NORTHFIELD, Minn. (AP) — County officials have closed Minnesota beaches after the city of Northfield discharged 1 million gallons of wastewater into the Cannon River.

The Star Tribune reports Dakota County closed the Lake Byllesby Regional Park beach on Tuesday, and Northfield has warned people downstream to avoid contact with the river until Friday.

A pipe break at the city's treatment plant forced officials to discharge the wastewater early Tuesday. The release was below 1 percent of the river's total flow at that time.

Dakota County shut down the beach because the river flows into Lake Byllesby. Goodhue County also closed a beach on the lake until samples show safe waters.

The Minnesota Pollution Control Agency has been informed.

Northfield officials are working on plant maintenance repairs and monitoring operations, the release said. The cause of the breakdown is still being evaluated.