Clarity

During our boat tour of Crater Lake, I was interested to learn that the lake is fed almost entirely by rain or snow in the caldera basin (this little waterfall was the only one I saw on our boat trip.)  The average snowfall at Crater Lake is 43 feet.  That's AVERAGE!  Last year they only had 21 feet of snow, which still seems like an awful lot.  The lake drains out slowly through an underground pumice section on one wall, so there is very little fluctuation in water level.  Given its confined water source, the lake water is extremely pure.  In fact, when the tour ended we filled our water bottles in the lake before our hike back up to the rim!  It's this clarity that helps give Crater Lake its trademark blue.  Water, without any sediments, algae, pollution, etc. can absorb all colors of the light spectrum except blue. And with 4.6 trillion gallons of water in the lake, there is a lot of blue to reflect!  The area photographed here is in one of the few shallow sections near the shore.  Our boat tour stopped here to talk about the water clarity, because it was so easy to see the lake bottom for a bit before it plunged over 1000 ft.  Crater Lake holds the record for clarity.  They measure it with a secchi disk, which looks like a pie with four alternating black and white slices.  The disk is attached to a rope and lowered into the water.  And the record for viewing the secchi disk is at a depth of 134 ft!