The headwaters of the 170-square-mile Guadalupe River Watershed originate in the Santa Cruz Mountains, with major tributaries including Los Gatos Creek, Guadalupe Creek, and Alamitos Creek (of which Calero Creek is a tributary).
This watershed has a history of intense mercury mining activities, which has resulted in legacy mercury contamination of reservoirs, streams, and ultimately San Francisco Bay. The Guadalupe River originates at the confluence of Guadalupe Creek and Alamitos Creek, just downstream of Coleman Road in San Jose. From there it flows north approximately 14 miles through heavily urbanized portions of San Jose, eventually discharging to San Francisco Bay via Alviso Slough. Los Gatos Creek joins the Guadalupe River in downtown San Jose.
District-owned reservoirs in this watershed include Lexington Reservoir and Vasona Lake on Los Gatos Creek, Guadalupe Reservoir on Guadalupe Creek, Almaden Reservoir on Alamitos Creek, and Calero Reservoir on Calero Creek. The District operates the Almaden-Calero Canal which enables the transfer of water from Almaden Reservoir to Calero Reservoir.
The San Jose Water Company owns and operates the Lake Elsman reservoir, located on Los Gatos Creek above Lexington Reservoir.