Water Quality

Recent water crises across the US have elevated awareness regarding the importance of water and rivers for communities. By being proactive, we can avoid the struggles and costs associated with the maltreatment of an important resource. At Friends of the Big Sioux River, we are concerned about the public health ramifications of our water. Between May and September every year, we conduct weekly water testing throughout the watershed. We test for three primary contaminants that impair water quality: 1) total suspended solids from soil erosion, 2) E. coli from animal waste, and 3) nitrates from fertilizer. The test results are used by the South Dakota Department of Agriculture and Natural Resources and posted weekly on our website. When contaminant levels are high and immersion is unsafe, we believe that warning the public is the proper thing to do. To learn more about water quality and view our testing results, scroll down or click the buttons below.

Why Water Quality?

State of Our River

FBSR Annual Results

2024 Water Quality Report

Past Testing Results

Water Quality is Important For:

Growth & Development

People are attracted to a community for its quality of life, which includes clean water, scenery, and recreation.

Recreation & Tourism

A clean river attracts tourists and residents who want to fish, kayak, and swim. According to a 2022 report by the Bureau of Economic Analysis, outdoor recreation in the United States generates 5 million direct jobs and $1.1 trillion in consumer spending. In South Dakota, outdoor recreation generates 18,134 direct jobs and $1.7 billion in consumer spending. A healthy river equals a healthy economy.

Safe Local Water

Protecting local water allows communities to source water locally, which is cheaper and simpler than piping it in from long distances. Cleaner water is cheaper water. In treating water for the city of Des Moines, the Des Moines Water Works spent $7,000 a day removing excess nitrates, a cost that is ultimately passed on to the consumers.

Health of People & Wildlife

Every living creature needs clean water for healthy development. Unclean water can be hazardous, even deadly.

State of Our River

2024 DANR Integrated Report for Surface Water Quality Assessment Data

The following information and map are gathered and developed from the 2024 South Dakota Integrated Report for Surface Water Quality Assessment prepared by the South Dakota Department of Agriculture and Natural Resources. Stream data in the report were collected between October 2018 and September 2023.

Total Suspended Solids (TSS)

75% Impaired

75% of Big Sioux River segments are impaired for TSS. Only 25% meet the beneficial use standard of warm water semipermanent fish life propagation (158 mg/l).

E. Coli

75% Impaired

75% of Big Sioux River segments are impaired for E. coli. Only 25% meet the beneficial use standard of limited contact recreation (1,178 CFU/100 ml) and/or immersion recreation (235 CFU/100 ml).

Nitrates

0% Impaired

100% of Big Sioux River segments meet the beneficial use standard for nitrates of domestic water supply 10 mg/L.

2004-2024 Big Sioux River Impairment Status

Every two years, SD DANR produces an Integrated Report for Surface Water Quality Assessment for all waterbodies in the state. The Big Sioux River is split into 16 segments, each with a list of beneficial uses. A waterbody is considered impaired when it does not meet its beneficial use criteria. The graph to the right indicates the percent of impaired river segments for three contaminants in the Big Sioux River from 2004 through 2024. E. coli was not added to the report until 2010. In the mid-2010s, TSS impairment spiked to 81%. Since 2020, TSS impairment has remained at 75%. In 2016, E. coli impairment spiked to 88% but has declined since then. In 2024, E. coli increased slightly to 75% due to the number of impaired river segments increasing from 11 in 2022 to 12 in 2024. Nitrate impairment has been at 0% since 2010. Overall, these data show an improvement in water quality in the Big Sioux River over the last five years.

**2004-2024 Big Sioux River E. coli Beneficial Use Status**

SD DANR lists E. coli as having two beneficial use criteria: Limited Contact Recreation and Immersion Recreation. Of the 16 segments of the Big Sioux River, nine are designated for Immersion Recreation (235 CFU/100mL) and 16 for Limited Contact Recreation (1,178 CFU/100 mL). Due to the disease risk posed by E. coli, we believe it is important to inform the public of the river’s E. coli impairment status. Since 2012, all nine Immersion Recreation segments have been considered impaired or unsafe for swimming. Limited Contact Recreation impairment peaked in 2016, but it has been steadily declining ever since. These data indicate that E. coli levels in the river are improving year over year.

