Lake Spaulding No. 3 Auxiliary is a concrete gravity dam located in Nevada County, California, near the city of Washington. Built in 1919, this hydroelectric structure stands at 91 feet tall and has a capacity of 74,773 acre-feet, serving as a vital component of the South Yuba River's water resource management system. Managed by a private entity, this dam is regulated and inspected by the California Department of Water Resources for safety compliance.

The dam's spillway type is uncontrolled, with a width of 90 feet, and it has a high hazard potential due to its location and structural components. The dam's emergency action plan was last revised in December 2020, ensuring that proper guidelines are in place for potential risks. Lake Spaulding No. 3 Auxiliary has a moderate risk assessment rating, indicating the need for ongoing monitoring and risk management measures to maintain public safety and environmental integrity in the face of changing climate patterns and water resource demands.

As a crucial part of the Federal Energy Regulatory Commission's oversight, this dam plays a significant role in supporting hydroelectric power generation and water supply for the surrounding area. With its historical significance and engineering ingenuity, Lake Spaulding No. 3 Auxiliary stands as a testament to the enduring importance of sustainable water resource management in the face of evolving climate challenges.