

measured in this study (table 4). However, only 4 percent of fish had muscle THg concentrations 

exceeding the EPA human health criterion of 300 ng/g ww, and less than 1 percent had concentrations 

above the level at which GLAG recommends that no fish be consumed (950 ng/g ww).
14

As with the other benchmarks, the proportion of fish exceeding human risk thresholds varied 

greatly among parks. Grand Teton and Great Basin NPs had the lowest proportion of fish exceeding the 

GLAG unlimited consumption threshold (18 percent), whereas 100 percent of fish analyzed from 

Glacier NP exceeded this threshold (table 4). In 17 parks (81 percent), more than one-half of sampled 

fish had concentrations above the GLAG threshold. In 11 (61 percent) of the 18 parks from which

species consumed by humans (that is, excluding speckled dace, threespine stickleback, and torrent 

sculpin) were analyzed, no fish had muscle THg concentrations exceeding the EPA human health 

criterion. In the remaining 7 of 18 parks (39 percent) with fish exceeding the EPA human health 

criterion, the proportion of fish with concentrations above 300 ng/g ww was typically only 1–3 percent 

of individuals, with the exception of Lake Clark, Wrangell-St. Elias, and Yosemite NPs, where 40.7, 

18.3, and 6.7 percent of fish exceeded the guideline, respectively (table 4). Yosemite was the only park 

in which any fish exceeded the GLAG no consumption guideline, with 3 percent of the analyzed fish 

having muscle concentrations over the guideline (table 4).

When examined at the finer site scale, 6 (8 percent) of the 79 sites from which fish species 

consumed by humans were sampled had no fish exceeding the GLAG unlimited consumption guideline, 

whereas at 23 of these sites (30 percent) all fish analyzed exceeded this guideline. At 56 sites (71

percent) at least 50 percent of the fish analyzed exceeded the unlimited consumption guideline. Thirteen 

sites (17 percent) had fish exceeding the EPA human health criterion, with more than 50 percent of

individual fish from Lake Clark (80 percent) in Lake Clark NP and Tanada Lake (85 percent) in

Wrangell–St. Elias NP exceeding the guideline. Mildred Lake in Yosemite NP was the only lake from 

which fish (7 percent) exceeded the GLAG no consumption guideline.

Size-Specific Risk

We used the same approach presented for fish and birds to model risk to humans across the size 

spectra of 54 populations with size-THg relationships. These models predicted that muscle THg 

concentrations in fish from every population would exceed the GLAG unlimited consumption guideline 

at some length over the observed range of sizes (fig. 11). The sole exception was cutthroat trout from 

Death Canyon Creek in Grand Teton NP, where even the largest fish sampled (260 mm SL) were 

predicted to have muscle concentrations below this level. In 40 of the 54 populations (74 percent)

modeled, the unlimited consumption threshold was predicted to be exceeded by some fish across the 

entire range of observed sizes (fig. 11). In 8 populations (15 percent), all fish were expected to exceed 

this threshold across the entire range of sizes sampled. In the remaining populations, the average size at 

which 50 percent of the fish in a population were expected to exceed the threshold varied substantially, 

ranging from 40 mm SL in brook trout from Golden Lake in Mount Rainier NP to nearly 400 mm SL in 

northern pike from Lake Chilchukabena in Denali NP. When limited to brook, rainbow, and cutthroat 

trout, which comprise nearly 65 percent of the fish analyzed, the average size at which 50 percent of the 

fish in a population were modeled to exceed the unlimited consumption guideline was 179 mm SL (n = 

36 populations).

Eighteen populations were modeled to exceed the EPA criterion for human consumption at some 

point across the measured size spectra (fig. 11). In six of these populations, models estimated that 50

percent or more of the individual fish at a certain size threshold within a population were predicted to 

exceed the EPA human health criterion, and all lake trout down to the smallest size (410 mm SL) from 
15

Tanada Lake in Wrangell-St. Elias NP were predicted to exceed the EPA human health criterion (fig. 

11). For the three brook trout populations where at least one-half of the fish at a given size were 

predicted to exceed the EPA criterion (Horseshoe Lake in Lassen Volcanic, Golden Lake in Mount 

Rainier, and Mildred Lake in Yosemite), the average size at which 50 percent of the individuals 

exceeded it was 258 mm SL.

After modeling risk across the entire sampled fish size range, nine populations (17 percent of all 

populations) are predicted to include some fish that exceed the GLAG no consumption guideline (fig. 

11). Of these nine populations, the models predicted that only two populations (suckers from the Fall 

River in Rocky Mountain NP and brook trout from Mildred Lake in Yosemite NP) were expected to 

have more than 50 percent of individuals in the population exceeding the threshold at some length along 

the size spectra for each population. The sizes at which 50 percent of individuals exceeded this 

threshold were 353 and 250 mm SL in suckers from the Fall River and Mildred Lake, respectively (fig. 

11).

Discussion

Our results indicate that Hg bioaccumulation and risk to aquatic ecosystems of national parks in 

the Western United States is widespread, yet highly variable. Total Hg concentrations in individual fish

ranged over two orders of magnitude across more than 1,400 individuals analyzed, with the lowest 

concentrations near 10 ng/g ww and the highest concentrations exceeding 1,100 ng/g ww. Importantly, 

this variation in Hg concentrations not only occurred across parks, but also among different sites within 

parks, even in light of site selection criteria that included restricting sites to mostly oligotrophic, 

headwater systems. These results highlight the significance of both local and regional-scale processes in 

determining Hg risk. As a result of this variability, many of the parks contained fish that were all below 

even the most conservative benchmarks of risk to fish (13 of 21 parks) and piscivorous birds (7 of 21 

parks). Moreover, although all parks contained one or more fish that exceeded the GLAG unlimited 

consumption benchmark, most parks (14 of 21) did not have any fish in exceedance of the 300 ng/g ww 

EPA fish tissue criterion. Conversely, for those parks with fish that did exceed ecological and human 

health benchmarks, a substantial proportion of the fish had concentrations that were above those 

thresholds of concern. This was particularly true in the case of avian risk, where more than one-half of 

the fish sampled in several locations exceeded thresholds for risk to reproductive impairment in highly 

sensitive and moderately sensitive bird species. Although we did not directly assess risk to mammalian 

wildlife, the benchmarks chosen for avian consumers correspond closely with the no-observed-affectlevel (NOAEL) benchmark for dietary Hg in mammalian wildlife (110 ng/g ww; Basu and Head 2010).

Thus, our data suggest that mammalian wildlife also are likely to be at risk across these parks. Finally, 

although the geographic distributions in species occurrence impeded direct comparisons across all parks

simultaneously, our data identify two regions of particular concern—(1) some parks in Alaska, as well 

as Glacier NP, had THg concentrations in large top predator fish species that approached or exceeded 

human consumption guidelines, and (2) some of the smallest “forage fish” sampled in the arid 

Southwest region had among the highest THg concentrations of the entire study, greatly exceeding 

wildlife risk thresholds for reproductive impairment. Although many plausible explanations exist for 

these patterns, investigating the potential mechanisms was beyond the scope of this study. Thus, more

work is needed to better understand the landscape drivers of THg concentrations in these fish, as well as 

any deleterious effects these Hg concentrations might be having on resident biota in these parks.

Additionally, information regarding the species composition, size ranges, and consumption rates of fish 

consumed by subsistence fishers in Alaskan parks is important for better characterizing human health 

risk in those parks.
16

THg concentrations in fish from this study generally are consistent with those of other studies in 

freshwater habitats of protected lands in the Western United States. For example, the Western Airborne 

Contaminants Assessment Project (WACAP) measured fish THg concentrations in 14 lakes from eight

western national parks, six of which also were included in this study (Landers and others, 2008). Mean 

whole-body concentrations ranged from less than 40 ng/g ww in Glacier NP to slightly more than 200 

ng/g ww in Noatak NP, Alaska (Landers and others, 2008). However, because the WACAP study was 

designed specifically as a screening study, there was limited replication within parks for evaluating sitespecific variability in relation to regional variability. The need for such replication is indicated by a 

comparison of Hg concentrations reported from Glacier NP by Landers and others (2008) and the 

current study. Landers and others (2008) found Hg concentrations in cutthroat trout from two lakes in 

Glacier NP to be among the lowest measured in their study, whereas in the current study, concentrations 

from a third lake in Glacier were among the highest observed.

We specifically addressed this issue by sampling two parks (Mount Rainier and Rocky 

Mountain) intensively, with 17 and 19 different sites in each park, respectively. This higher resolution 

sampling revealed up to 20-fold variation in size-normalized fish THg concentrations among lakes

within an individual park. This level of variation within a park is important to demonstrate and 

incorporate into park-level assessments, but is not unexpected given the well-established linkages 

between site-level characteristics and both methylation and bioaccumulation processes (Hall and others, 

2008; Mitchell and Gilmour, 2008; Gabriel and others, 2009; Rolfhus and others, 2011; Hsu-Kim and 

others, 2013). Regardless, relatively little information exists about this variability in remote and highaltitude habitats that were the focus of this study. Recent studies do suggest that Hg bioaccumulation in 

osprey nesting in alpine habitats is regulated by a combination of local processes and atmospheric 

deposition (Guigueno and others, 2012). Similarly, Hg loadings to western Canadian alpine lakes was 

most strongly related to site-specific processes such as organic matter supply and catchment weathering 

(Phillips and others, 2011). Moreover, a recent study of THg concentrations in fish from sub-alpine 

lakes in the Wallowa-Whitman National Forest in northeastern Oregon and western Idaho focused on 

among-lake variation in fish THg concentrations within a relatively localized (Eagles-Smith and others, 

2013). Consistent with the current study, mean fish THg concentrations among lakes varied by more 

than an order of magnitude (25–443 ng/g ww), even though all lakes were within 100 km of one 

another. Conifer density (basal area) within the catchment of each lake was the strongest predictor of 

fish THg concentrations among lakes (Eagles-Smith and others, 2013), highlighting the importance of 

watershed characteristics on downstream Hg cycling processes. At an even broader scale, the percentage 

of land covered by coniferous forests (coupled with wet Hg deposition) across six States in the southcentral U.S. was an important factor influencing fish THg concentrations (Drenner and others, 2013).

