In the streams of the Santa Monica Mountains, native fish are an important component of aquatic ecosystems. A few native fish can be found here including the arroyo chub (Gila orcuttii) and the federally endangered steelhead trout (Onchorynchus mykiss). The mountain streams are also home to a number non-native fish including largemouth bass, bluegill and goldfish. Non-native fishes pose a major threat to native species such as the Baja California Treefrog, California Newt and native fish through predation and competition for food resources.
Ecological restoration is occurring at several park sites to improve access to spawning habitat for the steelhead trout.