The Sacramento Headwaters Watershed (HUC 18020005) covers an area of approximately 1,399 square miles in northeastern California. The headwaters of the Sacramento River originate in this watershed, making it a vital source of surface water for downstream communities and agricultural operations. The hydrology of the region is heavily influenced by snowpack, which accumulates in the high elevations during the winter months and provides a slow release of water throughout the spring and summer. Major reservoirs in the watershed include Lake Shasta and Lake Siskiyou. The watershed is subject to a Mediterranean climate with hot, dry summers and cool, wet winters. In recent years, the region has experienced reduced snowpack and earlier snowmelt due to climate change, which has impacted water availability and quality in the watershed.