well of course!! Its a pond partially fed by a small underground saltwater tributary and while investigating the path the water takes they discover an ancient cave full a noxious gas, long thought not to exist anymore, where freshwater and salt water mix with the gas and travel to the pond and have an adverse affect on the frogs (and fish). In the end they find out that some diabolical foriegner planned on people eating the fish and frog legs so that they could control the town to send them into the world to do their evil bidding