The hierarchical spatial design of the current study, combined with the gradient in landscape types, 

altitudes, and fish species that occur over the approximately 4,000 km distance, complicate a similar 

landscape scale analysis without even greater data density and replication among sites. However, our 

results support the notion that Hg risk is driven by a dynamic balance of local, regional, and global 

processes. What is unclear, is how the relative importance of these processes changes across locations, 

which should be addressed in focused future research in order to facilitate more informed management 

of Hg risk.

Although we do not formally address risk to the unique ecological communities across the parks

studied, the model-adjusted fish THg concentrations provide a valuable index of relative risk to fish, 

wildlife, and human health. Our results suggest that although risk is low in many locations, there are 

substantial concerns about the impact of Hg on ecological health in other locations. In particular, THg 

concentrations in speckled dace, a small invertebrate-foraging minnow from Zion and Capitol Reef NPs,
17

commonly exceeded some of the highest values in top predators, such as lake trout, from other parks.

Size-normalized (50 mm) mean THg concentrations in these fish exceeded 200 ng/g ww in both parks, 

and mean concentrations in one site exceeded 300 ng/g ww. Moreover, across the range of fish sampled 

in these parks (approximately 70–100 mm SL), most fish exceeded these values. Because speckled dace 

occupy intermediate trophic positions, they serve as potential prey items for predatory fish and 

piscivorous birds, and dietary Hg concentrations at these levels are associated with biochemical and 

reproductive effects in fish (Depew and others, 2012a), as well as reproductive impairment in birds 

(Depew and others, 2012b). Moreover, it suggests that other invertebrate-feeding organisms in the park 

could be at risk. Amphibians and riparian- or aquatic invertebrate-feeding birds are two groups in 

particular that are both sensitive to Hg, and likely to be exposed due to their foraging ecology (Bergeron 

and others, 2011a, 2011b; Jackson and others, 2011; Metts and others, 2012; Willson and Hopkins, 

2013).

THg concentrations in fish from Wrangell-St. Elias, Lake Clark, and Glacier NPs approached or 

exceeded all three benchmarks associated with reproductive impairment in piscivorous birds (90, 180, 

and 270 ng/g ww), and the EPA criterion for protection of human health. It is unclear whether these 

elevated concentrations are the result of enhanced MeHg production in these systems, or simply the fact 

that these were large fish (400–650 mm SL) that were likely many years old and had reached a growth 

asymptote in systems with only moderate Hg availability. This information gap is an important 

component to address with future work because it will help better gauge risk to park visitors and 

wildlife. Both Wrangell-St. Elias and Lake Clark support subsistence hunting and fishing activities for 

native and non-native rural Alaskans. If toxicological risk is mostly restricted to large, older fish, then 

guidelines can be better established to inform subsistence users of how to minimize exposure risk.

Moreover, relatively few wildlife species are capable of consuming these large individuals, suggesting 

fewer species would be at risk from fish consumption and the species that are would likely be more 

easily monitored. Thus, understanding the relative risk posed across the size spectra of a population 

provides important insights into how that risk can be monitored and managed. Conversely, if certain 

habitats or locations within these parks are particularly sensitive to Hg methylation, the food web 

contamination may be more widespread, potentially necessitating a broader communication and 

monitoring strategy that might incorporate a more comprehensive array of subsistence foods and other 

wildlife taxa. Progress is already being made to address this potential concern, and USGS and WrangellSt. Elias NP are currently completing a study to assess THg concentrations in several additional 

locations and species, as well as to evaluate the age structure of the fish being sampled. Although 

subsistence harvest is not a concern in Glacier NP, one of the species we measured, the bull trout, is 

listed as federally threatened under the endangered species act. Hg concentrations that we measured in 

bull trout from Lake McDonald in Glacier NP approached levels of concern for tissue-based fish 

toxicity. Because we only sampled fish from a single lake in Glacier NP, it is unclear if this is a 

widespread concern for toxicity to bull trout or their predators, but our data suggest that a follow-up 

study is warranted.

The unprecedented spatial breadth of this study facilitates the most thorough understanding of 

Hg bioaccumulation patterns in fish of western national parks to date. Our analysis and data compilation 

provide novel insight into the broad-scale distribution of Hg in fish communities of remote, protected 

habitats. Of note, many locations show limited Hg risk, and our data confirm that even with continued 
18

increases in global Hg releases (Sunderland and Selin, 2013), many protected NPS lands in the United 

States still exhibit relatively low Hg risk. However, our results also raise new questions and can be used 

to guide the development of future research to help manage the unexpected number of locations in this 

study where Hg contamination could be an ongoing or emerging threat to ecosystem health. The high 

degree of variation within parks and that the parks with the most intensive sampling had the greatest 

range in THg concentrations. These findings strongly suggest that more intensive research and 

monitoring efforts within parks will undoubtedly reveal both low and high risk environments. Thus, 

monitoring programs should not focus on a small number of “indicator” sites and we recommend that 

where feasible, newly established monitoring or investigation efforts focus on sampling at the largest 

spatial scale possible within a park to better understand this variability.

Additionally, our focus on high-altitude habitats provided little insight regarding the magnitude 

of risk in lower altitude lakes and wetlands. Recent work in Mount Rainier NP suggests that Hg 

bioaccumulation in wetlands and lakes is substantially higher in the lowest-altitude habitats (C.A. 

Eagles-Smith, U.S. Geological Survey, unpub. data, 2013). Additional monitoring in low-altitude

habitats that integrate a broader range of watershed processes is warranted.

Beyond monitoring, a more quantitative understanding of the biogeochemical and food web 

factors that regulate within-park variability will facilitate greater certainty in predicting areas across 

these parks with the greatest risk likelihood. Future interdisciplinary research across a range of 

replicated aquatic habitat types that couples key biogeochemical process-level measurements with 

detailed food web processes and quantification of bioaccumulation pathways would provide valuable 

insight for developing these predictive models. A new collaborative, citizen-science effort between 

USGS, NPS, and University of Maine will make initial progress in this area by evaluating Hg 

bioaccumulation in biosentinel dragonfly larvae in relation to a range of biogeochemical and landscape 

drivers. One benefit of this upcoming effort is that the use of dragonflies as biosentinels will inform the 

parks about risk to aquatic habitats that are not fish-bearing. Another impending contribution in this 

realm will be provided by an empirical model being developed by the USGS Mercury Research 

Laboratory that will predict aqueous MeHg concentrations in surface water based on water chemistry 

and watershed structure. Coupling this model with biological assessments may provide more predictive 

power to assess ecological risk.

Although these suggestions will greatly increase the understanding of the drivers of Hg cycling 

in national parks, estimates of risk will continue to be speculative and of limited confidence without 

empirical research on toxicological responses in resident park biota. This lack of robust toxicological 

benchmarks for many taxa was a particular concern in the current study because few taxa extended 

across the large spatial extent and ecologically diverse habitats sampled. Although our choice of 

toxicological benchmarks were appropriate given the constraints of the current study, generalized 

benchmarks, such as our bird risk thresholds, do not provide definitive estimates of risk to specific park 

resources. Specifically, the data presented here suggest that toxicological assessments of key ecological 

endpoints in Capitol Reef, Zion, Lassen Volcanic, Yosemite, Wrangell-St. Elias, Lake Clark, and 

Glacier NPs are warranted. Direct assessments of the physiological, behavioral, and reproductive 

responses of wildlife and fish in these parks will be tremendously valuable for calibrating risk estimates 

that have been derived on different taxa in unrelated habitats, and provide a baseline from which 

meaningful benchmarks for evaluating the integrative risk of Hg toxicity to whole parks or ecosystems 

could be developed.
19

National Park Summaries

Capitol Reef National Park

All fish sampled from Capitol Reef NP were speckled dace, a small insectivorous “forage fish.”

Despite their intermediate position in the food web, these fish contained some of the highest Hg 

concentrations measured in this study, exceeding those measured in many of the largest predatory fish.

As smaller fish, speckled dace serve as potential prey items for predatory fishes and piscivorous birds, 

and dietary Hg concentrations at these levels are associated with biochemical and reproductive effects in 

fish (Depew and others, 2012a), as well as reproductive impairment in birds (Depew and others, 2012b).

Moreover, such high Hg concentrations suggest that other invertebrate-feeding organisms in the park 

could be at risk. Amphibians and riparian- or aquatic invertebrate-feeding birds are two groups in 

particular that are both sensitive to Hg, and likely to be exposed due to their foraging ecology (Bergeron 

and others, 2011a, 2011b; Jackson and others, 2011; Metts and others, 2012; Willson and Hopkins, 

2013). However, we only sampled a single species at three sites in Capitol Reef NP, all of which were 

along the Freemont River. Therefore, we are unable to speculate whether the fish communities 

throughout the park contain similarly high concentrations, or whether these values were the result of a 

localized process. Future sampling of additional sites and species within the park is necessary to fill this 

important knowledge gap.

