GEF

Unit 3  |  Water Use and Human Water Systems 74 water. At present, about 16 percent of global electricity produc- tion is generated from hydropower. While there are benefits provided by dams, dams also present a range of problems which have made many people question their sustainability. Large dams drastically alter the natural water flow of rivers, often fragmenting a unified ecosystem into a series of disconnected units. Organisms that require free-flowing rivers suffer with dam construction—the most well-known example is salmon that live as adults in the ocean and breed in rivers around the world. Dams constructed along the Columbia River in Washington State and the Sacramento River in California have drastically reduced Chinook salmon habitat, despite the incorporation of fish ladders and other means for fish to traverse dams. Dam construction also changes water temperature, turbidity , and water chemistry, to the detriment of many organisms. In addition, curtailment of natural flooding regimes degrades wetlands and other important habitats, with negative consequences for many plant and animal species. Fish ladders can help fish survive in dammed rivers. FISH LADDER A mechanical device that allows fish to pass by or through dams. TURBIDITY The level of suspended solids in a water body.