The water in Crater Lake ranges from 60 to 68 degrees F in summer.  On extremely hot days the lake surface can heat up to 74 degrees F.   The lake water cools quickly as you go deeper and deeper. The water remains at a constant 38 degrees F all year round once you go down to 260 feet.

During the winter the lake’s surface measures 32 degrees F.  The surface of the lake does not freeze except on a rare occasion.  In 1949, the entire surface of the lake froze for three months.  This was the very last time the lake froze.

There are hydrothermal vents at the bottom of the lake that heat up pockets of water at the bottom of the lake.  These hydrothermal vents heat the water up to 68 degrees F while the rest of the water at the bottom of the lake is 38 degrees.   This is an indication that the volcano is not dead but is actually resting, even after a half million years.