The lake has never been known to freeze, altho others in the vicinity and at lower altitudes are covered with ice each winter. The water level changes about four feet throughout the year, being highest during maximum melting of snow, after the winter season and lowest in September or early October. Precipitation is estimated to average over 60 inches per year. Great amounts of snow are blown over the edge of the rim. Then too, the numerous springs add to the accretion.
Evaporation is estimated to be about forty inched per year.
Calculations on the rate of lowering and rate of evaporation indicate a more rapid lowering than could be accounted for by this agency alone. Since there is no surface outlet the surplus probably escapes through the porous rocks of the walls reappearing as springs which are numerous on the southeast base of Mt. Mazama. Nature Notes is produced by the National Park Service.