10/19/2026
Soap Lake is a meromictic soda lake in the town of Soap Lake, WA formed by the Missoula Floods at the foot of the Grand Coulee.
Soap Lake features the earth's longest documented two-layer permanent lake stratification (meromictic), meaning its upper and lower waters have not mixed for at least 2,000 years.
The water contains 23 different dissolved minerals and mineral salts (including sodium, carbonate, sulfate, bicarbonate, and chloride), giving it a higher and more diverse mineral concentration than the ocean
The water is hyper-saline and hyper-alkaline, with a pH level ranging between 9.8 and 10
Similar to the Dead Sea, the dense mineral content makes it remarkably easy to float in the water
Wind action on the high concentrations of carbonates and natural foam creates a frothy suds line on the shore, while the water itself leaves a slick, soapy, or oily feel on the skin
Local Indigenous tribes (including the Colville) historically treated the lake as a neutral ground and used its sulfurous black mud and mineral-rich waters to heal wounds, soothe aches, and treat animals.
In the early-to-mid 20th century, Soap Lake became a famous world health resort and sanitarium (such as McKay Hospital and Siloam Sanatorium), famously treating World War I soldiers suffering from Buerger's disease (a rare circulation/gangrene-like ailment)