Crater Lake National Park

Kokanee and rainbow trout were sampled from two sites in Crater Lake NP. The two species had 

similar Hg concentrations and were among the lowest measured in this study, ranging from 16.8 to 76.0 

ng/g ww. Overall our results indicate that Hg concentrations in fish from Crater Lake are unlikely to put 

fish or avian consumers at risk.

Denali National Park

We sampled northern pike from a single lake in Denali NP. Despite their large size and position 

as top predators, northern pike from Denali NP had the lowest size-normalized Hg concentrations in the 

400 mm SL size class (47.4 ng/g ww at 400 mm SL) and some of the lowest observed in the entire 

study. In fact, the THg concentrations in northern pike from Denali were similar or less than THg 

concentrations in smaller fish species from the other parks in Alaska (Wrangell-St. Elias, Lake Clark, 

Glacier Bay). Moreover, past work in Denali found similarly low THg concentrations in burbot (Lota 

lota) and whitefish (Landers and others, 2008). Such low Hg concentrations may be the result of this 

site’s isolated nature. However, at other similarly isolated sites in Alaska, northern pike have been found 

to have consistently higher Hg concentrations (110–1,500 ng/g ww on average; Jewett and Duffy,

2007). Any additional sampling from Denali NP should aim to assess whether these data are 

representative of other water bodies and species in the park.
20

Glacier Bay National Park

We sampled Dolly Varden from two lakes and one stream in Glacier Bay NP. Mean THg 

concentrations across these three sites (90.2 ng/g ww) were slightly above the global mean 

concentration in fish across all sites and parks in this study (77.7 ng/g ww). When modeled at 200 mm, 

the mean Hg concentration in fish from Glacier Bay NP (102.3 ng/g ww) was among the highest in the 

size class. However, we also observed a 3-fold variation in the mean concentrations among the three 

lakes indicating that local processes are likely important drivers of Hg bioaccumulation in fish within 

this park. The THg concentrations measured in Dolly Varden from Glacier Bay NP were similar to 

concentrations (40–230 ng/g ww) found in Dolly Varden from other sites in Alaska (Jewett and Duffy,

2007).

Glacier National Park

Lake whitefish and bull trout were sampled from Lake McDonald in Glacier NP. Both species 

had high Hg concentrations relative to the mean across all fish in the study, and after accounting for the 

effects of size and species, fish from Glacier NP were some of the highest in the large (400 mm SL) size 

class. Mercury concentrations in Glacier NP fish approached or exceeded the EPA criterion for 

protection of human health and the level at which reproductive impairment to piscivorous birds could 

occur. Additionally, Hg concentrations in many individuals exceeded the level at which tissue-based 

toxicity to fish is a concern. This is particularly important considering bull trout is federally listed as 

threatened under the endangered species act. Because we only sampled fish from a single lake, we 

cannot assess whether these data are representative of other lakes in the park. However, Landers and 

others (2008) found that fish from two other lakes within Glacier NP had the lowest Hg concentrations 

among the 14 lakes measured across national parks in the West. These contrasting results suggest that 

substantial variation in Hg concentrations exists among water bodies within Glacier NP and more 

detailed analysis of local processes may be necessary to effectively manage risk.

Grand Canyon National Park

At the three sites we sampled in Grand Canyon NP, unadjusted mean THg concentrations (76 

ng/g ww) were similar to the average across all fish in the study. However, size adjusted (200 mm SL)

THg concentrations were among the highest in the size class (101.2 ng/g ww) across all parks.

Moreover, size-adjusted THg concentrations in Shinumo Creek (178.8 ng/g ww) were more than 2-fold 

higher than those in the other two sites (71.5 and 81.0 ng/g ww), suggesting that Hg exposure within the 

park is variable.

Grand Teton National Park

Mercury concentrations in fish from the two lakes and one stream sampled in Grand Teton NP 

were consistently among the lowest measured in this study. It is unclear whether these low 

concentrations are the result of low local inputs of Hg, the Hg methylation potential of the water bodies 

measured, or some biological characteristic of the fish.
21

Great Basin National Park

We sampled brook trout from two creeks and a lake in Great Basin NP. Among these three sites 

Hg concentrations were uniformly among the lowest measured in the current study suggesting that at the 

time of sampling the ecological risk posed by Hg in these systems is likely low. Atmospheric dry 

deposition in Great Basin NP was among the highest measured in six western national parks (Wright 

and others, 2014).

Great Sand Dunes National Park

Mercury concentrations in fish from one of the two sites (Medano Lake; 70.1 ng/g ww) sampled 

in Great Sand Dunes NP were similar to the average across parks, whereas fish from the second site 

(Sand Creek; 52.7 ng/g ww) were considerably lower. Based on these data, the risk of Hg exposure to 

wildlife is likely low at these sites; however, data from these two sites may not adequately characterize 

risk at other locations within the park.

Lake Clark National Park

Lake trout from three lakes in Lake Clark NP were included in this study. Two of these sites 

(Lake Clark and Lake Kontrashibuna) were sampled in both 2011 and 2012, although Hg concentrations 

were not significantly different between the 2 years. Although THg concentrations across all sites within 

the park were among the highest observed in the 400 mm SL size class, there was considerable variation 

among lakes within the park. The mean THg concentration in Lake Clark (365.2 ng/g ww) was more 

than 3-fold higher than that in Telaquana Lake (109.0 ng/g ww) and 1.8 than that in Lake Kontrashibuna 

(204.0 ng/g ww). At the lower end of this range, THg concentrations pose limited risk to park wildlife 

and human users. However, the concentrations observed in Lake Kontrashibuna exceeded the 

benchmark for reproductive impairment to piscivorous birds, and the tissue-based criterion for fish 

toxicity. Moreover, fish from Lake Clark exceeded these benchmarks and the EPA criterion for 

protection of human health.

Lassen Volcanic National Park

There was greater than 4-fold variation in mean fish THg concentrations among the three lakes 

that brook trout were sampled from in Lassen Volcanic NP. Mercury concentrations were lowest in 

Summit Lake (43.7 ng/g ww), whereas Ridge Lake (111.3 ng/g w) and Horseshoe Lake (180.7 ng/g 

ww) had concentrations above the mean concentration for all fish in this study. Some of this variation in 

Hg concentrations among lakes in the park was due to the size of fish. After adjusting fish THg 

concentrations to a 200 mm SL fish size, the variation among lakes was substantially reduced. Sizebased risk assessments were conducted for Horseshoe and Summit Lakes, and the resulting risk profiles 

contrast sharply. Our modeled risk estimates suggest that there is limited toxicological risk to fish, 

wildlife or humans across the fish size range in Summit Lake. Conversely, brook trout from Horseshoe 

Lake were modeled to reach concentrations of concern for tissue-based fish toxicity and risk to even the 

least sensitive species of avian consumers within the range of sizes sampled. Furthermore, a high 

proportion of fish from Horseshoe Lake were modeled to exceed the EPA criterion for protection of 

human health at sizes exceeding 280 mm SL.
22

Mesa Verde National Park

Speckled dace were sampled from a single location, the Mancos River, in Mesa Verde NP.

Despite the small size of these fish (43–69 mm SL), their THg mean concentration (74.9 ng/g ww) was

to the study-wide mean value. However, the THg concentrations from speckled dace from the lone site 

in Mesa Verde NP were much lower than those measured in dace from nearby Capitol Reef and Zion 

NPs. This difference suggests that the high concentrations observed in dace from these other parks is not 

solely due to some aspect of this species biology, but may reflect environmental processes occurring at 

the site or watershed scale.

Mount Rainer National Park

Mount Rainer NP is one of two parks in which we sampled a large number of sites in order to 

characterize intra-park variation. Although the average fish THg concentration across the 17 sites from 

which fish were sampled (71.5 ng/g ww) was similar to the study-wide mean across all fish, we found a 

12-fold range in mean concentrations among sites before accounting for the effects of size. Sizenormalized Hg concentrations in the 200 mm SL size class were even more variable among sites. The 

highest mean concentration at a site (193.2 ng/g ww) was nearly 23-fold higher than the lowest site 

mean concentration (8.5 ng/g ww). Such extreme variation among sites in Mount Rainer NP suggests 

that local-scale factors play an important role in determining the ecological risk of Hg and emphasizes 

the need to sample from multiple locations in order to accurately characterize Hg risk to park resources 

as a whole.

North Cascades National Park

All three of the sites sampled in North Cascades NP had mean Hg concentrations below the 

average of all fish sampled in this study. After standardizing the fish to 200 mm SL, the mean Hg 

concentration in fish from North Cascades NP (73.3 ng/g ww) was similar to the mean of 200 mm fish 

across all parks. These data suggest that the ecological risk of Hg at the three sites sampled in North 

Cascades NP is low relative to many of the other parks. However, given the variation demonstrated 

among sites in this study, the limited sampling it is difficult to generalize across other sites in the park 

without more extensive sampling.

