University of Utah researchers have identified a large freshwater reservoir sitting beneath the hypersaline waters of Great Salt Lake, upending conventional assumptions about how water moves underground in the region. The discovery, based on airborne electromagnetic surveys and direct subsurface measurements, suggests that freshwater is flowing toward the lake’s interior rather than pooling at its edges. As the lake continues to shrink from drought and water diversions, the finding raises immediate questions about whether this hidden resource could help slow an environmental crisis already threatening air quality across northern Utah.
Helicopter Surveys Reveal a Hidden Layer
In February 2025, a team from the University of Utah hired a Canadian firm called Expert Geophysics to fly a helicopter-mounted electromagnetic survey over the eastern margin of Great Salt Lake, focusing on Farmington Bay and the area near Antelope Island. The pilot airborne electromagnetic, or AEM, survey sent electromagnetic pulses into the ground and measured the returning signals to distinguish conductive materials, like brine, from resistive ones, like freshwater-saturated sediment.
A three-dimensional inversion of that AEM data, described in a Scientific Reports paper, identified a laterally extensive resistive layer sitting beneath the lake’s highly conductive brine. In plain terms, the data showed a broad sheet of relatively fresh groundwater trapped below the salt-heavy surface water, extending well beyond the shoreline and into the lake bed itself. That geometry defied the standard expectation that freshwater inputs would concentrate along the periphery, where rivers and streams enter the basin.
To refine the geophysical interpretation, the team also drew on modeling tools accessed through a Nature platform login, allowing them to test how different subsurface configurations would affect the survey signals. The best-fitting models consistently required a relatively low-salinity layer beneath the lake, reinforcing the conclusion that the AEM data were detecting freshwater rather than simply variations in sediment composition or porosity.
Ground-Level Evidence From 56 Piezometers
The airborne survey did not stand alone. A companion field study, published in the Journal of Hydrology, provided direct physical confirmation. Researchers deployed a network of 56 nested piezometers, small monitoring wells screened at depths of approximately 1.5 to 33 meters, across multiple shore and playa locations around Great Salt Lake. Those instruments measured hydraulic head gradients, the pressure differences that reveal which direction groundwater is moving and how forcefully.
The piezometer readings showed artesian conditions, meaning groundwater at depth was under enough natural pressure to push upward toward the surface. That upward pressure is consistent with a confined freshwater aquifer being recharged from somewhere inland and discharging into the lake from below. The field data also helped calibrate the AEM results, giving the research team confidence that the resistive layer detected from the air genuinely represented freshwater rather than some other geological feature or instrument artifact.
By combining the hydraulic measurements with geophysical profiles, the scientists could map zones where pressure gradients and resistivity anomalies overlapped. Those hotspots lined up with areas where vegetation patches and subtle surface depressions had long hinted at subsurface springs, but until now, the scale and coherence of the underlying aquifer had not been recognized.
Freshwater Flowing the Wrong Direction
Perhaps the most striking finding is the direction of flow. Conventional hydrological models for terminal lakes like Great Salt Lake assume that freshwater enters at the margins, where tributary rivers deposit their loads, and that salinity increases steadily toward the center. The new evidence flips that picture. According to a NASA Earth Observatory overview of the work, freshwater appears to be entering the subsurface toward the lake’s interior, not its periphery as would be expected.
That reversal matters because it suggests a deeper, more structurally controlled plumbing system than scientists had accounted for. If freshwater is migrating through buried geological pathways toward the center of the basin, then the lake’s water budget (the accounting of all inflows and outflows that determines whether lake levels rise or fall) has been missing a significant input. Researchers working on the project have pointed to circular phragmites mounds, dense clusters of reeds that dot the exposed lakebed, as visible surface clues. These mounds appear to mark “windows” where pressurized freshwater reaches the surface, creating small oases that stand out against the otherwise barren playa.
The pattern hints that faults or other subsurface structures could be channeling groundwater upward in discrete zones. Understanding that architecture will be essential for any future management decisions, because tapping the aquifer in the wrong places could redirect flow away from the lake or depressurize the system in ways that are hard to reverse.
