Rio Vista is a city located in the eastern end of Solano County, California in the San Francisco Bay Area, on the Sacramento River, in the Sacramento River Delta region. The population was 4,571 at the 2000 Census. Rio Vista was visited by a lost Humpback whale in 1985, despite being 60 miles (100 kilometers) upriver from the Pacific Ocean. The young whale, nicknamed "Humphrey", attracted throngs of curiosity seekers before he was eventually guided back to sea by rescuers. Again in May 2007, Humpbacks were sighted in Rio Vista. "Delta" and "Dawn," mother and calf, stopped at least twice in the river near the town. Rio Vista is home to the annual Bass Festival in October.