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.