Heavy machinery is used to create the West Pond, a habitat pond, at the Species Conservation Habitat Project at the south end of the Salton Sea, Calif., Sept. 13, 2024.
Salton Sea, California – On blistering summer days, when desert winds sweep across California’s southeastern interior, the Salton Sea sends a familiar warning into the air: a stench of decay, unmistakably like rotten eggs. Now, new scientific research confirms that this smell—caused by the release of hydrogen sulfide gas—is not only becoming more frequent but is also appearing at levels higher than previously recorded.
The findings, published in the journal GeoHealth, document an intensifying threat in the region surrounding California’s largest lake. As the Salton Sea continues to shrink and degrade, researchers say its emissions are compounding air quality concerns for communities already burdened by environmental stressors. The lake’s retreat has exposed vast stretches of toxic playa, unleashing windblown dust into the air, while the lake itself, overloaded with agricultural runoff, produces gases that may carry yet unmeasured risks to public health.
Hydrogen sulfide, or H?S, is a byproduct of decomposing algae and organic material in oxygen-starved waters. At sufficient concentrations, the gas is known to cause a range of symptoms—from nausea and headaches to depression and respiratory irritation. While researchers have widely studied workplace exposure to the gas, the long-term effects of chronic, low-level exposure—like that endured by residents near the Salton Sea—remain poorly understood.
Communities surrounding the lake, including the Torres Martinez Desert Cahuilla Indian Reservation and several low-income, predominantly Latino towns, have long reported symptoms like headaches and nosebleeds during the late summer months, when the odor peaks. The new study affirms these accounts with hard data, showing sustained hydrogen sulfide levels far above state air-quality thresholds.
Researchers from Brown University, in collaboration with local nonprofit Alianza Coachella Valley, analyzed data from existing air monitors and installed a new sensor directly over the lake’s surface. That sensor recorded 177 hours of hydrogen sulfide levels exceeding state limits between May and July of 2024. By contrast, a nearby onshore monitor detected just four such hours during the same period. The disparity, scientists say, suggests that standard monitoring systems may be dramatically underestimating the scope of exposure.
The Salton Sea’s troubled history is rooted in an accident. Formed in 1905 when the Colorado River breached irrigation canals, the lake became a popular vacation destination in the mid-20th century. But over time, as water from agricultural runoff became its primary inflow, the lake’s salinity increased and its ecosystems began to collapse. A water transfer deal in the early 2000s hastened the decline, diverting flows to urban areas and reducing the agricultural runoff that had kept the lake from vanishing altogether.
Today, the Salton Sea is twice as salty as the ocean and nearly 13 feet lower than it was two decades ago. Its shrinking shoreline exposes more toxic sediment, and its warming waters become increasingly hospitable to algal blooms and microbial decay—perfect conditions for hydrogen sulfide accumulation.
In response to worsening dust and air pollution, California has recently initiated wetland restoration projects around the lake’s perimeter. But the impact of these measures on gas emissions remains unclear. Researchers have called for improved monitoring, more robust regulation of nutrient inputs, and greater coordination between water and air quality agencies.
Without urgent action, the communities that have lived in the shadow of this lake for generations may continue to pay the price for decisions made far upstream.
