Why is Mono Lake water so salty? Mountains surround Mono Lake forming a closed hydrological basin--water flows into the lake, but it doesn't flow out. The only way for water to leave Mono Lake is through evaporation. Four vertical feet of water can evaporate off of Mono Lake during the course of a year, and without fresh water streams to replace the evaporated water there would be no lake. Freshwater streams and underwater springs have brought trace amounts of minerals into Mono over the eons. Because the lake has no outlet, it is naturally saline. An estimated 280 million tons of solids are dissolved within the lake, and it is 2-3 times saltier than the ocean depending on its water level fluctuation over the years. Periodic eruptions of volcanic ash have also added considerably to Mono's chemical mix.
