What Exactly is in the Tijuana River?
SDSU’s public health researchers are testing the water to find out.
By Kellie Woodhouse
The fog is just beginning to lift on an overcast February morning as Lilianna Landin dips a sampling stick into the Tijuana River. The water in the vessel at the end of the pole looks clear, but Landin and classmate Alex Fox will take it back to the lab and test for harmful bacteria, toxicants and pollutants.
Downstream from the South Bay collection site, the river empties into the Pacific Ocean at Imperial Beach, a community that restricts access to its coastal waters much of the year due to high concentrations of human waste in the water. Sewage flows into the United States from Mexico via the waterway—the result of aging sanitation systems in Tijuana and overburdened water treatment systems near the border—and pollutes the vital Tijuana River National Estuary and nearby coast.
Landin and Fox are part of a team of students helping San Diego State University public health professor Kari Sant test water from more than a dozen sites along the Tijuana River, border-region tributaries and estuary.
“The bacteria levels are high. It’s concerning to see how high they are, especially during certain weather events,” says Fox, a master’s student studying public health and Latin American studies.
When rainfall overwhelms existing treatment systems near the border, it brings particularly high concentrations of potentially noxious materials and bacteria—like E. coli and other fecal coliform—into the waterways. The result is poor water quality that puts the public and environment at risk, especially in heavily trafficked areas of southern San Diego’s shoreline. A heavy rainfall can close coastal waters as far north as the tourism-dependent beach community of Coronado.
“It’s not just a U.S. thing, it’s not just a Mexico thing. It’s a transborder issue,” Fox says. “It’s been eye-opening. The river is not just an important ecosystem, but a lot of people live around it and interact with it. Just being aware of that allows you to ground yourself in the research.”
Providing a Baseline
Though water quality at the border is a widely acknowledged issue, there is no comprehensive understanding of which pollutants—outside of unsafe levels of human waste and related bacteria—threaten the river and surrounding communities.
Sant is hoping to change that by forging one of the most comprehensive and collaborative analyses of the health of the Tijuana River in recent history. Her team is testing water as soon as it enters the U.S. from the border, following the flow of the river until it reaches the ocean.
“We are looking near recreational and residential sites, so we can contextualize data and find out whether any of these materials poses a public health risk,” Sant explains. “I want to bridge different areas and look at it more comprehensively than has been done before. You don’t know what’s out there until you look for everything.”
She is sequencing bacterial DNA found in the water and determining levels of harmful pathogens, which can sicken people and animals and impair critical habitats. Wildlife like fish rely on the water to provide enough oxygen to survive, but bacteria can deplete oxygen levels.
Sant has already found that water quality improves drastically as the river flows through the estuary wetlands. She wants to assess whether the plants and soil in the salt marsh filter and purify the water as it flows toward the ocean. Test sites near the border have bacteria levels exponentially higher than what is considered environmentally safe following major rainfall. Yet, water near the ocean often meets California’s surface water recreation goals, unless it has rained recently.
Meanwhile, SDSU public health researcher Eunha Hoh is conducting a non-targeted chemical analysis of the same water samples, establishing a more complete picture of the hazardous materials polluting the water. And Scripps Institution of Oceanography researcher Dimitri Deheyn is analyzing the water for microplastics, which can persist in the environment and potentially harm wildlife and people.
Researchers are in the data collection phase of the project and plan to analyze results in the summer. The effort comes at just the right time.
As part of the United States-Mexico-Canada Agreement reached in December 2019, the federal government earmarked $300 million to improve water quality near the U.S.-Mexico border and clean up the river and estuary. Sant’s project will provide a critical baseline of information just as the Environmental Protection Agency considers how to allocate the funds.
“The work Sant is doing is critical,” says Jeff Crooks, research coordinator for the Tijuana River National Estuarine Research Reserve, who has worked closely with Sant. “The ultimate goal is to improve water quality, but we have to measure and understand the system in the first place so that we can use data and science to make sound decisions.”
Sant's work is just one facet of SDSU’s research enterprise near the border. University researchers are studying climate change, plant life, pollution and public health issues in the region. Sant and Hoh, along with associate professor of environmental engineering Natalie Mladenov and others, are studying water scarcity as part of the Blue Gold Area of Excellence Initiative. SDSU also launched its first RE:BORDER Conference in 2019, with the aim of tackling pressing issues by collaborating with researchers from institutions on both sides of the border.
For Sant, the project goes far beyond helping improve water quality in the border region—it’s training and inspiring the next generation of public health researchers.
“It’s been really meaningful to the students because they are going to be the ones working on this issue as they go out into their careers,” she says. “They are getting to apply their public health skills and knowledge to a critical real-world problem.”
Back in the lab after the morning at the collection site, environmental health master’s student Kelsey Faust pours water samples into beakers, mixing them with reagents that will help her measure the concentration of pollutants like nitrates and phosphates.
After a few minutes, the liquid in one flask turns dark blue—indicating high levels of phosphates due to untreated sewage in the water.
“We’ve seen some crazy stuff,” says Faust, referring not just to what’s in the water samples but to the process of collecting them. Some of her fellow students have gotten stuck in the mud, but they don’t mind. She says, “It’s been good to get the hands-on experience, to get out in the field and get dirty.”