NASA Sensor Maps Tijuana Sewage Plume from Space

A NASA sensor is able to detect signs of sewage contamination in the Pacific Ocean, a new study has concluded.

The authors of the study examined the mouth of the Tijuana River and tracked a large sewage plume using an image spectrometer known as Earth Surface Mineral Dust Source Investigation (EMIT).

The EMIT sensor was installed on the International Space Station in 2022, and it will remain there, actively collecting data, until at least 2026. The highly sensitive instrument measures light in visible and infrared wavelengths, splitting them into hundreds of color bands, according to NASA.

Although scientists have tracked algal blooms using satellite imagery for years, pre-EMIT images were not sensitive enough to detect sewage in water. However, EMIT is able to detect phycocyanin, a pigment in cyanobacteria. Cyanobacteria thrive in wastewater.

The imaging spectroscopy technology behind EMIT is used for myriad purposes, including tracking forest health, wildfires, and climate change.

“When toxic wastewater pollution is so out of control that it’s visible from space,” said Imperial Beach Mayor Paloma Aguirre in a statement, “that’s no longer a local crisis—it’s a flashing red alert. I hope this NASA report is a wake-up call for every level of government. The science is clear, the health risks are real, and seeing it all from space satellites just underscores what South County families are being forced to endure.”

Imperial Beach is the city most impacted by the ongoing sewage problem, and in 2024, the city reached 1,000 consecutive days of beach closures.

Projects are currently underway to rehabilitate and expand the wastewater infrastructure in both the United States and Mexico that contribute to the problem. In the meantime, millions of gallons of untreated wastewater are dumped into the Pacific Ocean each day.

The Environmental Protection Agency on May 19 announced it would accelerate the South Bay International Treatment Plant’s expansion, increasing its capacity from 25 million gallons per day (MGD) to 35 by Aug. 27. That expansion was originally anticipated to take two years from the project’s launch last fall.

Ultimately, the full expansion will also be accelerated from its original, five-year timeframe, but the United States International Boundary and Water Commission, which oversees the project, has not yet announced new projections.