San Diego Water Board moves to protect region from Tijuana wastewater flows after recent federal action

SAN DIEGO – Building on recent action by the federal government and Mexico, the San Diego Regional Water Quality Control Board today approved an order that will allow the federally operated South Bay International Wastewater Treatment Plant to increase treatment of flows from the current 25 million gallons per day of sewage (mgd) to 35 mgd. The order will help reduce dry weather sewage flows in the Tijuana River and aims to improve air and water quality for San Diego County communities that for decades have been burdened by transboundary untreated sewage flows and pollution. The order facilitates a recent memorandum of understanding between Mexico and the federal government, allowing the plant to expand treatment capacity.

the top priority for the San Diego Water Board. Binational agreements and funding commitments have focused on increasing the U.S. Section of the International Boundary and Water Commission’s (IBWC) and Mexico’s wastewater treatment capacities and enabling upgrades to aging pipelines. However, substantial amounts of untreated sewage, chemicals, bacteria and trash continue to flow from Mexico across the border, polluting San Diego County waterways and beaches.

“These waters are among the most impaired in California and have been our top priority since 2009 when we convened the Tijuana River Valley Recovery Team," said David Gibson, executive officer for the San Diego Water Board. "The temporary order will help protect sensitive ecosystems and nearby communities by expediting the IBWC's plant expansion. The board continues to work in close coordination with federal, state and local agencies and will keep using every tool in its toolbox to address transboundary flows of waste.”

On July 24, 2025, the federal government and Mexico reached a memorandum of understanding that outlines specific actions the countries will take to address the Tijuana River environmental crisis, including expanding the South Bay International Wastewater Treatment Plant’s capacity.

Wednesday’s order will allow the IBWC to expedite facility upgrades and significantly boost treatment capacity. The order maintains the board’s oversight over the plant to protect water quality and the IBWC must meet interim effluent limitations, comply with a time schedule of remedial and preventative actions, and submit documents regarding design, operation and maintenance of the system.

The board’s order, which supports the MOU, regulates the IBWC plant under the National Pollutant Discharge Elimination System permit, allowing the plant to exceed its effluent flow limitation of 25 mgd. If IBWC fails to comply with any provision of the order, the board may take any further action authorized by law.

For more information about the board’s work on Tijuana River water quality issues, please visit its website.

The San Diego Region stretches 85 miles of coastline from Laguna Beach to the U.S.- Mexico border and extends 50 miles inland to the crest of the coastal mountain range. Its growing population enjoys many water-related activities; however, the area receives little precipitation. About 90% of the water supply is imported from Northern California and the Colorado River.