MADISON, Wis. -- Dane County health officials have closed all local beaches after an overflow in the sewer system sent untreated wastewater spilling into two Madison lakes.

The Madison Metropolitan Sewage District said Wednesday that the overflows were caused by the heavy rains over the weekend.

In a statement, the district said the untreated wastewater entered lakes Monona and Mendota in various locations, meaning raw sewage might be present in the water.

Residents are advised not to swim or wade in the lakes.

The statement said the Public Health Laboratory carried out tests Wednesday at all Madison beaches, including the one adjoining the University of Wisconsin-Madison's student union.

Results were expected later Wednesday.