The State of Our River: A Look at the 2024 Integrated Report
In early 2024, the South Dakota Department of Agriculture and Natural Resources (DANR) released the 2024 Integrated Report for Surface Water Quality Assessment. This report provides an assessment of the condition of the state’s surface water resources for the United States Environmental Protection Agency and South Dakota citizens. It also identifies impaired waterbodies that require a Total Maximum Daily Load (TMDL), a management tool that must be developed for impaired waterbodies. Stream data in the report were collected between October 2018 and September 2023, and lake data were collected between October 2012 and September 2023.
DANR analyzed data from 45 lakes and 34 stream segments in the Big Sioux River watershed. These data show the primary causes of stream impairment continue to be E. coli and total suspended solids (TSS). E. coli, a bacterium found in the intestine of warm-blooded organisms, is found in local streams due to manure runoff from farms, ranches, and feedlots; discharge from storm sewers and some wastewater treatment plants; and runoff from wildlife and pet waste. TSS includes anything that floats or “suspends” in water, including clay, gravel, sand, silt, algae, and bacteria. Sources of TSS in the Big Sioux River watershed include runoff from cropland and streambank erosion.
Data also show the primary causes of lake impairment in the watershed to be from chlorophyll-a and mercury in fish tissue. Chlorophyll-a is a measure of the amount of algae growing in a waterbody. While algae is a natural part of a freshwater ecosystem, 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. Mercury, a highly toxic contaminant, enters bodies of water through various sources, including atmospheric deposition, direct discharge from industrial and mining wastes, and leaching from rocks and soil. When fish absorb methylmercury, it bioaccumulates in their tissue. 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.
Overall, the 2024 Integrated Report did not show significant changes in water quality in the Big Sioux River watershed since the previous report was released in 2022. Therefore, it is of the utmost importance that we work together as a watershed community to implement on-the-ground conservation practices in rural and urban areas to improve water quality. You can view a greater in- depth analysis of the 2024 Integrated Report data on our website at fbsr.org/water-quality-monitoring.