Researchers have identified a substantial body of freshwater trapped beneath the salty surface of Utah’s Great Salt Lake, according to a University of Utah study that combined airborne electromagnetic sensing with magnetic inversions and field observations.
What researchers found
Teams from the university’s Consortium for Electromagnetic Modeling and Inversion flew 154 miles of survey lines over Farmington Bay and the northern tip of Antelope Island in February 2025, towing electromagnetic sensors beneath a helicopter. The airborne system distinguishes brine from freshwater by measuring how readily the subsurface conducts electrical current — brine is far more conductive than fresh water.
The survey showed conductive, saline material near the surface but a transition to less conductive signals consistent with fresh water beginning around 10 meters below the playa and persisting across the mapped area. Because the airborne method senses only to roughly 100 meters, researchers then used magnetic data inversion to image the deeper basin geometry and basement rock.
| Parameter | Value |
|---|---|
| Survey flight lines | 154 miles |
| Airborne sensing depth | ~100 meters |
| Basement drop | 3–4 kilometers |
| Reed mound diameter | ~100 meters |
| Reed height | ~5 meters |
The deeper image revealed an unexpected structure beneath much of the playa: shallow basement rock in most places — less than 200 meters deep — that then plunges off a steep face into a low where the basement sits between three and four kilometers deep. That sediment-filled gap corresponded spatially with one of the prominent reed mounds on the surface. University researchers interpret the pore space in those sediments as being occupied by fresh water.
Field work and local features
Dozens of near-perfect circular mounds of tall reeds, some roughly 100 meters across with stalks reaching about 5 meters, have risen through the drying crust of Farmington Bay. Reporters have described them as "phragmites oases" or mystery islands. Graduate student Ebenezer Adomako-Mensah spent two years visiting the drying mudflats, installing pressure gauges in the reed mounds and collecting on-site data to test the hypothesis that groundwater is pushing upward under pressure.
- Airborne electromagnetic data indicated a shallow saline layer overlying fresher water beginning around 10 meters depth.
- Magnetic inversion mapped a deep basin in which sediment pore spaces appear to contain fresh water down to kilometers below the surface.
- Surface reed mounds align with inferred upward-pressured water, suggesting active discharge at the playa.
The work was published in Scientific Reports in late February and is described by lead analyst Michael Zhdanov as a pilot study — a first, focused look that raises as many questions as it answers. The research combines geophysical imaging with on-the-ground measurements to propose that substantial fresh groundwater exists beneath a body of water long regarded as overwhelmingly saline.
Implications and open questions
The finding does not immediately translate into a new, accessible water supply. Airborne electromagnetic sensing reveals contrasts in electrical conductivity but does not directly measure volume, extractability or connectivity to usable aquifers. Nor do the published results quantify how much of the pore space is saturated, how pressurized the water is across the broader basin, or whether tapping it would be technically feasible without harming ecosystems tied to the lake.
Still, the presence of fresh water under one of the nation’s saltiest terminal lakes could reshape regional understanding of groundwater architecture. The study highlights how complex basin geometry can trap and compartmentalize water in ways that are invisible from the surface. It also underscores the value of integrating remote geophysics with field observation when evaluating subsurface resources.
Researchers caution that these results represent an initial slice of the Great Salt Lake system. Additional surveys, deeper geophysical imaging, and careful hydrologic testing will be required to determine the extent, age, recharge mechanisms and potential uses or vulnerabilities of the newly identified freshwater reservoir.
