Suisun Bay ( sə-SOON; Wintun for "where the west wind blows") is a shallow tidal estuary (a northeastern extension of the San Francisco Bay) in Northern California. It lies at the confluence of the Sacramento River and San Joaquin River, forming the entrance to the Sacramento–San Joaquin River Delta, an inverted river delta. To the west, Suisun Bay is drained by the Carquinez Strait, which connects to San Pablo Bay, a northern extension of San Francisco Bay. Grizzly Bay forms a northern extension of Suisun Bay. Suisun Bay is between Contra Costa County to the south and Solano County to the north.
The bay was named in 1811, after the Suisunes, a Patwin tribe of Wintun Indians.
The Central Pacific Railroad built a train ferry that operated between Benicia and Port Costa, California, from 1879 to 1930. The ferry boats Solano and Contra Costa were removed from service when the nearby Martinez railroad bridge was completed in 1930. From 1913 until 1954 the Sacramento Northern Railway, an electrified interurban line, crossed Suisun Bay with the Ramon, a distillate-powered train ferry.
On April 28, 2004, a petroleum pipeline operated by Kinder Morgan Energy Partners ruptured, initially reported as spilling 1,500 barrels (264m³) of diesel fuel in the marshes, but, this was later updated to about 2,950 barrels. Kinder Morgan pleaded guilty to operating a corroded pipeline (and cited for failing to notify authorities quickly after the spill was discovered) and paid three million dollars in penalties and restitution.