Olympic National Park

Mercury concentrations in fish across the five lakes sampled in Olympic NP (85.0 ng/g ww) 

were slightly higher than the mean concentration across the entire study. However, we found substantial 

variability in fish THg concentrations among lakes. In particular, size-adjusted THg concentrations in 

fish from Hoh Lake (253.0 ng/g ww) were more than 3.5-fold higher than those in Gladys Lake (71.5 

ng/g ww), which had the lowest site-specific THg concentrations in the park. Our models of Hg risk to 

consumers reflects these higher concentrations and suggest that fish in Hoh Lake are likely to approach 

or exceed the EPA criterion for protection of human health and the avian benchmark for reproductive 

impairment above 180 mm. These results are similar to those reported by Landers and others (2008),

who found Hg concentrations in fish from Hoh Lake were among the highest measured during their 

screening of national parks.
23

Rocky Mountain National Park

We sampled 19 sites in Rocky Mountain NP, allowing us to more rigorously examine within 

park variability in Hg concentrations among sites. Overall, the mean Hg concentration in fish from 

Rocky Mountain NP ( ng/g ww) was slightly lower than the study-wide mean across all parks. Across 

sites within Rocky Mountain NP, concentrations varied by more than 6.5-fold between the sites with the 

lowest (Lake Haiyaha; 19.8 ng/g ww) and highest (Mirror Lake; 121.2 ng/g ww) concentrations. Our 

models of Hg risk suggest that most of the sites we sampled from Rocky Mountain NP had fish THg 

concentrations below the benchmarks of risk that we selected. However, brook trout from Mirror Lake 

and suckers from the Colorado and Fall Rivers are likely to exceed both the EPA human health criterion

level and the avian reproductive impairment benchmark when the fish exceed 250 mm SL. In addition, 

we examined inter-annual variation at four sites in Rocky Mountain NP. At two of these sites (Nanita 

Lake and Mirror Lake), we found that there was no significant difference between the years sampled, 

whereas fish THg concentrations at Poudre Lake and Ypsilon Lake were significantly lower in 2012 

compared to 2009. Additionally, two of the lakes sampled in this study (Mills Lake and Lone Pine 

Lake) also were sampled for another study in 2003 (Landers and others, 2008). Rainbow trout THg 

concentrations in Mills Lake were higher (87.5 ng/g) than in 2003 (less than 60 ng/g ww). Whereas THg 

concentrations in brook trout from Lone Pine Lake were lower (57.8 ng/g ww) than in 2003 

(approximately 70 ng/g ww). Consistent with the results from Mount Rainer NP, our more intensive 

sampling at Rocky Mountain NP indicates substantial variation among sites, highlighting the 

importance of sampling multiple sites when characterizing the risk of Hg exposure within a national 

park.

Sequoia–Kings Canyon National Park

Four high-altitude lakes were sampled from Sequoia–Kings Canyon NPs. The mean fish THg 

concentration across all these sites (43.8 ng/g ww) was below the study-wide average across all fish 

analyzed in this study. Size-adjusted (200 mm SL) THg concentrations remained similarly low in all but 

Center Basin Lake, where the mean THg concentrations in golden trout increased to 207.3 ng/g ww.

However, based on the size distribution of our sample of 30 individuals, 200 mm fish are likely rare in 

this population. Furthermore, two of the lakes from Sequoia–Kings Canyon NPs were sampled in 2008 

(Center Basin Lake) or 2009 (Kern Point Lake) and again in 2012. Comparisons between sampling 

years indicate that Hg concentrations in fish from Kern Point Lake were remained similar between 

years, whereas Hg concentrations in Center Basin Lake fish were higher in 2012 than in 2008. Landers 

and others (2008) reported Hg concentrations higher than those observed in the current study from two 

additional high-altitude lakes in Sequoia–Kings Canyon NPs (Pear and Emerald Lakes), demonstrating 

that even among high-altitude lakes with potentially limited Hg inputs, fish THg concentrations can be 

quite variable.

Wrangell-St. Elias National Park

Lake-specific mean fish THg concentrations from the three lakes sampled at Wrangell-St. Elias

NP spanned nearly 8-fold between rainbow trout from Summit Lake (53.3 ng/g ww) and Lake Trout 

from Tanada Lake (416.6 ng/g ww), which had the highest mean Hg concentration of any site from all 

of the parks examined in this study. After size-adjusting fish THg concentrations, we found that 

concentrations in 200 mm SL fish from Copper Lake (147.4 ng/g ww) were substantially higher than 

those from Summit Lake (65.4 ng/g ww). The mean size-adjusted THg concentration for 400 mm SL

fish from Copper Lake (242.0 ng/g ww) and Tanada Lake (321.2 ng/g ww) approached or exceeded the 
24

EPA fish tissue criterion, the avian reproductive impairment benchmark, and the tissue-based criterion 

for fish toxicity. Tanada Lake was one of the few lakes in the present study in which a relatively high 

proportion of fish were expected to exceed upper benchmarks for fish toxicity, reproductive impairment 

in low sensitivity birds, and at the largest sizes sampled, the no-consumption guideline proposed by the 

GLAG. The cause of such high concentrations in some fish from Wrangell-St. Elias NP is unclear and 

may reflect some combination of local biogeochemical processes that stimulate methylmercury 

production, the ecological structure of the lake’s food web, or physiological characteristics of the fish 

themselves. For example, fish with high Hg concentrations may be exceptionally old and thus may have 

accumulated large quantities of Hg over their extended lives. Alternatively, fish in such northern lakes 

may grow slowly compared to fish in warmer, more productive systems resulting in little biodilution of 

ingested Hg through somatic growth.

Yellowstone National Park

Across all lakes, mean fish THg concentrations in Yellowstone NP (101.2 ng/g ww) were above 

the study-wide mean value from all parks. Size adjusted THg concentrations for 200 mm SL fish (119.8 

ng/g ww) were among the highest measured in this study. Importantly, natural geothermal Hg sources 

occur throughout Yellowstone, though it is unclear if those sources play a role in fish bioaccumulation.

Yosemite National Park

The two sites sampled at Yosemite NP display starkly contrasting patterns of Hg concentrations. 

At one site, Spillway Lake, fish THg concentrations were uniformly low; the site mean (38.7 ng/g ww) 

was one-half of the study-wide mean across all parks. In contrast, THg concentrations in fish from 

Mildred Lake (174.4 ng/g ww) were more than twice the study-wide mean. Moreover, individual fish 

concentrations had a 15-fold range within the lake. Importantly, the highest individual fish THg 

concentration in the entire study (1,109 ng/g ww) was measured in a brook trout from Mildred Lake.

This was the only fish that exceeded the no-consumption guideline proposed by the GLAG, and was 

1.6-times greater than the next highest concentration measured in this study. The source of such 

variation within a lake is unclear, but future efforts should aim to identify the factors regulating 

accumulation in individuals and determining whether this variability is representative of other lakes in 

the park.

Zion National Park

As in Capitol Reef NP, all fish sampled from Zion NP were speckled dace and displayed high 

Hg concentrations (241.5 ng/g ww) for a small, low trophic level fish. At both sites along the Virgin 

River, mean Hg concentrations were more than 3-fold higher than the study-wide mean concentration.

Furthermore, variation within and between these isolated sites was very low. As in Capitol Reef, the 

potential for dace to serve as prey for higher trophic position consumers, and indicators of Hg exposure 

in other invertebrate-feeding taxa, suggest that more research should examine factors regulating Hg 

accumulation in the lower trophic levels of these systems.
25

Acknowledgments

This study was funded by the National Park Service, Air Resources Division, the U.S. 

Geological Survey Forest and Rangeland Ecosystem Science Center, and the U.S. Geological Survey 

Contaminants Biology Program within the Environmental Health Mission Area. We thank Tamara Blett 

and Kristi Morris for their support in facilitating this study. This effort would not have been possible 

without the efforts of a long list of park staff including, but not necessarily limited to: Andrea Blakesley,

Danny Boiano, Sandra Borthwick, Phyllis Bovin, Fred Bunch, Paul Burger, Sue Consolo Murphy, 

Brook Cox, Tonnie Cummings, Ninette Daniele, Chris Downs, Annie Esperanza, Steven Fradkin, Scott 

Girdner, Brian Healy, David Hering, Todd Koel , Michael Magnuson, Molly McCormick, Erik Meyer, 

Stephen Monroe, Steve Monroe, Jack Oelfke, Emily Omana Smith, Mark Pepper, Adam Pfleeger, 

Ashley Rawhouser, John Reber, Ben Roberts, Judy Rocchio, Barbara Samora , George San Miguel, 

Chris Sargeant, Dave Sharrow, Jeff Shearer, Chad Soiseth, Lee Tarnay, Kathy Tonnessen, Melissa 

Trammell, Eric Veach, Mary Kay Watry, Chad Whaley, and Dave Worthington. We are grateful for the 

efforts of Brandon Kowalski, John Pierce, Kevin Donner, and Nick Baker for their laboratory efforts, 

and Branden Johnson and Drew Bingham for database support and assistance with maps, figures, and 

tables. We also thank Jesse Lepak, Jim Wiener, Dixon Landers, Sarah Nelson, Marty Fitzpatrick, 

Tamara Blett, and Cathy Tonnessen for comments on previous versions of this report.

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29

Figure 1. Spatial distribution of the 21 national parks in the Western United States sampled in this study between 

2008 and 2012. Shaded polygons on base map indicate park boundaries. Red circles within each inset park 

boundary indicate specific sampling locations for each park.
30

Figure 2. Total mercury (THg) concentrations (ng/g ww) in fish muscle from 21 national parks in the Western 

United States. Bar height and bolded error bars represent the park-wide geometric mean THg concentration and 

95-percent confidence interval, respectively. Colored circles and thin error bars represent site-specific geometric 

mean THg concentration and 95-percent confidence interval, respectively. Parks are ordered by decreasing 

latitude, and park abbreviations can be referenced to park names in table 1.
31

Figure 3. Total mercury (THg) concentrations (ng/g ww) in fish muscle from individual sites within 21 national parks in the Western United States.

Bar height and bolded error bars represent site-specific geometric means and 95-percent confidence intervals. Circles represent species-specific 

geometric means in 95-percent confidence intervals within each site. Parks are ordered by decreasing latitude, and park abbreviations and site 

numbers can be referenced to park name in table 1.
32

Figure 4. Size-normalized least-square (LS) total mercury (THg) concentrations in fish from 21 national parks in the Western United States. LS 

mean concentrations control for the influence of fish species and site within each park. Blue bars are LS means for fish species normalized to 50 mm 

size, green bars are LS means for fish species normalized to 200 mm size, orange bars are LS means for fish species normalized to 400 mm size.

