[4] Initial construction was completed in 1927, at a site located 39 miles (63 km) upstream of the Niobrara's confluence with the Missouri River.

The combined length of the powerhouse and spillway was 404 feet (123 m); the rest of the dam was an earth embankment extending to the south side of the Niobrara valley.

[5] Although this did not affect hydropower generation since the dam was operated to match the river flow,[1] twice-annual sluicing had been conducted since 1948 to clear sediment away from the power intakes.

[3] In 2007, in regards to severe declines in the flow of the Niobrara River as a result of upstream irrigation, NPPD requested that the state of Nebraska make farmers pay as compensation for lost power generation.

[3] In September 2015, NPPD announced that it would be decommissioning the Spencer hydropower plant in 2017 due to increasingly uneconomical cost of power generation at this site.

The water rights would be sold for $9 million to the Nebraska Game and Parks Commission and five local natural resources districts to manage the river for agriculture, recreation and wildlife conservation.

[6] On the early morning of March 14, 2019, the dam was breached after a major storm caused heavy rain, snowmelt and ice breakage to swell the Niobrara River.

The Chief Standing Bear Memorial Bridge across the Missouri River below the Niobrara confluence was temporarily closed as the Nebraska approach flooded, but it reopened a few days later.

NPPD later said that workers had attempted to open the dam's manually operated gates to release floodwater, but some were frozen shut by the cold weather and may have contributed to water overtopping the earthen embankment a short while later.