The majority of Lassen County is included in the North Lahontan Hydrologic Region. Hydrologic regions are defined as "major drainage basins" by The California Water Plan. This means that much of the County's surface water, including the Susan River, drains to the series of alkaline lakes, such as Honey Lake, that make up the region, and do not feed to the ocean. In addition, much of the western portion of the County contributes surface water to the Sacramento River Hydrologic Region, eventually feeding the Pacific Ocean through the Sacramento-San Joaquin Delta. In addition to the Susan River and Honey Lake, prominent water resources include Eagle Lake and a portion of the Pitt River.

For information on the Department of Water Resources' activities in Lassen County, browse Our Work, and to learn more about the County, visit the official Lassen County web site.