U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2017–3087

April 2018

The Midwest Stream Quality Assessment—Influences of 

Human Activities on Streams

Printed on recycled paper

Healthy streams and the fish and other organisms that live in them contribute to our quality of life. Extensive modification of the 

landscape in the Midwestern United States, however, has profoundly affected the condition of streams. Row crops and pavement have 

replaced grasslands and woodlands, streams have been straightened, and wetlands and fields have been drained. Runoff from agricultural 

and urban land brings sediment and chemicals to streams. What is the chemical, physical, and biological condition of Midwestern 

streams? Which physical and chemical stressors are adversely affecting biological communities, what are their origins, and how might 

we lessen or avoid their adverse effects? 

IOWA

KANSAS

OHIO

MISSOURI

MINNESOTA

NEBRASKA

ILLINOIS

WISCONSIN SOUTH DAKOTA

INDIANA

MICHIGAN

KENTUCKY

EXPLANATION

Developed

Cultivated crops

Forest

Pasture/hay

Water, wetlands

Grasslands and other

Agriculture

Undeveloped

Urban

Site type Land cover

Landscape

Urbanization

Agriculture

Geology, soils

Stressors

Habitat alteration

Nutrients

Contaminants

Biology

Algae

Invertebrates

Fish

Sites sampled during the Midwest Stream Quality Assessment, May–August 2013.

In 2013, the U.S. Geological Survey (USGS) conducted the Midwest Stream Quality Assessment (MSQA) to evaluate how human 

activities affect the biological condition of Midwestern streams. In collaboration with the U.S. Environmental Protection Agency 

(EPA) National Rivers and Streams Assessment, the USGS sampled 100 streams, chosen to be representative of the different types 

of watersheds in the region (Garrett and others, 2017). Biological condition was evaluated based on the number and diversity of fish, 

algae, and invertebrates in the streams. Changes to the physical habitat and chemical characteristics of the streams—“stressors” in the 

diagram above—were assessed, and their relation to landscape factors and biological condition was explored by using mathematical 

models. The data and models help us to better understand how the human activities on the landscape are affecting streams in the region.
Biological Conditions

Algae

Algae are plant-like organisms at the base of the aquatic food 

chain. They tend to respond rapidly to changes in their environment, 

which makes them especially sensitive indicators of effects of human 

activities on aquatic life in streams. Algal sampling by MSQA focused 

on diatoms, a common type of algae that generally are attached to 

hard surfaces such as rocks and wood.

The healthiest algal communities were in MSQA streams with 

rock and gravel substrate, cool water, and low levels of herbicides 

(Munn and others, 2018). The MSQA streams with more finegrained sediment—silt and sand rather than gravel—had fewer 

“sensitive” diatoms, those most commonly lost as a stream is 

degraded. Sensitive diatom abundance also was lower in streams 

with warmer water temperature and higher levels of triazine 

herbicides, such as atrazine. 

In streams, algae often 

grow on rocks, top. Algae 

are sampled by scraping 

the rock surface with a stiff 

brush, bottom.

Invertebrates

Invertebrates—animals without backbones—include insects 

(such as mayflies and caddisflies), mollusks (such as snails and 

clams), worms, and crustaceans (such as amphipods and crayfish). 

Invertebrates are a critical part of the aquatic food web, both as 

predators and as food for fish and birds. 

As with algae, physical and chemical 

alterations to MSQA streams adversely affected 

invertebrate communities (Waite and Van Metre, 

2017). Habitat variables—excessive finegrained sediment, riparian condition, stream 

velocity, and channel shape—were associated 

with degradation of the invertebrate community, 

such as loss of sensitive insect species. These 

variables are affected by stream straightening and 

human development near streams. Ammonia (a form of nitrogen) 

and pesticides in streams, in particular the pyrethroid insecticide 

bifenthrin, also were associated with degradation of invertebrate 

communities (Rogers and others, 2016; Moran and others, 2017; 

Waite and Van Metre, 2017). 

Mayfly larvae are among the invertebrates sampled in streams, left

(Alan Cressler, USGS). A biologist uses a fine-mesh net to collect 

invertebrates from a stream riffle, right.

Fish

Fish occupy many roles in stream ecosystems. Some species are predators, 

consuming invertebrates and other fish; other species consume algae and plants. 

