The Dead Sea, located between Israel and Jordan, is considered one the saltiest bodies of water on earth, giving swimmers a peculiar buoyancy when immersed. Interestingly, the electrolyte composition of the Dead Sea is quite different from that of ordinary seawater. The salt composition of most ocean water is 97% sodium chloride, whereas the salt composition of the Dead Sea surface water is only 30.4% sodium chloride with additional contributions from calcium chloride (14.4%), potassium chloride (4.4%), and a shockingly high magnesium chloride (50.8%).
This latter point explains why near-drowning victims from the Dead Sea can exhibit profound elevations in the serum calcium and serum magnesium levels, which according to this article by Porath et al can reach levels up to 28.8 and 33 mg/dL, respectively! The authors make the case that early dialysis to rapidly lower serum calcium and magnesium levels is necessary to prevent the major electrophysiologic and hemodynamic consequences of hypercalcemia and hypermagnesemia. Interestingly, in this article and another by Oren et al, the authors point out that the presence of hypercalcemia in these patients is actually protective, in that high calcium levels help protect against the catastrophically high magnesium levels which might otherwise cause respiratory arrest in the setting of hypocalcemia.