I did'nt think they would grow in more than 3 feet of water. However, I read a post awhile back
and someone commented that they had seen cattails growing in 6 feet of water. I have always liked the look in natural ponds of cattails. They would provide both cover and shade. They are also not strong enough to hold up a poaching heron or water turkey. I was concerned however about how invasive they might be.