Sycamore alluvial woodlands require natural flooding and channel-forming flows and scour that historically characterized many of the creeks in the foothills of the watershed.

[21] Pacheco Creek's Central Coast California sycamore woodlands stretch from Bell Station to the Hollister plain and represent almost 7% of the total remaining in the state.

[22] Pacheco Creek historically hosted steelhead trout (Oncorhynchus mykiss) as evidenced by a physical specimen collected in 1945 by D.H. Simpson in the California Academy of Sciences, "19.5 miles east of Gilroy on Hwy.

"[24] In addition, resident rainbow (the landlocked form of steelhead trout) successfully rear in fast-water habitats grow rapidly and reach smolt size by the end of their first summer.

In many years in late spring, prior to reservoir releases for agriculture, low stream flows and high water temperatures severely impact steelhead fry and small juveniles.

[25] Other native fish in Pacheco Creek include Monterey sucker (Catostomus occidentalis mniotiltus) and Sacramento pikeminnow (Ptychocheilus grandis).

[26] The Santa Clara Valley Habitat Agency (SCVHA) has identified the Pacheco Creek undercrossing below Pacheco Pass Highway (California State Route 152) as a key wildlife linkage to enable smaller animals to safely cross beneath this high-speed road at the border of Santa Clara County and San Benito County.