Water quality in the Lower Minnesota River Watershed has persistent problems with excess phosphorus, sediment, bacteria, and other contaminants, according to a 2017 report by the Minnesota Pollution Control Agency (MPCA). The watershed covers 1,835 square miles of south-central Minnesota and includes 87 miles of the Minnesota River, from just north of St. Peter, to its confluence with the Mississippi River. The watershed comprises the Minnesota Valley National Wildlife Refuge, 133 lakes larger than 10 acres, 2,482 miles of tributaries to the Minnesota River, and the cities of Bloomington, Prior Lake, Winthrop, Waconia, New Prague, and Le Sueur.
As part of its regular water-monitoring cycle, the MPCA assessed water quality at more than 200 sites and found violations of state water quality standards throughout the watershed. Elevated levels of phosphorus are fueling nuisance algae blooms, which can deter recreation and create public health hazards. Sediment is clouding the water in lakes and streams and can harm habitat for fish and other aquatic life. The bacteria contamination detected could pose human health risks.
Of the bodies of water assessed, 84% of streams and 57% of lakes do not protect fish, bugs, and other aquatic life. Fifty-five percent of lakes failed to meet water quality standards for recreation. In lakes tested for mercury in fish, 74% exceeded standards.
Despite the problems, the MPCA’s report also noted some good news. Four lakes in the watershed — Crystal, McMahon, Mitchell, and Bryant — are now meeting water quality standards that they failed to meet previously. The improvements are the result of successful restoration efforts by local organizations.
Land use is a major factor affecting water quality, and in this watershed it runs the gamut from almost exclusively row-crop agriculture in the west, to residential suburbs and urban industry in the northeast. More than 90% of the wetlands present prior to European settlement have been drained to accommodate cropland. The lack of wetlands prevents water retention on the landscape and leads to increased storm-related runoff and discharges that can destabilize stream banks and increase sediment into the water. Similarly, in urban and suburban environments, impervious surfaces send huge volumes of water into storm drains and nearby bodies of water.
Local and state entities have made major efforts toward restoring and protecting the Lower Minnesota Watershed’s water quality. But dramatic improvements on the landscape are still needed to meet water quality standards in the watershed’s lakes, rivers, and streams.
The next step in the MPCA’s watershed management process will be to identify “stressors” — the conditions contributing to water quality problems in the watershed. For more information, read the full Lower Minnesota River Watershed Monitoring and Assessment Report.