Lake O'Neill Dam, located in San Diego, California, is a vital water resource managed by the US Marine Corps for fire protection, stock, and small fish pond purposes. Built in 1883, this earth dam stands at a height of 14 feet and has a hydraulic height of 17 feet, with a storage capacity of 1395 acre-feet. The dam's primary source agency is the Department of Defense USMC, and it is owned and funded by the US Navy.

With a surface area of 115.7 acres and a drainage area of 9 square miles, Lake O'Neill Dam plays a crucial role in water supply and recreation activities in the region. Despite being classified as having a high hazard potential, the dam's condition is assessed as fair. Although it has no outlet gates, an uncontrolled spillway with a width of 20 feet is in place to manage excess water flow. The dam has not been modified in recent years, and the last inspection in June 2017 revealed a need for regular monitoring and maintenance.

Lake O'Neill Dam's risk assessment is rated as moderate, highlighting the importance of implementing robust risk management measures to ensure its continued safety and functionality. As a key component of the local water infrastructure, this dam serves as a critical resource for the surrounding community and underscores the intersection of water resource management and climate resilience in the region.