Dam on the Tijuana River in Mexico.
|Countries||Mexico, United States|
|States||Baja California, California|
|District||San Diego County (California)|
|Municipality||Ensenada; Tijuana, Tecate and San Ysidro (Baja California)|
|- left||Arroyo de las Palmas|
|Source||Sierra de Juárez|
|- location||Municipality of Ensenada|
|- elevation||614 ft (187 m)|
|- location||Imperial Beach|
|- elevation||0 ft (0 m)|
|Length||120 mi (193 km)|
|Basin||1,750 sq mi (4,532 km2)|
|Discharge||for Nestor, San Diego|
|- average||42.5 cu ft/s (1 m3/s)|
|- max||33,500 cu ft/s (949 m3/s)|
|- min||0 cu ft/s (0 m3/s)|
The Tijuana River (Spanish: Río Tijuana) is an intermittent river, 120 mi (195 km) long, near the Pacific coast of northern Baja California state in northwestern Mexico and Southern California in the western United States.
The Tijuana River drains an arid area along the U.S.—Mexico border, flowing through Mexico for most its course then crossing the border into Southern California for its lower 5 mi (8 km) to empty into the ocean in an estuary on the southern edge of San Diego.
Its lower reaches provide the last undeveloped coast wetlands in San Diego County amidst a highly urbanized environment at the southern city limits of Imperial Beach. The river has been the subject of great controversy in recent decades regarding pollution, flood control, and U.S. border protection.
The Tijuana River rises in the Sierra de Juárez of northern Baja California, approximately 45 mi (70 km) ENE of Ensenada. It flows WNW through Tijuana, crossing the border approximately 5 mi (8 km) from the Pacific. It flows west, just skirting the international border south of the San Ysidro section of San Diego. The lower 2 mi (3 km) of the river form the broad mud flat estuary, and the Tijuana River Estuary is a rich habitat for wildlife, including over 370 species of birds.  It is naturally prone to flooding during heavy rains. The Tijuana River enters the Pacific 10 mi (15 km) south of downtown San Diego at the southern city limits of Imperial Beach.
The river is impounded in Mexico southeast of Tijuana by the Abelardo L. Rodríguez Dam for drinking water and irrigation. Former Baja California Governor Milton Castellanos Everardo constructed concrete barriers along the riverbank to prevent flooding during his tenure.
Nature reserves 
The Tijuana River National Estuarine Research Reserve protects 2,293 acres (928 ha) and studies the Tijuana River Estuary.  It was established as part of the National Estuarine Research Reserve system in the United States.  The reserve is managed in part as a Biological Field Station by the San Diego State University (SDSU) College of Sciences, which also protects part of the estuary near the ocean within the United States. 
The Tijuana Slough National Wildlife Refuge is part of the San Diego National Wildlife Refuge Complex, and is also within the Estuarine Research Reserve. The Tijuana Slough Refuge protects one of southern California's largest remaining salt marshes without a road or railroad trestle running through it. Designated as a Globally Important Bird Area by the American Bird Conservancy, over 370 species of birds have been sighted on the refuge.
Wastewater treatment 
The river has been used as a wastewater conduit for much of the last several decades. Partial progress was made in the 1980s with a Clean Water Grant from the U.S. Environmental Protection Agency to improve wastewater treatment, by creating the San Diego-Tijuana Wastewater Treatment Plant to protect estuary waters. Raw sewage overflows on the Mexican side, from canyons along the river, are a recurring problem despite cross-border efforts to clean it up. According to a 1993 report by the city of San Diego, the city of Tijuana had collected an average of 13 million gallons (50 million liters) per day of raw sewage, that then was released and flowed across the border into California. 
The Tijuana River Valley Regional Park is located in the Tijuana River Valley district of San Diego. It protects over 1,800 acres (730 ha), including dense riparian forests along the Tijuana River. It has an extensive system of trails for walking and equestrian access. 
The mouth of the Tijuana River is the location of the legendary Tijuana Sloughs big-wave surfing break. Alan "Dempsey" Holder, a pioneering California big-wave surfer, surfed waves over a mile from shore at the mouth of the Tijuana River starting in the 1930s. Through the 1950s he surfed the break with legends such as Peter Cole, Kimble Daun and Ron "Canoe" Drummond. A small underground group of big-wave surfers continue to surf the sloughs on 9-10' surfboards, but pollution and flooding has adversely impacted the waves. Big-wave surfing in the region has shifted to other areas, such as Todos Santos Island and the Cortez Bank.
See also 
- Border Field State Park
- Imperial Beach
- Playas de Tijuana
- Tijuana River Estuary
- Tijuana Slough National Wildlife Refuge
- List of rivers in California
- Parks.ca.gov: Tijuana Estuary . accessed 6.16.2012
- Islas Parra, Victor (2011-10-11). "Murió ayer Milton Castellanos". El Mexicano. Retrieved 2011-10-25.
- TRNERR — Tijuana River National Estuarine Research Reserve at the Tijuana Estuary . accessed 6.16.2012
- National Estuarine Research Reserve System: Tijuana River . accessed 6.16.2012
- SDSU Field Station
- Refuge profile
- S.D. Earthtimes: San Diego Report
- County of San Diego: Tijuana River Valley Regional Park . accessed 6.16.2012
|Wikimedia Commons has media related to: Tijuana River|
- San Diego State University (SDSU) Tijuana River Watershed webpage
- San Diego Earth Times: Tijuana River Controversy
- NOAA: Tijuana River Reserve
- San Diego National Wildlife Refuge Complex