SPRING LAKE TOWNSHIP, Mich. (AP) — More than one in five Great Lakes beach closing orders based on bacteria concerns may be unnecessary, according to a University of Michigan researcher who is testing that idea this summer.

David Rockwell of the university's School of Natural Resources and Environment is using a $140,000 U.S. Environmental Protection Agency grant to study the relationship between E. coli test results and actual health risk to swimmers.

The project is a collaboration of Michigan and the National Oceanic and Atmospheric Administration's Great Lakes Environmental Research Laboratory in Ann Arbor.

"My estimate is that 23 percent of the time that swimming is prohibited at Great Lakes beaches due to high bacteria levels, those decisions are actually mistakes," said Rockwell. He is beach water quality forecasting coordinator at the Cooperative Institute for Limnology and Ecosystems Research, a collaboration between the university and the National Oceanic and Atmospheric Administration.

Swimming advisories or closures were posted at Great Lakes beaches on 3,136 days in 2010, according to the university. Most often, authorities issue advisories and swimming closures after heavy rainstorms wash bacteria-contaminated water into lakes.

"This new tool helps us make better beach-management decisions so we can get the situation called correctly," Rockwell said in a statement Monday. He said early testing of the Forecast Decision Support System showed that it was more accurate than current beach-monitoring techniques about 70 percent of the time.

The new forecasting tool is being extensively tested at five Michigan beaches, said university spokesman Jim Erickson.

"Using equations generated by the forecast tool, water-quality forecasts for the five beaches are issued four times a day by the National Weather Service," Erickson said. "After the swimming season closes, those forecasts will be compared with actual bacterial levels in water samples collected at the beaches throughout the summer to determine the system's accuracy."

The standard beach monitoring method is based on lab tests for E. coli colonies from water samples, which can take up to 24 hours to complete. That means advisories can be issued after the danger has passed.

One site for the water-quality forecasts is North Beach Park in Ottawa County's Spring Lake Township, near Grand Haven. The others are Grand Haven State Park Beach in Ottawa County, Bay County State Recreation Area Beach in Bay County, and Memorial and Metro beaches in Macomb County.