13-06-2025
NASA Satellite Detects Sewage on California Beach
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Scientists have discovered signs of sewage in the water at a beach in southern California in NASA satellite images.
In their study, researchers examined a large wastewater plume at the mouth of the Tijuana River, south of Imperial Beach near San Diego, using NASA's EMIT (Earth Surface Mineral Dust Source Investigation) instrument.
EMIT, which orbits the Earth aboard the International Space Station, was able to detect the sewage by observing sunlight reflecting off the planet.
NASA's Jet Propulsion Laboratory (JPL) explained that the EMIT's "advanced optical components split the visible and infrared wavelengths into hundreds of color bands."
Scientists were able to differentiate what molecules were present based on their unique spectral "fingerprint" by analyzing each satellite scene pixel by pixel.
The EMIT's observations of the Tijuana River plume were compared with water samples tested on the ground.
The comparison revealed "a spectral fingerprint pointing to phycocyanin, a pigment in cyanobacteria, an organism that can sicken humans and animals that ingest or inhale it."
A stock image of a view from the California side of the United States/Mexico border into Tijuana, where the border fence meets the Pacific Ocean.
A stock image of a view from the California side of the United States/Mexico border into Tijuana, where the border fence meets the Pacific Ocean.
Getty
Paper author and oceanographer Eva Scrivner of the University of Connecticut said that the findings "show a 'smoking gun' of sorts for wastewater in the Tijuana River plume."
Christine Lee, a scientist at JPL in Southern California who is a co-author of the study, added: "It's like a diagnostic at the doctor's office that tells you, 'Hey, let's take a closer look at this.'"
"From orbit you are able to look down and see that a wastewater plume is extending into places you haven't sampled."
Hundreds of millions of liters of untreated wastewater are discharged into the Tijuana River each year. This water brings harmful pollutants through two major cities—with more than three million combined residents—as well through a protected estuarine reserve before emptying into the Pacific Ocean, the researchers note.
Contaminated coastal waters not only impact human health but also harm marine ecosystems, fisheries, and wildlife.
Scientists have monitored water quality issues, such as harmful algal blooms, for decades using satellite instruments that analyze ocean color. However, other pollutants and harmful bacteria are harder to track as they are more difficult to decipher using traditional satellite sensors.
The researchers say that "current monitoring methods are resource-intensive and limited in coverage" and "optical satellite imaging may enable broader spatiotemporal monitoring."
The findings of the latest study provide a base for future projects to develop "remote sensing derived wastewater plume maps that also estimate associated water quality parameters such as bacterial concentrations in this system."
The scientists concluded: "The ability to do so fills a critical gap in our ability to study how wastewater plumes impact regional biodiversity, local economies and public health at varying spatial and temporal scales."
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Reference
Scrivner, E., Mladenov, N., Biggs, T., Grant, A., Piazza, E., Garcia, S., Lee, C. M., Ade, C., Tufillaro, N., Grötsch, P., Zurita, O., Holt, B., & Sousa, D. (2025). Hyperspectral characterization of wastewater in the Tijuana River Estuary using laboratory, field, and EMIT satellite spectroscopy. Science of The Total Environment, 981.
