Our pond did basically the same thing. I was told to not get to worried about it and it should be OK in a couple years. It was wicking and finally we have a full pond with very little drop between rains. Our pond builder happen to stop by a week ago and said it was a common thing in our area for a pond to drop due to the banks wicking. The pond is doing just fine now. The fish are happy and eating food like crazy. The pond is less then a 1/4 acre. Maybe your pond is wicking and hopefully it will be OK.

Jim at FishinPals
"If You Too Busy To Go Fishing, You're Just To Busy"