A year before the Trump administration awarded Greenwater Services a $1.7 million no-bid contract to clean the algae-filled Reflecting Pool, it gave the company, owned by a Trump donor, a $2.4 million no-bid contract to test its “nanobubble” technology in California’s polluted Tijuana River. Critics have questioned the results of the pilot and whether the technology can deliver on its promise to address a sewage crisis that has exposed nearby communities to contaminated water and air for decades.
Greenwater’s project, as first reported by The Washington Post, was to test its nanobubble technology, which injects ozone into a body of water to kill bacteria and eliminate odors, in the Tijuana River sewage flows. Greenwater began the project on Sept. 9, 2025, but it was cut short on Oct. 14, 2025, when a storm flooded the river, washing away some of Greenwater’s equipment and spilling diesel fuel into the waterway.
Oscar Romo, executive director of the conservation nonprofit Alter Terra, has spent more than 40 years working to restore the polluted river. He told MS NOW that Greenwater’s project ultimately made his job harder.
“There was no improvement or satisfactory results,” Romo said. He added that while Greenwater’s pilot was operating, “the smell became even worse” and the water was “milky for a few minutes, and then back to black.”
Romo shared photos that show Greenwater’s rental equipment scattered across a trash boom, that he installed and works on, after the storm. A trash boom is a floating barrier designed to capture garbage, plastic and other debris before it flows into larger waterways. One image appears to show an overturned generator leaking diesel into the river. Romo also alleges Greenwater neglected the project after the storm, leaving rental equipment behind for nearly a month. He said he warned Greenwater employees that the storm was coming, but they ignored the warnings and boasted about the company’s relationship with President Donald Trump.
Greenwater disputes Romo’s account. A company spokesperson told MS NOW that only one trailer drifted downstream during the storm and was later recovered.
Greenwater said the pilot generated valuable scientific data and noted it ultimately received only about half the project’s original $2.4 million budget. In its final report to the government, the company acknowledged a five-gallon diesel spill but concluded the pilot had demonstrated nanobubble technology was a “safe and effective method” in a “complex and unpredictable river system.”
The U.S. section of the International Boundary and Water Commission also characterized the pilot as successful in a news release, while noting that “significant equipment design modifications would be required for an effective scale-up” in the Tijuana River and other waterways with “troublesome, unpredictable flow conditions.”
Several scientists who spoke to MS NOW questioned those conclusions.
Wen Zhang, an engineering professor at the New Jersey Institute of Technology who has studied nanobubbles for more than a decade, said the issue was not necessarily the technology itself, but how and where it was deployed. Nanobubbles, he said, can work well in controlled environments, but open river systems like the Tijuana are far more unpredictable and require rigorous scientific evaluation before the technology can be used effectively.
Dr. Kim Prather of the Scripps Institution of Oceanography, a leading researcher on the Tijuana River sewage crisis, told MS NOW that she warned the company before the pilot that the river’s volatile conditions made it an unsuitable testing environment for nanobubble filtration, but that the company ignored those concerns. Greenwater declined to respond when asked about Prather’s warnings.
Prather said it was “reckless to bubble a reactive gas in a river that is filled with unknown chemicals” and that to test the project in an already vulnerable community was “one more example of environmental injustice.” Prather added that the project collected too little data to be judged a success.
Phillip Musegaas, executive director of San Diego Coastkeeper, called the project a waste of taxpayer money that raised public expectations that this kind of technology could provide a solution to a decadeslong public health issue while diverting resources from solutions that could have made a greater impact.
The Trump administration awarded Greenwater another no-bid contract roughly a year later — this one worth $1.7 million — to address the algae problem in the Reflecting Pool.
Greenwater installed temporary nanobubble units on June 7. About a week later, the units were taken offline. Within 24 hours, an algae bloom returned, prompting the company to put the units back into service. But the algae proved difficult to eliminate, and the water stayed green and murky for about a week. On June 25, Greenwater installed a permanent system that it said had cleared the water. The Reflecting Pool has since been drained again — and as of the end of July, remains closed for another round of repairs.
The Tijuana River is still suffering from a sewage crisis. Romo said “the solution is not even close to being reached.” But according to a recent press release from the Environmental Protection Agency, Administrator Lee Zeldin is moving at a “Trump Speed” to secure a “100% solution to permanently and urgently end the crisis.”
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