Parks are ordered by decreasing latitude, and park abbreviations can be referenced to park name in table 1. Species comprising each size category 

is discussed in section, “Methods.”
33

Figure 5. Least-square mean fish muscle total Hg concentrations (ng/g ww) in three size-normalized classes 

(blue/left = 50 mm, green/middle = 200 mm, orange/right = 400 mm) from 21 national parks in the Western United 

States.
34

Figure 6. Least-square mean (whiskers = standard error) total mercury (THg) concentrations in fish muscle from individual sites in 21 national parks

in the Western United States. Concentrations are size normalized for (A) 400 mm SL, (B) 200 mm SL, (C) 50 mm SL fish. Park abbreviations and 

site numbers can be referenced to park name in table 1.
35

Figure 7. Inter-annual comparisons of fish total mercury concentrations (ng/g ww) in muscle tissue from 10 sites in 

four national parks in the Western United States. Error bars represent standard error. Asterisks indicate significant 

differences (p<0.05) between years within a site. OLYM, Olympic NP, ROMO, Rocky Mountain NP; SEKI, SequoiaKings Canyon NP; and LACL, Lake ClarkNP.
36

Figure 8. Example size-risk profile to evaluate proportion of fish exceeding defined toxicological benchmarks. Each 

color represents a defined risk benchmark. Solid lines indicated the estimated proportion of fish exceeding 

benchmarks across the size spectrum. Shaded regions represent the 95-percent prediction interval around the 

benchmark. A solid line at 0 or 100 percent indicates that all no fish or all fish, respectively, exceed the specified 

benchmark across the size spectra.
37

Figure 9. Modeled percentage of fish across the size range sampled in each population with whole-body total mercury concentrations that exceed 

benchmarks at a given size for a generic no-observed-effects residue (green; 200 ng/g ww), and lowest-observed-effects-residue (red; 300 ww) for 

fish health at 21 national parks in the Western United States. Parks are ordered by decreasing latitude. Figure continues on next page.
38

Figure 9.—Continued. Modeled percentage of fish across the size range sampled in each population with whole-body total mercury concentrations 

whole-body total mercury concentrations that exceed benchmarks for a generic no-observed-effects residue (green; 200 ng/g ww), and lowestobserved-effects-residue (red; 300 ng/g ww) for fish health in 21 national parks in the Western United States. Parks are ordered by decreasing 

latitude.
39

Figure 10. Modeled percentage of fish across the size range sampled in each population with whole-body total mercury concentrations that exceed 

dietary toxicity benchmarks for piscivorous birds that can be classified as high (green; 90 ng/g ww), medium (orange; 180 ng/g ww; common loon 

reproductive impairment), or low (red; 270 ng/g ww) sensitivity in 21 national parks in the Western United States. Parks are ordered by decreasing 

latitude. Figure continues on next page.
40

Figure 10.—Continued. Modeled percentage of fish across the sampled size range in each population with whole-body total mercury concentrations 

that exceed dietary toxicity benchmarks for piscivorous birds that can be classified as high (green; 90 ng/g ww), medium (orange; 180 ng/g ww; 

common loon reproductive impairment), or low (red; 270 ng/g ww) sensitivity in 21 national parks in the Western United States. Parks are ordered by 

decreasing latitude.
41

Figure 11. Modeled percentages of fish across the sampled size range in each population with muscle total mercury concentrations exceeding the 

Great Lakes Advisory Group’s (GLAG) unlimited consumption threshold (green; 50 ng/g ww), the Environmental Protection Agency’s fish 

consumption criterion (orange; 300 ng/g ww), and the GLAG’s no-consumption threshold (red; 950 ng/g ww) in 21 national parks in the Western 

United States. Parks are ordered by decreasing latitude.
42

Figure 11.—Continued. Modeled percentages of fish across the sampled size range in each population with muscle total mercury concentrations 

exceeding the Great Lakes Advisory Group’s (GLAG) unlimited consumption threshold (green; 50 ng/g ww), the Environmental Protection Agency’s 

fish consumption criterion (orange; 300 ng/g ww), and the GLAG’s no consumption threshold (red; 950 ng/g ww) in 21 national parks in the Western 

United States. Parks are ordered by decreasing latitude.
43

Table 1. Site locations and sampling information for 21 national parks in the Western United States sampled 

between 2008 and 2012.

Park Site

ID Latitude Longitude Altitude 

(m)

Habitat Species Year

Sampled n

Standard Length

(mm) SRa

Site Mean Range

Capitol Reef

Fremont River #1 1 38.2827 -111.1157 1502 river speckled dace 2012 15 58 46-74 Y

Fremont River #4 2 38.2815 -111.1794 1577 river speckled dace 2012 15 61 55-71 Y

Fremont River #7 3 38.2856 -111.2416 1649 river speckled dace 2012 15 67 53-99 Y

Crater Lake

Crater Lake 1 42.9057 -122.1017 1884 lake kokanee 2011 15 207 172-265 Y

rainbow trout 2011 12 254 137-370 Y

Denali

Lake Chilchukabena 1 63.9153 -151.5083 191 lake northern pike 2012 17 407 232-546 Y

Glacier

Lake McDonald 1 48.5691 -113.9362 963 lake bull trout 2008 5 434 386-494 N

Glacier Bay

Falls Creek 1 58.4443 -135.5988 226 creek Dolly Varden 2012 15 96 73-127 N

North Skidmore Lake 2 58.8451 -136.6839 98 lake Dolly Varden 2012 15 161 128-203 N

Stonefly Lake 3 58.9674 -136.3379 38 lake Dolly Varden 2012 15 141 61-219 Y

lake whitefish 2008 10 396 371-431 Y

Grand Canyon

Bright Angel Creek 1 36.1228 -112.0800 887 lake brown trout 2012 2 139 104-174 N

rainbow trout 2012 10 131 96-263 N

Havasu Creek 2 36.2980 -112.7402 621 creek rainbow trout 2012 15 200 140-268 N

Shinumo Creek 3 36.2515 -112.33186 794 creek rainbow trout 2012 15 171 131-222 Y

Grand Teton

Death Canyon 1 43.6702 -110.87452 2564 creek cutthroat trout 2012 15 214 162-253 Y

Grizzly Bear Lake 2 43.8027 -110.8107 2814 lake cutthroat trout 2012 15 254 219-315 Y

Lake Solitude 3 43.7926 -110.8448 2758 lake cutthroat trout 2012 15 227 137-278 Y

Great Basin

Baker Lake 1 38.9577 -114.3100 3243 lake brook trout 2011 9 230 200-252 N

Lehman Creek 2 38.9246 -114.2381 2404 creek brook trout 2011 15 150 127-167 N

Snake Creek 3 39.01468 -114.2428 2281 creek brook trout 2011 15 154 122-204 N

Great Sand Dunes

Medano Lake 1 37.8564 -105.4847 3513 lake cutthroat trout 2009 15 165 110-212 N

Sand Creek 2 37.9350 -105.5230 3365 creek rainbow trout 2009 14 190 153-258 N
44

Park Site

ID Latitude Longitude Altitude 

(m)

Habitat Species Year

Sampled n

Standard Length

(mm) SRa

Site Mean Range

Lake Clark

Lake Clarkb 1 60.0187 -154.7574 77 lake lake trout 2011 16 476 364-648 N

lake trout 2012 12 478 428-580 N

Lake Kontrashibuna 2 60.1795 -154.2223 140 lake lake trout 2011 14 358 315-398 N

lake trout 2012 2 383 378-387 N

Telaquana Lake 3 60.9520 -153.7625 372 lake lake trout 2011 15 483 412-586 N

Lassen Volcanic

Horseshoe Lake 1 40.4724 -121.3358 1996 lake brook trout 2009 15 249 197-305 Y

Ridge Lake 2 40.4138 -121.4630 1984 lake brook trout 2009 17 187 143-210 N

Summit Lake 3 40.4929 -121.4233 2038 lake brook trout 2009 15 221 165-346 Y

Mesa Verde

Mancos River 1 37.2204 -108.3410 1886 river speckled dace 2012 10 56 43-69 N

Mount Rainier

Bench Lake (LZ27) 1 46.7622 -121.6986 1386 lake brook trout 2012 6 262 237-298 Y

Golden Lake (LM17) 2 46.8887 -121.9002 1372 lake brook trout 2012 16 73 36-229 Y

Green Lake (LC07) 3 46.9769 -121.8590 974 lake cutthroat trout 2012 6 257 214-285 N

Lake George (LN02) 4 46.7917 -121.9040 1308 lake torrent sculpin 2012 16 49 37-62 Y

Louise Lake (LZ21) 5 46.7704 -121.7157 1405 lake brook trout 2012 6 171 145-192 Y

Lower Deadwood Lake 

(LW33) 6 46.8871 -121.5227 1602 lake rainbow trout 2012 11 239 185-353 Y

sticklebackc 2012 6 42 34-59 Y

Lower Palisades Lake 

(LH12) 7 46.9533 -121.5903 1682 lake brook trout 2012 19 277 180-365 Y

Wetland 1244 8 46.7704 -121.7259 1487 lake brook trout 2012 7 158 122-179 Y

Wetland 1614 9 46.7401 -121.8836 669 lake cutthroat trout 2012 7 108 89-135 Y

Unnamed Lake (LW05) 10 46.9561 -121.5719 1649 lake cutthroat trout 2012 11 238 195-278 Y

