DULUTH — Researchers detected SARS-CoV-2, the virus that causes COVID-19, in the water at four Lake Superior beaches in Duluth earlier this month.

A "detectable level" of virus was found in water samples at area beaches over the weekends of Sept. 11 and Sept. 18 at several beaches, according to the University of Minnesota Medical School, Duluth Campus, which is regularly testing the lake water at eight area beaches.

Results showed levels of the virus within 100 to 1,000 copies per liter, 10,000 times lower than levels found in wastewater, the medical school said. The Centers for Disease Control and Prevention is "not aware of any scientific reports that indicate the virus can spread to people through exposure to lake water," the medical school added.

"At this time, the source or sources of the virus are unknown. Because of that, Minnesota Sea Grant will extend funding support to continue the Medical School’s monitoring of the eight Duluth beaches," the medical school said in a statement. "They will also work with experts in lake currents and with the Minnesota Department of Health to seek more information on possible sources."

The medical school urged beachgoers to continue wearing masks and social distancing.

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As reported last month, researchers from the University of Minnesota Medical School's Duluth campus are regularly testing water at beaches for the virus on weekends. Since the virus is shed in a person's stool, it is likely to be rinsed off a swimmer's body.

The researchers — assistant professors Richard Melvin and Glenn Simmons Jr. — are also studying the virus's presence in raw sewage across Minnesota with the hopes of determining how many people in a community might have the illness based on the amount of virus in a sample.

The wastewater research has given them early signs of outbreaks and reflected rising levels of cases throughout the state.

Samples are also being taken of wastewater leaving dorms on the University of Minnesota's Twin Cities and Duluth campuses.