San Diego Creek

San Diego Creek is a 16-mile (26 km) waterway flowing into Upper Newport Bay in central Orange County in the U.S. state of California. Its basin covers 112.2 square miles (291 km2) in parts of eight cities, including Irvine, Tustin, and Costa Mesa. The major tributary of the northeast-flowing stream is Peters Canyon Wash, which joins a few miles above its mouth. Now mostly channelized, San Diego Creek serves an important function for flood control, but it has been extensively monitored for sediment loads. The purpose of this studying is that Upper Newport Bay, which San Diego Creek is the primary freshwater input of, is a rich ecological habitat and preserve.

Most of the watershed is residential or commercial, with large amounts of open space, nearly 15,700 acres (64 km2). There are a few surviving pockets of agriculture, although that has been mainly been taken over by more urban development. A large part of the basin is also occupied by the El Toro Marine Corps Air Base, which is being converted into the Orange County Great Park. There are also some lands dedicated to industry. Interstate 5 and Interstate 405 run southeast-northwest through the watershed, which borders that of Santiago Creek on the northeast, the Santa Ana River on the northwest, and Aliso Creek on the southeast.

Its name is likely a corruption of that of Santiago Creek, a river whose watershed borders San Diego Creek to the north and east.