South Bay residents affected by sewage gases from releases along the Tijuana River reported multiple health symptoms – including headaches, insomnia and trouble concentrating – according to a preliminary study conducted by San Diego State University.
Researchers said 514 people completed surveys and this spring 75% reported headaches, over 50% reported trouble sleeping and brain fog with approximately 45% reporting difficulty concentrating.
An SDSU research team led by Paula Stigler-Granados, associate professor and chair of Environmental Health in SDSU’s School of Public Health, conducted the study.
The colorless, toxic hydrogen-sulfide gas is often described as having a rotten egg odor, but Stigler-Granados said she experiences it “more like burning, rotten tennis shoes.”
“Whatever it is,” she added, “it affects everybody a little differently. I think that’s the most important thing to understand.”
The nightly infiltration of gases stems from untreated Tijuana sewage that has overwhelmed Mexican infrastructure as well as a treatment plant on the U.S. side of the border.
On July 7, researchers presented early findings from the Healthy Water, Healthy Air Survey collected over the last 18 months from people living or working in the South Bay regions of San Diego County. The majority were located in Imperial Beach, the San Diego Border and San Ysidro. There were 19 submissions from Coronado.
Stigler-Granados said there were some reports of odor in Coronado, but most complaints were from residents along the Tijuana River. “But, definitely, the pollution is in the water at Coronado Beach and it’s been closed multiple times in the last several years,” she added.
The survey asked about respiratory symptoms, concerns about air and water quality, stress symptoms, lifestyle changes and allergies.
According to Stigler-Granados, during the winter of 2025 almost 80% of survey respondents said they limited their time outdoors.
“Reduced time outdoors corresponds with people smelling frequent odors and also with perceiving the air quality to be poor,” she said.
According to researchers, half of the respondents reported respiratory symptoms this summer.
Stigler-Granados said headaches were the number one issue. Other symptoms included agitated behaviors and loss of appetite.
The research team, according to Stigler-Granados, is analyzing linkages between the health experiences and hydrogen sulfide.
Across water, air, and soil samples, the team found a diverse mix of contaminants in the Tijuana River that can be traced to industrial waste, agricultural runoff and untreated sewage.
“We found about 350 tentative compounds and, of those, several of them are quite toxic,” said Stigler-Granados. “We really want to understand those a little bit better.”
“We’re definitely finding the highest airborne contamination signature at the Saturn Boulevard hotspot where it’s becoming aerosolized,” she added.
Stigler-Granados said the team plans monthly online sessions beginning in August to talk about environmental pollution and how it’s impacting communities.
Tijuana wastewater pollution has contaminated south San Diego County for decades causing beach closures, health problems for residents and economic impacts. The U.S. and Mexico have signed agreements and allocated funding to resolve the crisis, noting that work is underway but could take years to complete.
“I personally have not seen this much national and state and local attention to this issue since I’ve started dealing with it 20 years ago. And so are we closer? I think we’re moving that direction,” said Stigler-Granados. “Keep talking with the researchers, keep talking with your local advocacy groups and community politicians, ask them to do something. That’s the best we can do right now.”
To learn more about the study, visit: http://tjriver.sdsu.edu.
