Lower Twin Lake is a privately-owned reservoir located in Napa, California, with a primary purpose of water supply. Built in 1985, this Earth dam stands at a height of 18 feet and has a storage capacity of 127 acre-feet. The reservoir covers an area of 12 acres and is fed by Tr Pope Creek, offering recreational opportunities along its shores while also serving irrigation needs in the region.

Managed by the California Department of Water Resources (DWR) under the Safety of Dams program, Lower Twin Lake is regulated, permitted, inspected, and enforced to ensure its safe operation. The dam is classified as having a low hazard potential and a fair condition assessment as of September 2017. With a maximum discharge capacity and spillway details not specified, this dam is a vital part of the local water infrastructure, especially in times of drought or water scarcity.

In the event of an emergency, the reservoir's emergency action plan (EAP) status, inundation maps, and risk assessment details are not explicitly mentioned in the available data. Despite this, Lower Twin Lake remains a crucial water resource for the surrounding area, contributing to irrigation, recreation, and overall water supply needs while being overseen by state regulatory agencies for its safe and sustainable operation.