I'm a native Michigander. I was born in Michigan, and lived there for several years. I still have family in Michigan, and, though it's been 7 years since my last visit, I still fondly remember the state.
When I was a child, we'd go and visit in June. This coincided with fish fly season. The fish flies would come in, cover everything, and die. When they died, they smelled like fish (hence the name). The fish flies are harmless, but there sure are a bunch of them. They're more of a nuisance than anything else, but fortunately they only stuck around a few days.
At least, they used to. Now, reports are saying that Fruit Flies are staying longer, from three to six weeks. And they're thicker, too. One anecdote in the Free Press Article I've linked above mentions a dockworker who slipped on a giant pile of fish flies and fell into the Clinton River (while not the River Rouge, still not the best body of water to fall into).
Sometimes I really miss Michigan.