AG Research: Lake Michigan

A decent sized chunk of my next AquaGirl story is going to involve her swimming around in Lake Michigan. But being a UK citizen, I know virtually nothing about it other than what I can dig up on a Wikipedia trawl. So, since I figure some of you probably live a little nearer it than I do, I thought I'd pick your brains... :)

I gather there's some boat traffic, and I assume the waters are patrolled by the US Coastguard (who would be the logical people to mentor her). I gather there is still some waste dumped in the lake, so combined with the need to avoid being seen from the shore (could raise a few eyebrows!), staying a couple of miles offshore seems sensible.

But how much boat traffic is there - and of what type? If she's going to be swimming around for a few hours, will she encounter many fish?

Is there anything else I need to know, or would be useful to know, to make the description of the environment realistic...
...and avoid the wrath of nitpicking pedants :)