What this does to people

People in Imperial Beach, Nestor, San Ysidro, and nearby neighborhoods have reported headaches, nausea, coughing, and other symptoms for years. Surveys and research since 2024 have started to document what residents describe, though long-term effects are still being studied.

This page summarizes public research and health guidance. It isn't medical advice. If you have symptoms, talk to your doctor and mention where you live and any exposure.

How exposure happens

• Water contact. Swimming, surfing, or wading in sewage-contaminated water. Researchers have found viruses, antibiotic-resistant bacteria, and hundreds of chemicals, including pesticides, solvents, and flame retardants, in water sampled in the region.
• Sea spray. Research led by San Diego State University and Scripps found that bacteria and chemicals from sewage-polluted water can become airborne in sea spray and travel inland, well beyond the shoreline.
• Hydrogen sulfide. Churning sewage releases this gas, recognizable by its rotten-egg smell. Levels in the Tijuana River Valley have been measured far above typical urban air. Research published in Science found that high sewage flows and low winds push levels up.

What residents are reporting

• CDC and county survey, 2024. In October 2024, the CDC and San Diego County interviewed residents of 189 households near the Tijuana River Valley. Residents reported nausea, headaches, and coughing, and 62% reported respiratory symptoms.
• San Diego State University survey, 2024 to 2026. More than 500 people in Imperial Beach, Nestor, San Ysidro, and as far north as Coronado and National City took the Healthy Water, Healthy Air survey. Researchers reported nausea, headaches, brain fog, stomach issues, anxiety, tiredness, and sleep problems. In an earlier summary, 76% of participants reported respiratory issues, over 90% reported poor air and water quality, and about three-quarters had cut back on outdoor activity.
• Local doctors. A San Diego pediatrician has organized a network of hundreds of local physicians to document pollution-related problems, including ear infections, allergic rhinitis, skin rashes, and gastrointestinal illness.
• Schools. School staff in Imperial Beach have described students with headaches, asthma flare-ups, rashes, and trouble concentrating on bad odor days.

These surveys record what people report; they don't by themselves prove what caused each symptom. That's what the studies below are designed to find out.

What's still being studied

• A second CDC and county survey began in September 2026 to see how residents' health has changed since 2024.
• A UC San Diego exposure study, started in 2026 with the county, is identifying and modeling the airborne chemicals of concern and where exposure is highest.
• A retrospective study planned by the county will look for evidence of serious health effects from past exposure.

How to protect yourself

When hydrogen sulfide levels are high, San Diego County recommends:

• Limit outdoor activity if odors are bothersome.
• Keep doors and windows closed while odors are present, and air out your home once they improve.
• Use fans or air conditioning on recirculation mode.
• Run an air purifier with a HEPA filter and activated carbon with potassium permanganate, which works well for hydrogen sulfide. The California Air Resources Board lists verified models.
• If you have asthma, COPD, or another lung condition, keep rescue medication on hand.
• Contact your doctor about persistent or worsening symptoms, and seek emergency care if symptoms feel life-threatening.

You can sign up for county air district alerts by email or text when hydrogen sulfide passes 30 parts per billion. Households in eligible South Bay neighborhoods may qualify for free air purifiers through the AIRE program. For the water, check Is it safe today? and the county's beach status before any contact, and stay out for at least 72 hours after rain.