Portneuf, also known as Chesterfield Reservoir, is a privately owned dam located in Caribou, Idaho, near the city of Lava Hot Springs. Built in 1912, this earth and stone dam stands at a height of 54.6 feet and has a storage capacity of 20,504 acre-feet. The dam is situated on the Portneuf River, a tributary of the Snake River, and serves multiple purposes beyond flood control, making it a vital resource for the region.

Despite its fair condition assessment and high hazard potential, Portneuf has been regulated and inspected by the Idaho Department of Water Resources. The dam features an uncontrolled spillway with a width of 40 feet and outlet gates for controlled release of water. With a risk assessment rating of moderate, the dam is actively managed to mitigate potential risks and ensure the safety of downstream communities in the event of an emergency. Overall, Portneuf plays a crucial role in water resource management and climate resilience efforts in the region.