Bolinas Lagoon

Bolinas Lagoon is the largest tidal lagoon on the central California coast and, as such, is a valuable feeding and wintering area for migratory birds and a productive fish and shellfish area. Approximately 240 hectares (600 acres) are exposed mudflats at low tide. The average depth is 1.5 meters (5 feet), with a maximum of 3.5 meters (12 feet) in the tidal channels.

Vegetation is varied, ranging from green and blue-green and red algae in the open waters to coastal scrub on the uplands and islands within the lagoon. Sea lettuce, Ulva spp., is found in the upper basin and at the southeastern end. Eel grass, Zostera marina, once abundant, is found now in only the main channel. There is a small amount of freshwater marsh, with Scirpus sp. and Typha sp., near the freshwater inlets, but the dominant vegetation is saltwater marsh.

The salt marsh is divided into three vertical zones, with the indicator plants, from low to high, being cord grass, Spartina foliosa, pickleweed, Salicornia virginica, and salt grass, Distichlis spicata var. stolonifera. On Kent Island there are five zones; ranging upwards from the Distichlis they are Vancouver rye grass, Leymus mollis, Grindelia stricta var. platyphylla, Ambrosia chamissonis, and red fescue, Festuca rubra. Two rare plants, Cordylanthus maritimus ssp. palustris and Dichondra donnelliana, occur within the area.

During the migratory season as many as 30,000 -35,000 birds may be observed here. Some 75 species of water-oriented birds have been sighted in the area. Among the more noteworthy are the Virginia rail, Rallus limicola, clapper rail, Rallus longirostris, and parasitic jaeger, Stercorarius parasiticus. The more abundant ducks include ruddy, Oxyura jamaicensis, scaup, Aythya spp., bufflehead, Bucephala albeola, and white-winged scoter, Melanitta deglandi.

Harbor seals, Phoca vitulina, haul out in the lagoon. Forty-three species of fish have been collected; surfsmelt, Hypomesus pretiosus, topsmelt, Atherinops affinis, and anchovy, Engraulis mordax, are among the more common. The area is an important nursery for various commercially important species of several perch and flatfish. It is also rich in invertebrates and is well known as a clamming area, with six species present, Macoma incospicua, Macoma irus, Macoma nasuta, Macoma secta, Mertrix lusoria and Mya arenaria.

The lagoon lies in the San Andreas Fault Zone and is a drowned valley mouth. It was formed between 5,000 and 7,000 years ago during the post-glacial sea-level rise and was perhaps up to 15 meters (50 feet) deep.

Integrity: Siltation has been a major problem and, until recently, pollution. The latter is coming under control.

Use: Research, educational, observational, light recreation.

Ref: Giguere, P. E. 1970. The Natural Resources of Bolinas Lagoon, Their Status and Future. Calif. Dept. of Fish & Game, Sacramento, Calif. 107 pp.
Molina, A. and A. Rathbun, 1968. The Zonation of the Conspicuous Phanerogams on Kent Island, Bolinas Lagoon, Marin County, Calif. Mimeo. College of Marin, Bolinas F.S. 17 pp.

July 1976