Sewage Pollution within the Tijuana River Watershed

Tijuana River Watershed

The Tijuana River Watershed is a large binational watershed of approximately 1,750 square miles that lies across the California - Mexico border. A large portion of the watershed (approximately 75%) is within Mexico and encompass the densely urbanized City of Tijuana, Mexico. The watershed drains into the Tijuana River Estuary in the U.S. and ultimately to the Pacific Ocean in the City of Imperial Beach. Below is an image of the Tijuana River Watershed


Tijuana River Pollution Status Reports

San Diego Water Board Sampling Event

Sewage Problems

Over the past 30 years, Tijuana, Mexico has experienced tremendous population and industrial growth, along with rapid urbanization which has put a strain on the aging Mexican sewage infrastructure in the region to meet the expanding needs. The emerging sewage infrastructure inadequacies have created recurring sewage pollution problems on both sides of the California - Mexico border. At times, sewage generated on the Mexico side of the watershed travels north into California through the Tijuana River or other cross-border canyon tributaries, in the Tijuana River Valley. The sewage flows degrade water quality in the Tijuana River Estuary and adjacent beach coastal waters and also pose a significant public health risk to residents and visitors along both sides of the border.

Efforts to Address Sewage Problems

The border sewage flows present a difficult challenge for California due to the lack of U.S. jurisdiction in Mexico, making the development of cooperative binational approaches that are coordinated within and across governments essential. Governmental organizations on both sides of the border are working collaboratively on multiple fronts to prevent the sewage spills from crossing the border and to address the underlying sewage infrastructure problems. The U.S. and Mexico Sections of the International Boundary and Water Commission (IBWC) are the lead binational agencies responsible for implementing water treaty rights and obligations/minutes between the U.S. and Mexico, including those related to sewage problems and the associated water quality problems in the Tijuana River Watershed. Efforts on both sides of the border have led to the construction and ongoing operation of diversion structures, pump stations and treatment plants to reduce the frequency, volume, and pollutant levels of transboundary sewage flows. (See IBWC Minute Nos. 270, 283, 298, 311 and 320).

This infrastructure includes but is not limited to the following:

  • Several pump stations and wastewater treatment plants in Tijuana, Mexico.
  • The River Diversion Structure and Pump Station CILA divert dry weather flows from the Tijuana River at a point just south of the international border to a Pacific Ocean shoreline discharge point approximately 5.6 miles south of the California - Mexico border. The River Diversion Structure is designed to collect dry weather river flows and any river flows of up to 1,000 liters per second (35.3 cubic feet per second).
  • The South Bay International Wastewater Treatment Plant (SBIWTP) located just north of the California - Mexico border in the City of San Diego. SBIWTP provides secondary treatment for a portion of the sewage from Tijuana, Mexico and dry weather runoff collected from a series of canyon collectors located in Smuggler Gulch, Goat Canyon, Canyon del Sol, Stewart's Drain, and Silva Drain (see below image for locations of canyon collectors, shown with a yellow dot). SBIWTP discharges the secondary-treated wastewater to the Pacific Ocean through the South Bay Ocean Outfall, in accordance with Order No. R9-2014-0009, NPDES No. CA0108928


In addition to the above infrastructure, Order No. R9-2014-0009 contains requirements to improve communication between the U.S. and Mexico on border sewage issues that require binational cooperation. These requirements include but are not limited to standardized procedures for public notification of all known transboundary sewage flow events and Binational Technical Committee meetings to discuss the border sewage problems. Due to limitations in available legal authorities, Order No. R9-2014-0009 does not fully regulate all transboundary sewage flows such as those that occur within the main channel of the Tijuana River. Order No. R9-2014-0009 sets up a framework for the U.S. Section of the IBWC to coordinate with the Mexican Section of the IBWC in a structured manner to develop and coordinate long-term solutions to reduce or eliminate transboundary sewage flows from any source along the border.

More Information Regarding Recent Events

On March 2, 2017, the San Diego Water Board's Executive Officer sent a letter to the U.S. and Mexican IBWC commissioners in response to large cross-border release of untreated sewage in February 2017 into the Tijuana River Valley via the main channel of the river. The letter included recommendations with respect to improved communication, infrastructure, and water quality monitoring.

On April 3, 2017, the IBWC released an investigative report entitled Report of Transboundary Bypass Flows into the Tijuana River, which was produced in response to the February 2017 incident. The report finds that the sewage release occurred as the Tijuana municipal utilities department (Comisión Estatal de Servicios Públicos de Tijuana, CESPT) made repairs to the sewage collection system in central Tijuana. During the repairs, an estimated 28 million gallons of untreated sewage were discharged into the Tijuana River from February 6-23, 2017. The report includes recommendations with respect to improvements in equipment, emergency protocols, communication, infrastructure assessment, and data collection.

On May 14, 2018, the San Diego Water Board and the California Attorney General, on behalf of the people of California, filed a Notice of Intent to Sue the U.S. Section of the IBWC for violations of the Clean Water Act related to transboundary discharges of waste.

On February 5, 2020, the San Diego Water Board issued Investigative Order No. R9-2020-0030, which requires the U.S. Section of the IBWC to submit technical reports pertaining to the investigation of pollution, contamination, and nuisance from transboundary flows in the Tijuana River Valley. The purpose of the required comprehensive technical and investigative monitoring reports is to identify the extent, magnitude, durations, trends, and risks associated with pathogens, toxic pollutants, and trash that are discharged through infrastructure owned, operated, and controlled by the U.S. Section of the IBWC. To request a copy of the investigative order, please contact Melissa Corona at

Contact Information

The U.S. Section of the IBWC contact information and website:
Headquarters in El Paso, TX: (800) 262-8857
San Diego Field Office: (619) 662-7600

For public health concerns affecting San Diego County residents, please contact the Department of Environmental Health and Quality.

The Department of Environmental Health and Quality contact information and website:
San Diego County | Department of Environmental Health and Quality
5500 Overland Avenue, Suite 210
San Diego, CA 92123
Tel: (858) 495-5186

For information on the California Environmental Protection Agency (CalEPA) Border Affairs Program, which promotes interagency cooperation on environmental programs in California and Baja California, Mexico, please visit the CalEPA website.