Unnamed Pond (LH11) 11 46.9554 -121.5932 1666 lake brook trout 2012 15 159 122-201 Y

Wetland 583 12 46.8918 -121.5948 1125 lake brook trout 2012 9 164 131-188 N

Unnamed wetland 

(LH15) 13 46.9517 -121.6178 1679 lake cutthroat trout 2008 14 218 187-276 Y

Mowich Lake (LM04) 14 46.9339 -121.864 1506 lake torrent sculpin 2008 7 99 92-105 Y

torrent sculpin 2012 2 56 53-59 Y

Reflection Lake (LN19) 15 46.7693 -121.7294 1483 lake brook trout 2012 21 175 114-227 Y

Snow Lake 16 46.7570 -121.6992 1432 lake brook trout 2012 13 210 179-239 N

cutthroat trout 2012 2 217 193-241 N

Upper Deadwood Lake 

(LW32) 17 46.8890 -121.5248 1599 lake rainbow trout 2008 7 261 203-305 Y

North Cascades

George Lake 1 48.7061 -121.1722 268 lake rainbow trout 2011 10 189 171-226 N

Middle Blum Lake 2 48.7500 -121.4956 1529 lake brook trout 2008 15 142 91-220 Y

Upper Wilcox Lake 3 48.6011 -121.1717 1569 lake cutthroat trout 2008 12 204 170-248 Y
45

Park Site

ID Latitude Longitude Elevation (m) Habitat Species YearSampled n SL (mm)a

SRb

Site Mean Range

Olympic

Gladys Lakeb 1 47.8767 -123.3578 1646 lake brook trout 2011 15 166 159-180 N

brook trout 2012 15 167 150-182 N

Hagen Lake 2 47.6192 -123.2680 1446 lake cutthroat trout 2012 15 212 175-238 N

Hoh Lake 3 47.8988 -123.7863 1387 lake brook trout 2012 15 165 142-185 Y

Sun Up Lake

b 4 47.5314 -123.4862 1227 lake cutthroat trout 2011 15 242 232-257 N

cutthroat trout 2012 15 250 219-269 N

Upper Lena Lakeb 5 47.6331 -123.2080 1389 lake rainbow trout 2011 15 171 149-187 N

Rocky Mountain

Black Lake 1 40.2653 -105.6410 3242 lake brook trout 2012 15 188 126-226 N

Colorado River 2 40.2773 -105.8504 2647 river brown trout 2012 20 272 152-413 Y

sucker spp 2012 20 193 145-292 Y

Fall River 3 40.4014 -105.6063 2590 river brown trout 2012 20 229 166-338 Y

sucker spp 2012 20 273 220-359 Y

Fern Lake 4 40.3368 -105.6763 2913 lake cutthroat trout 2012 15 209 126-270 Y

Fourth Lake 5 40.2217 -105.6861 3167 lake brook trout 2012 15 178 146-206 Y

Haynach Lake 6 40.3467 -105.7646 3378 lake cutthroat trout 2012 15 237 141-340 Y

Lake Haiyaha 7 40.3047 -105.6622 3120 lake cutthroat trout 2012 15 255 182-309 N

Lake Louise 8 40.5083 -105.6206 3369 lake cutthroat trout 2012 14 271 222-314 N

Lake Nanitab 9 40.2560 -105.7165 3291 lake cutthroat trout 2008 8 231 187-258 Y

cutthroat trout 2012 15 188 111-260 Y

Lone Pine Lake 10 40.2327 -105.7232 3134 lake brook trout 2012 14 141 91-178 N

Mills Lake 11 40.2895 -105.6417 3033 lake rainbow trout 2012 15 226 167-295 Y

Mirror Lake

b 12 40.5380 -105.6984 3364 lake brook trout 2009 15 211 153-237 Y

brook trout 2012 15 190 115-238 Y

Poudre Lakeb 13 40.4222 -105.8089 3282 lake brook trout 2009 15 202 129-242 N

brook trout 2012 15 203 108-264 N

Sky Pond 14 40.2782 -105.6688 3315 lake brook trout 2012 15 215 162-246 Y

Spruce Lake 15 40.3423 -105.6871 2950 lake cutthroat trout 2012 15 206 148-242 Y

Ten Lake Park 16 40.2104 -105.7194 3415 lake cutthroat trout 2012 14 239 206-288 Y

The Loch 17 40.2925 -105.6570 3109 lake cutthroat trout 2012 15 218 148-285 Y

Upper Hutcheson Lake 18 40.1736 -105.6470 3417 lake cutthroat trout 2012 15 208 183-250 N

Ypsilon Lakeb 19 40.4436 -105.6633 3218 lake cutthroat trout 2009 15 215 156-275 Y

Sequoia-Kings Canyon

Bench Lake 1 36.9488 -118.4651 3224 lake brook trout 2009 15 131 92-165 Y

Center Basin Lakeb 2 36.7305 -118.3960 3517 lake golden trout 2008 30 136 103-156 Y

golden trout 2012 15 138 100-157 Y

Kern Point Lakeb 3 36.6013 -118.4319 3281 lake rainbow trout 2009 15 166 108-224 Y

Lake 10310 4 36.9591 -118.4354 3297 lake brook trout 2012 15 143 101-168 Y
46

Park Site

ID Latitude Longitude Elevation (m) Habitat Species YearSampled n SL (mm)a

SRb

Site Mean Range

Wrangell-St. Elias

Copper Lake 1 62.4256 -143.5550 886 lake arctic grayling 2008 15 326 274-374 N

kokanee 2008 15 295 278-311 Y

lake trout 2008 13 417 365-470 Y

Summit Lake 2 61.3156 -144.1919 lake rainbow trout 2009 15 250 123-405 N

Tanada Lake 3 62.4258 -143.3717 880 lake lake trout 2009 13 466 418-542 Y

rainbow trout 2012 12 180 151-198 N

Yellowstone

Beula Lake 1 44.1598 -110.7670 2261 lake cutthroat trout 2012 15 239 204-300 Y

Grebe Lake 2 44.7516 -110.5578 2450 lake arctic grayling 2012 15 166 128-255 Y

rainbow trout 2012 15 234 152-273 Y

Lewis Lake 3 44.3068 -110.6305 2375 lake brown trout 2012 15 187 109-394 Y

Yellowstone Lake 4 44.4659 -110.3330 2361 lake cutthroat trout 2012 15 266 243-294 N

lake trout 2012 15 273 240-325 N

cutthroat trout 2012 15 221 115-262 Y

Yosemite

Mildred Lake 1 37.8202 -119.4407 2916 lake brook trout 2009 15 204 117-269 Y

Spillway Lake 2 37.8408 -119.2321 3189 lake brook trout 2009 15 192 124-263 Y

rainbow trout 2012 15 170 73-252 Y

Zion

E. Fork Virgin River 1 37.1594 -112.9686 1192 river speckled dace 2012 15 50 40-61 Y

N. Fork Virgin River 2 37.2413 -112.9588 1294 river speckled dace 2012 15 39 34-44 N

a Size regression used: Y-yes, N-no.

b Lakes used in inter-annual comparison. Lake Kontrashibuna was excluded from intra-annual comparisons because only two 

fish were collected in 2012.

c Threespine stickleback.
47

Table 2. Total mercury concentrations (THg; ng/g ww) in muscle of fish from 21 national parks in the Western United States.

[Values are reported as geometric means, 95percent confidence intervals (CI), and range, and least-square mean (LSM) concentrations controlling for the effects 

of size, species, and site at 50, 200, and 400 mm standardized lengths]

Park Park

Abbreviation

Total

n

Geometric

Mean

95percent

CI Range

50 mm 200 mm 400 mm

n LSM SE n LSM SE n LSM SE

Capitol Reef CARE 45 325.6 281.4 - 376.9 136.7 - 805.4 45 207.9 3.7 - -

Crater Lake CRLA 27 38.0 32 - 44.3 16.8 – 76.0 - 27 26.6 2.6 -

Denali DENA 17 49.3 37.9 - 64.1 23.7 - 88.8 - - 17 47.4 1.6

Glacier GLAC 15 232.4 211.6 - 255.3 167.3 - 297.9 - - 15 234.1 9.1

Glacier Bay GLBA 45 90.2 79.1 - 102.9 41.0 - 203.1 - 45 102.3 19.6 -

Grand Canyon GRCA 42 76.0 66.1 - 87.5 31.8 - 241.2 - 42 101.2 9.6 -

Grand Teton GRTE 45 32.6 28.3 - 37.6 16.2 – 99.0 - 45 31.3 4.5 -

Great Basin GRBA 39 40.0 36.3 - 44.2 19.0 - 85.5 - 39 34.5 5.0 -

Great Sand Dunes GRSA 29 52.7 45.8 - 60.6 29.1 - 136.6 - 29 62.4 5.6 -

Lake Clark LACL 59 229.3 192.8 - 272.8 35.8 – 691.0 - - 59 201.0 2.9

Lassen Volcanic LAVO 47 96.4 78.1 - 119 28.6 - 493.4 - 47 65.3 9.5 -

Mesa Verde MEVE 10 74.9 59.9 - 93.7 45.7 - 115.4 10 74.9 2.9 - -

Mount Rainier MORA 207 71.5 65.8 - 78.5 12.5 - 384.5 35 80.4 1.9 172 61.0 7.3 -

North Cascades NOCA 37 54.9 46.7 - 64.4 22.4 - 209.3 - 37 73.3 7.2 -

Olympic OLYM 117 85.0 80 - 90.3 34.9 - 208.8 - 337 109.7 12.1 -

Rocky Mountain ROMO 385 66.1 61.4 - 71.1 9.9 - 528.3 - 385 54.8 6.3 -

Sequoia - Kings Canyon SEKI 105 43.8 39.1 - 49 13.3 - 124.5 - 105 69.5 6.3 -

Wrangell-St. Elias WRST 71 107.9 87.4 - 133.1 27.8 - 632.3 - 45 98.15 9.41 26 278.8 7.4

Yellowstone YELL 90 101.2 92.7 - 110.5 44.6 - 312.2 - 75 119.8 10.2 15 116.0 4.3

Yosemite YOSE 30 82.1 57.5 - 117.2 24.9 - 1108.6 - 30 70.0 10.2 -

Zion ZION 30 241.5 209.7 - 278.2 95.9 - 532.6 30 242.5 5.4 - -
48

Table 3. Total mercury concentrations (THg; ng/g ww) and coefficients of variation (CV) in fish muscle from 86 sites 

in 21 national parks in the Western United States.

