EPA biologists have suggested general safety standards for bacteria in swimming waters, but they admit the science of testing remains imperfect. Macomb County officials have adopted a bacteria threshold based on a standard suggested by the state, which based its standard on EPA numbers. Michigan officials say that, while state rules for fecal testing in public drinking water are well defined, less attention has been paid to swimming and boating waters. The standard for drinking water is zero colonies of E. coli. State law is very general.
Most scientists say the confusion begins with the public's understanding of fecal pollution.
E. coli is an index for harmful bacteria and a very common one. In short, when E. coli are concentrated in swimming waters, chances are that pathogens are also there in force. Macomb's standard for E. coli is less rigorous than readings used by Ohio health officials to monitor Lake Erie and more strict than the standards used by Illinois and Indiana. It's a jumble of standards that many find hard to reconcile within the Great Lakes region. Given that, the testing system does have one shortfall.