Every day, the Tijuana River spews millions of gallons of untreated sewage from Mexico into California, much of which ends up in the ocean. For decades, this steady churn of wastewater has overloaded aging infrastructure on both sides of the border, posing a major ecological and public health issue for communities in Tijuana and San Diego.
Last week, the two countries took a major step toward slowing the flow. On Thursday, U.S. Environmental Protection Agency Administrator Lee Zeldin and Alicia Bárcena Ibarra, Mexico’s secretary of the environment and national resources, signed an agreement that pledges to “address and solve the decades-long Tijuana River sewage crisis” through major updates to wastewater treatment plants at the border, according to the EPA.
“This is a huge win for millions of Americans and Mexicans who have been calling on us to end this decades old crisis,” Zeldin said in a statement.
Experts say wastewater infrastructure updates are crucial as populations continue to boom in cities like Tijuana and climate-fueled flooding triggers sewage overflows around the United States. However, these projects can be costly and time consuming. Delayed fixes leave many communities exposed to bacteria-laden waterways, particularly along the coast, where sea-level rise poses a dual threat to outdated infrastructure.
A Cross-Border Conundrum: The Tijuana River is widely considered one of North America’s most degraded waterways. The river winds through urban areas in Mexico, where communities dump sewage, trash and other waste directly into the water or onto the streets, where it can wash in during a storm.
There are two major treatment plants to remove solids, pathogens and contaminants from the sludge once it reaches the border area—the San Antonio de los Buenos treatment plant in Mexico and the South Bay International Wastewater Treatment Plant in San Diego. Both facilities have deteriorated in recent decades due to overuse and lack of funding, creating tensions between the U.S. and Mexico.
As I reported in 2024, the problem is especially bad during heavy rainfall events such as the atmospheric rivers that hit the West Coast that year. This deluge sent billions of gallons of sewage into San Diego, where local communities have reported high levels of gastrointestinal illnesses and other health problems in recent years that were most likely attributable to wastewater, according to the U.S. Centers for Disease Control and Prevention.
To help remedy the problem, Congress has appropriated hundreds of millions of dollars toward increasing capacity at the South Bay plant. In 2022, Mexico pledged $144 million to update its own plant but has failed to meet this target—a fact that Zeldin criticized at a press conference in April.
“There’s no way that we are going to stand before the people of California and ask them to have more patience and just bear with all of us as we go through the next 10 or 20 or 30 years of being stuck in 12 feet of raw sewage and not getting anywhere,” he said following a meeting with Mexican officials about the sewage issue. “Mexico needs to fulfill its part in cleaning up the contamination that they caused.”
Since then, the countries have “been working collaboratively to urgently finalize a permanent 100% solution to this longstanding issue,” according to an EPA statement. Under the new deal, Mexico will allocate $93 million toward sanitation infrastructure, and complete all projects by Dec. 31, 2027, while the U.S. pledged to release once-withheld funds to Mexico to rehabilitate a pump station and collection pipes that help treat sewage in the river.
Bárcena Ibarra said in a statement that the agreement “strengthens collaboration to address environmental and health challenges along the Northern border.”
California politicians praised the move but are wary.
“This agreement is a step forward in the right direction, but the reality is, South Bay communities are continuing to suffer every single day,” San Diego County Supervisor Paloma Aguirre told The San-Diego Union Tribune. The “agreement is a sign that our voices have been heard. I hope to see real progress in the next few months, and not the next few years.”
Widespread Waste: The majority of cities and towns in the U.S. have sewage systems with separate sets of pipes for wastewater and rainwater. However, roughly 700 communities across the country still have older systems that combine the two, which often overflow when the amount of runoff exceeds what the pipes can hold.
Then, instead of reaching a sewage treatment plant, the effluent and other contaminants discharge into the environment, where they can spread disease, trigger harmful algal blooms and kill local plants or coral.
