Most rabbits can swim to one degree or another, even while young (2-3 weeks). There actually is a species called a swamp rabbit that can swim very well. They are however usually found along The Gulf Coast. This is what the University of Minnesota says about swamp rabbits.
Swamp rabbits are adept swimmers. When a predator gets close, these rabbits are likely to jump in the water and swim away, or dive under roots or overhangs to escape. In Georgia in 1979, there was a well-publicized incident involving a swamp rabbit and then-President Jimmy Carter, in which a swamp rabbit that was being chased by hounds jumped in the water and swam up to President Carter’s fishing boat. He shooed it away by splashing water with a paddle.