U.S-Mexico Border Water Quality


  • On June 12, the State Water Resources Control Board Division of Financial Assistance launched the solicitation for the Proposition 4 United States-Mexico Border Grant Program. Proposition 4 (Prop 4) was approved by California voters in the general election on November 4, 2024. Among other funds, Prop 4 provided $50 million for grants to projects that will address water quality problems arising in the California-Mexico cross border rivers and coastal waters. The adopted guidelines are posted on the Division of Financial Assistance Prop 4 United States-Mexico Border Grant Program website.
  • At the June 10 meeting of the San Diego Water Board, staff from the United States section of the International Boundary and Water Commission (USIBWC) gave a presentation on Spill and Transboundary Flow Events, Influent Action Levels and Source Control Requirements, State of the Ocean, State of the Tijuana River Valley, and Update on the Expansion of the South Bay International Wastewater Treatment Plant. The meeting recording is available on the San Diego Water Board’s YouTube channel.
  • As of late May 2026, Non-profits Alter Terra and Rural Community Assistance Corporation (RCAC), have reported that the Tijuana River Trash Boom is functioning as expected, intercepting trash generated in Mexico, and preventing it from reaching the Tijuana River Estuary and Pacific Ocean. RCAC and Alter Terra report that the Tijuana River Trash Boom has intercepted over 1,500 tons of trash in the 2025-2026 wet season. This $4.7 million pilot project was funded by the State Water Resources Control Board to study the most effective mechanism for trash interception and disposal and to inform a more permanent solution in accordance with Project J in the June 2023 USIBWC-USEPA Joint Record of Decision for the Final Programmatic Environmental Impact Statement for the United States-Mexico-Canada Agreement Mitigation of Contaminated Transboundary Flows Project.
  • On May 14, the California-Mexico Border Relations Council met at the San Diego Water Board’s office. San Diego Water Board staff provided an update on water quality conditions in the San Diego – Tijuana Border Region and updated the Council on its permitting and interagency coordination in the Tijuana River Valley. The meeting recording is available on San Diego Water Board's YouTube channel.
  • As of late April, authorities in Mexico have partially restarted PB-CILA, a dry weather river diversion structure and pump station, which diverts dry weather flows in the Tijuana River to PB-1. From PB-1, flows are conveyed to the SBIWTP by gravity or pumped to the San Antonio de los Buenos Wastewater Treatment Plant. Flows greater than the San Antonio de los Buenos Wastewater Treatment Plant’s 18 MGD capacity are comingled with the treated effluent and discharged at the shoreline approximately 5 miles south of the international border Treated effluent from the SBIWTP is discharged approximately 3.5 miles offshore through the South Bay Ocean Outfall.
  • On April 17, San Diego Water Board staff joined the office of Assemblymember David Alvarez to visit the SBIWTP, Tijuana River Trash Boom, and San Antonio de los Buenos Wastewater Treatment Plant in Mexico. At San Antonio de los Buenos, Board staff heard an update from the State Public Utilities Commission for Tijuana (CESPT) regarding operations, future planning, and infrastructure improvements in Tijuana
  • On April 8, the San Diego Water Board adopted Order No. R9-2026-0005, amending USIBWC’s National Pollutant Discharge Elimination System Permit (NDPES Permit) for the SBIWTP. Order No. R9-2026-0005 updates USIBWC’s effluent limitations to authorize the advanced primary treatment of an additional 10 MGD of wastewater from Mexico. Order No. R9-2026-0005 also includes: 1) updated performance goals and influent action levels to reflect the higher volume of flow being treated at the SBIWTP; 2) a requirement for USIBWC to submit a Treatment Optimization Report to the San Diego Water Board by December 1, 2026, that evaluates treatment optimization to reduce pollutants in the blended effluent; and 3) changes to USIBWC’s Monitoring and Reporting Program to require weekly monitoring of fecal coliform and Escherichia coli (E. coli) at Dairy Mart Bridge. USIBWC’s amended NPDES Permit will remain in effect until the San Diego Water Board reissues the NPDES Permit. For the reissuance, San Diego Water Board staff will develop a tentative NPDES permit that authorizes the larger expansion to 50 MGD of full secondary treatment. Orders adopted by the San Diego Water Board are posted on the Board’s Adopted Orders website..
  • On April 3, San Diego Water Board staff presented to the Tijuana River Working Group, comprised of staffers from the State and federal legislative delegation from San Diego. The staff presentation focused on the 10-MGD accelerated incremental expansion of the SBIWTP and other efforts related to border water quality.
  • Agency for Toxic Substances and Disease Registry (ATSDR)
    • On June 10, the Agency for Toxic Substances and Disease Registry (ATSDR) shared the following fact sheet outlining their effort to evaluate potential health risks in the Tijuana River Valley.
  • San Diego State University (SDSU) School of Public Health Publications
  • Public Health Surveys
  • San Diego County Air Pollution Control District (SDAPCD)
  • U.S. Environmental Protection Agency (USEPA) Evaluation

