The Tomales-Drake Bays watershed (HUC 18050005) covers an area of approximately 215 square miles in Marin County, California. The watershed is characterized by a Mediterranean climate with wet winters and dry summers. The hydrology of the area is driven by the Russian River, which flows into the Pacific Ocean through Tomales Bay. Specific snowpack data for the area is limited, but the watershed experiences occasional snowfall in higher elevations during winter months. Surface water in the watershed is primarily sourced from rainfall and snowmelt, with some contribution from irrigation and groundwater. Reservoirs in the area are used for water supply and storage, and have been known to contain elevated levels of sediment, nutrients, and pollutants. Climate trends in the region include rising temperatures and decreasing precipitation, which may impact the hydrology of the watershed in the future.