Well given the Elwha dam deconstruction was actually a group of dams, then can we remove a group? I would say each one on the Snake River (but if it had to be just a few then the Hells Canyon Complex).

http://www.nwcouncil.org/history/HellsCanyon.asp
The Pacific Fishery Management Council has estimated that prior to 1850, when Euro-American people began to settle in the Northwest, the Snake River Basin produced about 1.4 million Chinook, 200,000 coho and 150,000 sockeye annually. Steelhead numbers are harder to estimate, but one researcher estimated in 1970 that steelhead habitat existed throughout the Columbia Basin at a ratio of about 1.7 to 1 compared to coho habitat. Thus, the Snake Basin probably produced about 340,000 adult steelhead per year, an estimate based on the estimated abundance of coho. Based on the Pacific Council’s estimate of salmon and steelhead production in the entire Columbia Basin, this means that the Snake produced 41 percent of all Chinook salmon, 16 percent of all coho, 16 percent of all steelhead, and 23 percent of all sockeye. Expressed another way, Peter Hassemer, an Idaho Department of Fish and Game biologist, wrote in 1992 that before the Federal Columbia River Power System in the Snake and Columbia rivers was completed in the mid-1970s, the Snake River produced about 40 percent of the adult spring Chinook salmon, 45 percent of the adult summer Chinook salmon and 55 percent of the summer steelhead that returned from the ocean each year to spawn.