Alamitos Creek or Los Alamitos Creek is a 7.7-mile-long (12.4 km) creek in San Jose, California, which becomes the Guadalupe River when it exits Lake Almaden and joins Guadalupe Creek. Los Alamitos Creek is located in Almaden Valley and originates from the Los Capitancillos Ridge in the Santa Cruz Mountains, near New Almaden. This creek flows through the Valley's Guadalupe Watershed, which is owned by the Santa Clara Valley Water District. The creek flows in a generally northwesterly direction after rounding the Los Capitancillos Ridge and the town of New Almaden, in the southwest corner, before ambling along the Santa Teresa Hills on northeast side of the Almaden Valley. Its environment has some relatively undisturbed areas and considerable lengths of suburban residential character. Originally called Arroyo de los Alamitos, the creek's name is derived from "little poplar", "alamo" being the Spanish word for "poplar" or "cottonwood".

The Guadalupe River mainstem is an urban, northward flowing 14 miles (23 km) river in California whose much longer headwater creeks originate in the Santa Cruz Mountains. The river mainstem now begins on the Santa Clara Valley floor when Los Alamitos Creek exits Lake Almaden and joins Guadalupe Creek just downstream of Coleman Road in San Jose, California. From here it flows north through San Jose, where it receives Los Gatos Creek, a major tributary. The Guadalupe River serves as the eastern boundary of the City of Santa Clara and the western boundary of Alviso, and after coursing through San José, it empties into south San Francisco Bay at the Alviso Slough.