Dr Gary Wockner ( an international environmental writer and activist based in Colorado where he also works to protect the Cache la Poudre and Colorado Rivers) (2015): “ The principal environmental menace of hydroelectric dams is caused by organic material—vegetation, sediment and soil—that flows from rivers into reservoirs and decomposes, emitting methane and carbon dioxide into the water and the air throughout the generation cycle. Studies indicate that in tropical environments and high-sediment areas, where organic material is highest, dams can release more greenhouse gas than coal-fired power plants. Philip Fearnside, a research professor at the National Institute for Research in the Amazon, in Manaus, Brazil, and one of the most cited scientists on the subject of climate change, has called these dams “methane factories.” And, according to Brazil’s National Institute of Space Research, dams are “the largest single anthropogenic source of methane, being responsible for 23 percent of all methane emissions due to human activities.” … Hydropower is dirty energy, and should be regarded just like fossil fuel. And environmentalists, far from embracing it, should be battling to shut down hydropower plants and block the arrival of new ones just as vigorously as we work to close and prevent construction of dirty coal plants” (Gary Wockner, “The hydropower methane bomb no one wants to talk about”, EcoWatch, 6 October 2015: http://ecowatch.com/2015/10/06/hydropower-methane-bomb/ ).