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Water Quality Information

If you've browsed our website so far, you know that we proudly display our motto on all we do:

We are water quality.  

We also know that water quality is not a simple concept.  We've created this page to help others understand some of the key concepts surrounding water quality in the Big Sioux River watershed.

We are water quality.  BSRP - Big Sioux River Project

What is Water Quality?

Water quality describes the condition of the water based on the chemical, biological, and physical characteristics. These characteristics have allowable limits for certain impairments, such as E. coli, total suspended sediment (TSS), and nitrates. The thresholds for each of these items are established by the Environmental Protection Agency (EPA) and referred to as the TMDL (total maximum daily load) for that contaminant in its designated beneficial use. Each stream segment and lake is evaluated by the state, and they are individually rated for their capability to sustain certain uses. These are referred to as the waterbody's designated beneficial use (sometimes shortened to beneficial use or designated use).

Understanding Designated Beneficial Uses

When we talk about various streams, lakes, and rivers as being "impaired," that simply means that they are not currently meeting the water quality standards for their intended beneficial use. 


The designated beneficial use classifications indicate what that particular segment of a waterbody can support for fish and wildlife (cold/warm water species permanent/semi-permanent habitat, nesting/spawning areas, etc.) and for use by humans (irrigation, swimming, kayaking/canoeing, drinking, etc.). Each of these designated beneficial uses is assigned a TMDL - total maximum daily load - for specific known contaminants that compromise the ability of that waterbody to meet the needs of the beneficial use. For example, if a stream or lake has a designated beneficial use of "Warm water Permanent Fish Life Propagation Waters", such as  Lake Alvin, the water cannot exceed specific thresholds and still support warm water fish habitats. Lake Alvin is currently listed as "impaired" for temperature. This means that it meets the requirements for all other thresholds associated with the uses Lake Alvin can support, but the temperature of Lake Alvin is not able to support stable fish populations.  

It is important to note that waterbodies are either impaired or meet the TMDL requirements. Streams and lakes are not listed as 5% impaired or 90% impaired, and the percentage of improvement or degradation of a particular impairment is not communicated in its impairment status.  It either currently meets or fails to meet the standards of its designated use.  

Each beneficial use comes with its own threshold for various contaminants.  The TMDL for E. Coli in limited contact recreation areas (watercraft sports) is 1,178 mpn/100 mL while the immersion recreation (swimming) daily maximum standard is 235 mpn/100 mL.  If a stream was listed for both beneficial uses, it could meet the limited contact TMDL, but still be listed as impaired for E. Coli if it does not the immersion recreation standard.

Not all streams and lakes are designated for immersion recreation.  In fact, there are only 11 lakes and stream segments in the Big Sioux River watershed that are designated for swimming.  That's why we look at each stream segment and its designated beneficial uses to determine the best course of action to address the water quality needs.

Interact with the South Dakota Surface Water Quality Standards map to discover the designated beneficial uses of your favorite streams and lakes.


The BSRP focuses on BMPs that address three major contaminants impacting the Big Sioux River watershed's ability to meet the designated beneficial uses of its streams and lakes.

E. Coli

E. coli stands for Escherichia coli, which is a type of bacteria.The presence of E. coli in water is a strong indication of sewage or animal waste contamination.


TSS are actual physical particles that are suspended in the water, for example, particles of clay or silt. Suspended solids are small enough to “float” but not so small they dissolve, and not so large that they settle out of the water quickly. ‍


High levels of nitrate in water can be a result of runoff or leakage from fertilized soil, wastewater, landfills, animal feedlots, septic systems, or urban drainage.

As you engage with the DANR surface quality map, you will notice that some lakes and streams are listed as "Impaired" for conditions other than TSS, nitrates, or E. coli.  This is why targeted best management practices are so important to what we do here at the Big Sioux River Project.  Our staff uses a science-backed approach to the practices we recommend to producers that address the priority concerns in adjacent streams.  

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