About 30 residents of San Ysidro rallied Tuesday outside Smythe Elementary School to demand action on raw sewage flowing from Tijuana into the Tijuana River Valley. The protest came one day after San Diego County’s Air Pollution Control District confirmed that hydrogen sulfide, a toxic gas produced by decomposing sewage, hit 384 parts per billion over a four-hour stretch on the night of April 5. That reading exceeded the federal acute exposure guideline of 360 ppb. Some readings reached 400 ppb in recent days, with the worst concentrations recorded during nighttime and early morning hours.
Protesters carried signs reading “We want clean air” and “We can’t breathe.” Most live near Coral Gate Park, Sunset Avenue, and Smythe Avenue, all within a few hundred meters of the Tijuana River channel on the U.S. side. A monitor at Berry Elementary School, less than 800 meters from the river, captured the elevated readings. County officials noted that a drop in elevation at that point creates a waterfall effect in the sewage flow, generating foam and intensifying gas emissions into the surrounding air.
Tijuana Sewage Spill Crisis Dates Back Decades
Cross-border sewage from Tijuana has contaminated the Tijuana River Valley for more than 100 years, but the problem has worsened dramatically since the early 2000s as Tijuana’s population grew faster than its wastewater infrastructure. CESPT, Tijuana’s municipal water and sewer utility, operates a system built for a city far smaller than today’s estimated 2.2 million residents. Aging pipes, illegal sewer connections, and frequent equipment failures mean millions of gallons of raw or partially treated sewage flow into the Tijuana River and its tributaries each year.
The International Boundary and Water Commission (IBWC), the binational body responsible for managing shared waterways along the U.S.-Mexico border, operates the South Bay International Wastewater Treatment Plant in San Ysidro. That plant was designed in the 1990s to handle 25 million gallons per day of Tijuana sewage diverted before it reached the ocean. But the volume of cross-border flows regularly exceeds that capacity, and dry-weather spills send untreated waste directly into the river channel.
In 2024, the U.S. EPA broke ground on a $620 million expansion of the South Bay plant, funded in part by the 2021 bipartisan infrastructure law. That project aims to boost capacity to 60 million gallons per day and add secondary treatment. Construction is expected to take several years. In the meantime, the existing plant continues to operate beyond its design limits.
Paloma Aguirre, San Diego County Supervisor for District 1, confirmed that since 2024 multiple U.S. agencies, including environmental regulators, public health departments, and water quality authorities, have coordinated on the cross-border sewage problem. Aguirre, a former mayor of Imperial Beach, said the county has committed $2.5 million for immediate work at a critical discharge point on Saturn Boulevard, identified as a major source of gas emissions.
But Aguirre stressed that a permanent fix requires a state and federal emergency declaration to unlock larger funding streams. “Our children, with developing brains and lungs, are breathing unsafe air on their way to school,” she said in a video posted on her social media accounts.
Hydrogen Sulfide at 400 ppb Poses Real Health Risks at the Border
Hydrogen sulfide is the rotten-egg smell familiar to anyone who has driven through the Tijuana River Valley on a warm morning. At low concentrations (below 30 ppb), it is mainly a nuisance. Above 100 ppb, it can cause eye irritation, coughing, and headaches. At the 384 to 400 ppb range recorded last weekend, prolonged exposure can trigger serious respiratory distress, especially in children, elderly residents, and people with asthma.
If you cross through the San Ysidro Port of Entry during early morning hours, you may encounter these elevated levels. The port sits roughly 2.5 kilometers west of the Tijuana River channel. Pedestrian and vehicle wait times at San Ysidro often exceed one to two hours, meaning border crossers can spend significant time outdoors in the affected air shed. County officials have advised residents to stay indoors during high-contamination episodes, use air purifiers, and limit outdoor activity.
Readings dropped sharply to 5 ppb by the morning of April 6, showing how volatile conditions can be from one hour to the next. The county maintains continuous monitoring at Berry Elementary and other stations in the valley.
Olga, one of the protest organizers, told reporters the group plans to rally every two weeks at locations across San Ysidro until California Governor Gavin Newsom and San Diego Mayor Todd Gloria respond. The next demonstration has not yet been scheduled. This story was first reported by Punto Norte.