Most species of shark will leave people alone. Bull Sharks are not one of them though. They will put a hurt on you.
I had not heard the Midhigan one before, but it doesn't surprise me a whole lot. They have a serious tolerance for fresh water. There was a Bull Shark about 100 years ago on the East coast that killed a few people over a bit of time, all in fresh water fairly far from the sea. I have heard of them being caught in states without coastlines. The biggest one known to science was caught in freshwater in South Africa. They get aroumd.