Water plants for food?

I've heard from many sources that aquaculture is more efficent than land systems. I understand a person could harvest fish, mussels, crayfish, algae, waterfowl, etc from farm ponds. What about plants?

The only one I could think of is rice.

What plant can you grow in ponds or the water's edge for human consumpsion or use?

I live in a temperate climate, in zone 5a in Moberly, Missouri!