I had the same problem, even though I was wearing a swimsuit that had bike-type shorts. I think the water helps keep your belly buoyant so that it wouldn't cause as much damage as it would out of the water, if you know what I mean.
Tight nylon underwear seem to help this problem, or weight lifting tights. If you can't find them in your size, (once upon a time I was 361 and I couldn't find them in my size) Try a swimsuit underneath your clothing. That worked for me