Run-off from agricultural land is the biggest contributor of nutrients like phosphorous and nitrogen to lakes and rivers. Those elements feed toxic algae that coats waterways.
The MPCA's standards for those nutrients vary based on the type of waterway.
Mark Tomasek oversees the MPCA's water quality standard rules. He says this is the first time Minnesota has developed standards to cap the amount of nutrients like nitrogen and phosphorous entering the state's lakes and rivers.
"As you get more nutrients, you get excess growth of algae and reduced clarity," said Tomasek. "That impacts recreational use of swimming and other general uses of lakes."
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Tomasek says the agency wrote the country's first water quality standards for two common corn herbicides, acetochlor and metolachor.
"There's two exceedences of the aceochlor standard that have been monitored in the state and none for metolachor," Tomasek said.
The LeSeur River and Beauford Ditch both exceed the standard of 3.6 micrograms per liter. Tomasek says initially that standard was significantly lower but agricultural groups argued for a less stringent standard.
AN overabundance of algae can also de-oxygenate the water, killing fish. Contact with the algae can also be toxic to humans and animals.