Billions of Gallons of Freshwater Sit Beneath the Great Salt Lake — and Nobody Knows What to Do With It

A University of Utah team has confirmed a massive freshwater reservoir extending kilometers beneath the bed of the shrinking Great Salt Lake. As Utah faces a mounting water crisis, the discovery raises urgent questions about extraction, ecology, and whether the American West can resist repeating its worst mistakes.

The Discovery

In February 2025, a helicopter towing electromagnetic survey equipment flew 154 miles of east-west transects over Farmington Bay and Antelope Island on the southeastern edge of Great Salt Lake [1]. The team, led by University of Utah geophysicist Michael Zhdanov and hydrologist Bill Johnson, was chasing a mystery: freshwater springs had been welling up through the lake's exposed playa, forming strange mounds choked with phragmites reeds [1].

What the airborne electromagnetic (AEM) surveys revealed, published in Scientific Reports in March 2026, exceeded expectations [1][2]. Freshwater saturates the sediments beneath the lake's hypersaline surface to depths of 3 to 4 kilometers — roughly 10,000 to 13,000 feet [1][2]. A thin saline layer exists within the first 10 meters of the surface, but below that, the subsurface turns resistive, indicating fresh water [1].

"You clearly see near the surface is saline water, 10 meters underneath is resistive freshwater," Zhdanov explained [1]. More surprising still was the freshwater's direction of flow. "You'd expect the freshwater from the mountains to come in somewhere at the periphery," Johnson said. "But we find it's coming in towards the interior of the lake and possibly under the entire lake. We don't know" [3].

The survey covered only the southeastern corner of a lake spanning roughly 1,500 square miles [2]. If the freshwater system extends further — and the data suggests it might — the reservoir's total volume could be enormous, though no precise estimate has been published.

What We Know — and What We Don't

The discovery has rewritten part of the Great Salt Lake's hydrology. Discharge from these freshwater springs may account for as much as 12 percent of the lake's total water budget, far more than the roughly 3 percent that hydrologists had previously assumed [1]. Researchers believe hundreds of groundwater-fed oases are spread across newly exposed portions of the playa [1].

But critical unknowns remain. No volume estimate — in acre-feet or cubic kilometers — has been published. The water's potability, mineral content, and precise salinity are uncharacterized beyond the basic conductivity measurements that distinguish it from the brine above [2][3]. Most importantly, the recharge mechanism is not yet understood: whether this is ancient water trapped in deep sediments, actively cycling snowmelt from the Wasatch Range, or some combination [3].

A companion study led by geophysicist Mike Thorne used electrical resistivity tomography (ERT) at 30 locations around the lake's southern and eastern margins and found a "patchy and complex" underground picture, shaped by geology, rivers, mountain recharge, and the lake's long history of expansion and contraction [4]. The subsurface is not a single, uniform aquifer but a patchwork of fresh and saline groundwater [4].

A Lake in Crisis

The discovery arrives at a precarious moment for the Great Salt Lake itself. When the 2025 water year ended, the lake's south arm stood at 4,191.1 feet — its third-lowest recorded elevation since detailed measurements began in 1903, well within what managers call the "serious adverse effects" range [5][6]. On July 3, 2022, the lake hit an all-time record low of 4,190.1 feet [7]. Its historic average is approximately 4,200 feet [7].

Source: USGS / Utah Division of Water Resources

Data as of Mar 22, 2026CSV

The causes are well documented. Municipal and industrial water use diverts water from the rivers feeding the lake before it arrives. Warmer average temperatures increase evaporation. Rainfall remains low [5]. About 800 square miles of lakebed are now exposed, releasing dust laced with heavy metals into the air breathed by communities along the Wasatch Front [1][8].

Between 2021 and 2025, conservation and water-leasing programs delivered nearly 400,000 acre-feet of water to the lake [5]. But thirty-year projections from the Utah Division of Water Resources indicate that a sustained additional inflow of 800,000 acre-feet per year is needed to return the lake to a healthy elevation of 4,198 feet by 2055 [5].

The Temptation to Tap It

Utah's population stood at approximately 3.42 million in 2023 [9] and is projected to reach 5.5 million by 2060 — a 65 percent increase from 2020 levels [10]. The state expects to hit 4 million residents between 2032 and 2033, and 5 million between 2050 and 2051 [10]. At 2015 consumption rates, Utah's reliable water supply would be exceeded sometime between 2030 and 2040 [11]. With continued conservation, that timeline could extend to 2055 [11]. To support growth, the state and its water providers will need an estimated $38 billion in infrastructure investment [11].

Against that backdrop, discovering a deep freshwater reservoir beneath one of the state's most prominent geographic features immediately raises the question: why not use it?

The economics alone present obstacles. Extracting water from depths of 3 to 4 kilometers would require infrastructure that dwarfs conventional well drilling. By comparison, surface water from the Colorado River costs municipal districts an average of $512 per acre-foot [12]. Desalination runs between $4,000 and $7,000 per acre-foot at facilities like the Carlsbad plant in San Diego County [12]. Deep groundwater extraction at the depths identified beneath the Great Salt Lake has no established cost benchmark, but would almost certainly exceed even desalination costs given the engineering challenges involved.

Conservation remains the cheapest option. Agricultural conservation programs in the Colorado River basin save water for as little as $70 per acre-foot [12]. Utah's own water conservation programs pay approximately $390 per acre-foot [13].

Who Owns the Water?

Utah follows the prior appropriation doctrine — "first in time, first in right" — a system dating to the 1850s California Gold Rush [14]. Groundwater and surface water are regulated separately, and individuals or entities must obtain a permit from the state engineer before accessing groundwater for any purpose [14][15].

