Water-quality prospects on the western end of the U.S.-Mexican border brightened in 2022, when a lawsuit involving a binational wastewater-treatment plant ended in a settlement featuring a multiyear plan to reduce cross-boundary water pollution carried by the Tijuana River.

Two years later, however, U.S. and Mexican residents are complaining about off-the-charts water pollution flowing north from Tijuana into the Pacific Ocean—the consequence, critics say, of an ongoing failure to implement infrastructure improvements called for in the settlement. “It has definitely gotten worse here since we filed that lawsuit,” says Sarah Davidson of the Surfrider Foundation, one of the plaintiffs in the suit.

The 2022 settlement was reached with the U.S. section of the International Boundary and Water Commission (USIBWC), which owns the South Bay International Wastewater Treatment Plant. Located in San Diego County, the plant processes wastewater from Mexico before discharging it into the Pacific Ocean. At the time of the 2022 settlement, the facility’s capacity to treat the fast-growing waste stream from Tijuana had long since been exceeded.

U.S. government plans affirmed in the settlement call for expansion of the plant so that it can treat 50 million gallons per day (MGD)—double the current level—and handle peak flows up to 75 MGD. The Good Neighbor Environmental Board, a federal committee that advises the White House on U.S.-Mexican border issues, estimates the expanded plant will reduce flows of untreated wastewater into the ocean by 80% once the project is completed in late-2027.

In Mexico, meanwhile, the government is replacing a non-functioning wastewater treatment facility—the San Antonio de los Buenos plant in Punta Banderas, on the coast southwest of Tijuana—with a new one that will have a capacity of 18 MGD.

Concern about crossborder flows of untreated wastewater overwhelming the region’s infrastructure capacity has deepened in recent years. In 2020, US$300 million for upgrades to the South Bay international wastewater plant was included in the United States-Mexico-Canada Agreement (USMCA), the three-nation accord that replaced the North American Free Trade Agreement.

U.S. and Mexican authorities in 2022 signed Minute 328, a binational infrastructure agreement that reaffirmed the call for expansion of the plant and for the execution of other environmental-infrastructure improvements. Meanwhile, official estimates of the overall cost of getting untreated wastewater flows under control rose from US$627 million in 2021 to US$801 million in 2022. Then last year they climbed to $900 million, with some experts saying $1 billion or more would be needed when maintenance and operations expenses are figured in.

Thus far, Mexico and the United States have committed at least US$574 million collectively to make the necessary environmental-infrastructure improvements. That includes the $300 million in U.S. funds earmarked for the South Bay plant in the USMCA and $144 million that Mexico pledged in Minute 328 to put toward replacement of the San Antonio de los Buenos plant.

For Stephen Mumme, a border-water-policy expert and former political science professor at Colorado State University, the ecological crisis and accompanying legal and financial scramble follows a familiar pattern stretching back some 80 years.

“The money comes in increments; there’s a [funding] authorization, but not an appropriation,” says Mumme, author of a 2023 book on U.S.-Mexican border water issues and accompanying environmental campaigns, lawsuits, infrastructure boondoggles and budget battles. “It’s dribs and drabs.”

Mumme recalls cross-border water pollution ranked high on the agenda of a 1979 summit between then-U.S. President Jimmy Carter and his Mexican counterpart, José López Portillo. He notes that in 2008, a binational Tijuana River Valley Recovery Team was formed, comprising representatives of 45 Mexican and U.S. public agencies and non-governmental groups.

Referring to the USMCA provision that earmarked US$300 million for border environmental infrastructure, Mumme adds: “It seemed to me that it was going to be inadequate because that’s the history of the thing—everything is inadequate.”

Indeed, climate change and inflation in the U.S. and Mexico and population growth in and around Tijuana have only further stressed the binational wastewater system. Last year’s Hurricane Hilary and other intense rain events overwhelmed aging wastewater infrastructure on both sides of the border. A single, severe storm this January pushed 14.5 billion gallons of “sewage-tainted” wastewater to a point just south of Imperial Beach in San Diego County, says Paloma Aguirre, the city’s mayor.

