A massive freshwater reservoir is hiding under the Great Salt Lake

A massive hidden freshwater reservoir beneath the Great Salt Lake could reshape both science—and solutions to its growing dust crisis.

Date:

March 21, 2026

Source:

University of Utah

Summary:

A hidden freshwater system deep beneath the Great Salt Lake has been revealed using airborne electromagnetic surveys. Scientists found that freshwater extends much farther under the lake than expected, reaching depths of up to 4 kilometers. The discovery began with mysterious reed-covered mounds formed by pressurized groundwater pushing upward. Researchers are now investigating whether this underground water could help control hazardous dust from the drying lakebed.

A pragmities-covered mound that has formed on the dry playa of Farmington Bay. It was formed in recent years by freshwater getting pushed to the surface of the exposed lakebed. Credit: Brian Maffly, University of Utah

A newly identified underground freshwater system beneath the Great Salt Lake is becoming clearer thanks to a study that used airborne electromagnetic (AEM) surveys to map geologic formations below Farmington Bay and Antelope Island along the lake's southeastern edge.

Researchers from the University of Utah analyzed the data and found that freshwater fills sediments beneath the lake's highly salty surface, reaching depths of 3 to 4 kilometers, or about 10,000 to 13,000 feet. The helicopter-based survey was carried out last year after scientists observed freshwater emerging under pressure in parts of the exposed lakebed in Farmington Bay, forming unusual mounds covered in dense phragmites reeds.

According to lead author Michael Zhdanov, the study marks the first time AEM technology has successfully detected freshwater beneath the thin layer of conductive saltwater at the surface of the Great Salt Lake. The team also mapped how far the freshwater extends beneath Farmington Bay and estimated how deep the water-saturated sediments go by identifying the underlying basement structure.

"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. If you know how deep, you know how wide, you know the porous space, you can calculate the potential freshwater volume," said Zhdanov, a distinguished professor of geology & geophysics and director of the Consortium for Electromagnetic Modeling and Inversion, or CEMI.

State-Funded Research on a Newly Discovered Aquifer

The findings were published in the Nature-affiliated journal Scientific Reports. This work is part of a broader research initiative led by the University of Utah's Department of Geology & Geophysics and funded by the Utah Department of Natural Resources. The goal is to better understand groundwater beneath the Great Salt Lake, the largest terminal lake in the Western Hemisphere.

Senior faculty and graduate students have contributed to this ongoing effort, which has already produced two additional studies, with more expected.

The new results indicate that freshwater may be moving into the subsurface toward the lake's interior rather than staying near the edges, which is what scientists typically expect. Hydrologist Bill Johnson, a co-author on the groundwater studies, highlighted how unusual this pattern is.

"The unexpected part of this wasn't the salt lens that we see near the surface across the playa. 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," Johnson said on a recent appearance on KPCW's Cool Science Radio show. "What we would normally expect as hydrologists is that that brine would occupy the entire volume underneath that lake. It's denser than the freshwater. You'd expect the freshwater from the mountains to come in somewhere at the periphery. But we find it's coming in towards the interior. And there's what appears to be deep volume of this freshwater coming in underneath that saline lens."

Freshwater Could Help Reduce Toxic Dust

The research was prompted by the appearance of circular mounds on the dried lakebed in Farmington Bay over recent years. These features measure 50 to 100 meters across and are covered in tall reeds reaching about 15 feet. As water levels in the lake have dropped, around 800 square miles of exposed lakebed have become a growing source of dust pollution affecting nearby communities.

Johnson and his colleagues are investigating whether the artesian groundwater could be used safely to reduce dust, which contains harmful metals.

"There are beneficial effects of this groundwater that we need to understand before we go extracting more of it. 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," Johnson said. "To me, that's a primary objective because it's very practical and it's unlikely we'll be able to fill Farmington Bay and other parts of the playa enough to avoid some dust spots appearing at the higher elevations. This would be a great way to get at that."

Johnson, along with colleagues including Mike Thorne and Kip Solomon, is seeking funding to expand the research to cover a larger portion of the lake.

Airborne Surveys Reveal Subsurface Structure

In this study, scientists used airborne electromagnetic surveys to measure electrical resistivity down to about 100 meters, allowing them to distinguish freshwater from saltwater, which conducts electricity more easily. To carry out the work, Johnson and Zhdanov hired a Canadian geophysical team to fly instruments suspended beneath a helicopter in February 2025. The aircraft completed 10 east-west survey lines across Farmington Bay and the northern part of Antelope Island, covering a total of 154 miles.

Zhdanov's team used the data to map where freshwater meets saline water underground. One of the reed-covered mounds was located directly above a point where freshwater was rising through a break in the impermeable layer beneath the lake.

"Red means very conductive, blue is resistive," Zhdanov said while explaining the map. "You clearly see near surface is saline water, 10 meters underneath is resistive freshwater. You see clearly it's everywhere."

3D Imaging Reveals Deep Geological Features

The CEMI research group developed a method to create detailed 3D images of the subsurface by combining airborne electromagnetic data with magnetic measurements. Using this approach, the team produced a tomographic model extending deep below Farmington Bay, offering new insight into the area's geological and hydrological framework.

Their analysis shows that the basement beneath the playa is relatively shallow, less than 200 meters deep, before dropping sharply to depths of 3 to 4 kilometers. This abrupt transition occurs beneath one of the phragmites mounds and marks a major structural boundary that warrants further investigation.

"This is why we need to survey the entire Great Salt Lake. Then we'll know the top and the bottom," Zhdanov said. "To study the top we use airborne electromagnetic methods, which gives us the thickness of the saline layer and where the freshwater starts under the saline layer. To study the bottom, we use magnetic data. We use different techniques to study the vertical extent of this freshwater-saturated sediments, to find the depth to the basement."

Although this initial study covered only a small section of the lake, Zhdanov believes it is feasible to extend airborne surveys across the lake's full 1,500-square-mile area.

A comprehensive survey could support regional water management decisions and help guide similar efforts to locate freshwater beneath terminal lakes around the world.

Story Source:

Materials provided by University of Utah. Note: Content may be edited for style and length.

Journal Reference:

1. M. S. Zhdanov, M. Jorgensen, L. Cox, W. P. Johnson, D. K. Solomon. Airborne geophysical imaging of freshwater reservoir beneath the eastern margin of Great Salt Lake. Scientific Reports, 2026; DOI: 10.1038/s41598-026-40995-5