Lake County describes Clear Lake as California's largest natural freshwater lake by surface area, at roughly 68 square miles.
Archaeological evidence cited by the county indicates human habitation around the Clear Lake basin for about 12,000 years, with Indigenous communities deeply tied to the lake and its native fish.
Clear Lake's local water-level language uses the Rumsey datum: zero Rumsey represents the natural low-water reference at the Grigsby Riffle, while a 'full lake' is 7.56 ft Rumsey.
Modern lake management balances recreation, downstream water supply, flood control, cyanobacteria/water-quality work and conservation of the threatened endemic Clear Lake Hitch.