Aerial view of the Tijuana River crossing the Mexico-US border -marked by a line on the river bank (R)- as seen from Tijuana, Baja California state, Mexico, on March 14, 2020. - April 22, 2020 commemorates the 50th anniversary of the World Earth Day. (Photo by GUILLERMO ARIAS / AFP) (Photo by GUILLERMO ARIAS/AFP via Getty Images)
San Diego, California – A NASA instrument aboard the International Space Station has confirmed the presence of sewage contamination spilling into the Pacific Ocean from Mexico—once again drawing attention to the ongoing environmental crisis at the U.S.–Mexico border.
Using a device originally designed to map desert minerals, scientists have now repurposed the Earth Surface Mineral Dust Source Investigation (EMIT) instrument to monitor ocean water quality. In a recent analysis, EMIT detected phycocyanin, a pigment found in cyanobacteria, within a large wastewater plume flowing from the Tijuana River into the ocean near San Diego.
The findings offer sobering confirmation of what many Southern California residents already know too well: raw sewage from Mexico continues to pollute U.S. waters.
The Tijuana River, which originates in Mexico and crosses into California before draining into the Pacific, has long been a conduit for untreated sewage, industrial runoff, and stormwater. For decades, environmental groups and border communities have raised alarms over the river’s contamination, which frequently leads to beach closures, ecosystem disruption, and serious health concerns.
The March 2023 satellite imagery, captured by Sentinel-2 and analyzed in part using the EMIT instrument, showed a visible plume of polluted water spreading from the mouth of the Tijuana River into U.S. coastal waters. The ability to identify phycocyanin within that plume gives scientists a clearer fingerprint of the microbial contaminants present, pointing to the presence of cyanobacteria, which can pose both environmental and health hazards.
That this discovery came not from a boat-based water test or local government sensor—but from a scientific tool orbiting Earth—is equally impressive and troubling in no small measure. The discovery shows the scale and persistence of the problem, as well as the failure of multiple government efforts to contain it. It makes one wonder how no one has handled the deeply disturbing issue.
Communities in San Diego County have long borne the brunt of the crisis. Beaches from Imperial Beach to Coronado are frequently closed due to contamination, and residents have repeatedly reported rashes, respiratory issues, and other health effects after contact with the water. The spill also threatens marine biodiversity and local economies that rely on clean, accessible beaches.
The fact that an instrument 250 miles above the Earth can detect pollution in Southern California’s waters should be a wake-up call. While satellite technology may offer new tools to measure and monitor the problem, the pollution itself is anything but new—and the need for a cross-border, enforceable solution is long overdue.
