Kurulunuji puumaj Identify the cost or costs of hydroelectric power plants: Sometimes a lot of water is released by a dam at a given time, resulting in flooding downstream. This affects both wildlife and drinking water. Flooding also often occurs during the construction of a dam as the reservoir fills in areas that were once above the water level forcing people and animals to relocate due to lost habitat. All of these are some of the possible costs of hydroelectric power plants. Dams without side channels interfere with fish needing to swim upstream to lay eggs for reproduction may not be able to get past the dams and young fish that are swimming downstream may be killed by the turbine blades. This has caused a severe decrease in sockeye salmon populations in areas of Northwest U. S. Water at the bottom of the reservoir lake (behind the dame contains colder water with less oxygen than surface water. When this is released into the rive downstream, it ca affect the fish living these that are accustomed to warmer, oxygen-rich water.​