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    Light in WaterWater is a great conductor of sound, but not of light. Most sunlight that hits a lake or ocean is absorbed within the first 20 – 50 m depth. Sunlight contains many different colors (which are separated in a rainbow). Water mostly reflects, rather than absorbs, blue light waves, which is why the sky and water bodies are blue! 



    Plants require light for photosynthesis. Loss of light in ever deeper water limits the depth to which many attached plants can grow. This is a primary reason why most plants in open waters float. Microscopic algae, floating duck weed, or mats of cyanobacteria have all evolved mechanisms for staying near the sunlight. 


    Many aquatic animals also need to see to find catch, find mates, or avoid predators. Increases in turbidity caused by suspended sediments or plant material restrict this ability to see under water. Some fish, such as catfish, have evolved other mechanisms for surviving in dark or turbid waters. In lakes, many zooplankton (tiny animals that live suspended in the water,) and bottom dwelling macroinvertebrates take advantage of the more abundant food at the surface while also avoiding being eaten by fish by “migrating” down into darker waters during the day and moving up to the surface waters at night. 


    The color of lakes changes due to high concentrations of microscopic algae (turning the water green), suspended sediment particles (turning the water brown) or by marl (tiny particles of calcium carbonate) that can turn a water milky blue (like Bear Lake). 


    There are multiple ways to measure light.  The easiest way is using a Secchi disk.  Learn how to make your own Secchi disk in the Utah Lakewatch Kids Book

    Utah Water Watch - citizen monitoring

    Secchi Dip-In - nationwide

    Utah Lake Watch Reports