It's bentonite - that's Grant Woods. He's down in the Branson area I think. Bentonite is good stuff. I do believe you have to be somewhat careful with it, but like most things, if you follow directions it's easy to work with. I know they sell a lot of it locally at Dickey Bubs. Missouri's old moniker on their license plates was "The Cave State". There's so much limestone and so many underground cave systems in parts of Missouri that it's not uncommon at all for small lakes and ponds to develop leaks.