Torrential downpours this month washed nearly a year's worth of sediment into the Minnesota River and its tributaries, along with more than 30 times the proposed pollution limit.
"We had high intensity rain, and we've got overland flow and stormwater runoff going into the river," said Pat Baskfield, of the Minnesota Pollution Control Agency, and coordinator of a statewide river monitoring program. "What we find is events like this often account for upwards of 80 percent of the sediment load that pass through the river over the course of the year."
The levels of farm fertilizers like phosphorus were as much as 10 times the proposed pollution limit, Baskfield added. The runoff came from farm fields, river banks and from the numerous gullies that line steep hills leading to the streams.
"The numbers were exceptionally high," Baskfield said.