Lake Pepin in southeast Minnesota is close to meeting its custom water-quality standard designed to minimize algae, with more work needed upstream to meet the goal, according to a study recently released by the Minnesota Pollution Control Agency (MPCA). The study focuses on phosphorus levels in Lake Pepin and the Mississippi River upstream, from the Crow River near Dayton, Minn., to the St. Croix River near Hastings, Minn.
The study also references the need to reduce phosphorus in several other rivers, including the Minnesota and Cannon rivers. These river systems are addressed in separate studies.
Phosphorus comes from many sources, including wastewater discharged by communities and industries, and runoff from farm fields and urban areas. Both urban and agricultural sources need to reduce the phosphorus they send to rivers and eventually Lake Pepin. About two-thirds of the algae in Lake Pepin are produced upstream. As such, the study calls for reducing phosphorus from upstream rivers by 10-70 percent.
Lake Pepin, which has characteristics of both a lake and river, is about 21 miles long and one of the widest parts of the Mississippi River. Nearly 50,000 square miles — roughly half of Minnesota plus a bit of three neighboring states — drain to Lake Pepin through the Upper Mississippi, St. Croix, and Minnesota rivers. Eighty-two percent of Minnesota residents live in this basin. No other water-quality project in Minnesota has addressed such a large area.
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