The Iowa Department of Natural Resources says a sewer line leak was discovered Wednesday morning at Big Creek State Park.
The DNR says the leak was near the handicap fishing pier on the east side of the lake, about half a mile from the beach. Up to 50 gallons of untreated wastewater reached the lake after traveling about 100 yards over the ground.
Workers have fixed the sewer line and lime is being applied to the ground between the leak and the lake Wednesday afternoon.
DNR officials warn people to avoid the area until the lime has been placed.