Robison,
You have been given some good advise. Especially regarding the permits you may or may not need. The fines can be huge, don't ask how I know. /forums/images/graemlins/blush.gif
As for the ability to do it. Well, every situation is a little different and the amount of weight and movement it can take will very widely. I have a beach I work on (speaking of fines)and pulled on it with a mid size CASE BH. Went fine for about 20' then right to the frame it went. I can pull on that same beach with my Kubota and not sink as long as I do not move around much. If I start to move back and fourth down it goes. I do not enter the water, ever with the tractor. Are you reading this D.E.C.?" /forums/images/graemlins/grin.gif
Personnally I wouldn't even consider pulling my machine into the water for fear of the damage that could be done. Water ingestion is just plain not pretty. This could turn out to be a fairly expensive operation. Murphy's law has an amazing way of taking hold of a situation like this. What could happen. You try it, sink the tractor past the air intake and sieze the engine, the axles get water in them and seize the bearings, the neighbors call the authorities who slap a fine on you and make you clean up the mess after you go through the long permit process and pay environmental engineers to tell what you can do and how you will do it, along with the Army Corp getting involved and you still did not accomplish what you set out to do. Thats just off the top of my head.
Not to mention if this is a Trout pond the damage to the fish from all the contaminents of the tractor will do to them.
Best advise I can give. Call the authorities and see if you need any permits. Then use a large excavator with lots of reach and leave it on the bank. Pull up and several scopes later your done and your JD is still running.
Good Luck