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Last week fog crept over the Tijuana Estuary in Imperial Beach, oozing a pungent rotten-egg smell, as hydrogen sulfide bubbled up from the polluted Tijuana River.
Virginia Castellanos, the school nurse for Bayside STEAM Academy near the estuary, worried that students would get headaches, upset stomachs or breathing problems from the foul odor. She had another pressing concern: her own seven-year-old daughter was home sick with asthma, which flares up when pollution spikes.
“I’ve been having headaches and nausea this whole week,” Castellanos said. “The smell has been so bad. And I was already expecting my daughter to get sick and sure enough, in the last couple days, she’s showing symptoms and she said, ‘Mom, I need my inhaler.’”
Later that day, Thursday, March 19, air pollution monitoring data showed hydrogen sulfide levels at 500 parts per billion, more than 15 times the California state standard of 30 parts per billion. News reports stated that high temperatures last week, combined with cross-border sewage flows from a broken pump in a Tijuana sewage facility, contributed to the odor.
Castellanos had to leave work early the previous day to bring her daughter home, and expected to do so again Thursday to take her to the doctor. The risk went beyond the asthma attack itself; on previous occasions the respiratory distress progressed to pneumonia and weeks of illness.
“When I can smell it starting again I can guarantee you she’s going to get sick,” Castellanos said.
The symptoms that Castellanos sees among her students and her own family are common among residents of Imperial Beach and other parts of south San Diego affected by Tijuana River pollution.
When raw sewage enters the river in Mexico because of wastewater system failures or spills, the health impacts are felt across the border. Imperial Beach residents describe asthma, migraines, rashes, nausea, eye irritation, dizziness and brain fog when the sickening smell of hydrogen sulfide wafts off the water.
“The patients tell us,” said Dr. Kimberly Dickson, a physician who runs South Bay Urgent Care. “They come in and say ‘The air smells terrible, I need to use my inhaler more. The air smells terrible, I have headaches.’”
The foul odor often keeps children indoors, away from parks or beaches. At school it forces them to stay in the classroom and off the playground, and sometimes leaves them home sick. The coastal environment that drew many families to the seaside community has become a hazard.
“We like working and living here and having our kids in school close to home, but it is toxic,” said Bethany Case, an Imperial Beach resident, Surfrider volunteer and mother of two teenage sons. “We’re living in this beach community and we’re not living a beach life.”
Parents try to manage the effects of pollution by stocking inhalers, using air purifiers and limiting outdoor activity. But they wonder if the exposure puts children at risk of worse health problems in the future.
“They’re smelling this air, and they’re being exposed on a daily basis,” Castellanos said. “What kind of damage is happening to their lungs? What kind of damage is happening to their bodies, their eyes, their nose. We don’t know what’s going to happen down the line. What kind of health impacts are going to happen to these children?
A field trip, then a rash
For 9-year-old Alan Gonzalez, the problems started after a class visit to the estuary.
The salt marsh is the backyard to Bayside Academy. It’s a haven for wildlife, where egrets, ducks and other shorebirds wade in ponds dotted with aquatic plants. Western fence lizards sun themselves on the walkway, and cottontail rabbits dart through grass along the wetland.
On a recent nature walk, Alan and his classmates uprooted invasive flowers and planted native vegetation, said his mother, Farron Espinoza. He was uncomfortable when he got home, but he’s on the autism spectrum and has a hard time verbalizing his experience.
“The next day he was really upset and irritated,” and told her his whole body was itchy, she said. “So when I checked him he had a rash all over.”
Espinoza called Alan’s doctor, who diagnosed him with an allergic reaction and prescribed benadryl and topical lotion.
A week later, Alan was still distressed. He scratched so much he cut himself. Espinoza had to wrap him in hugs to keep his hands still.
“I couldn’t itch for a while, because my mom was threatening me to go to the doctor,” Alan said.
