A soda lake or alkaline lake is a lake on the strongly alkaline side of neutrality, typically with a pH value between 9 and 12. They are characterized by high concentrations of carbonate salts, typically sodium carbonate, giving rise to their alkalinity. In addition, many soda lakes also contain high concentrations of sodium chloride and other dissolved salts, making them saline or hypersaline lakes as well. High pH and salinity often coincide, because of how soda lakes develop. The resulting hypersaline and highly alkalic soda lakes are considered some of the most extreme aquatic environments on Earth.

Wadi El Natrun is a depression in northern Egypt that is located 23 m (75 ft) below sea level and 38 m (125 ft) below the Nile River level. The valley contains several alkaline lakes, natron-rich salt deposits, salt marshes and freshwater marshes.