I think your proposed letter is fine.

I did have another thought about it though. I think the first order of need is to meet or talk to your new neighbors for general purposes. So I would focus on just getting that opportunity to meet/talk, and not emphasize anything about the pond in the letter. Once you do meet/talk to them, you can then ask questions about many things including the pond.

Ideally, when talking about shared ownership of a body of water, it's probably best if the other owners don't really care about the pond so that you are free to do as you choose with the pond. As such, I wouldn't want to state my own strong interest in the pond until I got a sense of what the new neighbors are like; if they are not such great people, then I'd want them to know less about my own interests.