Espinoza eventually did take her son to see a doctor, who gave him a new diagnosis and a course of antibiotics.
“He did say that he’s seen other children with this kind of rash, and normally it’s because they had been to the beach and they were exposed to bacteria,” she said. “It has been foggy lately, so this can actually be airborne bacteria. Yes, they’re saying it could be aerosolized.”
Even after the rash subsided, it left Alan with new fears about the natural environment near his school and home. Espinoza had hoped to enroll him in a Saturday nature program where kids explore the estuary and learn about habitat and wildlife.
“He doesn’t want to do that anymore because he’s scared that he’s going to get a reaction.”
Health impacts on students
The Tijuana River has posed complicated challenges since the U.S. and Mexico began jointly managing its flows more than 80 years ago. A wastewater system on both sides of the border kept pollution in check for decades, but those facilities began to fail in the early 2000s, contaminating beaches and sickening swimmers and surfers. The problems escalated about a decade ago, following major spills from the dilapidated wastewater plants.
Unsafe conditions have closed parts of the Imperial Beach shoreline for three years, and in 2024, researchers revealed that the pollution could become airborne, confirming concerns of residents who complained of foul odors and baffling ailments.
“I didn’t notice the smell until it got really bad three years ago,” Castellanos said. “It never crossed my mind that it was coming from the sewage.”
As the problem escalated, the San Diego Health and Human Services Agency asked the Centers for Disease Control and Prevention to help measure it. There are no studies that comprehensively documented effects on schools and students, but two public health studies published in October, 2024 examined how sewage pollution from the Tijuana River was disrupting the lives of residents, including school aged children.
A CASPER study, or community assessment for public health emergency response, found that about 20 percent of households in the area reported disruption to school or work during the previous month due to sewage pollution, and nearly 8 percent had disruptions to daycare.
Another, called an ACE investigation, or assessment of chemical exposure, reported even more widespread problems. Nearly two-thirds of residents surveyed said their child missed work or daycare because of symptoms they believed were linked to the Tijuana River sewage crisis.
South Bay Union School District tracks pollution levels using monitoring data from the San Diego County Air Pollution Control District, Amy Cooper, an executive assistant to the superintendent, said in an email to CalMatters. The air district operates monitoring devices on district property near Berry Elementary, the campus closest to the source of pollution. Schools also received more than half million dollars from the air district to buy 199 air purifiers and a five-year supply of replacement filters.
When levels of hydrogen sulfide exceed state standards, officials call a “rainy day schedule” to keep kids in the classroom and run air purifiers in all indoor spaces, Cooper said. That’s what happened last Thursday, March 19, when the heat and pump malfunction triggered the sewer smell.
Public school funding is based on average daily attendance, so when students are absent because of pollution-related illness, that can mean lost revenue. Cooper said the district tracks illness-related absences based on what parents report, but a 2024 search of its database found no instances of “border sewage” or “sewage” as reasons given for absences.
“Since we are unable to attribute specific absences to the pollution crisis and we have no evidence that the pollution is directly impacting ADA, we cannot file to recoup ADA as we would do in the case of natural disaster like wildfire,” she wrote in an email to CalMatters.
Even when students remain in class, symptoms caused by hydrogen sulfide odor may interfere with learning, Dr. Dickson said.
“They’re walking to school in the middle of this and then they have brain fog when they get there,” she said. “And then they go to school and they’re expected to perform.”
Despite schools’ steps to mitigate pollution exposure, parents regret that their kids are missing opportunities for outdoor activity and adventure. Espinoza grew up in Imperial Beach, and recalls a childhood spent on the water, with beach field trips a regular part of her school schedule. She hoped Alan would enjoy the same opportunities.
“As a parent, you want your children to experience all the beautiful things that you had in your own childhood,” she said. “You try to kind of recreate those moments, and we really can’t do that. I really can’t take him to the bay because it’s dirty and it smells.”
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