Don't panic. I doubt you're going to start losing water tomorrow.
Having trees on the dam is not a good idea, but It doesn't automatically mean you're doomed to have a dry hole where your pond used to be.
You've received some options in this thread, so step back and think about it for awhile. Evaluate your own abilities if this is to be a do it yourself project... Maybe have someone with some equipment, and a good understanding of dams come out and take a look with you. Get their input, and some idea of the costs involved. Once you know that, you will be in a better position of how to proceed.
