The owners of a dam in Washington's South Cascades used 700 pounds of TNT to breach the 99-year-old structure Wednesday.

PacifiCorp decided to blow up the hydroelectric dam after learning it could cost as much $100 million to build the fish passage structures required to relicense it. At 125 feet, it's the second largest dam ever to be demolished in the U.S.

Since it was built in 1911, salmon in the White Salmon River have either gone extinct or are listed for protection under the Endangered Species Act.

It could take as long as two years for fish to return to the river.

Watch this video from CNN's Newsroom, broadcast Oct. 26, 2011.

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