 Today, the upper Santiago Creek remains much in its natural state, while the lower creek is listed as "highly disturbed" and no longer supports much native vegetation and wildlife.Historically, the creek is known to have sustained a population of steelhead trout "(Oncorhynchus mykiss)", but with the construction of Villa Park and Santiago Creek dams, their anadromous spawning runs from the sea have been destroyed.However, 13 specimens of the land-locked form of steelhead, rainbow trout, were fin-sampled recently from Harding Canyon and genetic analysis has shown them to be of native and not hatchery stocks.