    • USEPA conducted a preliminary evaluation of the Lower Tijuana River Valley for eligibility to be added to the National Priorities List (NPL) under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), also known as Superfund. This was in response to an October 24, 2024, petition from local elected officials to investigate the Tijuana River Valley for Superfund designation with the goal of obtaining federal resources to clean up hazardous substances and protect the health of people and sensitive environments.

      • On January 3, 2025, USEPA responded that further evaluation of the Tijuana River Valley was not warranted, in part, because contaminants detected in water and sediment samples do not exceed USEPA’s screening levels for protection of human health.

    Transboundary flows in the main channel of the Tijuana River and those that bypass canyon collectors in the Tijuana River Valley severely impact areas in and around Border Field State Park and the Tijuana River National Estuarine Research Reserve, including closure of access to Border Field State Park, invasive plant infestations, significant increases in mosquito populations, critically low dissolved oxygen levels in the Tijuana River Estuary, and reduced fish species and overall presence of fish.

    The U.S. International Boundary and Water Commission (USIBWC) collection and treatment facility consists of the following:

    • South Bay International Wastewater Treatment Plant (SBIWTP)
    • Five diversion structures (also referred to as canyon collectors) located at:
      • Stewart's Drain
      • Silva Drain
      • Canyon del Sol
      • Smuggler's Gulch
      • Goat Canyon
    • Two Pump stations:
      • Hollister Street Pump Station
      • Goat Canyon Pump Station
    • Two junction boxes:
      • Junction Box 1
      • Junction Box 2
    • South Bay Land Outfall
    • South Bay Ocean Outfall
    • Other associated infrastructure, such as the pipes and conveyances between the diversion structures, pump stations, and the wastewater treatment plant.

    Together, these comprise a federally-owned treatment works and are collectively referred to as the Facility.

    The SBIWTP may receive domestic and industrial wastewater from the following sources:

    • City of Tijuana’s municipal collection system;
    • Five canyon collectors: Stewart’s Drain, Canyon del Sol, Silva Drain, Smuggler’s Gulch, and Goat Canyon; and
    • Transboundary flows from other locations collected by vacuum trucks.

    SBIWTP influent is unlike influent at other wastewater treatment plants because the SBIWTP receives wastewater, sediment, and debris from a collection system in Mexico that USIBWC does not control. Lack of control over influent quality and flow rates puts the SBIWTP in a vulnerable state, necessitating ongoing corrective maintenance.

    The Facility is regulated under San Diego Water Board Order No. R9-2021-0001 as amended by Order No. R9-2023-0009, National Pollutant Discharge Elimination System No. CA0108928, Waste Discharge Requirements for the United States Section of the International Boundary and Water Commission South Bay International Wastewater Treatment Plant Discharge to the Pacific Ocean Through the South Bay Ocean Outfall (Order). The Order and reports required by the Order are available on the California Integrated Water Quality System Project (CIWQS) web page.

    In August 2024, USIBWC awarded a contract for a SBIWTP rehabilitation and expansion project. USIBWC has set a self-imposed deadline of December 2027 to complete the SBIWTP rehabilitation and expansion. The plant will remain in operation throughout design and construction. The project includes essential rehabilitation of existing infrastructure and capacity expansion to double treatment capacity of 25 MGD to reach 50 MGD average flow, with a peak hydraulic flow capacity of 75 MGD.

    On May 20, 2025, USIBWC and USEPA announced a planned 10-MGD expansion of the SBIWTP treatment capacity from 25 MGD to 35 MGD and projected completion and start-up within 100 days, by August 28, 2025. On August 27, 2025 the San Diego Water Board adopted Cease and Desist Order No. R9-2025-0139, which established interim effluent limitations for USIBWC’s 10-MGD expansion and requires compliance with USIBWC’s final permitted effluent limitations by June 30, 2026. In September 2025, USIBWC began treating up to 35 MGD of influent wastewater through advanced primary treatment followed by 25 MGD of secondary treatment using existing activated sludge processes. The advanced primary treatment consists of chemically-enhanced primary treatment (CEPT), using coagulants to increase solids removal. USIBWC blends up to 10 MGD of advanced primary effluent with the 25 MGD secondary effluent prior to discharge to the Pacific Ocean via the SBLO and SBOO.

