If you were at the beach with your dog and a huge wave came in and swept your dog out to sea...wouldn't your first instinct be to jump in and save your dog? Unfortunately doing just this has caused a few deaths in California. I'm not sure about every case, but I do know that in at least one of them, the dog survived.
Please read the article above and follow the advice in it. It could save your life (and your dogs life! consider a life vest for certain breeds!).