[Values are reported as geometric means and 95 percent confidence intervals (95% CI), and least-square mean (LSM) 

concentrations controlling for the effects of size, species, and site at 50 mm, 200 mm, and 400 mm standardized lengths]

Park Geometric 

Mean

95% 

CI

50 mmb 200 mmb 400 mmb

CV

Site LSM SE LSM SE LSM SE

All Parks 77.7 73.6 - 80.8 0.67

Capitol Reef 325.6 281.4 - 376.9 207.9 3.7 0.88

Fremont River #1 407.3 318.3 - 521.1 301.0 9.4 0.31

Fremont River #4 244.7 199.8 - 299.7 157.8 4.9 0.31

Fremont River #7 346.5 260.4 - 461.1 189.4 5.9 0.30

Crater Lake 38.0 32 - 44.3 26.6 2.6 NA

Crater Lake 38.0 32.7 - 44.3 26.6 2.6 0.28

Denali 49.3 37.9 - 64.1 47.4 1.6 NA

Lake Chilchukabena 49.3 37.9 - 64.1 47.4 1.6 0.23

Glacier 232.4 211.6 - 255.3 234.1 9.1 NA

Lake McDonald 232.4 211.6 - 255.3 234.1 9.1 0.15

Glacier Bay 90.2 79.1 - 102.9 102.3 19.6 0.49

Falls Creek 56.4 50 - 63.6 56.4 10.9 0.22

North Skidmore Lake 113.7 102.3 - 126.4 113.7 22.1 0.18

Stonefly Lake 114.7 91.9 - 143.1 167.0 32.4 0.27

Grand Canyon 76.0 66.1 - 87.5 101.2 9.6 0.54

Bright Angel Creek 57.8 46.7 - 71.7 71.5 7.0 0.35

Havasu Creek 66.0 53.3 - 81.8 81.0 8.2 0.50

Shinumo Creek 108.9 89.1 - 133.2 178.8 18.0 0.28

Grand Teton 32.6 28.3 - 37.6 31.3 4.5 0.28

Death Canyon 22.9 21 - 25 25.1 3.7 0.10

Grizzly Bear Lake 52.1 40.9 - 66.4 42.4 6.3 0.40

Lake Solitude 29.0 24.1 - 34.9 28.8 4.3 0.29

Great Basin 40.0 36.3 - 44.2 34.5 5.0 0.12

Baker Lake 41.6 29.2 - 59.3 35.6 5.4 0.52

Lehman Creek 35.1 30.5 - 40.3 30.0 4.4 0.24

Snake Creek 44.7 40.4 - 49.4 38.3 5.6 0.16

Great Sand Dunes 52.7 45.8 - 60.6 62.4 5.6 0.37

Medano Lake 70.1 61.6 - 79.7 81.8 12.1 0.28

Sand Creek 38.8 34.6 - 43.5 47.6 4.8 0.21

Lake Clark 229.3 192.8 - 272.8 201.0 2.9 0.57

Lake Clark 365.2 327.4 - 407.4 365.2 9.2 0.31

Lake Kontrashibuna 204.0 147.9 - 281.4 204.0 7.3 0.41

Telaquana Lake 109.0 82.5 - 144 109.0 4.1 0.56
49

Park Geometric 

Mean

95% 

CIa

50 mmb 200 mmb 400 mmb

CV

Site LSM SE LSM SE LSM SE

Lassen Volcanic 96.4 78.1 - 119 65.3 9.5 0.45

Horseshoe Lake 180.7 132.3 - 246.9 84.8 12.5 0.29

Ridge Lake 111.3 89.9 - 137.9 95.4 14.0 0.39

Summit Lake 43.7 38.1 - 50.1 34.5 5.1 0.12

Mesa Verde 74.9 59.9 - 93.7 74.9 2.9 NA

Mancos River 74.9 59.9 - 93.7 74.9 2.9 0.30

Mount Rainier 71.5 65.8 - 78.5 80.4 1.9 61.0 7.3 0.55

Bench Lake 34.0 20.4 - 56.7 8.5 1.3 0.29

Golden Lake 66.6 47.7 - 93 193.2 28.5 0.14

Green Lake 66.2 58.3 - 75.2 77.3 11.9 0.12

Lake George 87.5 73.2 - 104.5 89.8 2.7 0.27

Louise Lake 86.1 63.2 - 117.3 105.9 16.2 0.19

Lower Deadwood Lake 82.9 65.5 - 104.8 50.6 2.0 77.9 8.0

Lower Palisades Lake 116.3 103 - 131.4 92.9 13.6 0.21

MORA_1244 58.4 44 - 77.4 60.6 9.2 0.34

MORA_1614 227.4 157.5 - 328.2 97.8 14.9 0.30

MORA_230 121.2 86.7 - 169.4 80.7 12.0 0.32

MORA_234 66.2 53.1 - 82.5 87.4 12.9 0.29

MORA_583 19.2 14.4 - 25.5 16.4 2.5 0.46

MORA_LH15 66.4 51.1 - 86.2 62.5 9.2 0.36

Mowich Lake 97.2 72.9 - 129.6 114.1 5.6 0.17

Reflection Lake 80.8 62.3 - 104.9 101.0 14.8 0.44

Snow Lake 37.3 30.4 - 45.9 33.3 4.8 0.37

Upper Deadwood Lake 47.0 33.5 - 66.1 42.9 4.6 0.36

North Cascades 54.9 46.7 - 64.4 73.3 7.2 0.45

George Lake 44.1 33.5 - 58 54.1 5.6 0.34

Middle Blum Lake 62.2 46.3 - 83.5 118.5 17.5 0.36

Upper Wilcox Lake 56.2 41.8 - 75.5 61.5 9.1 0.18

Olympic 85.0 80 - 90.3 109.7 12.1 0.60

Gladys Lake 83.5 75.5 - 92.4 71.5 10.4 0.28

Hagen Lake 93.5 78.1 - 111.9 109.1 16.1 0.30

Hoh Lake 125.7 104.7 - 150.9 253.0 37.3 0.26

Sun Up Lake 85.2 79.1 - 91.7 99.4 14.5 0.19

Upper Lena Lake 66.1 58.9 - 74.1 81.1 8.0 0.27

Rocky Mountain 66.1 61.4 - 71.1 54.8 6.3 0.43

Black Lake 54.4 45.7 - 64.8 46.6 6.9 0.31

Colorado River 118.0 104.3 - 133.6 100.4 10.6 0.40

Fall River 106.2 83.3 - 135.5 59.3 6.3 0.43

Fern Lake 59.1 46.4 - 75.3 65.3 9.6 0.35

Fourth Lake. 70.4 58.8 - 84.3 71.6 10.6 0.27

Haynach Lake 19.8 15.9 - 24.5 19.4 2.9 0.26

Lake Haiyaha 18.5 15.9 - 21.5 21.6 3.2 0.26

Lake Louise 56.5 48.7 - 65.5 65.9 9.7 0.25

Lake Nanita 70.5 55 - 90.4 80.0 11.7 0.34

Lone Pine Lake 57.8 50.2 - 66.5 49.5 7.3 0.26

Mills Lake 87.5 68.5 - 111.9 94.0 9.5 0.37

Mirror Lake 121.2 86.2 - 170.5 102.4 14.9 0.36
50

Park Geometric 

Mean

95% 

CI

50 mmb 200 mmb 400 mmb

CV

Site LSM SE LSM SE LSM SE

Rocky Mountain cont.

Poudre Lake 82.6 70.9 - 96.2 70.8 10.3 0.50

Sky Pond 30.7 23.2 - 40.6 21.4 3.2 0.30

Spruce Lake 89.3 69.7 - 114.4 97.5 14.4 0.30

Ten Lake Park 68.3 57.5 - 81 63.2 9.4 0.28

The Loch 38.9 27.1 - 56 38.6 5.7 0.82

Upper Hutcheson Lake 30.8 28 - 33.8 35.9 5.3 0.16

Ypsilon Lake 62.3 51.6 - 75.3 61.7 9.0 0.45

Sequoia - Kings Canyon 43.8 39.1 - 49 69.5 6.3 0.38

Bench Lake. 21.7 18.1 - 26.1 30.3 4.5 0.32

Center Basin Lake 67.0 60 - 74.9 207.3 39.8 0.28

Kern Point Lake 43.5 37.2 - 50.9 71.4 7.0 0.24

Lake 10310 24.9 20.1 - 30.9 52.1 7.7 0.41

Wrangell-St. Elias 107.9 87.4 - 133.1 98.2 9.4 278.8 7.4 0.57

Copper Lake 91.7 73.4 - 114.5 147.4 14.5 242.0 9.8 0.24

Summit Lake 53.3 48.5 - 58.5 65.4 6.6 0.18

Tanada Lake 416.6 358.4 - 484.2 321.2 13.0 0.19

Yellowstone 101.2 92.7 - 110.5 119.8 10.2 116.0 4.3 0.23

Beula Lake 107.1 95.5 - 120.1 111.1 16.4 0.18

Grebe Lake 110.5 94.2 - 129.7 168.8 16.4 0.19

Lewis Lake 69.2 56.5 - 84.9 92.3 10.1 0.25

Yellowstone Lake 108.9 92.8 - 127.7 119.3 17.6 116.0 4.3

Yosemite 82.1 57.5 - 117.2 70.0 10.2 0.86

Mildred Lake 174.4 115.1 - 264.1 142.4 21.0 0.58

Spillway Lake 38.7 32.3 - 46.2 34.4 5.1 0.31

Zion 241.5 209.7 - 278.2 242.5 5.4 0.57

E. Fork Virgin River 234.9 180 - 306.5 236.8 7.4 0.29

N. Fork Virgin River 248.3 215.8 - 285.7 248.3 7.7 0.32
51

Table 4. Proportion of fish with wet weight mercury concentrations exceeding toxicity benchmarks from 86 sites in 

21 western national parks in the Western United States.

