I camped on Superior near Ironwood about 10 years ago in August....34 degrees that nite....water cold ...I guess low 60s water temp.
ouch
That's cold even for this "Troll"(South of the bridge). I think that's close to record cold for the summer even in the UP, although it's usally 10-15 degrees colder there than where I'm at.
I've been to the UP and most parts of the state, but I've never made it to the Western UP. Ironwood is about an 10-11 hour drive from where I live and over 1/2 of that is on two lane roads. That's about as long for me as a drive to Louisville and back.
One of the old traditions among some of the Finns and others up north is to drink a lot of beer, go to the sauna, then run through the snow and jump into the lake - and this is during November deer camp.