Officials say about 2.5 million gallons (9.5 million liters) of partially treated sewage recently flowed from a lagoon at a mobile home park in mid-Michigan into the Grand River.
WOOD-TV says a report to the Michigan Department of Environmental Quality by the operator of the lagoon near Portland, about 100 miles (161 kilometers) northwest of Detroit, blamed it on a "miscommunication/oversight between (the) contractor and waste water operator."
The report says the new lagoon was brought online June 29 and no discharge was seen when it was checked June 30, but a discharge valve was noticed to be open July 2.
The TV station says water was tested for E. coli bacteria on July 2 and the results showed everything was OK.