Pool classes start late March, then we gotta wait for the rest of the ice to melt, then we get to be cold!I'd be more worried about staying warm, doing your open water in late March in Wisconsin.
I'll be fine though, I am 6'3" and 350, plenty of insulation, getting cold for me even in cold water has never been much of an issue. We do a polar plunge every New Year in Lake Michigan, even if we have to cut a hole!