State of Our River

Segment Analysis

Beneficial Uses

The Environmental Protection Agency requires all states to specify goals and expectations for how each water body is used. Based on these requirements, the South Dakota Department of Agriculture and Natural Resources (DANR) has designated all surface waters in the state for one or more of 11 beneficial uses.

A water body is considered impaired (non-supporting) if it does not meet its beneficial use standard(s). When a water body is considered impaired, a Total Maximum Daily Load (TMDL) must be developed. A TMDL is the amount of pollution a water body can receive and still support its designated beneficial uses. The TMDL should specify quantifiable targets and associated actions that will allow the water body to support its designated beneficial uses.

Scroll through the following slides to learn more about the 11 beneficial uses for surface waters in South Dakota!

Domestic Water Supply Waters: Surface waters that are suitable for human consumption, culinary or food processing purposes, and other household purposes after suitable conventional treatment.

Coldwater Permanent Fish Life Propagation Waters: Surface waters are capable of supporting aquatic life and are suitable for supporting a permanent population of coldwater fish from natural reproduction or fingerling stocking. Warmwater fish may also be present.

Coldwater Marginal Fish Life Propagation Waters: Surface waters are capable of supporting aquatic life and are suitable for stocked catchable-size coldwater fish during portions of the year. However, because of critical natural conditions including low flows, siltation, or warm temperatures, the waters are not suitable for permanent coldwater fish population. Warmwater fish may also be present.

Warmwater Permanent Fish Life Propagation Waters: Surface waters are capable of supporting aquatic life and are suitable for the permanent propagation or maintenance, or both, of warmwater fish.

Warmwater Semipermanent Fish Life Propagation Waters: Surface waters are capable of supporting aquatic life and are suitable for the propagation or maintenance, or both, of warmwater fish but which may suffer occasional fish kills because of critical natural conditions.

Warmwater Marginal Fish Life Propagation Waters: Surface waters will support aquatic life, particularly more tolerant species of warmwater fish. Aquatic life will be supported naturally or by frequent stocking and intensive management. However, they will suffer frequent fish kills because of critical natural conditions.

Immersion Recreation Waters: Surface waters that are suitable for uses where the human body may come in direct contact with the water, to the point of complete submersion, and where water may be accidentally ingested or where certain sensitive organs such as the eyes, ears, and nose may be exposed to water.

Limited Contact Recreation Waters: Surface waters that are suitable for boating, fishing, and other water-related recreation, other than immersion recreation, where a person's water contact is limited to the extent that infections of the eyes, ears, respiratory or digestive systems, or urogenital areas are normally avoided.

Irrigation Waters: Surface waters that are suitable for irrigating farm lands, ranch lands, gardens, and recreational areas.

Commerce and Industry Waters: Surface waters that are suitable for use as cooling water, industrial process water, navigation, and production of hydroelectric power.

Fish and Wildlife Propagation, Recreation, and Stock Watering Waters: A beneficial use classification assigned to all surface waters of the state that: (a) May support recreation, in and on the water, and fish and aquatic life, when sufficient quantities of water are present for sufficient duration to support those uses; (b) Provide habitat for aquatic and semiaquatic wild animals and fowl; (c) Provide natural food chain maintenance; and (d) Are of suitable quality for watering domestic and wild animals.

Common Parameters

Click the arrow buttons on the slideshow below to learn about the 12 water quality parameters tested for in the Big Sioux River watershed by the South Dakota Department of Agriculture and Natural Resources and partner organizations.

Alkalinity indicates that the pH of a body of water is above 7. Calcium carbonate, which is often a result of streams flowing over limestone, is a contributor to alkalinity. While high levels of calcium carbonate do not pose an immediate threat to human or aquatic organism health, calcium carbonate deposits in plumbing can be problematic. Higher alkalinity and excessive calcium carbonate make chlorine less effective at cleaning water, meaning more is required, which can further corrode plumbing.

