Officials say more than 20,000 gallons of untreated wastewater has accidentally been discharged into a part of Big Spirit Lake.
The Iowa Great Lakes Sanitary District inspected an overflowing manhole Wednesday morning near Orleans on the southeast side of the lake.
It was then discovered that untreated wastewater had discharged to a storm sewer, flowing into the lake about 1,400 feet northeast of the Orleans beach.
The state Department of Natural Resources says a pipeline below the manhole had collapsed.
The district stopped the discharge and is working to repair the pipeline.
State officials are taking water samples Wednesday and telling residents to stay away from the area.