A hidden reservoir of freshwater, potentially vast in scale, lies beneath the Great Salt Lake, a discovery that could reshape how Utah manages its dwindling water resources and combats a growing public health crisis. Researchers at the University of Utah have, for the first time, mapped this subsurface freshwater system, finding it extends to depths of 3 to 4 kilometers (roughly 10,000 to 13,000 feet) beneath the lake’s highly saline surface. The findings, published in Scientific Reports, offer a glimmer of hope as the Great Salt Lake continues to shrink, exposing toxic dust and threatening both human health and the region’s unique ecosystem.
The research stems from observations of unusual mounds covered in dense phragmites reeds emerging from Farmington Bay, a section of the lake. These mounds, first noticed as water levels dropped, were found to be fed by freshwater rising under pressure. To understand the extent of this phenomenon, scientists employed airborne electromagnetic (AEM) surveys, a technology that measures electrical resistivity to differentiate between freshwater and saltwater. The surveys, conducted in February 2025, covered 154 miles across Farmington Bay and the northern part of Antelope Island.
“We were able to answer the question of how deep is this potential reservoir and what is its spatial extent beneath the eastern lake margin,” explained Michael Zhdanov, lead author of the study and a distinguished professor of geology & geophysics at the University of Utah, who also directs the Consortium for Electromagnetic Modeling and Inversion (CEMI). “If you understand how deep, you know how wide, you know the porous space, you can calculate the potential freshwater volume.” The team’s analysis revealed that the freshwater isn’t simply pooling at the edges of the lake, as previously expected, but appears to be flowing towards the interior, a surprising discovery that challenges conventional hydrological understanding.
Unconventional Flow and a Potential Lifeline
Hydrologist Bill Johnson, a co-author on the research, highlighted the unexpected nature of the freshwater’s movement. “The unexpected part of this wasn’t the salt lens that we observe near the surface across the playa,” Johnson said during an appearance on KPCW’s Cool Science Radio show. “It’s that the freshwater underneath it extends so far in towards the interior of the lake and possibly under the entire lake. We don’t know.” Traditionally, hydrologists anticipate brine, being denser than freshwater, to occupy the entire volume beneath a terminal lake like the Great Salt Lake. The observed flow pattern suggests a more complex system at play.
The discovery is particularly significant given the dire situation facing the Great Salt Lake. Decades of water diversion for agriculture and urban use have led to a dramatic decline in water levels, exposing approximately 800 square miles of lakebed. This exposed playa is a major source of toxic dust, containing harmful metals like arsenic, which poses a serious health risk to nearby communities. According to the Utah Department of Environmental Quality, the dust contributes to increased rates of respiratory illness and other health problems.
Dust Mitigation and Future Research
Researchers are now investigating whether the newly discovered artesian groundwater could be used to mitigate the dust problem. The idea is to strategically wet dust hotspots with the freshwater, suppressing the airborne particles. “There are beneficial effects of this groundwater that we demand to understand before we go extracting more of it,” Johnson cautioned. “A first-order objective is to understand whether we could use this freshwater to wet dust hotspots and douse them in a meaningful way without perturbing the freshwater system too much.”
The initial study focused on a relatively small area of the lake. Zhdanov believes extending the airborne surveys across the Great Salt Lake’s full 1,500-square-mile area is feasible and crucial. “This is why we need to survey the entire Great Salt Lake. Then we’ll know the top and the bottom,” he stated. Combining airborne electromagnetic data with magnetic measurements allows his team at CEMI to create detailed 3D images of the subsurface, revealing the depth of the saline layer and the extent of the underlying freshwater. Their analysis already shows the basement beneath the playa is relatively shallow in some areas, dropping sharply to depths of 3 to 4 kilometers in others, indicating a complex geological structure.
The research is part of a broader initiative led by the University of Utah’s Department of Geology & Geophysics and funded by the Utah Department of Natural Resources. This ongoing effort has already yielded two additional studies, with more expected as the team continues to analyze the data. The ultimate goal is to develop a comprehensive understanding of groundwater dynamics beneath the Great Salt Lake, informing sustainable water management strategies for the region.
The potential implications of this discovery extend beyond Utah. Terminal lakes around the world, facing similar challenges from climate change and water scarcity, could benefit from the techniques and insights gained from this research. Understanding how freshwater accumulates and flows beneath these systems is critical for preserving these vital ecosystems and protecting the communities that depend on them.
Researchers are currently seeking additional funding to expand the scope of the surveys and conduct more detailed hydrological modeling. The next major milestone is expected in late 2026, when preliminary results from the expanded surveys are anticipated to be released. The future of the Great Salt Lake, and the health of the surrounding communities, may well depend on unlocking the full potential of this hidden freshwater reservoir.
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