Napa River

The Napa River is a river that flows through Napa Valley in California north of San Francisco and is approximately 55 miles (89 km) long.

It drains a famous wine-growing region, called the Napa Valley, in the mountains northeast of San Francisco. Milliken Creek and Mt. Veeder watersheds are a few of its many tributaries. The mouth is at Vallejo where the inter-tidal zone of fresh and salt waters flow into the Carquinez Straits on San Pablo Bay.

The Napa River rises in northwestern Napa County just south of the summit of Mt. St. Helena in the Mayacamas Mountains of the California Coast Ranges. The source begins as seasonal Kimball Canyon Creek in Robert Louis Stevenson State Park at an elevation of 3,745 feet (1,141 m) which descends the southern slope of Mt. St. Helena to Kimball Canyon Dam.[1] [6] It flows south for 4 miles (6 km), entering the head of the slender Napa Valley north of Calistoga. In the valley, it flows southeast past Calistoga, St Helena, Rutherford, Oakville and through Napa, its head of navigation. Downstream from Napa, it forms a tidal estuary, entering Mare Island Strait, a narrow channel on the north end of San Pablo Bay. It discharges into San Pablo Bay through the Napa Sonoma Marsh.

Watershed
The Napa River watershed encompasses approximately 426 square miles (1,103 km²). Larger tributaries, such as Dry, Conn, and Soda creeks, show signs of recent incision and have graded to the incised current level of the mainstem Napa River. In some cases, smaller tributaries cutting across the valley floor have not fully adjusted to the lowered level of the mainstem and are elevated at their confluence with the mainstem, forming potential barriers to upstream fish migration. Several large dams were built between 1924 and 1959 on major eastside tributaries (Conn, Rector, Milliken, and Bell dams) and the northern headwaters of the Napa River (Kimball Dam). In addition, many smaller dams can be found throughout the watershed. These numerous dams are impassable barriers to salmon and steelhead seeking their historic spawning grounds.

Ecology
May 2014 photo of beaver gathering shore grasses on the Napa River. Courtesy of Cheryl Reynolds, Worth a Dam.

Beaver Lodge on Tulucay Creek at Soscol Avenue in downtown Napa, courtesy of Rusty Cohn

The river also supports a remarkable diversity of fishes and recovering salmonid populations, especially chinook salmon(Oncorhynchus tshawytscha) and steelhead trout(Oncorhynchus mykiss). In 2003 the Napa County Resource Conservation District began an ongoing salmon monitoring program, and have recorded a run of approximately 400 - 1000 fall-run Chinook salmon the past several years. The Chinook run begins in late October through January. Conclusive evidence of historical chinook salmon populations in the Napa River basin have not been established, but the river provides appropriate habitat for salmon and its location near the entrance to the Sacramento/San Joaquin Rivers make it likely that salmon would have at least ventured into the Napa River. In 2013, a genetics study of Napa River chinook salmon revealed that two adults migrated from the Klamath River and successfully spawned in the Napa River, since four juvenile chinook collected from the Napa River in 2010 were proved to be siblings from the close similarity of their DNA and that the latter was characteristic of Klamath River chinook.These findings have important implications for the protection of the federally endangered Coastal California Chinook Salmon ESU since the Napa River, nor any stream in the Bay Area, was included in this ESU.

The Napa River basin is estimated to have historically supported a spawning run of 6,000–8,000 steelhead, and as many as 2,000–4,000 coho salmon (Oncorhynchus kisutch). By the late 1960s, coho salmon were extirpated from the watershed and the steelhead population is now reduced to less than a few hundred adults. Flow reductions in key rearing streams have reduced food availability for juvenile steelhead, causing reduced growth and survival. Recently, a chum salmon (Oncorhynchus keta) was caught in the river. In addition, a fourth salmon species, sockeye salmon (Oncorhynchus nerka), was also identified in the Napa River.

Although diminished, the Napa River basin continues to support a fish community of greater diversity than even the Sacramento and San Joaquin River systems, including a nearly intact community of sixteen native fish species, including Steelhead, fall-run Chinook salmon, Pacific (Lampetra tridentata) and river lamprey (Lampetra ayresi), hardhead (Mylopharodon conocephalus), hitch (Lavinia exilicauda), tule perch (Hysterocarpus traski), and Sacramento splittail (Pogonichthys macrolepidotus). Because of this diversity the Napa River has been prioritized for special protection. White sturgeon (Acipenser transmontanus) and many other native and non-native fishes currently utilize the Napa River watershed.

The California golden beaver (Castor canadensis subauraticus) was historically extant. Recently beaver have recolonized the Napa River. and have been documented in Napa as well as near Rutherford and Oak Knoll.