BLACK RIVER FALLS, Wis. -- A Jackson County lake re-opens after more than 200 people became sick from fecal contamination.

Lake Wazee near Black River Falls was closed last week after the Jackson County Health Department received reports of several people with stomach-flu symptoms after swimming in the lake July 4.

Samples taken from the lake and analyzed at the Wisconsin State Lab of Hygiene show norovirus is to blame for the illnesses.

USDA officials tested the lake water Monday, and found no fecal contamination. The Jackson County Health Department says this incident is isolated and likely caused by human feces.