Eureka, also known as Eureka Lake, is a state-owned dam located in Johnsville, California, within Plumas County. Built in 1866, this earth dam stands at 29 feet high and spans 410 feet in length, with a storage capacity of 220 acre-feet. Operated by the California Department of Water Resources (DWR), Eureka serves primarily as a water supply source while also offering recreational opportunities for visitors.

Managed and regulated by the DWR's Safety of Dams program, Eureka is classified as a significant hazard dam with a satisfactory condition assessment as of September 2017. The dam overlooks Eureka Creek and plays a crucial role in maintaining the water supply for the surrounding area. Despite being under state jurisdiction, Eureka is not associated with any federal agencies and has not undergone any major modifications in recent years.

With a notable presence in the beautiful landscape of Plumas County, Eureka dam stands as a testament to California's commitment to water resource management and safety. From its historical significance to its ongoing role in providing essential water supply, Eureka remains a vital infrastructure for the region's water needs and a destination for recreational enjoyment.