Ranas (1972)

Freelance photographer Pickett Smith is taking pictures of the pollution in a swamp in Florida for a magazine of ecology in his canoe. Out of the blue, he is hit by a motorboat piloted by Clint Crockett and his sister Karen Crockett and capsizes. Clint and Karen invite Pickett for the party in the private island of their grumpy grandfather Jason Crockett, an old fashioned disabled patriarch that enjoys celebrating his birthday on the 4th of July with his family. Pickett realizes that the island is infested of frogs and reptiles, and Jason has ordered his caretaker to poison his real estate to get rid off the amphibians and creepy crawlies. But soon Pickett finds that they are living the payback of nature against humanity.