The arguments over the dam split the Crow into factions. The Mountain Crows sided with Yellowtail in opposition. The River Crows saw potential in the electricity revenues the government promised. For a time, the tribe considered leasing the land for fifty years at one million dollars annually. In the end, they sold it outright for 2.5 million dollars, and controversy burned for decades afterward. Robert Yellowtail had already made headlines in 1934 when he became the first Native American to serve as superintendent of his own tribe's reservation. His opposition to the dam that would bear his name cemented his legacy as a defender of Crow sovereignty, even in defeat. The irony of the naming was not lost on anyone who knew the history.

Morrison-Knudsen, the Boise-based contractor that had built Hoover and Grand Coulee dams, landed the contract in 1961. Workers first bored a diversion tunnel through solid rock, then raised a cofferdam to reroute the Bighorn while they poured concrete. Six years later, in December 1967, the arch dam was topped out. For a structure of its scale, the construction claimed only one life. The dam rises 525 feet from bedrock to crest, its curved face holding back Bighorn Lake's waters. Four Francis turbines at the base, each rated at 87,500 horsepower, generate 250 megawatts of electricity. The powerhouse began operations in 1966, a year before the dam was even complete, feeding peaking power into Montana's grid.

Before the dam, the Bighorn was a warm-water river. After it, something unexpected happened. Water released from the depths of Bighorn Lake runs cold, and that temperature shift transformed the downstream ecosystem. Rainbow and brown trout now spawn where warm-water species once dominated. The lower Bighorn became one of the finest wild trout fisheries in the United States. Average trout run large here, and the fishing lodges of Fort Smith have built an industry on the dam's unintended gift. Yet the transformation came at a cost. The dam traps sediments that once built islands and sandbars downriver, flattening the Bighorn's character. The fishery thrives in altered conditions that have erased much of the river's original habitat.

Bighorn Lake extends upstream from the dam, crossing the Montana-Wyoming border. Nearly two-thirds of the reservoir's surface area lies in Wyoming, while the trout fishery downstream is entirely Montana's concern. This geography has created ongoing tension. Wyoming wants higher lake levels for boating and water skiing. Montana wants steadier releases to keep the trout healthy. A prolonged western drought forced the Bureau of Reclamation to reduce downstream flows, and the fishing industry on the lower Bighorn declined by over forty percent. Wyoming's recreational usage dropped even more steeply, by over sixty percent. The bureau now tries to balance both interests, maintaining minimum flows below the dam while keeping the lake at levels that satisfy neither state completely.

Because the power station operates on peaking demand, releases from Yellowtail Dam can vary dramatically throughout a single day. To smooth these fluctuations, engineers built a smaller dam downstream, the Yellowtail Afterbay. This secondary structure captures the irregular flows and releases a constant stream into the Bighorn, creating the stable conditions trout need. The Afterbay reservoir has become a destination in its own right, popular for trout fishing from shore and by boat. Above it all, the main dam stands as a monument to mid-century ambition and tribal loss, generating power, holding back floods, and bearing the name of a man who never wanted it built. Robert Yellowtail died in 1988, having lived to see his name etched into concrete that drowned his people's sacred canyon.