San Diego County District Attorney Summer Stephan has filed a formal request with Mexico's federal environmental protection agency, seeking records on whether Tijuana industrial businesses with American ownership are contributing to the pollution fouling local waterways. The request targets inspection reports, enforcement actions and pollution complaints covering nearly four years, from January 2023 through September 2026.
The records request went to Mexico's Federal Attorney for Environmental Protection, known by its Spanish acronym PROFEPA, which functions as that country's counterpart to the U.S. Environmental Protection Agency. According to the San Diego County District Attorney's Office, the office is seeking inspection reports, technical findings, administrative proceedings, fines, warnings, closures and citizen complaints tied to potential illegal discharges or improper hazardous-waste handling that affect the Tijuana and Alamar rivers. As NBC 7 San Diego reported, the office is specifically examining whether Tijuana industrial businesses with U.S. ownership or parent companies contribute to cross-border pollution affecting San Diego County.
Stephan framed the cross-border dynamic in blunt terms, drawing a comparison to ordinary street crime that happens to cross a border. She said environmental violations that cross into San Diego County and harm the region's water, air and people carry consequences locally, likening jurisdiction over pollution violations to jurisdiction over a robbery that began in Mexico and continued into San Diego County. Her office also said it might be able to investigate companies with U.S. parent companies or ownership interests, calling the records request an important step toward identifying and gathering evidence on maquiladoras with U.S. financial interests, according to the same statement obtained by Times of San Diego.
A Coastkeeper Report Sparked the Request
The push traces back to findings published September 10 by San Diego Coastkeeper, a nonprofit environmental organization whose 2025 Tijuana River Valley Water Quality Monitoring Report documented chronic contamination in the watershed. The DA's office cited that report when announcing its records request, pointing to its identification of industrial and chemical pollutants in Tijuana River water.
Coastkeeper's monitoring, conducted monthly at two to four sites depending on flow conditions, found sewage contamination, chemical pollutants and aquatic-life threshold exceedances that remain chronic and widespread across the lower watershed and estuary, the organization said in its own release. E. coli levels at all four monitoring sites were often so high they exceeded the laboratory's measurable range for most of the year, per the same report. The 2025 water quality report also attributed some of the pollutants to Tijuana factories known as maquiladoras, saying the facilities discharge pollutants directly into surface waters or into the sanitary sewer system, sometimes because of inadequate wastewater treatment at the factories themselves.
What the Water Testing Turned Up
Coastkeeper's sampling identified volatile and semi-volatile compounds including heavy metals, pesticides, PFAS, acetone, phenols and benzoic acid in the river. A closer look at the chemical data, reported by the San Diego Union-Tribune, found that each sampling event typically turned up 10 to 20 different industrial chemicals, though the specific mix varied by event and location. No organochlorine pesticides were detected, the Union-Tribune reported, but pyrethroid pesticides including cypermethrin and permethrin exceeded toxicity thresholds whenever they were found.
San Diego Coastkeeper's senior attorney told KPBS, “We certainly hypothesize that… a lot of them are coming from maquiladoras on the Mexican side of the border,” while cautioning that the report did not pin down specific sources with certainty. The same KPBS interview noted that even if the binational wastewater treatment system worked exactly as designed, an estimated 20 million to 30 million gallons of sewage would still go untreated and end up in local waterways.
Billions of Gallons, Decades of Frustration
The Tijuana River carries billions of gallons of sewage into San Diego County every year, a flow that officials say jeopardizes the health of South Bay residents. State water-quality records have documented tens of billions of gallons of transboundary flow in the river, and the DA's office noted that wet-weather events can worsen the region's longstanding cross-border pollution crisis by sweeping untreated sewage, trash and other contaminants toward San Diego County communities and coastal waters. The International Boundary and Water Commission reported that thunderstorms in August caused increased transboundary flows that residents near the border could notice firsthand.
The scale of the problem has drawn outside researchers as well. A 2025 study cited by Voice of San Diego measured peak hydrogen sulfide concentrations in the Tijuana River Valley at roughly 4,500 times what would be expected in an average U.S. city, and the same researchers identified hundreds of other toxic gases rising from the polluted river and its ocean outflow. A 2024 survey found that 69 percent of respondents reported health problems they associated with the pollution, according to that outlet's reporting.
Infrastructure Fixes Lag Behind the Chemistry
Binational efforts to address the sewage crisis have focused mainly on treatment capacity rather than industrial chemicals. The United States and Mexico signed Minute 333 of the International Boundary and Water Commission in December 2025, an agreement that included funding for operations and maintenance, a Tijuana infrastructure master plan, and a feasibility study to expand the San Antonio de los Buenos treatment plant from 18.26 million to 43.37 million gallons per day, per the Union-Tribune's reporting.
But the region's main treatment facility, the South Bay International Wastewater Treatment Plant, was built to handle sewage, not the industrial chemicals and heavy metals Coastkeeper's testing has found, Voice of San Diego reported. The plant is designed to treat 35 million gallons a day, yet it sustained flows above 45 million gallons a day for 13 hours during a Tijuana pipeline repair in June, according to the International Boundary and Water Commission.
What the DA's Office Can Actually Do
The District Attorney's Environmental Protection Unit investigates and prosecutes cases involving the unlawful treatment, transportation, storage and disposal of hazardous materials and wastes, as well as discharges that affect the quality of California's waters, according to the office's own description of its environmental programs. The unit can also pursue civil complaints to halt ongoing violations and seek monetary penalties where appropriate.
For now, the office says it is evaluating whether potential environmental and consumer-protection violations tied to the Tijuana pollution fall within its enforcement authority and what legal options might follow. No findings have been announced naming specific companies or facilities, and whether PROFEPA will turn over the requested records remains an open question.
