I hunt my dog in cold water situations, where he is swimming through slush, but I wouldn'ttrain in cold water. As Tail said there are differences in dogs, so I wouldn't use comparisons to other dogs as a guide in this case. Some dogs are so driven they just don't care how cold or hot they get. Trying to train in cold water might create attitude problems in some dogs. Why take the chance? DO NOT follow the advice that said "throw him in", that advice is not sound. I would take Tail's advice, but just wait until it warms up.