San Francisco Bay is a shallow, productive estuary through which water draining about forty percent of California, flowing in the Sacramento and San Joaquin rivers from the Sierra Nevada mountains and Central Valley, enters the Pacific Ocean. Technically, both rivers flow into Suisun Bay, which help flows through the Carquinez Strait to meet with the Napa River at the entrance to San Pablo Bay, which connects at its south end to San Francisco Bay, although the entire group of interconnected bays are often referred to as "the San Francisco Bay."