Sewage Across Borders: The Tijuana River Is Spewing Wastewater Into San Diego Amid Historic Storms, Which Could Threaten Public Health

For Jose Cariman, the smell permeating his house is worst at night. 

A retired, stay-at-home dad, Cariman lives in a single-family home in the Coral Gate community of San Diego’s San Ysidro District, about 2 miles from Tijuana—close enough that his wife’s family can walk over the border from Mexico for dinner.

“The only problem,” he said on Tuesday, “is I didn’t realize when I bought the house, the proximity to the Tijuana River and all the complications that come with it.” 

Winding around 120 miles northward from Mexico to California before reaching the ocean on the U.S. side of the border, the Tijuana River carries millions—at times, billions—of gallons of sewage across the border each day. Extreme weather events like the unprecedented storms currently pummeling the San Diego area can overwhelm California’s and Tijuana’s sewage treatment plants, causing wastewater to overflow in South Bay communities, including San Ysidro, Imperial Beach and Coronado. Some estimates suggest that storms at the end of January sent at least 14.5 billion gallons of raw sewage into the Tijuana River Valley. 

The total average annual rainfall on the coast of San Diego is around 10 inches. Certain areas of the region saw 2 to 8 inches of rain in the past week alone, flooding streets and triggering a mudslide further inland. 

For Cariman, this influx of untreated wastewater means a near-constant odor lingering in his home, one that he can’t air out by opening the windows because that makes the problem worse, he said. 

“It’s horrible,” said Cariman. “The quality of life is diminished a lot, the price of the house is diminished ’cause who wants to buy a house in the neighborhood that smells like sewage?”

But it’s not just the smell that affects citizens in the San Diego area: Near daily ocean water testing has revealed high levels of bacterial contamination from the sewage, posing a potential public health risk for these communities, experts say. 

A study released last March found that bacteria and pollutants from the sewage are airborne, as well, carried by droplets flung off crashing waves that can travel for miles and expose people well beyond the beach. Some urgent care doctors say that illnesses surge each time a storm hits. 

As climate change accelerates, extreme weather events are projected to become increasingly frequent and severe, putting even more pressure on sewage infrastructure in California. However, data and research quantifying the potential health risks of this level of sewage exposure in the area are sparse—and scientists and officials are scrambling to fill in the gaps amid public outcry as waste-laden waters continue to inundate the San Diego area.

“The truth is most people don’t know the health effects of inhaling these things,” said Kimberly Prather, a marine chemist at Scripps Institution of Oceanography at the University of California, San Diego, who co-authored the March study. “Nobody’s ever studied it.”

Sewage Across Borders

Located just north of the California-Mexico border in San Ysidro, the South Bay International Wastewater Treatment Plant was built in 1996 to help remove hazardous contaminants from sewage flowing through the Tijuana River. 

While the U.S. paid for the majority of the project, the plant required binational agreement through the International Boundary and Water Commission, a body created by the U.S. and Mexico to determine rules for border lines and the allocation of water flow from rivers that cross through each country. On Mexico’s side, a different sewage treatment plant in San Antonio de los Buenos lies in Tijuana, about 6 miles from the border. 

But both structures are in various states of disrepair, particularly the one in San Antonio de los Buenos, which has been out of operation for years and spewing massive quantities of untreated sewage into the Tijuana River. 

During storms, the cracks in these dilapidated systems are even further exposed. For example, in August 2023, Tropical Storm Hilary battered the San Diego area with 2 to 6 inches of rain, an extremely unusual amount of precipitation for that time of year. 

More than 2 billion gallons of untreated wastewater breached the border during and after the storm, according to the International Boundary and Water Commission. In Imperial Beach, just north of San Ysidro, a pumping station that pushes sewage coming from Mexico to treatment plants malfunctioned, and discharged wastewater all over the street amid the downpours.

“It doesn’t take a medical degree to know that if you’re living with sewage running in your backyard, you can get sick.”

In the weeks following, Matt and Kim Dickson, married doctors who own an urgent care center in South Bay, started to see an influx of patients with gastrointestinal issues. When they later combed through their patient data from before and after the storm, they found a 560 percent increase in diarrheal illness cases. 

“We found a lot of bacterial infections that we generally don’t see in developed countries like the United States, things like E. coli, salmonella, shigella [and] Campylobacter,” a bacteria that causes a diarrheal illness, Matt Dickson said. “The thing that was really frightening for us was none of these people were going in the ocean because it was storming, it was rainy, yet they were still getting sick.” 

Though the Dicksons cannot yet confirm that these illnesses are a direct result of the sewage-tainted water and urban runoff, they suspect people may have become infected from tracking bacteria into their homes after passing through the pumping station site. 

“It doesn’t take a medical degree to know that if you’re living with sewage running in your backyard, you can get sick,” Kim Dickson added. The Dicksons say they are already seeing an uptick in gastrointestinal cases amid the storms currently passing through the San Diego area. 

The couple presented their initial findings at an October meeting of the California Coastal Commission hosted in Imperial Beach, at which scientists, politicians and citizens also voiced their concerns over health risks for sewage-contaminated water. 