But deep groundwater beneath a terminal lake doesn't fit neatly into existing legal categories. The state would likely assert ownership, but federal entities could have claims given the lake's significance as a federally recognized ecosystem. Private landowners on the lake's periphery might argue for access rights.

Tribal claims add another layer of complexity. The water right claims of the Navajo Nation, for example, have not been quantified, but under the Federal Reserved Rights Doctrine, tribal rights carry earlier priority dates than many state-approved appropriations [16]. Under the Ute Indian Water Compact, the Utes hold rights to an additional 105,000 acre-feet of depletion from Utah's apportioned waters [16]. Any attempt to develop a new, large-scale water source would face legal scrutiny over whether it affects tribal entitlements.

The Ecological Stakes

The Great Salt Lake supports an ecosystem whose economic and ecological value is difficult to overstate. The lake generates approximately $1.3 billion annually through mineral extraction and brine shrimp harvesting [17]. The mineral extraction industry alone — producing magnesium, road salt, and potassium fertilizer from more than 100,000 acres of solar evaporation ponds — accounts for close to $300 million per year [17].

Brine shrimp are the lake's keystone species. Great Salt Lake is the world's single largest source of brine shrimp, supplying roughly 45 percent of global brine shrimp egg production [18]. The harvest supports a $60 to $67 million annual industry that feeds fish farms worldwide, helping produce an estimated 20 billion pounds of seafood per year [18][19].

Around 10 million birds from more than 250 species depend on the lake during migration [18]. Approximately 90 percent of North America's eared grebe population stages at the lake, with individual birds consuming up to 30,000 brine shrimp per day [18]. Wilson's phalaropes — 33 to 40 percent of the global population — stop at the lake each summer, doubling their body weight on brine shrimp before continuing south [18].

Source: Utah Division of Wildlife Resources / USGS

Data as of Mar 22, 2026CSV

Extracting freshwater from beneath the lake could disrupt the delicate balance that sustains these populations. If groundwater discharge accounts for 12 percent of the lake's water budget [1], pumping it out instead of allowing it to flow upward could accelerate the lake's decline. "There are beneficial effects of this groundwater that we need to understand before we go extracting more of it," Johnson cautioned [3].

USGS simulations of groundwater pumping in the East Shore area have already shown concerning results: water-level declines of 35 to 50 feet near pumping centers and a decrease in ground-water storage of 80,000 to 115,000 acre-feet after 20 years [8].

The Precedent Problem

The American West has a troubled history with discovered groundwater reserves. The Ogallala Aquifer, a shallow water table aquifer beneath 174,000 square miles of the Great Plains, is the most instructive case [20]. After large-scale agricultural pumping began following World War II, yearly withdrawals quintupled between 1949 and 1974 [20]. Farmers in some areas withdrew four to six feet of water per year while natural recharge replaced just half an inch [20].

Today the Ogallala is being depleted at an annual volume equivalent to 18 Colorado Rivers [20]. Between 2001 and 2011, losses equaled a third of the aquifer's total cumulative depletion during the entire 20th century [20]. Scientists estimate natural processes would take 6,000 years to refill it [20]. The aquifer supplies at least one-fifth of the total annual U.S. agricultural harvest; if it runs dry, more than $20 billion in food and fiber vanishes from global markets [20].

The Aral Sea in Central Asia offers an even starker warning. Once the world's fourth-largest lake, Soviet-era irrigation diversions reduced it to roughly 10 percent of its original volume by 2007, collapsing fisheries, poisoning surrounding communities with toxic dust from the exposed lakebed, and creating a regional health catastrophe.

The parallels to the Great Salt Lake are unsettling. A terminal lake already at near-record lows. Toxic dust already blowing off exposed playa. An economy dependent on the lake's ecology. And now, a large freshwater source beneath it that some will inevitably argue should be tapped.

The Case for Restraint — and the Case Against It

Proponents of leaving the reservoir alone point to the unknowns. Without understanding the recharge rate, any extraction risks mining a non-renewable resource. If the water is ancient — trapped in deep sediments for thousands or millions of years — pumping it out would be a one-time draw with irreversible consequences. Even if active recharge exists from Wasatch Range snowmelt, climate change is reducing snowpack across the Western U.S., making future recharge uncertain.

The counterargument is pragmatic. Utah's population is growing by roughly 55,000 people per year [10]. The Colorado River is over-allocated, with every upper and lower basin state fighting over declining flows. Lake Powell and Lake Mead have spent years at historically low levels. If conservation alone cannot close the gap between supply and demand — and the state's own projections suggest it may not without significant agricultural water transfers — then sitting on a freshwater resource while communities face rationing demands justification.

The researchers themselves are cautious. The first proposed use isn't drinking water for Salt Lake City — it's wetting down exposed playa to reduce toxic dust storms [1]. That application would keep the water in the lake system rather than diverting it. "We need to understand whether we can use it to keep parts of the lakebed wet without perturbing the freshwater system too much," Johnson said [3].

What Comes Next

The AEM survey covered only a fraction of the lake. The University of Utah team, funded by the Utah Department of Natural Resources, plans to extend the survey across the full 1,500 square miles [2]. Future work will need to characterize the water's chemistry, model its recharge pathways, and determine whether any portion of the reservoir is actively cycling or effectively fossil water.

The discovery does not change the fundamental math facing the Great Salt Lake: the lake needs more water flowing in, not more water being pumped out. But it does add a new variable to an already complicated equation — one that will test whether Utah has learned from the West's long record of depleting the resources it depends on most.

The study, "Airborne Electromagnetic and Magnetic Survey of Freshwater Beneath the Great Salt Lake Playa," was published in Scientific Reports on March 20, 2026 (DOI: 10.1038/s41598-026-40995-5) [1].