Don,
Water snakes kill their prey by swallowing. Some snakes have fangs in the rear of their mouth, and they are used for bursting puffed up toads, frogs, and fish so they can be swallowed.
You pretty much don't need to fear any snake swimming in the water. The main reason is that snakes in the water aren't usually trapped or stepped on. All snakes want to do is run away. I guess 90% of snake bites are from the snake being stepped on.
Another good reason not to worry is that Cotton Mouth Moccasins are extremely shy, and almost never swim in sight of people. I guess 99.9% of all swimming brown snakes are water snakes. They can not hurt anything bigger than a small fish.
Sometimes water snakes can become habituated to people and become pests. If there's more than 10-15 hanging around, you may want to thin them out. I actually like to see a few in public waters, because they usually help me find the bream beds.
To protect you and your dogs from cotton mouth moccasins, all you have to do is remove any boards, tin, pipes, compost piles, overturned boats, or anything they may hide under. They will not stay out in the open.
It's a good thing I'm not afraid of snakes, or I would never go fishing. There are just too common around here.
