I've never had problems with mine going out for just a little bit, usually they work or they don't. I agree with Rev on checking your belt tension, it may be a little loose. I've hit water with a loose belt a few times and the belt would jump off of the pulleys.
I'm on my fourth alternator now. I like to play in the water quite a bit. Every time I have to replace one, it is because it is full of grass, straw, sticks, leaves, etc...
When I get stuck in the water I will turn my engine off, as long as there is no risk of getting water in the engine. That prevents quite a bit of the stuff from getting sucked into the alternator.
When the first one went out I replaced it with one with a one year warranty. I replaced it twice before the warranty ran out, just had to take all of the grass out of it first. I'm probably going to get one from Autozone with a lifetime warranty next.
