Rainbow Dam, Hydroelectric power station in Cascade County, Montana

Rainbow Dam is a hydroelectric facility that stretches 322 meters across the Missouri River to harness water flow for power generation. The structure contains eight generating units that contribute to the region's electricity supply.

The facility was built in 1910 and began operating with eight generating units right away. Shortly after, in 1912, Montana Power Company took control of the installation.

The dam is named after Rainbow Falls, a 45-foot waterfall just downstream that is the third of the five Great Falls of the Missouri. Because the powerhouse sits more than half a mile downstream, the falls and nearby Crooked Falls shrink noticeably in the dry season.

The dam lies six miles northeast of Great Falls, reached from the river's left bank where the three penstocks run about 0.8 km to the powerhouse. The flat walkway on top, edged by a railing on concrete piers, is the clearest line of sight; a small sign stands near its right end. The surrounding terrain is rocky and sparse, so footing off the bank is uneven.

The powerhouse sits more than half a mile downstream from the dam, so water released from the penstocks re-enters the Missouri a few hundred yards east of Crooked Falls. In the dry season this diversion noticeably reduces the flow over both Rainbow Falls and Crooked Falls.