I have a very small pond (approx 15' square) that was dug about 8' deep fed by an artesian well. Water is running strong and weather has been really wet. Funny thing is that water recently dropped 2" overnight, and then another 2" overnight a week later. Maybe a leak, but it has held full-pool for about 2 year before that. Water flow in has not decreased. I have seen the leaves and flowers clipped on the one water lily in the pond (turtle), but seen no muskrat activity although there are muskrats in the wetland maybe 40-50-feet below. Gonna wait and see, but here is no longer any overflow from the artesian pond. Might be due to lush plants around the pond sucking water, or a leak has formed.

I'd be doing some recon below your dam. To lose 4 feet of water with the same inflow, it has to going somewhere.

Typo now fixed (2 inches +2 inches). No dam, just a narrow core trench made on the lower side.

Funny thing is that the watertable in the aquifer must be dropping based on the slowing outflow even though we have been in a real wet spell. The drop is normal for mid June, but is still surprising to me with all the rain we have had. Lush plant growth must be sucking it up.

Depends on how deep your aquifer is and where its originated from. That area may not have recieved as much rain. It could be coming from miles away.