“It has been incredibly devastating for us,” Aguirre says. “We are a tourist-dependent economy. Our beaches have been closed this year and every day last year.”

The pollution has forced cancellation of public events, hurt small business, disrupted a youth camp, and created a health hazard for Border Patrol and U.S. Navy personnel. Meanwhile, storms have washed trash onto the Tijuana River floodplain, leaving a landscape that “looks like a bomb of plastic and styrofoam went off,” Aguirre says.

The problem goes beyond raw sewage and trash. Analyses of Tijuana River and Estuary soil sediments by San Diego State University (SDSU) and other organizations have detected more than 170 organic chemicals and inorganic elements, including polychlorinated biphenyls (PCBs) and the banned pesticides chlordane and DDT.

SDSU researchers found 392 organic chemical contaminants in border-area water. They also identified “significantly elevated levels” of microbes carrying antibiotic resistant genes and resistant strains of E. coli and Legionella. And they said they identified several other pathogens linked to “significant illness,” calling for “increased surveillance of a broader range of pollutants.”

Both Davidson and Mayor Aguirre consider the pollution an environmental injustice for Imperial Beach, which has a large low-income and majority Latino population and is the community hardest hit by the pollution. Increasingly, residents and public health experts are expressing alarm. Other San Diego County communities report impacts linked to river pollution, including Coronado and San Ysidro.

San Diego County’s Health and Human Services Agency says over 100 billion gallons of wastewater have flowed into the county from Mexico since 2018, with 58 billion of that amount registered between Dec. 28, 2022 and Feb. 13, 2024.

Exposure to water with high concentrations of bacteria can trigger serious gastrointestinal disorders, skin rashes and other maladies. In recent reports by the Scripps Institution of Oceanography at UC San Diego and SDSU, environmental-health researchers discuss how pollutants in ocean water can move into the atmosphere as sea-spray aerosol and pose public-health threats inland of the beach.

The SDSU report described a stew of harmful viruses, bacteria, parasites, and toxic chemicals as a “pressing public health crisis.” Citing an “emerging zoonotic pathogen of concern,” it noted that stranded bottle-nosed dolphins found on San Diego County beaches have died from sepsis caused by the bacterium E. rhusiopathiae. The bacterium is typically transmitted through exposure to food, water, or soil contaminated with feces or urine.

The ocean waters affected by pollutants from the Tijuana River host birds, cetaceans, sea turtles, rays, sharks, octopi, and many varieties of fish. Moreover, the Tijuana Estuary, through which sewage-tainted Tijuana River waters flow into the sea, is an internationally recognized Ramsar site. The largest coastal wetland in Southern California, it provides habitat for wildlife that includes over 370 bird species, some of them endangered.

The environmental crisis has prompted citizens’ groups and California elected officials including the state’s governor, Gavin Newsom, to demand action. Some have called for additional federal funding for wastewater-infrastructure upgrades, others for President Biden to declare an emergency in the San Diego area, and still others for both steps.

On April 11, two advocacy groups, San Diego Coastkeeper and the Coastal Environmental Rights Foundation (CERF), filed a federal lawsuit over the wastewater pollution. They charged the USIBWC and the agency subcontractor that operates and maintains the South Bay plant—Veolia Water North America-West LLC—with more than 500 violations of the South Bay facility’s Clean Water Act discharge permit.

“The historical patchwork of funding and planning clearly hasn’t worked,” says Marco Gonzalez, CERF’s executive director. The government, he says, needs to act with a “sense of urgency.”

San Diego Coastkeeper’s Executive Director Phillip Musegaas says securing court monitoring of the USIBWC facility is a major objective of the litigation.

In April, the U.S. conservation organization American Rivers named the binational Tijuana River the ninth most endangered river in the United States in the latest version of its annual list of the 10 most endangered U.S. rivers.

