A plume of wastewater emanating from the Tijuana River. Photo: NASA, SDSU and Eva Scrivner
The level of pollution in the Tijuana River is so bad there’s almost no news of it that could be shocking. Just last month, the Surfrider Foundation named San Diego County’s Imperial Beach, which is impacted by flows of stormwater, sewage, and industrial pollution through the Tijuana River Valley, to its list of Top 10 bacteria-laden U.S. beaches. It also had that dubious honor the year before. Imperial Beach Mayor Paloma Aguirre called the situation a “public health crisis” in early 2024. A failure at a San Diego pump station that released more than 300,000 gallons of wastewater later in the year didn’t help.
The list could go on. You get the picture. And it turns out the sewage running through the Tijuana River and into the Pacific Ocean is so significant that NASA is saying they can see it from space.
The discovery didn’t occur by accident. NASA researchers chose the location to test a sensor on the International Space Station known as EMIT (Earth Surface Mineral Dust Source Investigation). The sensor observes sunlight reflecting from Earth and displays “visible and infrared wavelengths into hundreds of color bands.” It was initially launched in 2022 to map minerals and dust in desert areas, but Eva Scrivner, a doctoral student at the University of Connecticut, believed the instrument could also be used to observe water.
By cross-referencing water samples taken from the Tijuana River, EMIT was able to identify a “spectral fingerprint” of molecules in the sewage plumes. In particular, they observed cyanobacteria, which can make humans and animals who ingest it sick.
“From orbit you are able to look down and see that a wastewater plume is extending into places you haven’t sampled,”said Christine Lee, who co-authored the new study. “It’s like a diagnostic at the doctor’s office that tells you, ‘Hey, let’s take a closer look at this.’”
Researchers now believe the discovery can be helpful in filling data gaps in monitoring and studying highly-polluted sites like the Tijuana River. While we have traditionally relied on tangible water samples to learn about the health of our beaches and watersheds, it seems EMIT can monitor the health of watersheds just by looking down from space.
