Increased water flow eroding Minn. River banks, adding pollutants

The confluence of the Minnesota River, on left, and the Mississippi.
The confluence of the Minnesota River, on left, and the Mississippi in an undated photo.
Minnesota Pollution Control Agency File

The muddy Minnesota River is straining from a big increase in water flow and the resulting sediment is offsetting slim gains in water quality.

Those are among the main findings of a study released Monday by the Minnesota Pollution Control Agency. It's the first time the MPCA has conducted such a comprehensive study entire length of the river, from the western border to where it dumps its sediment into the Mississippi River.

While there's less pollution per gallon of Minnesota River water, the study found, there's more water flowing in it — so the total pollution has not decreased.

Major pollutants are nitrate, phosphorous, bacteria and sediment. The report blames pollution on a mix of both increased rainfall and agricultural runoff.

More than 80 percent of land in the Minnesota River basin is used for agriculture. The MPCA says there are some signs of progress, and many farmers are exploring practices to reduce runoff.

The study also found the amount of water flowing down the Minnesota River has doubled in the past 80 years. Some comes from more rain, but much of it comes from farm drainage systems. The loss of marshes and wetlands where water can be stored on the landscape has compounded the problem.

Glenn Skuta, Watershed Division Director at the MPCA, said the Minnesota River's higher water levels and erosion are having adverse affects downstream. "Lake Pepin, a large natural lake on the Mississippi River, is filling in at a much accelerated rate, because largely of the sediment that's coming from the Minnesota River."

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