Guadalupe Creek is a 10.5 miles (16.9 km) northward-flowing stream originating just east of the peak of Mount Umunhum in Santa Clara County, California, United States.

The main purpose of the reservoir is to capture runoff from winter storms to recharge in the Alamitos percolation pond system during the summer.

The dam conveys water into the Los Capitancillos percolation ponds continually, unless Guadalupe Reservoir spills, in which case diversion operations terminate until the rainy season ends.

[8] Completed in 1962 and reconstructed in 1964, the Los Capitancillos percolation ponds occupy about 63 acres, from Almaden Expressway (east) to Camden Avenue (west).

[17] Observation with a Vaki Riverwatcher fishcounter installed at the Masson Dam fish ladder during the 2006-2007 and 2007-2008 spawning seasons confirmed that steelhead trout, Pacific lamprey (Lampetra tridentata), and Sacramento sucker (Catostomus occidentalis), and possibly a Chinook salmon (Oncorhynchus tshawytscha) ascended above it.

The creek below Guadalupe Reservoir and Dam supports the western pond turtle (Actinemys marmorata), foothill yellow-legged frog (Rana boylii), yellow warbler, double crested cormorant, in addition to rainbow trout.

[4] A half-mile stretch of Guadalupe Creek between Almaden Expressway and Masson Dam was restored in 2001 as mitigation for the downtown San Jose flood control project.