Bill,
I will try to answer your questions in the order you asked them.

1. Eelgrass is supposed to be a good oxygenator and I know that it provides cover for fish, it is easily available in a nearby river.
2. No
3. A little over a year old.
4. approximately 15 to 20 feet deep.
5. visibility right now is about 18 to 24 inches. It is greater in the winter and early spring, but the eelgrass does not grow then.
6. I feed the fish, but do not fertilize.
7. It is growing in a nearby river, depth from 1 to 5 ft (give or take). Length is around 3 to 5 feet.

Most of the pond drops off sharply around the edges, It was built by damming a small spring fed stream between two steep hills. Along one side there is a shelf of about 100' in length and 12' in width. Past this point there is another sharp dropoff to deeper water.The depth on the shelf is about 3', this is where I will plant the eelgrass. I am pretty sure that the eelgrass will not grow in the deeper water because of the lack of sunlight, so there should be no problem with the plant taking over the pond.
The pond is stocked with Coppernose Bluegill, Redear sunfish, Largemouth bass, Smallmouth bass, and a few channel cats. It is about 1/3 acre in size. I know that it is not recommended to stock bass in such a small pond, but I only have about 20 in the pond and they seem to be doing fine so far.
That's all I can think of right now. If there is anything else you would like to know, please ask.

Larry