The only down side is that it's too cold for smaller people to swim in comfortably. It can certainly be done; there's just some screaming involved in the beginning haha. But my lips start to turn blue if I stay in for more than 10-15 minutes.

I think the hottest the water got this past summer on the UP side of the lake was 64F (like 17 or 18C).

Edit: But the cold is also part of the reason why it's so beautiful and crystal clear. The climate is too cold for much farming, so there's not a ton of fertilizer runoff like we see with some of the other Great Lakes. Algae loves fertilizer.