??? about growing water lilies in lake garden

Hi,

I have a slip in a marina in the Atlanta, GA area. Recently I've
started experimenting a little bit, having submerged a wooden
platform about 40" deep, about 8'x12' in size. The idea was
to see if it would attract some small fish, since there are always
some of them hanging out in the shallow water at the end of
the dock (the water where my slip is is about 30'-40' deep).
The guy at Pike Nurseries gave me the false information that
elephant ears would do well in that environment. Now they
are about dead. In the spring I'd like to try growing water
lilies, and am now trying to find any advice or suggestions
I can in order to plan things out. How deep can they be
placed below the surface? Where to get them? If they
start out as just a root or small plant, do they need to be
near the surface and then moved down as they grow?
How much blooming will they do, and when? I'm interested
in plants I don't have to take out of the water every year
since this lake doesn't freeze, so the hardy type is probably
the way to go and not the tropical. How do blooms compare
between hardy and tropical? Also, since this is in a big lake
instead of an isolated artificial pond, can they survive on
just the nutrients in the lake without the need of adding
fertilizer? Someone told me they grow so well that there
can end up being too many of them. How to deal with
that? Should they be trimmed, and if so where and how?

Thanks!
David