Freeing the Fish

摘要

In 2010, engineers in the U.S. dismantled 60 dams, helping to reclaim rivers for wildlife. Most of these dams were small, though; removing large ones poses a much bigger challenge. In September, the National Park Service started the largest-ever dam-removal project in the U.S., on the 210-foot (the tallest ever removed) and 108-foot dams on the Elwha River in Olympic National Park in Washington State. For nearly a century, the dams have prevented salmon from swimming upstream to spawn. Blasting them with dynamite would do the job quickly, but it would also send 78 million cubic yards of water downstream at once, causing floods and damaging the ecosystem. Instead, crews will break down the structures over three years, releasing the water in the reservoirs at a rate that's more manageable for the animals and the people who live in the area. The U.S. Fish and Wildlife Service, the Army Corps of Engineers and the EPA are all watching closely.