Chemical stench, green in color: Urban runoff is not just rain, Tijuana community says

Green, brown, black, foamy. That’s how residents of Tijuana neighborhoods downhill from factories describe the water flowing down their streets into the Tijuana River watershed — and not just when it’s raining.

Those observations, published this year in a first-of-its-kind study, came from people who live and work in the densely populated Chilpancingo, Murúa and Loma Bonita neighborhoods — about a mile from the US-Mexico border.

The communities lie just south of the Otay Mesa port of entry, nestled in a basin directly below a plateau packed with several multinational factories, known as maquiladoras. The study logged months of observations at urban runoff sites, collected interviews with residents and tracked how the flows have impacted their lives.

Residents said that runoff often smells of chemicals and is making them sick. They say the next step is to test the water for contaminants and identify the runoff’s sources. Then they’re hoping the studies will persuade public officials to address their concerns.

The Colectivo Salud y Justicia Ambiental, an environmental justice group in Tijuana, teamed up with US-based researchers Carolina Prado and Guillermo Douglass-Jaimes to conduct the community survey. The team sought to raise awareness of the impacts of US economic policies that have fueled industrial expansion in Tijuana and outpaced the building of critical infrastructure.

Like international trade policies, the pollution concerns transcend the international border.

The Alamar River lies downhill from the neighborhoods to the south. The river absorbs much of the polluted runoff and feeds into the concrete Tijuana River channel that crosses back to the US where it flows into waterways in South Bay communities.

Tijuana media have covered the issue when there are major storm events leading to significant flooding. During these episodes, public officials have said the real problem is rain and lack of adequate stormwater infrastructure. But the study compiled community-sourced data that tracked runoff flowing through the streets during dry weather.

The study suggested the flow of polluted water may have another source.

The study identified a number of outfalls just down the hill from the factories, though the precise source of the runoff wasn’t clear. Researchers also noted reports of illegal waste dumping and other activities that make it difficult to trace the source of the runoff. Neighbors and community members say the flows often smell of raw sewage but also, at times, give off the stench of chemicals.

Some attribute gastrointestinal and respiratory issues to the runoff, as well as headaches. Some are forced to cross through the runoff on their way to work or while walking their children to school. Others say they feel the financial impacts of having to pay for transportation to avoid having to come in contact with the polluted water.

Prado, who teaches environmental justice at San Francisco State University, said the study set out to methodically document residents’ observations to reinforce what locals have experienced for years. Together with the Colectivo Salud y Justicia Ambiental, they devised a plan that would amplify the community experience.

Now, with the formally collected data, they hope to draw more attention to the problem.

“The community for a long time has been … trying to talk to their representatives about the fact that they see this is coming from industrial sources,” Prado said.

A spokesperson from the State Commission of Public Services of Tijuana said that it is in the process of planning the rehabilitation of sanitation systems in Chilpancingo, Murúa and Loma Bonita. They aim to implement the projects in the coming year “to guarantee the proper functioning of the sanitary system in the region.”

But for years, community concerns have been brushed aside by city officials, said Alejandra Nieto, a Colectivo member. She said they attributed it to stormwater, denying what locals observed.

“With all due respect,” said Nieto in Spanish, “you’re not going to come and tell me … what that color is, or what I see, smell and feel.”

Decades in the making

The problem of polluted urban runoff is decades old and has origins in the rapid growth of factories along the border. This development transformed the Mexican economy, drawing workers from across the country to take up industrial jobs.

The boom of the maquiladoras was a result of the North American Free Trade Agreement in the 1990s, which offered incentives for multinational companies to locate factories along the border. Many produce electronics, appliances and car parts that are sold worldwide.

NAFTA brought rapid expansion to Tijuana, but the infrastructure needed to handle that growth did not follow. Workers settled in neighborhoods near the factories, sometimes without plumbing or electricity, working jobs that put them into contact with toxic substances.

The cross-border sewage crisis impacting both sides of the border is largely a result of this policy, said Kevan Malone, a historian at Texas Tech University.

He said the pollution impacting the Tijuana River watershed is “one unintended consequence of the rapid growth that has benefited American companies, and I would argue more broadly, the American economy, at the expense of people who live in the border region.”

In recent years, the industrial zone in Tijuana has seen a new wave of expansion, including the construction of an Amazon fulfillment center on the south side of the neighborhood. Today, north of the neighborhood another factory building is under construction. 

For two decades, the Colectivo has pressured officials to improve their conditions. The group is made up mostly of mothers and grandmothers who meet while their kids are at school, some of them having worked in the factories.

Filmmakers documented the early work of the collective in the film “Maquilapolis,” which tracked the fight of the workers for labor rights in the early 2000s after experiencing impacts on their health while working in the factories. At the time, polluted runoff already plagued the neighborhood. The film also tracked the process of the group pressuring officials to clean up toxic waste left behind by a closed factory.

“We have been reporting this for years,” said Nieto in Spanish. “So, of course, what we wanted to do was to have the evidence, so that when the time comes we can show it.”

Where science and grassroots meet

While government officials come and go, families in the neighborhoods impacted by the runoff have long experienced the effects. With the study, the group sees a new path to holding officials accountable.

The researchers and the Colectivo plan on releasing more studies based on the data they gathered.

Long before she got her doctorate, Prado worked with the Colectivo as well as the Environmental Health Coalition, a US-based environmental justice group that has supported the collective since its beginnings.

Prado said this study was, in a way, a return to her own community with new tools to amplify the work. She said she is drawn to community-engaged research because it starts with the community informing the research, then the community can use it as a tool to drive policy changes. 

“All the residents, they already know the ways in which they’re impacted, because they’re experiencing it on a daily [basis], on a daily level,” Prado said.

Together, the group identified runoff sites and set up a system to aggregate observations about the color, smell, place and time of the runoff.

They also carried out interviews, and some community members agreed to share their locations in order to show how their movement to and from work was displaced by the flows.

Over four months, they completed 170 surveys, showing that on 65 days, the runoff was present without it having rained. The water was often brown, green or black and smelled of sewage or chemicals.

The study described the public transit fees community members had to incur to avoid runoff, and how key pedestrian paths in the neighborhood put community members in contact with the polluted water.

When inewsource visited the neighborhood on a sunny day, there was runoff in the street. Some community members walked over it with groceries in hand.

An earlier version of this story appeared on inewsource on April 10, 2025.