Policy makers in Minnesota and Wisconsin are trying to reduce another pollutant in the area's lakes and rivers -- phosphorus. State officials from the two states will sign an agreement Thursday to reduce the amount of phosphorous in the St. Croix River.
The St. Croix forms much of the border between Minnesota and Wisconsin. It's actually one of the region's cleanest rivers. But phosphorous levels started to rise dramatically in the mid-1900s, as fertilizer use and urban growth increased runoff into the river and its tributaries.
The agreement calls for a reduction of phosphorus levels in the St. Croix River by 20 percent by the year 2020.
Dan Engstrom, who studies the St. Croix for the Science Museum of Minnesota, will be at the signing ceremony at the University of Wisconsin-River Falls. He told MPR's Tom Crann that phosphorus poses a major threat to the river's health.