A Brief Guide to the Parapet View, Sinnott Memorial, Crater Lake National Park by John Campbell Merriam, 1938
View 8: Color an Outstanding Character of Crater Lake
The deep blue of the lake is believed to be caused chiefly by the scattering of light in water of exceptional depth and clearness. The color is thought to be due to the same cause that produces blue of the sky where light passes through deep atmosphere.The color of Crater Lake is generally recognized as the most attractive feature of this region. Among spectacular lakes of the world there are none in which depth of color and brilliance of blue are more striking. The blue of the deeper water is brought out in contrast with the brilliant green of shallow areas along the margin.
The extraordinary beauty of the lake arises in part from its great depth, clearness of the water and of the atmosphere above it, and from favorable conditions presented in viewing it from the high crater rim.