A 3mm suit is fine - some people don't want to wear any kind of wet suit when the water gets warmer - so a skinsuit is the minimum protection.plongeursousmarin:when you say skin suit, does that exclude a neoprene 3 mm wetsuit or does any suit (lycra skin or regular neoprene wetsuit) constitute adequate protection?
In the summer in less than 100', a 3mm can get pretty warm underwater. I wear a 1mm and there are days in the summer when I get warm in it, although not lately.