Water can also contribute to matting. If your long hair dog goes outside after rain and their belly rubs the wet grass, they’re likely to get matted between his legs or belly. If they enjoy swimming, chances are, they have experienced some matting as well. This is why a matted dog should not be bathed. This will only cause the mats to get tighter. If you wash your dog at home, be sure to thoroughly dry and brush out to prevent matting.