San Mateo Creek Non-Native Removal

San Mateo Creek, in northern San Diego County, is one of the last strongholds for Southern California Steelhead, and it also supports Coastal Rainbow Trout, California newts, Arroyo Toads, Arroyo Chub, and Southwestern Pond Turtles. But the creek's native species are under growing pressure from a threat that starts far from the stream itself: invasive fish and amphibians stocked in private ponds upstream escape into the watershed during winter rains, where they then compete with native species for food and habitat and prey directly on their eggs and young.

CalTrout is addressing this problem from both ends. In the upper watershed, that means working directly with private landowners on outreach and pond mitigation infrastructure to keep invasive species from escaping into the creek in the first place. Downstream, CalTrout partners with the California Department of Fish and Wildlife on in-stream removal of invasives, supported by equipment from the International Federation of Fly Fishers and Golden State Fly Casters, while the San Diego Regional Water Quality Control Board conducts eDNA studies to track where invasive species are hiding and monitor progress over time.

This work now carries real regulatory weight: in January 2025, aquatic invasives in the watershed were formally designated as water quality pollutants under a Nonpoint Source TMDL, a classification that opens the door to federal EPA funding to help carry the plan through. CalTrout and our partners are pursuing a 10 to 15 year effort to bring invasive species down to acceptable levels by 2037, restoring the balance of a watershed that native steelhead, trout, and wildlife, and the people who depend on clean water flowing through it, all rely on.