The majority of these designs, known as combined sewer systems, are located in the Northeast and around the Great Lakes region, where severe flooding is becoming more common with climate change.
New York City frequently experiences this issue during storms, as my colleague Lauren Dalban reported in November. Around 60 percent of the city’s nearly 200-year network of sewer pipes are part of a combined system, which redirects to the Hudson River and its estuaries during overflows.
A 2024 study found that sea-level rise and increased precipitation from climate change can pose a double whammy for coastal cities with combined sewage systems. The researchers modeled these climate impacts in Camden, New Jersey, where the main waterways often contain fecal bacteria levels unsafe for swimming, fishing or kayaking.
As storms continue to intensify, cities are scrambling to update their infrastructure, but it’s an expensive endeavor (as the Tijuana situation illustrates). The Camden County Municipal Utilities Authority has taken steps in recent years to reduce the amount of sewage discharging into the environment, but Trump administration cuts to the EPA could threaten these gains, WHYY reports.
New York has implemented a mix of green and gray infrastructure plans, such as building retention tanks for stormwater and planting vegetation on roofs to help absorb excess rain. Boston, meanwhile, has taken more drastic steps by raising parts of the city’s Deer Island Wastewater Treatment Plant to avoid flooding from sea level rise, which can also corrode pipes.
One thing seems clear: We’re all going to be thinking a lot more about sewage in the coming years than we ever did before.
More Top Climate News
More than 150 million people across the central United States, the Midwest, the Southeast and the East Coast are under heat alerts as these regions face another heat dome, with similar conditions as those that baked much of the country in June. On Sunday, Tampa reached 100 degrees Fahrenheit for the first time since monitoring began in 1890, Jack Prator and Michaela Mulligan report for the Tampa Bay Times. Meanwhile, in the Midwest, the heat is feeding severe thunderstorms that could bring damaging wind and flash flooding from Montana to Iowa.
A new study found that data from iNaturalist—a popular citizen science app—has been used in more than 5,000 peer-reviewed papers since 2008, Emily Anthes reports for The New York Times. As I reported in June (with help from you readers), it’s widely known in the scientific community that crowdsourced biodiversity information can help track shifts driven by climate change, identify new plants and animals, track the spread of invasive organisms and offer other valuable data. This paper just adds more evidence to that notion.
“There exists this technology in our pockets that just absolutely opens [the world] up. The potential is insane,” Corey Callaghan, an assistant professor of global ecology at the University of Florida and co-author on the new paper, told me in June.
The National Science Foundation plans to end operation of the RV Nathaniel B. Palmer, the only U.S. research vessel with the ability to reach the most remote areas of Antarctica and the Southern Ocean, Paul Voosen reports for Science magazine. The ship has helped researchers study areas that are extremely vulnerable to changes in the climate, and track how warming waters contribute to the melting of Antarctica’s ice sheet. On Monday, more than 700 scientists sent NSF and Congress a letter pushing back on what they called a “troubling” move. They urged a reconsideration of the decision.
“Even as automation and remote observations have increased our observational capabilities in this harsh region of the world, there’s no replacement for a dedicated research vessel that can access remote sea ice-covered regions of Antarctica and that allows sampling of the full depth of the ocean and coastal regions on land,” the researchers wrote in the letter.
Postcard From … Florida

For this week’s installment of “Postcards From,” our reader Noemi sent a verdant photo of wetlands in Florida at the Green Cay Nature Center and Wetlands near Delray Beach.
“I am a recent transplant to Florida so not yet used to how different nature presents itself here. We lived on City Island, the Bronx, New York for 25 years and we had wetlands as our border with the backyard but it’s a lot different from what south Florida has to offer. We had [raccoons] instead of alligators for one,” she said in an email.
“Some of the parks, waterways, and protected nature preserves here in Delray Beach are places of awe. I am becoming aware of how fragile these places can be and feel blessed to be able to enjoy so many sites close by.”
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