SAN DIEGO (AP) — A persistent odor of rotten eggs hangs over Steve Egger’s home in Southern California, especially after dark when the nearby Tijuana River churns with sewage flowing north from Mexico before reaching the Pacific Ocean.

Egger, 72, says he and his wife frequently suffer from headaches and often wake up congested, coughing up mucus. Their house is equipped with a hospital-grade air filtration system that circulates indoor air every 15 minutes.

Even with those precautions, “most nights we’re breathing in a terrible smell,” he said. “It’s unbearable.”

Since 2018, more than 100 billion gallons (378 billion liters) of untreated sewage mixed with industrial chemicals and trash have surged through the Tijuana River, according to the International Boundary and Water Commission. The river crosses land where three generations of Egger’s family once operated a dairy farm. Last year, the United States and Mexico reached an agreement to address the chronic pollution by modernizing wastewater treatment plants to handle Tijuana’s growing population and factory waste, much of it generated by U.S.-owned companies.

Steve Egger stands near what scientists refer to as the “Saturn hot spot,” a stretch of the Tijuana River where polluted water gushes from pipes and forms foamy pools near his home Friday, March 6, 2026, in San Diego. (AP Photo/Gregory Bull)

In the meantime, tens of thousands of residents continue to be exposed. During a February visit to San Diego, Environmental Protection Agency Administrator Lee Zeldin said resolving what has become one of the nation’s longest-running environmental crises could take about two years. The burden has fallen largely on a low-income, Latino community.

Raw sewage is more than a foul nuisance. It releases hydrogen sulfide, a toxic gas that can damage olfactory nerves and provoke asthma attacks. According to the Centers for Disease Control and Prevention, exposure can cause headaches, nausea, confusion, tremors, coughing, shortness of breath, irritation of the eyes and skin, and in extreme cases, death. Scientists are still studying the long-term consequences of repeated exposure.

There is no broad federal air safety limit for hydrogen sulfide beyond strict workplace standards for high-risk sites like wastewater plants and manure pits. A handful of states adopted limits decades ago, but those thresholds are outdated. In California, proposed legislation would update the state’s 56-year-old standard to reflect current scientific knowledge about the gas’s health effects. Lawmakers in Texas are also weighing revisions.

“When the standard was first created, it focused mainly on odor — on nuisance,” said Democratic Sen. Steve Padilla of California, whose district includes the Tijuana River Valley. “We didn’t fully understand the health implications then. Now we do.”

Even if the measure is approved, officials say a revised standard would likely not be finalized until 2030.

Toxic gas from the river’s sewage infuses the air

A sign warns of sewage- and chemical-contaminated water along a beach Tuesday, March 10, 2026, in Coronado, Calif. (AP Photo/Gregory Bull)

A “Stop the Stink” sign hangs on Egger’s fence, part of a campaign by Citizens for Coastal Conservancy urging authorities to halt the cross-border contamination.

The 120-mile (195-kilometer) river flows through the city of Tijuana, crosses into California and empties into the Pacific. Nearby San Diego County beaches have been closed for extended periods, and Navy SEALs training offshore have reported illnesses.

Since January alone, roughly 10 billion gallons (38 billion liters) of mostly untreated sewage and industrial waste have crossed into the United States via the river, according to commission data. For comparison, a ruptured pipe in January released 244 million gallons (924 million liters) of sewage into the Potomac River, affecting affluent communities and prompting swift federal action.

Trent Fry and Leila El Masri collect a water sample from the Tijuana River as part of a University of California, San Diego research team, Wednesday, March 11, 2026, in San Diego. (AP Photo/Gregory Bull)

Justin Hamlin and Maddie Tibayan walk along the Imperial Beach pier after gathering seawater samples for research, Wednesday, March 11, 2026, in Imperial Beach, Calif. (AP Photo/Gregory Bull)

A 2024 survey conducted by San Diego County and the CDC of about 40,000 households near the river found that 71% reported smelling sewage inside their homes, and 69% said at least one household member became ill after exposure.

“Even at lower concentrations, you feel it in your sinuses. The smell lingers and becomes a constant irritant,” said Ryan Sinclair, an associate professor of environmental microbiology at Loma Linda University School of Public Health.

The EPA says it is collaborating with local and state agencies to reduce odor impacts.

This year, San Diego County distributed more than 10,000 air purifiers to affected households. Still, the contamination persists, and the river’s foamy plumes are now visible from space.

Hydrogen sulfide levels stun researchers

Surfers watch as researchers gather seawater samples from the Imperial Beach pier, Wednesday, March 11, 2026, in Imperial Beach, Calif. (AP Photo/Gregory Bull)

In September 2024, Kimberly Prather, a chemistry professor at the University of California, San Diego, and her team installed air monitors in Egger’s neighborhood.

The results shocked them. Hydrogen sulfide readings were 4,500 times higher than typical urban background levels and 150 times above California’s air quality standard when nighttime river flows peaked.

Residents like Egger said the findings confirmed what they had long experienced.

“People were basically told it was just an odor issue — unpleasant but harmless,” Prather said. “That wasn’t the full picture.”

Her team has also identified thousands of additional airborne chemicals from the river, many odorless and potentially even more hazardous.

Doctors recommend people move

Trent Fry collects a seawater sample in Imperial Beach, Calif., Wednesday, March 11, 2026. (AP Photo/Gregory Bull)

Egger said physicians have advised him to consider relocating, though none have provided a formal diagnosis linking his symptoms directly to hydrogen sulfide exposure.

Leaving, however, would mean abandoning deep family roots. His wife was raised in Tijuana. His brother and his late brother’s family live next door on the former Egger Dairy property, where an aging milk barn and rusting equipment still stand.

“I’ve spent my entire life here — with my parents, my grandparents,” Egger said. “This is home.”

As a child, he swam in the river when it flowed only during rainy seasons. Today it runs year-round, filled largely with wastewater and industrial runoff. He argues the river should be redirected to its historic channel closer to the border and farther from neighborhoods and schools, preventing stagnant pools that create concentrated pockets of hydrogen sulfide.

Less than half a mile from his house, the odor intensifies where the river bursts from underground pipes near Saturn Boulevard.

Scientists have dubbed the area the “Saturn hot spot.” The smell seeps into passing cars, even with windows closed, and can linger inside for days.

When river flows go up, so do the number of patients

Oscar Romo walks among debris trapped by a trash barrier installed in the Tijuana River near the U.S.-Mexico border, Wednesday, April 8, 2026, in San Diego. (AP Photo/Gregory Bull)

Dr. Matthew Dickson and his wife, Dr. Kimberly Dickson, operate a clinic about a mile from the hot spot. Many patients report migraines, nausea, wheezing, eye irritation and mental fog. Those with asthma say they rely more heavily on inhalers when the odor intensifies.

“Patients tell us they feel better on days when the smell isn’t as strong,” Kimberly Dickson said.

In August 2023, a tropical storm caused the river to overflow into nearby streets. Within days, the clinic’s caseload tripled.

Electronic health records later confirmed their observations. When river flows increased, respiratory-related visits rose by 130%, they said.

“Every day this problem continues,” Matthew Dickson said, “more people are getting sick.”

A man walks along the aqueduct carrying the Tijuana River as it crosses from Mexico into the United States, Wednesday, April 8, 2026. (AP Photo/Gregory Bull)

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This story has been updated to clarify that the Tijuana River flows through the city of Tijuana; it does not originate there.