 On November 3, 1930, with the construction of the dam in full swing, Rock Island was officially incorporated as a Washington state town, with a population of 421 residents.The town boomed for a second time in its history as workers for the dam project created temporary villages near the town, but it could not last.When two of the dam's generators began producing power in 1931, and the final spillway was closed in 1932, Rock Island again faced a bust and a loss of residents.