Beneficial Uses:

Beneficial uses define activities that a body of water should be able to support.  The South Dakota Department of Environment and Natural Resources designates all surface waters in the state for one or more of the following eleven beneficial uses:

(1) Domestic water supply

(2) Coldwater permanent fish life propagation

(3) Coldwater marginal fish life propagation

(4) Warmwater permanent fish life propagation

(5) Warmwater semi-permanent fish life propagation

(6) Warmwater marginal fish life propagation

(7) Immersion recreation

(8) Limited contact recreation

(9) Fish and wildlife propagation, recreation, and stock watering

(10) Irrigation

(11) Commerce and industry

 

All streams are assigned the beneficial uses (9) and (10) unless otherwise stated in the Administrative Rules of South Dakota (ARSD) Chapter 74:51:03. All lakes are assigned beneficial use (9).  Additionally, all lakes listed in ARSD Chapter 74:51:02:04 are assigned the beneficial uses of (7) and (8) unless otherwise stated.

 

Each beneficial use is associated with numerical water quality criteria agreed upon by the state and the US Environmental Protection Agency.  On the graphs found on this website, the applicable numeric water quality criteria are shown with a horizontal line.

 

E. coli

Escherichia coli are a type of fecal coliform bacteria that is found in the intestines of warm-blooded animals, including humans. The presence of E. coli in a water sample is a strong indicator that the water has been recently contaminated by sewage and/or animal waste and could also contain harmful bacteria as well as other disease-causing organisms.  

Immersion Recreation [Beneficial Use (7)] is <235 cfu/100mL

Limited Contact Recreation [Beneficial Use (8)] is <1178 cfu/100mL

Nitrate

Nitrate is a nutrient that that is a vital building block for plant and algae growth.  Sources of nitrate include agricultural practices, septic tanks, precipitation, groundwater, and decaying organic matter. Nitrate can also be converted from ammonia by bacteria through a process called denitrification.  High levels of nitrate can contribute to excessive biological growth and lead to algal blooms. Ingestion of water containing elevated amounts of nitrate (greater than 10 mg/L) can be harmful to humans, especially infants, and lead to a condition known as “blue baby syndrome.”

All waters in South Dakota have a limit of <88 mg/L for nitrate.  Because current levels of nitrate are far below this number, the horizontal line for this criterion is not shown on any of the graphs.  Where the Domestic Water Supply [Beneficial Use (1)] is assigned, the applicable standard of < 10mg/L is shown.

pH

pH is a measure of how acidic or alkaline the water is based on a scale from 0 to 14.  On this scale, 0 is the most acidic value, 14 is the most alkaline value, and 7 represents neutral.  A change of 1 pH unit represents a 10-fold change in acidity or alkalinity.

Many sites displayed here have multiple pH ranges due to more than one beneficial use being assigned.  Depending on the site, pH values should remain above 6.0 or 6.5 and below 9.0 or 9.5.

Total Suspended Solids

Total Suspended Solids (TSS) are small particles that are suspended within the water column. Suspended solids include silt and clay, plankton, algae, fine organic debris, and other particulate matter. Excessive TSS can decrease water clarity which prevents sunlight from reaching aquatic plants and makes it difficult for sight-feeding organisms to find food. Elevated TSS can also lead to increased water temperatures.

Beneficial Uses (3), (4), and (5) is <158 mg/L

Beneficial Use (6) is <263 mg/L

Dissolved Oxygen

Dissolved oxygen is essential for fish and other aquatic life.  Because the solubility of oxygen increases as temperature decreases, cooler water will generally hold more oxygen than warm water.  Running water will also usually contain more oxygen than stagnant water. Dissolved oxygen concentrations can vary significantly over short distances within a body of water. Dissolved oxygen levels of at least 4-5 mg/L are needed to support a wide variety of aquatic life.  Very few species can exist at levels below 3 mg/L.

Beneficial Uses (3), (4), (5), (6), (7), and (8) are ≥5.0 mg/L

Beneficial Use (6) is ≥4.0 mg/L between October 1st and April 30th