“Giant Methane Factories”: Hydropower has long been touted as clean energy. But is it?

Researchers say that methane is one of the biggest issues with hydropower. As organic matter, including vegetation, dead animals and even fertilizer runoff, gets carried downstream, it piles up in large quantities behind dams and decomposes in the reservoirs. Normally, that decaying organic matter would eventually reach the ocean, where chemical reactions would convert the methane into carbon dioxide and other compounds. But in the oxygen-depleted waters of a dam reservoir, that transformation often can’t occur. The result is that artificial reservoirs end up having a far larger climate impact than lakes and other natural bodies of water.