In geologic terms, it’s a lake, not a sea. Since the water has so many dissolved minerals, it was named the "Dead Sea." The Dead Sea is 5 to 9 times saltier than the ocean. There is so much salt that many people could float on it. Several rivers flow into the Dead Sea, however, there isn’t an outlet. Water evaporates and the salt and minerals remain. Lakes and rivers stay fresh because they eventually flow into the ocean, depositing the dissolved minerals picked up along the way and are replenished by rain.

As the Dead Sea does not flow into the ocean,  salts and minerals stay in its water. As you get below 300 feet (100 meters), the water gets so saturated with salt that it can no longer hold it. The salt gets deposited on the seafloor, forming crystals. Not all of the salt in the Dead Sea is sodium chloride like the ocean salt. The Dead Sea salt consists of magnesium, potassium, calcium, and phosphorus. Visitors to the Dead Sea enjoy a nice float in the waters because the minerals are believed to boost health and wellness.

Bawab, A. A., Bozeya, A., Abu-Mallouh, S., Abu Irmaileh, B., Daqour, I., & Abu-Zurayk, R. A. (2018). The Dead Sea mud and salt: A review of its characterization, contaminants, and beneficial effects [PDF]. IOP Conference Series: Materials Science and Engineering. https://iopscience.iop.org/article/10.1088/1757-899X/305/1/012003/pdf  

Weisberger, M. (2016, September 09). Why is the Dead Sea so salty? Live Science. https://www.livescience.com/56047-why-is-dead-sea-so-salty.html

Mat, M. (2023, August 7). The Dead Sea. Geology Science. https://geologyscience.com/gallery/geological-wonders/the-dead-sea/?amp