Manganos,
I would wait and see if it fills up after a good rain. The key here is whether or not you have too small of a drainage, or a leak in your pond. If it fills up, and then quickly loses water (say 1 foot every week or two for a couple of months) you obviously have a leak.
Fixing a leaky pond can be expensive. I would contact your local Natural Resource Conservation Specialist (likely listed under Agriculture department in the phone book) to see if they can tell you what soil type you have. Check around to see if other folks are having your same problem. You don't want to fix something that isn't broken.
If you determine it is a leak, I would recommend breaching the dam and digging it out. Hopefully you will find clay and that can be spread out and used to seal the pond. If not, you then generally have two choices, sodium bentonite (a clay) or a liner. Unless you are made of money, a liner for your pond would likely be cost-prohibitive (> $10,000 acre). The sodium bentonite would be less expensive, if you have a local source.
If it is a small leak, you can sometimes fix it by dumping sodium bentonite into the existing pond while it still has water on it. This works best in the cases of a small, focused leak, perhaps at the base of the dam.
A well can keep a pond full, which is great, but it too is expensive.
Again, call your local NRCS or state fisheries office. They can send you in the right direction.