[Comparisons to fish (no observed effects residue [NOER] = 200 ng/g, lowest observed effects residue [LOER] = 300 ng/g) 

and bird (high sensitivity = 90 ng/g, moderate sensitivity = 180 ng/g, low sensitivity = 270 ng/g) benchmarks were made 

using whole-body concentrations whereas comparisons to human consumption (unlimited consumption = 50 ng/g, EPA 

criterion = 300 ng/g, no consumption = 950 ng/g) benchmarks used concentrations in axial muscle tissue]

Park Fish Toxicity Bird Toxicity Human Consumption

Site NOER LOER High

Sens.

Moderate

Sens.

Low

Sens.

Unlimited

Consumption

EPA

Criterion

No

Consumption

Among all parks 5 2 35 12 5 68 4 1

Capitol Reef 49 22 98 56 33 NA NA NA

Fremont River #1 67 33 100 80 60 NA NA NA

Fremont River #4 20 7 93 27 7 NA NA NA

Fremont River #7 60 27 100 60 33 NA NA NA

Crater Lake -- -- -- -- -- 19 -- --

Crater Lake -- -- -- -- -- 19 -- --

Denali -- -- -- -- -- 59 -- --

Lake Chilchukabena -- -- -- -- -- 59 -- --

Glacier -- -- 100 -- -- 100 -- --

Lake McDonald -- -- 100 -- -- 100 -- --

Glacier Bay -- -- 18 -- -- 87 -- --

Falls Creek -- -- -- -- -- 60 -- --

North Skidmore 

Lake -- -- 20 -- -- 100 -- --

Stonefly Lake -- -- 33 -- -- 100 -- --

Grand Canyon -- -- 10 -- -- 79 -- --

Bright Angel Creek -- -- -- -- -- 58 -- --

Havasu Creek -- -- 7 -- -- 73 -- --

Shinumo Creek -- -- 20 -- -- 100 -- --

Grand Teton -- -- -- --- -- 18 -- --

Death Canyon -- -- -- -- -- -- -- --

Grizzly Bear Lake -- -- -- -- -- 47 -- --

Lake Solitude -- -- -- -- -- 7 -- --

Great Basin -- -- -- -- -- 18 -- --

Baker Lake -- -- -- -- -- 33 -- --

Lehman Creek -- -- -- -- -- 7 -- --

Snake Creek -- -- -- -- -- 20 -- --
52

Park Fish Toxicity Bird Toxicity Human Consumption

Site NOER LOER High

Sens.

Moderate

Sens.

Low

Sens.

Unlimited

Consumption

EPA

Criterion

No

Consumption

Great Sand Dunes -- -- -- -- -- 59 -- --

Medano Lake -- -- -- -- -- 100 -- --

Sand Creek -- -- -- -- -- 14 -- --

Lake Clark 31 7 76 42 10 98 41 --

Lake Clark 54 14 100 79 21 100 75 --

Lake Kontrashibuna 19 -- 81 19 -- 94 19 --

Telaquana Lake -- -- 27 -- -- 100 -- --

Lassen Volcanic 2 -- 40 2 2 72 2 --

Horseshoe Lake 7 -- 87 7 7 93 7 --

Ridge Lake -- -- 35 -- -- 100 -- --

Summit Lake -- -- -- -- -- 20 -- --

Mesa Verde -- -- -- -- -- NA NA NA

Mancos River -- -- -- -- -- NA NA NA

Mount Rainier 1 -- 15 2 -- 72 2 --

Bench Lake -- -- -- -- -- 17 -- --

Golden Lake -- -- 19 -- -- 56 6 --

Green Lake -- -- -- -- -- 100 -- --

Lake George -- -- 6 -- -- NA NA NA

Louise Lake -- -- -- -- -- 100 -- --

Lower Deadwood 

Lake -- -- 18 -- -- 94 -- --

Lower Palisades 

Lake -- -- 21 -- -- 100 -- --

MORA_1244 -- -- -- -- -- 57 -- --

MORA_1614 29 -- 100 29 -- 100 29 --

MORA_230 -- -- 55 -- -- 100 -- --

MORA_234 -- -- 7 -- -- 73 -- --

MORA_583 -- -- -- -- -- -- -- --

MORA_LH15 -- -- 7 -- -- 64 -- --

Mowich Lake -- -- 11 -- -- NA NA NA

Reflection Lake -- -- 19 5 -- 71 5 --

Snow Lake -- -- -- -- -- 27 -- --

Upper Deadwood 

Lake -- -- -- -- -- 29 -- --

North Cascades -- -- 5 51 -- --

George Lake -- -- -- -- -- 40 -- --

Middle Blum Lake -- -- 7 -- -- 53 -- --

Upper Wilcox Lake -- -- 8 -- -- 58 -- --
53

Park Fish Toxicity Bird Toxicity Human Consumption

Site NOER LOER High

Sens.

Moderate

Sens.

Low

Sens.

Unlimited

Consumption

EPA

Criterion

No

Consumption

Olympic -- -- 6 94 -- --

Gladys Lake -- -- 3 -- -- 100 -- --

Hagen Lake -- -- 7 -- -- 100 -- --

Hoh Lake -- -- 33 -- -- 100 -- --

Sun Up Lake -- -- -- -- -- 100 -- --

Upper Lena Lake -- -- -- -- -- 74 -- --

-- --

Rocky Mountain 2 -- 15 3 1 66 3 --

Black Lake -- -- -- -- -- 60 -- --

Colorado River -- -- 28 3 -- 100 3 --

Fall River 10 3 33 10 5 80 10 --

Fern Lake -- -- -- -- -- 80 -- --

Fourth Lake -- -- -- -- -- 87 -- --

Haynach Lake -- -- -- -- -- -- -- --

Lake Haiyaha -- -- -- -- -- -- -- --

Lake Louise -- -- -- -- -- 57 -- --

Lake Nanita -- -- 17 -- -- 70 -- --

Lone Pine Lake -- -- -- -- -- 71 -- --

Mills Lake -- -- 13 -- -- 80 -- --

Mirror Lake 10 -- 57 17 -- 77 17 --

Poudre Lake -- -- 17 -- -- 100 -- --

Sky Pond -- -- -- -- -- 13 -- --

Spruce Lake -- -- 20 -- -- 87 -- --

Ten Lake Park -- -- -- -- -- 93 -- --

The Loch -- -- -- -- -- 27 -- --

Upper Hutcheson 

Lake -- -- -- -- -- -- -- --

Ypsilon Lake -- -- 10 -- -- 60 -- --

Sequoia - Kings Canyon -- -- -- -- -- 46 -- --

Bench Lake -- -- -- -- -- -- -- --

Center Basin Lake -- -- -- -- -- 73 -- --

Kern Point Lake -- -- -- -- -- 43 -- --

Lake 10310 -- -- -- -- -- 13 -- --

Wrangell-St. Elias 16 4 39 18 7 76 18 --

Copper Lake -- -- 35 5 -- 74 5 --

Summit Lake -- -- -- -- -- 60 -- --

Tanada Lake 85 23 100 85 38 100 85 --

Yellowstone -- -- 20 1 -- 94 1 --

Beula Lake -- -- 7 -- -- 100 -- --

Grebe Lake -- -- 30 -- -- 97 -- --

Lewis Lake -- -- 7 -- -- 80 -- --

Yellowstone Lake -- -- 23 3 -- 97 3 --
54

Park Fish Toxicity Bird Toxicity Human Consumption

Site NOER LOER High

Sens.

Moderate

Sens.

Low

Sens.

Unlimited

Consumption

EPA

Criterion

No

Consumption

Yosemite 7 3 27 7 3 60 7 3

Mildred Lake 13 7 53 13 7 100 13 7

Spillway Lake -- -- -- -- -- 20 -- --

Zion 20 3 90 27 3 NA NA NA

E. Fork Virgin River 30 -- 80 40 -- NA NA NA

N. Fork Virgin 

River 7 7 100 13 7 NA NA NA
Publishing support provided by the U.S. Geological Survey

Publishing Network, Tacoma Publishing Service Center

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

 Director, Forest and Rangeland Ecosystem Science Center

U.S. Geological Survey

777 NW 9th St., Suite 400

Corvallis, Oregon 97330

http://fresc.usgs.gov/
Eagles-Smith and others— Mercury in Fishes from 21 National Parks in the Western United States—Concentrations and Ecological Risk—Open-File Report 2014–1051

ISSN 2331-1258 (online)

http://dx.doi.org/10.3133/ofr20141051