Problems with Hydroelectric Power
Although hydroelectric power is admittedly one of the cleanest and most environmentally-friendly sources of energy, it too has the capability to alter or damage its surroundings. Among the main problems that have been demonstrated by hydroelectric power is significant change in water quality. Because of the nature of hydroelectric systems, the water often takes on a higher temperature, loses oxygen content, experiences siltation, and gains in phosphorus and nitrogen content.
Another major problem is the obstruction of the river for aquatic life. Salmon, which migrate upstream to spawn every year, are especially impacted by hydroelectric dams. Fortunately, this problem has been dealt with by the production of "fish ladders". These structures provide a pathway for fish to navigate past the hydroelectric dam construction.
This is a picture of Solkeye Salmon in Canada struggling upstream to spawn