Michigan has thousands of aging and under-maintained dams that could pose localized risks.The Michigan Department of Environmental Quality tells the Detroit Free Press that all but six of the state's 88 potential high-hazard dams are approaching 50 years old, the average engineered life span for a dam. The American Society of Civil Engineers gave Michigan a D grade on the condition of its dams in 2009, saying more than 90 percent of the state's nearly 2,600 dams would reach or exceed their design life by 2020 Any dam collapses in Michigan wouldn't be as bad as the possible Oroville Dam collapse in California, because that dam is much higher than Michigan's dams.