The dead sea is not really a sea, it is actually a land locked lake between Israel and Jordan. the water is so salty that nothing-plants or fish-can live in it, and that is why it is called 'dead'.
there are several rivers and streams that feed into the Dead sea, but none that drain out. one of the reasons the dead sea is so salty is because there are no outlets. the minerals that flow into it stay there forever. as water cannot flow out, evaporation is the only way water is released from the sea. with the hot temperatures, the water evaporates per day from the dead sea. as this occurs, it leaves behind any dissolved minerals in the sea, increasing it saltiness.