San Diego Creek is a 16-mile (26 km) urban waterway flowing into Upper Newport Bay in Orange County, California in the United States. Its watershed covers 112.2 square miles (291 km2) in parts of eight cities, including Irvine, Tustin, and Costa Mesa. From its headwaters in Laguna Woods the creek flows northwest to its confluence with Peters Canyon Wash, where it turns abruptly southwest towards the bay.