As Michigan markets its beaches to tourists with a multimillion-dollar “Pure Michigan” ad campaign, U.S. Environmental Protection Agency water data show sewage spills and storm water runoff are contaminating beachwater, particularly in the Great Lakes.

According to the Natural Resources Defense Council, which monitors EPA information:

Nationally, seven percent of beachwater samples violated health standards, showing no improvement from 2006. In the Great Lakes, 15 percent of beachwater samples violated those standards — the highest level of contamination of any coastal region in the continental U.S.

The group recommends that people planning on swimming at a beach call a local public health department first for water quality information.

Beach water quality standards are more than 20 years old and rely on outdated science and monitoring methods that leave beachgoers vulnerable to a range of waterborne illnesses including gastroenteritis, dysentery, hepatitis, respiratory ailments and other serious health problems. For senior citizens, small children, and people with weak immune systems, the results can be fatal.