Origin of the Lake.
The water of Crater Lake comes from rain and snow. The average annual precipitation is 69 inches. The lake has no inlet and no outlet, except seepage. Evaporation, seepage, and precipitation are in a state of relative balance which maintains an approximately constant water level. In 1957, the lake level was the highest recorded since 1908. There is an annual variation of from 1 to 3 feet, the level being highest in spring and lowest in autumn.