Ammonia, an inorganic chemical compound, is highly toxic to humans, animals, and aquatic life when high concentrations are present in bodies of water. Natural sources of ammonia include animal and human waste, as well as other decaying matter. Human-made sources of ammonia include fertilizers, industrial processes, and waste disposal sites. When high enough levels of ammonia are present in water, it is difficult for aquatic organisms to excrete the toxicant, leading to toxic buildup in internal tissues and blood and potentially death. Since ammonia poses a threat to human health, no blood-ammonia level is technically safe, and high levels of ammonia in the bloodstream can significantly impact a person's nervous system.

Chlorophyll-a is a measure of the amount of algae growing in a waterbody. While algae is a natural part of a freshwater ecosystem, high algae levels, such as an algal bloom, can be detrimental to aquatic life. Algal blooms often occur as a result of high temperatures and excessive nutrients from fertilizers or sewage brought by runoff. Too much algae can significantly decrease the amount of dissolved oxygen in a body of water, which is necessary for aquatic life. Algal blooms can be easily identified by any person, as the water often features a pungent odor and a green, scummy surface. Additionally, some algae produce toxins that, when ingested or breathed in, can be harmful to human health.

Dissolved Oxygen, more commonly referred to as DO, is a measure of the amount of oxygen present in a body of water. DO is a necessary component of healthy aquatic life, and when levels drop too low, it can be detrimental to freshwater organisms. Hypoxic or anoxic water (little to no oxygen present) is often the result of algal blooms, which require more decomposition, meaning the DO in the water is consumed. The biological effects of low DO include increased respiratory stress, changes in behavior, increased mortality, and changes in population and community structure in aquatic life. Low levels of DO can be observed by foul-smelling water, often from algal blooms, fish gulping for air at the surface, and large fish dying off first.

E. coli is a key indicator of how safe water is for recreational use, such as swimming, fishing, or boating. At Friends of the Big Sioux River, we test for E. coli weekly across 18 sites in the Big Sioux River watershed. E. coli measures fecal contamination in water and indicates the possible presence of disease-causing bacteria and viruses. Point sources of E. coli include leaky sewage pipes, poorly sited septic systems, and discharge from wastewater treatment plants. Nonpoint sources include runoff from feedlots, manure from farms and ranches, and other areas of wildlife.

Mercury, a highly toxic contaminant, enters bodies of water through various sources. These include the atmosphere, direct discharge from industrial and mining wastes, and leaching from rocks and soil. Additionally, bacteria can transform mercury into methylmercury, which can then be absorbed by aquatic organisms, including fish. When fish absorb methylmercury, it bioaccumulates in their tissue, including muscle. In turn, mercury will bioaccumulate in anything that consumes those fish, including larger fish, birds, other vertebrate animals, and humans. Methylmercury bioaccumulation can be highly dangerous to species, decreasing viable population sizes and disrupting the food web.

Nitrate is another contaminant Friends of the Big Sioux River measures throughout the summer. Excess nitrates are often a result of runoff from fertilizers, but they can also result from improperly disposed sewage, industrial waste, erosion of natural deposits, and many more. When nitrate levels reach unsafe levels, which is deemed anything above 10 mg/L, it can pose a risk to human health, especially in infants, pregnant women, and those with specific health concerns. Nitrates are also a contributor to algal blooms and can stunt fish growth and weaken their immune systems.

pH is a scale that measures how acidic or basic water is. The scale is from 0 to 14, 7 marking a neutral pH. For freshwater, an ideal pH falls between 6.5 to 9. Exceedingly high or low pH levels can make water conditions toxic to aquatic organisms and can lead to unsafe drinking water. High pH levels, also known as increasing alkalinity, can damage the gills and skin of fish and other organisms, and, in the worst cases, these organisms will die from ammonia poisoning. Low pH levels, also known as increasing acidity, make fish more susceptible to fungal infections and other diseases and allow for more heavy metals to dissolve in the water, increasing toxicity.

