Graphs in the Water Quality Dashboard present sample data for each assessment unit. Assessment units are lakes or segments of rivers and streams that are used to classify waters of the state for the purpose of assessing their water quality. Graphs include lines displaying water quality standards where applicable and, for lakes only, regional moving averages for select parameters. These lines can be turned on and off by checking the box associated with the line for the standard or regional moving average. More than one standard line may exist for water quality parameters where there is more than one threshold. E. coli standards include a threshold for single samples and a separate threshold for the geometric mean of a minimum of five samples collected in a 30 day period. Total Suspended Solids standards, in most cases, also have two thresholds - one for single samples and another separate threshold for the average of 5 samples collected within a 30 day period.
The beneficial use support status for each waterbody is presented in the “Support Status” tab. All waters in South Dakota are designated beneficial uses, which are uses for the waterbody deemed to be appropriate to the waterbody’s attributes. Examples of beneficial uses are Domestic Water Supply (drinking water), Irrigation, Limited Contact Recreation Waters (e.g. boating, fishing, kayaking), Immersion Recreation Waters (swimming, water skiing), and various beneficial uses designed to protect fisheries (e.g. Warmwater Marginal Fish Life Propagation, Coldwater Permanent Fish Life Propagation). Each beneficial use also assigns water quality standards for parameters that are important to protecting the beneficial use. For example, the Immersion Recreation beneficial use assigns a standard for E. coli to protect people recreating in the water from getting sick from bacteria, and the beneficial uses for fisheries assign standards for dissolved oxygen to protect fish from low oxygen levels that would cause fish kills. If all water quality standards associated with the beneficial uses assigned to a waterbody are being met, it is considered to be in full support of its beneficial uses. If one or more of the standards for a beneficial use is not being met, that waterbody is not in full support of its beneficial uses. Beneficial use support status is assessed every 2 years and is presented to the public in the South Dakota Integrated Report for Surface Water Quality Assessment.
Waters that are not in full support of their beneficial uses require a Total Maximum Daily Load (TMDL) report under the federal Clean Water Act. These reports detail the sources of pollution for the parameter of concern, and develop recommendations for how much of a pollutant can be in a waterbody while still meeting water quality standards and supporting its beneficial uses. TMDL reports are presented as links in the Projects and Reports tab. Other water quality documents are also available, such as watershed assessment project reports, watershed improvement project reports, and watershed strategic plans. These documents for each waterbody are linked in the Projects and Reports tab.