Along with refurbishing the sewage treatment plants at the border, it is crucial to continue fleshing out the potential link between illness and sewage in the San Diego area, Prather said. More than 75 percent of the bacteria that Prather and her team identified in the air during their March study could be traced back to sewage in the Tijuana River, including Acinetobacter bacteria, which can be found in hospital infections and are increasingly resistant to antibiotics. 

However, the team did not quantify the amount of bacteria in these aerosols, and Prather cautioned against jumping to any conclusions because they don’t yet have information on associated health impacts. A different team of researchers at Scripps is currently developing a model to forecast the presence of pathogens in San Diego ocean waters from untreated sewage. But population-wide epidemiological studies are going to be necessary to really understand more about sewage-associated health risks, Prather said. 

In the meantime, residents across South Bay are letting public officials know that they are sick of—and from—the stink. 

Stop the Poop

On Jan. 22, nearly 3 inches of rain fell in the San Diego area and flooded the beaches and streets, marking the wettest January day in the city’s history. 

With these floods came the sludge, said Jason Lindquist, the marine safety captain with the City of Imperial Beach. The ocean water “looks like you’re draining an RV septic tank,” he said. “It’s black.”

But this isn’t necessarily an unusual sight for Lindquist, who grew up in Imperial Beach and manages a team of lifeguards in the area. In southern California, it’s standard for beaches to close for at least 72 hours following a storm because runoff can pollute the water. But in the past few years, state officials have ramped up sewage pollution monitoring near the Mexican border, testing the waters each day for bacteria—which has led to near-constant closures for the past year and a half in Imperial Beach, according to the city’s website. 

However, that doesn’t mean that people, particularly surfers and tourists, aren’t still going in the water, Lindquist said. This poses a health risk for his staff, who are required to fill out a worker’s compensation form stating that they were potentially exposed to bacteria every time they enter the water during an advisory. 

Some of the lifeguards on his team have reported headaches, rashes and other illnesses after exposure, he said. Though it is not confirmed whether these issues arose from the contaminated waters, research shows that swimming in sewage-contaminated waters can cause gastrointestinal issues and other illnesses.

“We’re at a two- to three-year slump on hiring,” Lindquist said. “We can’t attract people because we’re not keeping up sometimes with our pay, and then now this constant blanket of polluted water.”

It’s not just people working in ocean-related fields who are concerned about risks. Citizens in Imperial Beach and the neighboring towns of San Ysidro and Coronado are fed up as well. A number of nonprofits and community advocacy groups are pushing for sewage infrastructure and public health reforms, organizing letter campaigns to California Gov. Gavin Newsome and a “Stop the Poop” rally outside of the International Wastewater Treatment Plant in September. Students at Coronado High School even formed a “Stop the Sewage” Club to demand change from their local officials, The Coronado News reported. 

“It’s affecting the economy in Coronado and is affecting health in Coronado, whether or not [government officials] want to admit it,” said Amy Steward, a retired teacher based in the area, who believes she, her husband and daughter have all been infected with stomach viruses from their exposure to the sewage. 

Treatment Plant Revamp

In January, the Mexican government launched a reconstruction of its rundown treatment plant, an announcement that has been met with tentative optimism from San Diego county residents and officials. 

“That source of pollution that hits us from the ocean, hopefully it will be eliminated in the next couple of years,” said Paloma Aguirre, the mayor of Imperial Beach. “But on our side, it’s been a bit of a journey.” 

In 2020, Congress approved a $300 million fund for the expansion of the South Bay International Wastewater Treatment Plant. However, memos obtained by The San Diego Union-Tribune in 2023 revealed that the plant had to first allocate $150 million of the federal funds to pay for deferred maintenance before any type of expansion could happen. 

In the wake of this setback, Aguirre and other politicians across South Bay have been advocating for an additional $310 million in federal funds “to offset the cost for the rehabilitation of the plant and account for inflation,” Aguirre said. 

In October, President Biden included this sewage allocation as part of an emergency supplemental funding request, but it has not yet been approved by Congress. Gov. Newsome has asked for support for the funding, and several members of Congress, including Rep. Scott Peters (D-San Diego), penned a letter in December urging majority approval. 

“Excess flows, bacteria-filled sediment, and contaminated aerosol pollutants pose a serious public health risk to the region,” they wrote. “Without this additional funding, [South Bay International Wastewater Treatment Plant] is forced to keep pumping untreated water into the ocean, threatening the health and national security of the region.”

At the end of January, a delegation of South Bay elected officials led by Aguirre, traveled to Washington to meet with members of Congress and the White House about their request, which is now being discussed, she said. 

Back in California, the County of San Diego is currently partnering with the Dickson’s at their South Bay Urgent Care to run a two-week study on the health impacts of sewage contamination as storms pass through the area. For now, Prather, who also studied airborne COVID-19 transmission, recommends staying away from the ocean and putting air filters inside homes. 

“Other cities worry about sea level rise and saltwater intrusion into their infrastructure. We’re worrying about that and the public health threat,” Aguirre said. “It’s apocalyptical in the Tijuana River Valley.”