We had similar thing happen to our pond. We had 8" of rain before they were finished. They cut dam and let out 8' of water in a 5ac pond to finish. Even after they finished and it now has 10' in it you can see bubbles coming up after 10 months they told me that as you said the ground all around the pond has to saturate. I don't see any water leaking behind the dam at all cause they put a "core" of packed clay in the dam. If it was built right it shouldn't leak. Evaporation can be a lot up where I am, depending what depth to surface ratio is
Good luck and good fishing


Pat