You guys are so lucky to live near such majestic lakes. Our lakes are quite a bit smaller. Finland used to possess the northwest shore of Lake Ladoga, which is about 200 km x 110 km in size, until the summer of 1944.
Lake Michigan is about 500 km long and about 130 km wide at the widest point. That's almost like the Gulf of Bothnia (length 666 km, width 233 km) between Sweden and Finland in the Baltic sea.
The strange thing is the Atlantic when I swam in it last year, was so much warmer than Lake Michigan!!
Could it have been because of the exact place you were swimming in?