    The July 2022 Minute 328 of the 1944 U.S.-Mexico treaty entitled Utilization of the Colorado and Tijuana Rivers and of the Rio Grande (1944 Water Treaty) and the USIBWC-U.S. Environmental Protection Agency (USEPA) June 2023 Joint Record of Decision (ROD) for the United States-Mexico Canada Agreement (USMCA) Mitigation of Contaminated Transboundary Flows Project both include the SBIWTP rehabilitation and expansion project, but the minute and ROD have different roles. Minute 328 is the agreement between Mexico and the U.S. that includes project responsibilities, such as operation and maintenance (O&M) and cost sharing. The ROD is what enables USEPA and USIBWC to proceed to the design phase for proposed projects.

    • Minute 320

      • The October 2020 International Boundary and Water Commission (IBWC) Minute 320 of the 1944 U.S.-Mexico treaty entitled Utilization of the Colorado and Tijuana Rivers and of the Rio Grande (1944 Water Treaty) establishes a framework of binational collaboration to address trash, sediment, and water quality issues in the Tijuana River Watershed. IBWC leads a Minute 320 binational core group and binational workgroups represented various stakeholder agencies, non-governmental organizations, and academia. These groups work to advance binational coordination/collaboration and projects to improve water quality and reduce trash and sediment loading in the Tijuana River Valley.

    • Minute 328

      • The July 2022 IBWC Minute 328 of the 1944 Water Treaty is an international agreement between Mexico and the U.S. that outlines 18 projects planned for 2022-2027 as well as seven potential projects for the unspecified future. The projects in Mexico include improvements to Tijuana’s wastewater collection and treatment systems to better manage wastewater and eventually reuse treated wastewater. Completion of this suite of infrastructure projects will provide benefit on both sides of the border, including reductions in wastewater in the Tijuana River Valley and Pacific Ocean. The public can access the U.S. International Boundary and Water Commission (USIBWC) Geographic Information System (GIS) web portal to view the location, description, and status of projects included in Minute 328.

    • USMCA Mitigation of Contaminated Transboundary Flows Project

      • The June 2023 USIBWC-USEPA Joint Record of Decision (ROD) for the United States-Mexico-Canada Agreement (USMCA) Mitigation of Contaminated Transboundary Flows Project contains ten proposed projects in Mexico and the U.S. aimed at reducing transboundary water pollution; four core project and six supplemental projects. The four core projects underwent a detailed analysis in the November 2022 USEPA-USIBWC USMCA Programmatic Environmental Impact Statement (PEIS). The six supplemental projects are still early in their planning phase and were not yet ready for detailed environmental review in the PEIS. To date, funding has not been identified for most of the ROD projects. Without full implementation of the projects needed to control transboundary flows, polluted water and trash are likely to continue to impact the Tijuana River Valley, Tijuana River Estuary, and coastal waters from the international border to the City of Coronado.

      Several of the projects specified in the ROD are the same as, or similar to, those included in Minute 328, but the minute and ROD have different roles. Minute 328 is the agreement between the two countries that includes project responsibilities, such as operation and maintenance (O&M) and cost sharing. The ROD is what enables USEPA and USIBWC to proceed to the design phase for proposed projects. Section 2.8 of the PEIS includes a comparison of USMCA and Minute 328 projects.

    • Minute 333

      • Minute 333 was signed by the US and Mexican IBWC Commissioners in December 2025 and calls for the following:

  • 1. The development of a new binational Tijuana River spill notification protocol to ensure notification of instances where, despite the use of best practices to avoid discharges into the river as required under existing Minutes and protocols, discharges of untreated wastewater to the Tijuana River occur.
  • 2. IBWC to establish an interagency binational Minute 333 Work Group and shall direct it to:

      • a. Evaluate the existing engineering and financial feasibility studies for possibly constructing an ocean outfall for the San Antonio de los Buenos Wastewater Treatment Plant (SAB WWTP) and, within 3 months of this Minute’s entry into force, make a recommendation to the Commissioners on additional studies and work that may be needed, who in turn shall make a recommendation to their respective Governments within 3 months thereafter about any potential actions that could be taken.

      b. Assess the technical and financial feasibility of expanding treatment capacity of the SAB WWTP from 18.26 MGD (800 lps) to 43.37 MGD (1900 lps).

      c. Evaluate supplementary treatment for the SAB WWTP effluent, and inform the Commissioners of the results of the evaluation within 12 months of this Minute’s entry into force.

      d. Prepare a scope of work within 3 months of the Minute’s entry into force in order to complete a mass balance flow analysis of the Tijuana water system, within 12 months of this Minute’s entry into force.

      e. Prepare a scope of work to develop a transparent, real-time binational monitoring system on flow inputs and outputs to the Tijuana River, taking into consideration interim monitoring efforts that could be established while the broader system is under development.

      f. Implement a systematic information exchange program on quality data of the effluent discharged by the wastewater treatment plants as soon as practical, within 6 months of the Minute’s entry into force.

