Unlike the vast majority of the world's oceans, the Dead Sea has no major lifeforms in it. This is due to its approximately 35% salt content, as compared to the 5-8% salt content of "normal" oceans and seas. However, as a result of this higher salt content, it is a silly amount of easy to float in the ocean. However, it is highly recommended you think before entering the Dead Sea, as any exposed cuts will sting and make your day miserable. Women and men are often advised NOT to shave for 2 or so days before they go into the Dead Sea.
However, with that said, it was a fantastic experience. You cannot swim in the Dead Sea, the salt content doesn't allow for easy swimming. But if you walk in and lean backward, your feet are lifted up from under you, and you're very suddenly floating. It takes no effort. In fact, the more difficult thing is getting your feet back underneath you! You can also see, that high salt content gets depositing on the shore rocks in and around the sea.