That's normal. You'll find that you simply organize for the trip over, and the boat ride is a real separation between city mindset and cottage mindset.
For certain, it's not for everyone, but people who like it, really like it.
In terms of the water temps, I think the coldest water I've ever swum in was up in Tobermory, if memory serves.
However, in the Archipelago, south of Parry Sound, you'll find the water warmer than the Muskoka Lakes or Lake of Bays. I've never understood why, because there is deep water everywhere. Temperatures depend on where you are on the Bay...