Don't be paranoid. There could have been mines at the bottom of the lake.
What kind of mine are you refering too? Did you know that there will be a Silver and Copper Mine in Michigan soon. Since it will be located on the UP, it might just run under the lake.
Lake is actually the ocean besides nothing makes any sense so far.
Said lake could have a whale who escape from sea world in it.
If we're talking an american lake, the probability that its chock full of discarded junk and dumped waste, is very liekly that its just an ordinary american lake.
Folks are finding all manner of invasive species these days.
Its possible there are pirahna in the lake that Steve is "floating" in.