Riddle: A man falls overboard and gets washed ashore on an island with nothing but sand. The island is 50 miles from the nearest land. He can't swim, the water's 100 feet deep, and the island has nothing to make a floatation device with. With no help from people, animals, fish, or machines he finds a way off the island.
How does he do it?
Answer: He waits for the lake to freeze, then he simply walks across!
( I never said it was a tropical island :)