NatureWater Lesson Plans Problems & Solutions: TEMPERATURE CONTROL Problem: Water in a reservoir stratifies by temperature. The water near the top absorbs heat from the sun and warms up more than the deeper water. Cold water is slightly heavier than warmer water, and stays on the bottom most of the year. The result: A temperature gradient from the surface to the depths of the reservoir - the warmest water on the top and the coldest water on the bottom. If the water for release downstream is drawn through the dam from near the surface of the reservoir, it can be too warm for the fish. Salmon eggs survive best in chilly water. If the temperature rises above 67 degrees Farenheit, all eggs die. Salmon fry and spawning adults also need cold water. Such a problem existed at Shasta Dam, on the Sacramento River. Chinook salmon eggs below the dam were dying because the water could only be drawn from the top of Shasta Lake. Solution: At Shasta Dam, the Bureau of Reclamation installed a huge set of shutters over the existing intake structures for the dam. The shutters can be opened selectively at different depths, to draw water from a specific layer of the reservoir. Now when surface water get too warm, managers of the dam can pull cold water through the power generator and into the river below. Picture of Shasta Dam 26K, 8 seconds on a 28.8 modem