Chinook salmon lay their eggs below Hells Canyon Dam in the fall. The eggs need the right flow of water to develop, so we control the water released from Brownlee Reservoir from October through December, until the eggs hatch. We keep the flow between 8,500 cubic feet per second (cfs) and 13,000 cfs.
To do this, we sometimes lower the water in Brownlee Reservoir upstream of Hells Canyon Dam. This enables Brownlee to absorb increased flows coming in while maintaining a steady flow going out. These lower water levels can limit our ability to generate hydropower through the three dams of the Hells Canyon Complex. We may buy power from other sources.
To monitor the health of the fall Chinook salmon population, the U.S. Department of Fish and Wildlife Service and Idaho Power survey their nests (also called redds) in the fall. View a chart of our total annual fall Chinook redd counts.