The Dead Sea is so called because of the high salt content of its waters. That spells instant death for fish that happen to wander in, as they occasionally do from the Jordan River. In fact it kills most animal and plant life--with the exception of tourists, who love the property of the salt water that makes it so easy to float on.
Bacteria survive in the Dead Sea, though, as do brine shrimp and a class of plants called halophytes that love salt water. So it's not entirely dead, although not exactly a wild and crazy place, either.
(Sources: The Handy Science Answer Book)