Fish are an important food source for wildlife and support substantial economic 

activity related to sport fishing—the American Sportfishing 

Association estimates over $15 billion in annual 

economic activity for the Midwestern States 

included in the MSQA (American Sportfishing 

Association, 2013). 

Fish species diversity is relatively high 

in Midwestern streams and rivers—135 fish 

species were identified in MSQA sampling, 

with the Green Sunfish being the most common 

(Meador and Frey, 2018). Total nitrogen was the most important 

stressor affecting fish communities, and fish species abundance decreased as nitrogen 

concentrations increased. Excessive fine sediment covering the streambeds also was 

related to the loss of fish species, particularly those species that require gravel or 

cobble streambeds to reproduce. Pesticides and other contaminants do not appear to be 

affecting fish communities in most of the streams studied (Nowell and others, 2018). 

Fish are electroshocked and netted for field 

identification, then released, left. Green Sunfish was 

the most common species in MSQA streams, right.
Habitat Alteration

Loss of Riparian Zone

The land adjacent to a stream is called the riparian zone. 

Undisturbed riparian zones provide shelter and food for aquatic and 

terrestrial organisms, shade the stream with trees, and inhibit runoff 

from agricultural and urban land from entering the stream. Stream 

straightening and encroachment of croplands and urban areas has led 

to widespread disturbance of riparian zones along Midwestern streams. 

Riparian zone disturbance was associated with adverse effects 

on invertebrate (Waite and Van Metre, 2017) and algal (Munn and 

others, 2018) communities in MSQA streams. Conversely, some 

MSQA streams with undisturbed forested riparian zones had healthy 

invertebrate communities even though the watershed was heavily 

developed. Massies Creek near Wilberforce, Ohio, for example, 

has a watershed that is 83 percent row crop, but its riparian zone is 

forested and only 7 percent developed. Massies Creek has a healthy 

invertebrate community, as reflected by an invertebrate multimetric 

index (MMI) of 79 (scale 0–100). Three Mile Creek near Ghent, 

Minn., has a watershed with less row crop (76 percent) but a more 

disturbed riparian zone (60 percent developed), and its invertebrate 

community is less robust (MMI of 49).

This satellite image from northeast Iowa illustrates the extensive 

modification of the Midwestern landscape by agriculture. The 

streams are visible as light green lines over which a grid of 

rural roads has been superimposed. The streams are devoid of 

riparian woodlands and, in many cases, straightened, which can 

cause severe erosion of the stream channel. 

Sediment

Excessive amounts of fine sediment bury gravel and cobble 

that are critical habitat for many algae, invertebrates, and fish, and 

fine sediment in the water column restricts penetration of light 

needed for plant growth. 

Excessive amounts of fine sediment in the streambed or 

water column in MSQA streams were related to degraded algal, 

invertebrate, and fish communities (Waite and Van Metre, 2017; 

Meador and Frey, 2018; Munn and others, 2018). Streambank and 

channel erosion contributed almost two-thirds of the fine sediment in 

streams, on average, whereas soil erosion accounted for just one-third (Gellis 

and others, 2017). Knowing the dominant sources of fine sediment may help 

guide management efforts to protect and restore streams. 

Surface soil 

36%

Bank and channel 

64%

Erosion of streambanks contributes about twice as much 

sediment to MSQA streams, on average, than does erosion 

of soils (Gellis and others, 2017). 

Nutrient Enrichment

MSQA streams with higher levels of nutrients were more likely 

to have degraded algal, invertebrate, and fish communities (Waite and 

Van Metre, 2017; Meador and Frey, 2018; Munn and others, 2018). The 

principal nutrients are nitrogen and phosphorus, which are contained 

in fertilizer and animal wastes. Large amounts of nutrients in streams 

promote excessive growth of algae, which can lead to oxygen depletion, 

fish kills, and toxic algal blooms. 

