This is my other pond which leaks badly. Both my ponds were just products of the reclamation process and the dams were not properly designed or compacted. No core in the dams I am sure. They both leak some - or the basin leaks. Who knows with the soil and rock all mixed together in the mining process. The upper lake has some shale pockets in the bottom and is so acidic nothing lives in it. It's pretty though - crystal clear and no weed problems in that one!