Our pond has been dropping for months and it finally is low enough that we can see the problem. There is a sinkhole about 3 foot across sucking water out. We lined the bottom of the pond with about 2 foot of clay, but there is alot of sand under it and I think that there is an underground spring that is pulling all the sand and clay down through it. We are going to try and dig out the area atleast six feet deep and cram it full of clay. If you have any suggestions, please let me know. Thanks