Thermalito Afterbay, located in Marysville, California, is a state-regulated water resource with a primary purpose of water supply. Completed in 1967, this earth dam stands at a height of 39 feet and spans a length of 42,000 feet, with a storage capacity of 57,041 acre-feet. The afterbay is situated off-stream from the Feather River and covers a surface area of 6,900 acres, serving multiple purposes including hydroelectric power generation, irrigation, recreation, and water supply.

Managed by the California Department of Water Resources (DWR) and regulated by the Federal Energy Regulatory Commission (FERC), Thermalito Afterbay plays a crucial role in water management in the region. With a high hazard potential and a very high risk assessment rating, the afterbay is subject to regular inspections and enforcement measures to ensure its safety and functionality. Additionally, the presence of controlled spillways and emergency action plans highlight the commitment to mitigating potential risks associated with the dam.

As a key component of the water infrastructure in Butte County, Thermalito Afterbay serves as a vital resource for the community, providing essential water supplies for agricultural and municipal needs. With its strategic location and multiple benefits, including recreational opportunities for residents, the afterbay stands as a testament to effective water resource management in the face of climate challenges.