California’s largest and most-polluted lake, the Salton Sea, is exuding hydrogen sulfide, a noxious gas, at rates that greatly exceed the state’s air quality standards. Alarmingly, a new study finds that California’s air quality monitoring systems may be severely underestimating how much toxic pollution is reaching people living near the lake.

Hydrogen sulfide, which smells like rotten eggs, is linked to a host of respiratory and neurological symptoms. The new study, published in the journal GeoHealth, highlights the risk the Salton Sea’s emissions pose to nearby communities, many of which are predominantly Latino or Torres Martinez Desert Cahuilla Indian.

“The communities around the Salton Sea are on the front lines of a worsening environmental health crisis,” study co-author Mara Freilich, an assistant professor at Brown University, said in a statement. “Our study shows that hydrogen-sulfide emissions are not only more intense than previous monitoring captured, but they are systematically underreported — especially when sensors are placed away from the lake or out of alignment with prevailing winds.”

The Salton Sea is located roughly 160 miles (258 kilometers) east of Los Angeles, just east of Palm Springs and the Coachella Valley. It was initially formed by accident in 1905, when the Colorado River breached its irrigation canal. It has no natural inflows or outflows and is, by state law, primarily sustained by fertilizer-and-pesticide-laden agricultural runoff. The lake has since become nothing short of an environmental catastrophe. Climate change, drought, and reduced water inflows have pushed the Salton Sea’s water levels lower and lower over the past two decades, increasing the lake’s production of hydrogen sulfide and kicking up toxic dust.

For the study, researchers from Brown University, UCLA, Loma Linda University, and UC Berkeley partnered with Alianza Coachella Valley, a local community organization, to examine the causes of hydrogen sulfide emissions from the lake.

To measure emissions, the researchers used data captured by South Coast Air Quality Management District (SCAQMD) monitors, installed by a local agency, at three locations and placed additional sensors within the lake. The study found that between 2013 and 2024, SCAQMD sensors at all three locations consistently exceeded California’s air quality standards. The readings peaked in the summer months and in August for each year from 2013 to 2024, Torres Martinez, the site closest to the lake, had an average of more than 250 hours of readings that exceeded state standards.

But even these frightening measurements were likely an underestimate, the authors wrote. An air quality sensor deployed in the lake’s shallow waters detected substantially higher concentrations of hydrogen sulfide, particularly when wind was blowing over exposed sediment and shallow water. This suggests that there may be significant and overlooked sources of hydrogen sulfide blowing into nearby communities.

“Our results indicate that a significant portion of [hydrogen-sulfide] emissions remains unaccounted for, potentially being transported to communities without air monitoring stations,” the researchers wrote.

Among the many communities on the Salton Sea, only three have air quality monitoring sites.

The problem will likely get worse. Mitigation efforts for the Salton Sea have not kept up with receding water levels, the study authors wrote, leading to “serious health impacts” in an area that already has high levels of asthma and other pulmonary ailments.