From an environmental standpoint, you might not immediately think about removing dams. Hydroelectric power, after all, is a renewable energy source — right? Not so fast.

“Hydropower is really not a renewable resource in the most strict sense of the term,” explains Jason Rainey, the executive director of International Rivers. “It's dirty energy in terms of polluting rivers and polluting the climate with methane emissions."

In fact, estimates say that dams and reservoirs account for four percent of man-made carbon emissions globally — equivalent to all of the world's airline traffic combined.

That's because, in the tropics, vegetation begins to decompose in the flooded areas created by dammed rivers. This sets off a chemical reaction that produces methane, which is released into the atmosphere. “There are examples of reservoirs in the Amazon that have four, five, even seven times more climate impact in their emissions than a coal power plant of similar megawatts,” Rainey explains.

Rainey's organization advocates for removing or stopping large hyrdoelectric dam projects and restoring rivers to their natural state. Doing so, he says, will cut pollution and restore health to ecosystems disrupted by dams.