If I lost that much tht fast I would say leak for sure. Maybe since you havnt had water in it very long it's not to late. My thoughts is drain it. Let it dry out completely if possible and maybe get a sheepsfoot roller to pack it. Not much worse than a dry pond to look at. If you cant het all the way to the bottom then try other means. Now I'm no expert at all just my ideas so if TJ or anyone else disagrees ya better listen to them lol. If its really mudding or already silted some it might not even be possible with just a roller.