COLOR (OF LAKE WATERS)

An effect of light penetration, radiation absorption and reflection. Related to: transparency and depth of water;type of lake bottom and matter held in solution; suspension or floating. Blues and greens are commonly observed in clear water lakes with clean bottoms of sand, rock or marl. Often, the blue tints are in deeper water and greens in shallower sections. Greens are often due to large populations of blue green and green algae in suspension or on the lake bottom. Yellows may be due to certain species of algae and to diatoms in large populations, and in certain types of lakes yellows have been attributed to sulfur bacteria. Pale yellows, yellow brown and coffee color or "black," can be produced by large quantities of dissolved humic substances and by particulate organic matter in suspension. Reds may be a reflection of the pigment color of certain algae; and may be caused by the presence of certain micro-crustaceans and other zooplankton; the "blood lakes" of central Europe are attributed to the presence of the microorganism Euglena sanguinea. Lake waters may be variously colored by suspended particulate inorganic matter especially that which is clayey or colloidal in nature. Some glacial lakes may be milky because of "glacial flour" in suspension, and the shallow water of marl lakes is often milky. Some colors are reflections of yellow sands on shallow bottoms, or from the black of organic sediments; or the blue of the sky. Colors vary with the weather, the time of day and the season. The words white and black have been used to describe lake waters. White has been applied where the water is merely colorless, and sometimes where it is milky from grey or white particulate matter in suspension. Black may be due to: large amounts of humic matter in solution, such as that in water flowing from some kinds of bogs; reflection of black bottoms; the dull appearance of some waters when the sky is heavily overcast. Unusual colors may be produced by pollution from industrial wastes.