“I’ve been working on water pollution issues for 20 years, and this is the worst I’ve seen,” Musegaas says. “It’s something like the 1950s before we had the Clean Water Act or any regulation of water pollution.”

Maria-Elena Giner, the U.S. commissioner of the IBWC, says the binational agency is spending $27 million for urgent repairs at the binational plant. “The goal is to achieve plant compliance with environmental regulations by August,” Giner said in a March press release.

Giner, who assumed office in 2021, has since told the USIBWC-sponsored San Diego Citizens Forum that the USIBWC was underfunded from 2010 to 2020, one reason why the South Bay plant has been “very vulnerable.” Said Giner: “This agency is largely catching up...We have to move from a reactive mode to a preventative mode.”

Driving the ecological pressure is the relentless growth of Tijuana’s population, which surged from 747,381 in 1990 to 1,922,523 in 2020. Virtually all of this growth stems from the city’s role both as a migration corridor to the United States and as an important manufacturing hub for its more affluent northern neighbor.

Oscar Alberto Pombo, a retired researcher from Tijuana’s Colegio de la Frontera Norte, says official census numbers underestimate Tijuana’s actual population, which he reckons is 2.2 to 2.5 million.

Untreated sewage from Tijuana does not just affect U.S. coastal areas at the mouth of the Tijuana River. It also impairs Tijuana’s own beaches and those south toward Rosarito. A prominent culprit on that score has been the long-troubled San Antonio de los Buenos plant, which was slated for replacement under Minute 328 and the cleanup plan unveiled two years ago.

A Baja California citizens’ group, Border Environmental Education Project (Peaf) conducts weekly sampling of five popular Tijuana-Rosarito coastal locations, rating recreational waters based on World Health Organization standards for fecal coliform bacteria. Testing over a 29-week period ending on May 23, 2024, found only two weeks in which all five beaches were suitable for recreational activity.

Work on the San Antonio de los Buenos plant has been fast-tracked by the Mexican government. A groundbreaking ceremony held in January was attended by Baja California Governor Marina del Pilar Ávila and U.S. Ambassador Ken Salazar. Spearheaded by Mexican Army engineers, the project is scheduled for completion on Sept. 30.

Pombo concurs that overhauling the Mexican plant will improve ocean water quality south of Tijuana. But another challenge that needs addressing, he says, concerns non-functioning small sewer plants in Tijuana that are connected to housing subdivisions whose developers went bankrupt and abandoned upkeep.

Many of these subdivisions are still inhabited, so untreated sewage flows through the idled treatment plants into ponds, creeks and canyons, ultimately reaching the Tijuana watershed. When it comes to wastewater, Pombo says, the so-called ghost plants are “possibly the biggest problem in the city right now.”

Amid such challenges, calls for definitive solutions have grown louder in both Mexico and the United States. A sign of partial progress came on March 23, when U.S. President Joe Biden signed a federal budget containing US$103 million in additional funds for the USIBWC to address the Tijuana River pollution crisis. The budget bill also authorizes the USIBWC to seek additional, more diverse sources of funding from multiple federal agencies, state and local governments, and nonprofits.

Border-wastewater-treatment advocates are pushing hard to make more progress. On April 14-17, some 170 civic leaders from San Diego County and the Mexican state of Baja California visited Washington, D.C. to meet with federal officials, the Tijuana River water-quality crisis high on their agenda.

Imperial Beach Mayor Aguirre, one of the participants, says she is pressing for increased funding for expansion of the South Bay treatment plant, on-time replacement of Mexico’s San Antonio de los Buenos plant by fall, and a state of emergency declaration by Biden.

For his part, Mumme, the emeritus Colorado State University professor, favors more fundamental action: organizational reform to boost joint U.S. and Mexican capacity for strategic thinking, long-term planning, and operational implementation. Specifically, he advocates creating a dedicated, binational sanitation authority to lead this work.

Without that capability, Mumme argues, Mexico and the United States might forever be “chasing the problem of the minute, solving yesterday’s problem, and not being adequate to the dynamics along the border.”