Why is Crater Lake so clear?
To appreciate the lake’s remarkable color and clarity, one must understand the relationship between ultraviolet (UV) light and the presence of dissolved organic matter in water. In most lake and ocean systems, dissolved organic matter, resulting from plants and animals within the watershed, limits the penetration of UV light. Only a very small amount of organic matter dissolved in water is needed to absorb the UV rays. Because the UV light is absorbed near the lake surface, aquatic organisms within the lake are mostly protected from the harmful UV rays. In Crater Lake, however, the natural concentration of organic matter is minimal, low enough to allow significant UV light penetration into the lake. Crater Lake has very little dissolved organic material near the surface compared to even the clearest ocean environments: less than half the absorption of the clear waters of the Gulf of Aqaba, the Red Sea, and the Tongue of the Ocean in the Bahamas. The level of organic material in Crater
