Swan Falls Dam is a concrete gravity type hydroelectric dam on the Snake River, in the U.S. state of Idaho. It is located near Murphy, Idaho.The dam was built in 1901 to generate electricity. It is the oldest hydroelectric dam on the Snake River. In the 1990s the original power plant was replaced with a new one. The dam was built with fish passage facilities, but they proved to be very poor in performance. For this reason, among others, the C. J.