  • 3. Prior to the start of the region’s 2026-2027 rainy season, the Government of Mexico shall construct a sediment basin in Matadero Canyon (Smuggler’s Gulch) in Mexico near the international boundary. The Commission shall oversee the adequate operation and maintenance of said sediment basin by the State Government of Baja California and the State Public Utilities Commission of Tijuana (CESPT).
  • 4. The Government of Mexico, through the State Government of Baja California, shall construct the Tecolote-La Gloria Wastewater Treatment Plant by no later than December 2028.
  • 5. The Mexican Section shall convene a workshop in Tijuana about stormwater management practices and control of construction runoff, within 6 months of this Minute’s entry into force, to evaluate best practices in the United States and Mexico that could potentially be initiated in Tijuana prior to the region’s 2026-2027 rainy season.
  • 6. The Commission shall identify different potential mechanisms and funding sources for implementation of sediment and solid waste control projects identified through the Minute 320 process, with a particular focus on projects that have long-term ownership and durability, and that highlight attention to transboundary Tijuana River basin issues. To that end, the Commission shall convene a Minute 320 Binational Core Group meeting within six months of this Minute’s entry into force.
  • 7. The Commission shall prepare a schedule and cost-sharing formula, prior to the region’s 2026-2027 rainy season, for sediment and solid waste removal from the Tijuana River channel, taking into consideration the areas adjacent to the international boundary under the jurisdiction of each Section, and, in consultation with the responsible institutions in the two countries, other areas of the Tijuana River.
  • 8. The Mexican Section shall share with the U.S. Section, within three months of this Minute’s entry into force, information pertaining to the potential additional water flows that would be introduced to the Tijuana wastewater system as a result of expanded water availability from the construction of the proposed desalination plant in Playas de Rosarito, B.C., and, if applicable, when any updated studies are undertaken, the Mexican Section shall share with the U.S. Section the relevant information within 3 months after the studies’ completion.
  • 9. The Commission shall coordinate with the binational O&M work group to develop strategies to ensure proper maintenance of the region’s sanitation infrastructure in order to extend its service life through the corresponding investments, including strategies related to the operating framework for the O&M account at the NADBank, as well as the identification of funding sources, financing structures, and implementation procedures. The Commission shall ask the Work Group to present recommendations to the Commission within 12 months of this Minute’s entry into force.
  • 10. The Government of Mexico, through the State Government of Baja California, shall prepare, within 6 months of this Minute’s entry into force, a scope of work for development of a Tijuana water infrastructure master plan, and, if considered necessary, shall coordinate this effort with NADBank. Once the scope of work is prepared and costs estimated to prepare the master plan, within 3 months thereafter, the Government of Mexico, through the State Government of Baja California, shall determine the means to develop the plan.
  • 11. The Commission shall make available to the public any data generated or obtained pursuant to the monitoring and information exchange program. The Commission shall establish suitable criteria by which information from the studies and projects from items 2.a), 2.b), 2.c), 2.d), 7, and 8 above may be made available to the public in both countries.
  • Please see USEPA’s website for Minute 333 for more information.

    • Three projects in the Tijuana River Valley were funded by Senate Bill 170 through the State Water Resources Control Board Division of Financial Assistance:

    • Tijuana River Flood Control Trash Control Structure ($4.73 million – Rural Community Assistance Center)
    • Smuggler’s Gulch Dredging Project ($4.25 million – County of San Diego)
    • Tijuana River Valley Hydrology and Habitat Restoration ($2 million – County of San Diego)

    Each of the three projects are deeply rooted in the 13 years of coordinated federal, State of California, local agency, and non-governmental organization efforts in the Tijuana River Valley Recovery Team to restore and protect water quality. They were originally proposed in the 2012 Tijuana River Valley Recovery Strategy: Living with the Water and refined and analyzed in the 2020 Tijuana River Needs and Opportunities Assessment Report.