Agricultural fertilizer is a major source of nutrients to Midwestern 

streams, as evidenced by the link between watershed corn production 

and nitrate concentrations (graph at right). Nitrate accounts for most 

of the total nitrogen in MSQA streams, which was the most important 

stressor identified for fish (Meador and Frey, 2018). The MSQA also 

demonstrated how annual rainfall patterns affect nitrate concentrations in 

streams. During the 2012 drought, nitrogen built up in the soils because 

agricultural crops grew poorly and did not use much nitrogen, and because 

there was little rainfall to cause nitrogen runoff. The 2012 drought was 

followed by heavy rains in 2013, and rainfall runoff in 2013 caused nitrate 

concentrations in many Midwestern streams to be higher than normal 

during the MSQA sampling (Van Metre and others, 2016). 

0

5

10

15

20

25

30

35

0 20 40 60 80

Mean nitrate concentration,

in milligrams per liter

Percentage of watershed planted in corn

Corn production in watersheds is strongly associated with 

concentrations of nitrate in MSQA streams. For the 36 MSQA 

streams with less than 20 percent of the watershed planted in corn, 

the mean nitrate concentration was only 1.2 milligrams per liter.

USDA Farm Service Agency, 2011
Contaminants

Pesticides in Water

Of the 228 pesticides analyzed, 184 were detected at least once in MSQA 

stream samples (Mahler and others, 2017; Nowell and others, 2018). During the 

3-month sampling period, an average of 54 pesticides were detected at each site 

and an average of 25 pesticides were detected in each water sample. Pesticide 

concentrations more frequently exceeded aquatic life benchmarks (levels expected 

to be harmful) for invertebrates and algae than for fish (Nowell and others, 2018). 

Chronic (sublethal) or acute (potentially lethal) toxic effects to invertebrates were 

indicated in 55 percent of streams, and 12 percent of those streams had at least one 

potentially lethal short-term spike in insecticide concentration during the study. 

Water in agricultural streams, which had higher concentrations of herbicides than 

urban streams, was predicted to be most toxic to algae, whereas water in urban 

streams, which had higher concentrations of insecticides than agricultural streams, 

was predicted to be most toxic to invertebrates (right). 

The neonicotinoid insecticide imidacloprid, pyrethroid insecticides, 

triazine herbicides, and the pesticide toxicity index (PTI)—a measure of estimated 

toxicity of pesticide mixtures (Shoda and others, 2016)—were significantly 

related to adverse effects on algal and invertebrate communities in MSQA streams 

(Waite and Van Metre, 2017; Munn and others, 2018). Bifenthrin, a pyrethroid 

insecticide that accumulates in sediment, also was associated with degraded 

invertebrate communities (Rogers and others, 2016; Moran and others, 2017;

Van Metre and others, 2017; Waite and Van Metre, 2017). 

93%

7%

92%

8%

Agricultural Urban

19%

70%

10%

67%

33%

48% 43%

9%

25% 33%

42%

None

Chronic

Fish

Algae

Invertebrates

None

Acute, likely reversible

Chronic community

None

Chronic

Acute

EXPLANATION

Type of toxicity benchmark exceeded

by one or more pesticides 

Water in the majority of the 100 MSQA streams is likely to be

toxic to aquatic organisms.

Contaminants in Sediment

Sediment from the MSQA streams was analyzed for pesticides, 

polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and 

metals (not all compounds were analyzed at all sites). Many of these chemicals 

accumulate in sediment and can harm biota. Sediment from 99 of the 100 streams 

also was tested for toxicity to 2 invertebrate species in the laboratory. 

MSQA streams have relatively uncontaminated sediment. Concentrations of 

sediment-bound contaminants were below sediment-quality benchmarks for the 

protection of aquatic life, and the incidence of toxicity in laboratory tests was low 

(Moran and others, 2017), in part because bed sediments were diluted by eroded 

streambank sediment in many streams (Gellis and others, 2017). Sediment toxicity 

found in laboratory tests was associated with the insecticide bifenthrin (see below). 

Sediment from urban streams had significantly higher concentrations of metals, 

PCBs, PAHs, and several pesticides (including chlordane and DDE) than sediment 

from agricultural streams (Moran and others, 2017). Sediment in urban streams, such as Wolf Creek in 

Cincinnati, Ohio, is frequently contaminated.

