Why You Float in the Dead Sea

The Dead Sea is not really a sea. It is a large salt lake in the Middle East, and its shore is the lowest land on Earth. Its water is almost ten times saltier than the ocean. It is so salty that fish cannot live in it, which is how it got its name.

All that salt changes the water in an important way: it makes it denser. A cup of Dead Sea water is much heavier than a cup of plain water, because it holds so much salt. And there is a simple rule in science: things float when they are less dense than the liquid around them.

Your body is about as dense as ordinary water, so in a pool you only just float. In the Dead Sea, the water is much denser than you are, so it pushes you up high. Visitors can lie on their backs and read a book, as if they were on a sofa.

Where does all the salt come from? Rivers carry water with small amounts of salt into the lake, but no river flows out of it. In the hot sun, the water slowly evaporates and the salt stays behind. Over thousands of years, the salt has built up more and more.