We have a dam full of water with a very slow leak, my father is concerned to fix it. He contacted a company in Australia polymerinnovations.com.au that is marketing a pond sealing compound made of two monomers (polyacrimide)that are sprinkled on the water surface of a 'full' but leaking pond or dam. They say it is innert and harmless to wild life and sinks and swells as it enters fissures to seal the dam by floculation with a high success rate. The advantage being the Dam does not have to be emptied nor soiled by pig faecies from gleying. Does anyone know if this kind of product is safe as claimed? I am naturally cautious of any manufactured materials. I'm interested in trying bentonite clay or plain local clay first and am also interested in second opinions about the commercial option. The obvious draw back of the commercial product is cost. $ 500 for a 30kg enough for a 350 m2 dam. If it can safely save 5 mega liters of water? Maybe worth the trouble? The dam holds water well but is very slowly leaking and we don't want it to get worse. Thoughts welcome, I gave the web site so interested parties can check for themselves. For what it's worth I'm not affiliated with that company, just came across them online.