Pond Boss Forums POND CONSTRUCTION Building a dam Spillway dilemma

Okay. (Forgive me for being doubly distracted on this thread - travelogueing plus the normal off-topic tangents.)

If you have an ample supply of good clay, you will want to apply and compact at least a foot of it (two feet thick is better) to any non-clay portions of the pond basin and dam. "Good" clay compacts to become very impervious to water seepage; one rule of thumb test is to squeeze a fistful of the suspect soil when damp - clay will hold together after squeezing, leakier soils tend to fall back apart (think sand as a worst case and you'll understand the fundamental difference).

All this is explained much better and in more depth in Lusk's "Perfect Pond: Want One?" book, which is the best money anyone considering or building a pond can spend.