Heavy rains threaten polluted Tijuana River Valley with flooding, health risks

As a North Pacific storm bearing down on San Diego County threatens to drop up to 3 inches of rain at the coast and more inland this weekend, residents of the Tijuana River Valley face compounded health risks from floodwaters mixing with the area’s severe pollution.

The National Weather Service has issued a flood watch for San Diego County from late Friday night through Saturday evening. San Ysidro, at the southern edge of the county near the river valley, could receive 1.5 inches to 2 inches of rain.

For communities already grappling with decades of sewage contamination flowing across the U.S.-Mexico border into the Tijuana River Valley, the storm presents immediate waterborne health threats, according to Paula Stigler Granados, an associate professor and division head of environmental health at San Diego State University’s School of Public Health.

“The primary concern is flooding, and during flooding the concern is not air pollution but waterborne contamination,” said Granados, a member of the Tijuana River Coalition. The river will swell with trash, sediment and pollutants, while urban runoff creates what she called a “first flush” effect, pushing additional contaminants into the water.

“Whatever was already in the river, along with everything else,” gets mixed together, Granados said. “And then it swells up, it floods, and then whatever was also in that river will also end up getting mixed in with the soil and the sediments.”

Health officials generally see spikes in gastrointestinal illnesses after flood events in the area, she said, as residents inevitably come into contact with contaminated floodwaters by driving through them, walking through them or becoming stranded.

The weather service warned that “roads may become impassable due to flooding or flood damage. Heavy rain on wildfire burn scars have an increased risk of flash flooding along with mud and debris flows.”

A particularly vulnerable area is Saturn Boulevard tucked between Imperial Beach and Nestor, which Granados identified as a hotspot that floods heavily with every rain event. During a major flood roughly two years ago, hundreds of horses had to be rescued and residents were stranded on one side of the river, she said.

“The key is to try to prevent these waves of illnesses,” Granados said, adding that the river valley is “a particularly sensitive, vulnerable area, not only for people, but for our habitat down here, as well the estuary and all the beautiful places that we have down here.”

Granados advised residents to stay out of flooded areas as much as possible and take precautions if they do come into contact with floodwaters.

“A lot of hand washing, being mindful if you’ve come into contact with any of the contamination,” she said. She also recommended wearing rubber boots, leaving shoes outside to avoid tracking pollutants indoors and washing feet before entering homes.

After floodwaters recede, contamination remains in the soil and sediment, Granados said. Once that material dries, it can become airborne.

“Whenever this dries up, mask up,” she said. “You know, lots of hand washing, protecting your animals, things like that. Just be consciously aware that just because it’s not wet, it’s still contaminated.”

Residents who become ill should inform their healthcare providers if they live in a flooded area and request testing to identify specific infections rather than accepting only symptomatic treatment, Granados said.