Conductivity is the measure of the ability of water to pass an electrical current. Specific conductivity, then, is the roughly constant range of a water’s conductivity. When conductivity falls drastically outside the range, it is often an indicator that something else is wrong. In general, human disturbances will increase the amount of dissolved solids and, therefore, increase conductivity.

While often not considered amongst other contaminants, abnormal temperatures can significantly affect water quality. Human activities can impact water temperature, including the removal of riparian buffer vegetation, altering channels, damming waterways, and removing surface or groundwater. Increased water temperature can have biological effects on aquatic organisms and can result in the absence of coldwater taxa where they are expected. Decreased water temperatures can have the opposite effect, with the absence of warmwater species in areas where they are expected.

Total Dissolved Solids in water include minerals, salts, dissolved metals, and organic matter. Therefore, high TDS does not necessarily equate to poor water quality, as it is entirely dependent on the content of the TDS. However, it is important to pay attention to TDS, as it can be a marker for pollution stemming from agricultural runoff, urban stormwater runoff, water treatment chemicals, or industrial wastewater. Additionally, drinking water carried through pipes can experience an increase in TDS due to poor pipes and plumbing.

Total Suspended Solids are the third and final contaminant we test for at Friends of the Big Sioux River. TSS measures the amounts of particles that are larger than 2 microns. TSS includes anything that floats or “suspends” in water, including clay, gravel, sand, silt, algae, and bacteria. While many of these do not pose a threat to human or wildlife health, particles such as clay and silt will muddy the waters. Those that are a threat to human or wildlife health are often the result of human pollution and toxic algal blooms. Additionally, high TSS can reduce a body of water’s dissolved oxygen levels, may increase the temperature of the water, and can block sunlight, which would decrease photosynthesis.

FBSR Annual Water Testing Results

What am I looking at?

Friends of the Big Sioux River recognizes three primary contaminants that impair water quality: 1) total suspended solids (TSS) from soil erosion, 2) E. coli from animal waste, and 3) nitrates from fertilizer. During the summer months, we test for these three contaminants to determine if bodies of water are meeting their beneficial use criteria. The safe levels have been assigned by the South Dakota DANR.

Testing Parameters

Nitrates: 10 mg/L
E. coli: 235 CFU/100mL
Total Suspended Solids (TSS): 158 mg/L

The South Dakota Department of Agriculture and Natural Resources designates all surface waters in South Dakota for one or more of 11 beneficial uses, also called designated uses. At Friends of the Big Sioux River, we recognize and use these criteria to indicate safe contaminant levels for our local waterbodies. We use the strictest beneficial use standards, as we firmly believe that our local waterbodies should be as clean and healthy as possible. The beneficial use criteria used by FBSR are as follows:

Daily maximum nitrate levels must be 10 mg/L or lower to meet the beneficial use of domestic water supply, e.g., drinking water.

Daily maximum E. coli levels must be 235 CFU/100 mL or lower to meet the beneficial use of immersion recreation. The geometric mean, which is a type of average of all the test results obtained during a reporting period, must be 126 CFU/100 mL or lower to meet the beneficial use of immersion recreation.
Daily maximum total suspended solids (TSS) must be 158 mg/L or lower to meet the beneficial use of fish life propagation for multiple fish species. The 30-day average must be 90 mg/L or lower to meet the beneficial use of fish life propagation for multiple fish species.

Why These Sites?

The sites selected by FBSR are common points of recreation and often have beneficial uses of swimming and limited contact recreation. If test results reveal contaminant levels that exceed established safe levels, they are not safe for their beneficial uses, including swimming and limited contact recreation. We are providing you with this water quality data so you can make safe, informed decisions about your summer recreation.

2024 Key Trends

In 2024, Sioux Falls received 19.42 inches of rain between May and September. In 2023, the watershed experienced a significant decrease in rainfall, with only 9.03 inches of rain falling in the city in the same time period. As a result, we saw a reduction in water quality in 2024.

E. coli

On average, in 2024, E. coli levels exceeded the beneficial use criteria of 235 CFU/100 mL at nine of the 18 sampled sites. Seventeen sites exceeded the beneficial use criteria at least once during the 2024 testing season.