I planted my plants in 2 to 3 feet of water and they grew well but this drought has killed a lot of them as the water has dropped about 4 feet. Even some of the further out transplants have ended up out of the water from the drought. I'm not sure just how deep these plants will grow in but probably a lot depends on the clarity of the water. I would guess they wouldn't grow in deep water and they are only about 6 inches high so I wouldn't think they would interfere with swimming.
