San Pablo Bay National Wildlife Refuge is a 13190 acres (53.4 km²) National Wildlife Refuge

National Wildlife Refuge

National Wildlife Refuge is a designation for certain protected areas of the United States managed by the United States Fish and Wildlife Service. The National Wildlife Refuge System is the world's premiere system of public lands and waters set aside to conserve America's fish, wildlife and plants...

 in California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

 established in 1970. It extends along the northern shore of San Pablo Bay

San Pablo Bay

San Pablo Bay is a tidal estuary that forms the northern extension of San Francisco Bay in northern California in the United States. Most of the Bay is shallow; however, there is a deep water channel approximately in mid bay, which allows access to Sacramento, Stockton, Benicia, Martinez, and...

 from the mouth of the Petaluma River

Petaluma River

The Petaluma River is a river in the California counties of Sonoma and Marin that becomes a tidal slough near its mouth. It springs from farmlands southwest of Cotati and flows generally southward through Petaluma's old town and of tidal marshes to end in northwest San Pablo Bay.-History:The word...

 to Tolay Creek

Tolay Creek

Tolay Creek is a southward-flowing stream in southern Sonoma County, California, USA, which flows through Tolay Lake and ends in north San Pablo Bay.-History:The Alaguali were a Coast Miwok community of northern San Pablo Bay in the Tolay Creek region...

, Sonoma Creek

Sonoma Creek

Sonoma Creek is a stream in northern California. It is one of two principal drainages of southern Sonoma County, California, with headwaters rising in the rugged hills of Sugarloaf Ridge State Park and discharging to San Pablo Bay, the northern arm of San Francisco Bay. The watershed drained by...

 and ends at Mare Island

Mare Island

Mare Island is a peninsula in the United States alongside the city of Vallejo, California, about northeast of San Francisco. The Napa River forms its eastern side as it enters the Carquinez Strait juncture with the east side of San Pablo Bay. Mare Island is considered a peninsula because no full...

. The refuge encompasses the largest remaining continuous patch of pickleweed

Pickleweed

Pickleweed is a common name used for two unrelated genera of flowering plants:*Batis, family Bataceae*Salicornia, family Amaranthaceae...

-dominated tidal marsh

Tidal marsh

A tidal marsh is a type of marsh that is found along coasts and estuaries of which the flooding characteristics are determined by the tidal movement of the adjacent estuary, sea or ocean . According to the salinity of the flooding water, freshwater, brackish and saline tidal marshes are...

 in the northern San Francisco Bay

San Francisco Bay

San Francisco Bay is a shallow, productive estuary through which water draining from approximately forty percent of California, flowing in the Sacramento and San Joaquin rivers from the Sierra Nevada mountains, enters the Pacific Ocean...

.

Historically, the wetlands surrounding San Pablo Bay were one of the largest tidal marsh complexes on the Pacific coast of North America. However, the area has been significantly impacted by human activities such as hydraulic mining

Hydraulic mining

Hydraulic mining, or hydraulicking, is a form of mining that uses high-pressure jets of water to dislodge rock material or move sediment. In the placer mining of gold or tin, the resulting water-sediment slurry is directed through sluice boxes to remove the gold.-Precursor - ground...

, salt production, diking, draining, filling, agriculture, and development. All told, about 85% of San Pablo Bay's tidal marshes have been altered.

The Refuge includes a variety of habitats including open water, mud flat, tidal marsh, and seasonal and managed wetlands. The refuge hosts millions of migratory

Bird migration

Bird migration is the regular seasonal journey undertaken by many species of birds. Bird movements include those made in response to changes in food availability, habitat or weather. Sometimes, journeys are not termed "true migration" because they are irregular or in only one direction...

 shorebirds and waterfowl, including the largest wintering population of canvasback

Canvasback

The Canvasback is the largest of the North American diving ducks, that ranges from between long and weighs approximately , with a wingspan of . The canvasback has a distinctive wedge-shaped head and long graceful neck. The adult male has a black bill, a chestnut red head and neck, a black...

s on the west coast. The Refuge also provides year-round habitat for sensitive species including the endangered California clapper rail

California Clapper Rail

The California Clapper Rail is an endangered subspecies of the Clapper Rail . It is found principally in California's San Francisco Bay, and also in Monterey Bay and Morro Bay...

 and salt marsh harvest mouse

Salt Marsh Harvest Mouse

The Salt Marsh Harvest Mouse , also known as the Red-bellied Harvest Mouse and some times called by Saltmarsh Harvest Mouse, is an endangered rodent endemic to the San Francisco Bay Area salt marshes in California. There are two distinct subspecies, both endangered and listed together on federal...

. Public access to the refuge is provided by the Tolay Creek Tubbs Island Trail.