San Pedro Creek is home to a few species of fish, including the prickly sculpin (Cottus asper), the three-spined stickleback (Gasterosteus aculeatus), and the Pacific lamprey (Lampetra tridentate). The most abundant and charismatic species in the stream is the steelhead trout (Oncorhynchus mykiss). The steelhead population in San Pedro Creek is part of the south/central California's population of steelhead which is a Federally listed Threatened Species. During the rainy season, it is a remarkable sight to see brightly-colored adult steelhead migrate upstream to spawn, passing right through people's back yards! Steelhead spawn in several stretches of San Pedro Creek, including the main portion of the stream that parallels Linda Mar Boulevard, and the middle and south forks in San Pedro County Park. Young fish will live in the stream for 1 to 2 years then most will depart for the open ocean to mature, where they will live for a year or two before returning to San Pedro Creek to spawn. Unlike species such as Chinook and Coho salmon, adult steelhead may return to sea after breeding and can return several times to spawn, up to 3 or 4 times in their lifetime.
Although the upper reaches of San Pedro Creek have healthy riparian areas and winter flows that support migrating steelhead; the lower reaches of the creek have migration barriers which make it difficult in certain flow conditions for fish to reach the prime spawning habitat. Efforts are being made to address these conditions so that steelhead in all life stages can
navigate the creek freely.