  • Tijuana River Flood Control Trash Control Structure

      • The Tijuana River trash control structure project involves the design, construction, operation, and maintenance of a floating trash boom system for one storm season in the main channel of the river, immediately downstream of the international border. The Rural Community Assistance Center deployed the trash boom system and hosted a ribbon cutting ceremony on December 17, 2024. This is a demonstration project. The information gathered will be used to develop permanent trash control infrastructure (Project J of the June 2023 U.S. International Boundary and Water Commission-U.S. Environmental Protection Agency [USIBWC-USEPA] Joint Record of Decision (ROD) for the United States-Mexico-Canada Agreement (USMCA) Mitigation of Contaminated Transboundary Flows Project).

  • Smuggler’s Gulch Dredging Project

      • The Smuggler’s Gulch dredging project involved the removal of approximately 30,000 cubic yards of accumulated sediment, trash, and debris in Smuggler’s Gulch and the Tijuana River Pilot Channel. The accumulated sediment, trash, and debris contributed to flooding, which threatens public and private properties and critical habitats. In March 2024, the County of San Diego initiated trash and sediment removal activities, which concluded in late 2024. This dredging is necessary prior to installation of permanent sediment and trash capture infrastructure at Smuggler’s Gulch, which will be funded by a separate grant.

  • Tijuana River Valley Hydrology and Habitat Restoration

      • The Tijuana River Valley hydrology and habitat restoration project consists of remediating a contaminated seven-acre property adjacent to the Tijuana River and restoring it to native upland coastal sage scrub habitat. Demolition of on-site structures, soil preparation, irrigation installation, and planting are complete. Habitat restoration is underway with successful natural recruitment and minimal non-native plant species present.

  • Proposition 4

      • Proposition 4, which includes $50 million for border river pollution grants, was approved by California voters in November 2024. Funding will start in Fiscal Year 25-26.

    The U.S. International Boundary and Water Commission (USIBWC) owns the South Bay International Wastewater Treatment Plant (SBIWTP). Discharges from the SBIWTP are regulated by San Diego Water Board Order No. R9-2021-0001 as amended by Order No. R9-2023-0009, National Pollutant Discharge Elimination System No. CA0108928, Waste Discharge Requirements for the United States Section of the International Boundary and Water Commission South Bay International Wastewater Treatment Plant Discharge to the Pacific Ocean Through the South Bay Ocean Outfall (Order). The Order is available on the California Integrated Water Quality System Project (CIWQS) web page.

    When the San Diego Water Board adopted Order No. R9-2021-0001 on May 12, 2021, it also issued corresponding Cease and Desist Order No. R9-2021-0107 (CDO) to require USIBWC to address shortcomings, inadequacies, and maintenance issues at the SBIWTP to ensure consistent compliance with Order No. R9-2021-0001.

    On December 21, 2021, the San Diego Water Board adopted Order No. R9-2021-0220, amending the CDO to revise certain time schedules and require USIBWC to submit quarterly compliance assurance reports.

    On March 8, 2023, the San Diego Water Board adopted amendments to Order No. R9-2021-0001.

    On December 18, 2023, the San Diego Water Board issued Time Schedule Order No. R9-2023-0189 (TSO) for USIBWC to achieve compliance with secondary effluent limitations by August 15, 2024. USIBWC did not achieve compliance with secondary effluent limitations by that date. However, the SBIWTP has been in compliance with secondary effluent limitations since November 2024.

    On August 27, 2025 the San Diego Water Board adopted Cease and Desist Order No. R9-2025-0139, which established interim effluent limitations for USIBWC’s 10-MGD expansion and requires compliance with USIBWC’s final permitted effluent limitations by June 30, 2026.

    Additional enforcement actions related to the Order, including notices of violation (NOVs), are available in CIWQS.

    The San Diego Water Board developed the Lower Tijuana River Indicator Bacteria and Trash Advance Restoration Plan (ARP) to address water quality impairments through an implementation plan with actions to restore and maintain water quality standards.

    The ARP implementation plan proposes a memorandum of understanding between the San Diego Water Board, USIBWC, and USEPA to establish agreements, roles, and responsibilities to control transboundary sources of pollution within specified timeframes, respective jurisdictions, and respective funding allocation.

    Interested parties can sign up for the following San Diego Water Board email notifications at https://www.waterboards.ca.gov/resources/email_subscriptions/reg9_subscribe.html:

    • South Bay International Wastewater Treatment Plant – NPDES
    • Tijuana River Valley Recovery
    • SBIWTP
    • Spills and Transboundary Flow
    • Tijuana River Flow Rate
    • USEPA Tijuana River Website
    • USMCA Projects
    • Minute 328 Projects
    • Advance Restoration Plan

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