I would rebuild the dam and install some sort of riser board system or something else to be able to control the water level so you can flood /drain at your will. if you have had a bunch of ducks then you may not need to plant anything like millet (ie have good mast producing trees like oaks or some emergent vegetation like burreed) but it never hurts to plant millet in those areas and then reflood in the fall. good natural flooded timber is hard to beat, thats why i am saying check what type of vegetation you have as you may have enough food already without planting.
"If you have to be crazy to be a duck hunter, i dont wish to be sane" Robert Ruark
Its always duck season, there is just a long break from february to september.