Missouri River Basin (Upper Big Sioux, Lower Big Sioux, Little Sioux, and Rock River Watersheds) Monitoring and Assessment Report

The Missouri River Basin in Minnesota is made up of four major watersheds - the Upper Big Sioux River, Lower Big Sioux River, Rock River, and Little Sioux River. The Missouri River Basin drains roughly 1783 mi2 of southwestern Lincoln, southwestern Murray, Rock, most of Nobles, and southwest Jackson counties. The four watersheds stretch from the South Dakota border near Lake Benton southeast to the Iowa border just west of Jackson. These four watersheds are all headwaters to the Big Sioux River and Little Sioux River which eventually flow into the Missouri River outside of the state. Drinking water, aquatic recreation and aquatic life uses are compromised by high nitrate, bacteria, and turbidity levels. These stressors are also likely impacting biological communities, a pattern observed across southern Minnesota. Unlike surrounding flatter watersheds, the Upper Big Sioux River, Lower Big Sioux River, and Rock River Watersheds have less channelized streams. This is mainly due to the presence of open pasture along the stream corridors instead of channelizing the streams for maximum row crop usage. The Little Sioux River Watershed is an exception with over 80% of the watershed channelized for agricultural purposes. More work is needed to bring surface waters into compliance with water quality standards. Future turbidity reduction efforts should include measures to stabilize stream banks and reduce erosion. Attainment of water quality standards for bacteria and nitrates should focus on nonpoint sources of pollution including fertilizer and livestock waste management, and failing septic systems. Best management practices (BMPs) should be implemented in a targeted approach toward sensitive features on the landscape that are known to impact surface water quality to ensure restoration resource dollars are spent in areas where they will do the most good. Local cooperation will be crucial to making surface water quality improvements, as using regulatory authority to reduce nonpoint source pollution is limited.