How Much Water Is Down There?
Quantifying the full volume of the reservoir remains an open question. The February 2025 AEM campaign covered only part of the lake’s eastern margin, and the piezometer network, while detailed, sampled specific shore and playa sites rather than the entire lakebed. No published estimate yet gives a total volume figure or a recharge rate derived from formal hydrological modeling, and the researchers caution against extrapolating too aggressively from the limited footprint of the initial surveys.
What the research team has estimated is the contribution of freshwater spring discharge to the lake’s overall inflow. Their analysis suggests that subsurface springs fed by this aquifer system may account for up to approximately 12% of the lake’s total water input. If that figure holds up under broader surveying, it would represent a substantial and previously untracked source of water for a lake that has lost roughly half its surface area over the past several decades. A state-funded research program, backed by the Utah Department of Natural Resources, is now focused on the newly discovered aquifer to better understand the groundwater system beneath Great Salt Lake.
Future work is expected to extend airborne surveys across a wider swath of the basin and to drill deeper monitoring wells that can capture the full thickness of the freshwater layer. Those efforts should clarify whether the aquifer is a continuous sheet or a patchwork of interconnected pods, and how quickly it responds to changes in snowpack, precipitation, and human groundwater pumping on the surrounding uplands.
Dust, Metals, and the Case for Careful Use
The discovery arrives at a moment when Great Salt Lake’s retreat is creating a public health hazard. As the lake shrinks, it exposes vast stretches of lakebed sediment laced with heavy metals, including arsenic and mercury, accumulated over decades. Wind picks up that sediment and carries it as fine dust into the Salt Lake City metropolitan area, home to more than a million people. Local officials worry that chronic exposure could worsen respiratory and cardiovascular problems, especially during winter inversions that already trap pollution in the valley.
The question of whether the artesian freshwater could be tapped to help is already being explored. One idea is to use some of the pressurized groundwater to create shallow, managed wetlands or moist soil zones on the exposed playa, reducing dust emissions by keeping sediments damp and anchored by vegetation. Another is to route a portion of the flow directly into the lake to help stabilize water levels, at least locally, around the most dust-prone shorelines.
Any such intervention would need to grapple with the lakebed’s geochemistry. Studies of similar saline environments, including work published in Applied Geochemistry, show that changing groundwater levels and salinity can mobilize or immobilize trace metals in complex ways. Lowering the water table might expose more sediments to oxidation, potentially increasing arsenic mobility, while sustained saturation in certain zones could lock contaminants into mineral forms that are less likely to become airborne.
Because of those uncertainties, scientists are urging a cautious approach. Pumping large volumes from the aquifer without understanding its recharge rate could not only diminish an important natural inflow to the lake but also alter pressure gradients that currently keep deeper, more saline groundwater from rising. That, in turn, could change how salts and metals move through the subsurface, with consequences that might not be immediately apparent at the surface.
Satellites, Science, and Policy Choices Ahead
The freshwater discovery also highlights the role of remote sensing in understanding stressed inland seas. Instruments aboard NASA satellites have been tracking Great Salt Lake’s shrinking footprint and rising salinity for years, providing context for the new subsurface findings. Those space-based observations, combined with airborne geophysics and ground measurements, are giving scientists an increasingly three-dimensional view of how water moves through the basin.
Recent coverage on NASA news channels has underscored how such integrated datasets can inform water management decisions, from setting diversion limits on tributary rivers to prioritizing which shorelines to protect or restore first. For policymakers, the message is that Great Salt Lake is not simply a surface reservoir but the visible expression of a much larger, dynamic groundwater system.
Whether the newly mapped aquifer becomes a tool for stabilizing the lake or another resource to be drawn down will depend on choices made in the coming years. The researchers behind the discovery emphasize that the safest path is to treat the freshwater as part of the lake’s life-support system rather than as a separate water bank to be mined. As Utah weighs options to protect both public health and a unique ecosystem, the hidden reservoir beneath Great Salt Lake is likely to move from scientific curiosity to central factor in the region’s long-term environmental strategy.
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*This article was researched with the help of AI, with human editors creating the final content.
