The Napa River watershed supports thirty native fish species, including several threatened and/or rare species such as steelhead/rainbow trout, fall-run Chinook salmon, Pacific and river lamprey, hardhead, hitch, tule perch, and Sacramento splittail. The Napa River is estimated to have historically supported a run of 6,000–8,000 steelhead trout, and as many 2,000–4,000 coho salmon (USFWS 1968). By the late 1960s, coho salmon had been extirpated, and steelhead trout had declined to an estimated run of fewer than 2,000 adults. The present-day run of steelhead trout is believed to be less than 200 adults.

Introductions of exotic fish species have impacted most freshwater ecosystems in California, including the Napa River. Habitat alterations can determine the species composition of a fish community by favoring certain species over another. Habitat alterations have occurred gradually, but constantly, during the past century. The Napa River system has changed from being dominated by pools and riffles to a morphology dominated by large, deep pools with increased water temperatures and slow-moving water. Much of the Napa River and its tributaries now provide the preferred habitat of predatory fish species, many of which are exotic, such as largemouth bass.

The Napa County Resource Conservation District (RCD) conducts fish monitoring in the Napa River watershed to collect information about native fish populations with the emphasis on two salmonid species - steelhead trout (Oncorhynchus mykiss) and Chinook salmon (Oncorhynchus tshawytscha). This monitoring program includes capturing and counting juvenile salmonids as they out-migrate to the ocean as “smolts”, counting adult fish and mapping their spawning distributions, observing juveniles through snorkeling surveys, and long-term tracking of individual fish with implanted transponder tags. Results and reports are available at

The central component of the RCD’s monitoring program is the rotary screw trap (RST), which is seasonally placed in the lower Napa River near Oak Knoll Avenue. This live capture and release trap is installed at the lowest non-tidal reach of the river where the RCD can collect steelhead and salmon smolts right as they enter the estuary. Other monitoring has been done throughout the watershed, with salmon surveys focused on the mainstem Napa River and steelhead surveys focused more in the tributary streams.

The mainstem Napa River provides approximately 29.8 miles of viable salmonid spawning habitat. Additionally, there are approximately 141 miles of tributary streams that support salmonid spawning and freshwater rearing. These totals exclude tidal reaches, which act as vital corridors and transition habitats between freshwater and the ocean.



Common name Scientific name Family
White Sturgeon Acipenser transmontanus  Acipenseridae
Sacramento Sucker Catostomus occidentalis Catostomidae
Pacific Herring Clupea pallasii Clupeidae
Northern Anchovy Engraulis mordax Clupeidae
Riffle Sculpin Cottus gulosus Cottidae
Coastrange Sculpin Cottus aleuticus Cottidae
Prickly Sculpin Cottus asper Cottidae
Pacific Staghorn Sculpin Leptocottus armatus Cottidae
Sacramento Pikeminnow Ptychocheilus grandis Cyprinidae
Hitch Lavinia exilicauda Cyprinidae
Sacramento Blackfish Orthodon microlepidotus Cyprinidae
California Roach Hesperoleucus symmetricus Cyprinidae
Hardhead Mylopharodon conocephalus Cyprinidae
Sacramento Splittail Pogonichthys macrolepidotus Cyprinidae
Shiner Perch Cymatogaster aggregata Embiotocidae
Tule Perch Hysterocarpus traski Embiotocidae
Three-spine Stickleback Gasterosteus aculeatus Gasterosteidae
Bay Goby Lepidogobius lepidus Gobiidae
Longjaw Mudsucker Gillichthys mirabili Gobiidae
Arrow Goby Clevelandia ios Gobiidae
Delta Smelt Hypomesus transpacificus Osmeridae
Jack Smelt Atherinopsis californiensis Osmeridae
Longfin Smelt Spirinchus thaleichthys Osmeridae
Pacific Lamprey Lampetra tridentata Petromyzontidae
River Lamprey Lampetra ayresi Petromyzontidae
Western Brook Lamprey Lampetra richardsoni Petromyzontidae
Speckled Sanddab Citharichthys stigmaeus Pleuronectidae
Starry Flounder Platichthys stellatus Pleuronectidae
Steelhead / Rainbow Trout Oncorhynchus mykiss Salmonidae
Chinook Salmon Oncorhynchus tshawytscha Salmonidae

Stillwater Sciences Limiting Factors Analysis, 2002 (based on information derived from Leidy 1997, CDFG surveys; see Appendix A2, and Moyle 2002.)