By National Geographic

A hole was blasted in the base of the 125-foot-tall Condit Dam on the White Salmon River in Washington. In less than 2 hours, the reservoir behind the dam drained completely and the White Salmon flowed unimpeded by a dam for the first time in 100 years.

From YouTube: http://www.youtube.com/watch?v=4LxMHmw3Z-U