Bifenthrin Effects

Bifenthrin, a widely used pyrethroid 

insecticide that collects in sediment, is highly toxic 

to aquatic invertebrates. Mesocosm experiments 

demonstrated that multiple ecological responses to 

bifenthrin occur at concentrations similar to those 

measured in MSQA stream sediment (Rogers and 

others, 2016). Low levels of bifenthrin altered the 

timing of adult insect emergence, which could 

disrupt reproduction and affect the terrestrial food 

web. Moderate and high levels of bifenthrin were 

lethal to some sensitive species, such as scrapers 

(invertebrates that consume algae they scrape from 

rocks). The disappearance of scrapers accelerated 

algal growth. The results of the mesocosm 

experiments were consistent with MSQA results, 

which reported a decrease in herbivorous mayflies 

with higher bifenthrin concentrations in streams.

Artificial “streams” (mesocosms) were 

used to test the effects of bifenthrin on 

natural invertebrate communities.

Bifenthrin, in nanograms per gram organic carbon

0 200 400 600 800

Percentage of total abundance

0

20

40

60

80

100

EXPLANATION

Field

Lab

In controlled experiments, an increase 

in bifenthrin caused a decrease in 

abundance of scrapers that consume 

algae from rocks. A similar effect was 

observed in the MSQA streams. 

Photograph by Travis Schmidt, USGS
Ecological Models Connect the Landscape and Instream Stressors to 

Measures of Biological Condition in the MSQA Streams

Landscape: Human development 

causes chemical and physical 

changes to the natural landscape, 

leading to instream stressors.

Bank and channel

erosion

Drainage

modification

Fertilizer and

wastewater Pesticide use Urbancontaminants

Stressors: The specific factors that 

degrade biological conditions in the 

streams, as indicated by ecological 

modeling results, are linked to 

agricultural and urban land use. 

Photo courtesy of Zleng, Creative Commons attribution 2.0

Photo courtesy of Andrew Hoffman, Creative Commons attribution 2.0

Riparian

disturbance

Altered flow

and temperature

Pesticide

toxicity index

Pyrethroid

insecticides

Excessive fine

sediment

Ammonia, nitrogen,

and phosphorus

Channel

complexity

Bed sediment

contaminant index

Biological condition: Biota living 

in the streams respond to different 

combinations of stressors, 

depending on the species and

the conditions in each stream. 

Ecological models have associated instream stressor variables (green boxes) with measures of the condition of biological 

communities in MSQA streams, as represented by arrows. For example, one model identified five stressors associated with the 

invertebrate multimetric index (MMI), an overall measure of the health of the invertebrate community (black arrows) (Waite 

and Van Metre, 2017). Other models demonstrate how consequences of agricultural and urban land use (tan ovals) are related to 

instream stressors (green boxes).
Conclusions

What have the results of the MSQA told us about 

stream quality in the Midwest and about which stressors are 

most important? 

First, there are no pristine streams in the region, as indicated, 

for example, by a minimum of 28 pesticides detected in water at 

any site (Van Metre and others, 2017). 

Second, no single stressor or stressor type is responsible for 

all of the changes to the biological communities—for almost every 

stream and every measure of biological condition, many stressors, 

both physical and chemical, are implicated. Further, each site has 

a unique mix of stressors, as illustrated by the site scorecards 

on the Regional Stream Quality Assessments (RSQA) website. 

These findings suggest that improving stream conditions across 

the region will require multiple approaches. In spite of this 

complexity, there are some consistent findings across sites 

and biological communities. Habitat, in particular excess fine 

sediment and the condition of the channel and riparian zone, are 

important to all biological communities. Pesticides, specifically 

the triazine herbicides and the pyrethroid insecticides, are 

affecting algae and invertebrates. Lastly, managing for one group 

of stressors by, for example, preserving or restoring riparian-zone 

buffers along streams might reduce other stressors as well.

Find Out More About 

Midwestern Streams

Data, publications, and results, 

including a scorecard of the condition 

of each MSQA stream, can be found on 

the RSQA website at http://webapps.

usgs.gov/RSQA/. 

References

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By Peter C. Van Metre, Barbara J. Mahler,

Daren Carlisle, and James Coles

Photographs by Peter Van Metre, USGS, unless otherwise noted.

Cover photograph of boy holding fish courtesy of Michael Peirce, Creative Commons attribution 2.0

ISSN 2327-6916 (print)

ISSN 2327-6932 (online)

https://doi.org/10.3133/fs20173087