An anchialine pool is a land locked body of water with a subterranean connection to the ocean. Typically, water near the surface is fresh water, becoming brackish with depth as salt water intrudes from the ocean connection at sea-level. Depending on the site, it is sometimes possible to access the deeper saline water directly in the anchialine pool or other times by cave diving.

In Hawaii, the pools are home to ‘opae’ula, a native shrimp. They reproduce in the subterranean portion of the pool, only to be seen in rare occasions.

Unbelievably, ‘opae’ula can live for as long as 20 years in captivity, and since they are very easy to care for, they are popular pets sold in pet stores all over Hawaii. Due to their largely subterranean life, it is unknown how long they live in their natural habitat.