The Great Salt Lake is remarkably shallow. At its historical average surface elevation of about 1,280 meters (4,200 feet) above sea level, the lake’s average depth is just 4.3 meters, or roughly 14 feet. Its maximum depth at typical water levels sits around 10 meters (33 feet), making it one of the shallowest major lakes on Earth relative to its surface area. But that number has been a moving target for decades, and the lake’s depth today tells a story about water use, climate, and an ecosystem under growing pressure.
A Vast Lake That Barely Qualifies as Deep
To put 4.3 meters in perspective, that is about the depth of the deep end of a large swimming pool. Yet at that average elevation, the Great Salt Lake covers roughly 4,400 square kilometers of surface area, making it the largest saltwater lake in the Western Hemisphere by area. The shallowness means that even modest changes in water level translate into dramatic swings in surface coverage. A rise of just three meters, from 1,280 to 1,283 meters elevation, pushes the lake’s footprint from 4,400 to nearly 6,000 square kilometers because the surrounding terrain is so flat.1PLoS ONE. How Do Changes to the Railroad Causeway in Utah’s Great Salt Lake Affect Water and Salt Flow? The reverse is equally true: when water drops, enormous stretches of lakebed become exposed to the air.
The lake sits in a broad, flat basin with gently sloping margins on most sides. There is no single deep trench or basin floor that holds water the way a steep-sided mountain lake might. Instead, the lakebed is essentially a wide, shallow pan. The south arm holds roughly 80 percent more volume than the north arm, but neither is what anyone would call deep.1PLoS ONE. How Do Changes to the Railroad Causeway in Utah’s Great Salt Lake Affect Water and Salt Flow? Most of the lake bottom lies within a few meters of the surface at any given time.
The Ghost of Lake Bonneville
The Great Salt Lake is the shrunken remnant of a much larger and much deeper body of water. During the last ice age, Lake Bonneville filled a vast portion of what is now western Utah, reaching depths of over 300 meters in places and covering an area comparable to present-day Lake Michigan. The Bonneville Salt Flats, the terraced benches visible on the Wasatch Range, and other landforms across the region are all remnants of that ancient lake’s shorelines.
Lake Bonneville existed from roughly 30,000 to 11,500 years ago, after which the climate warmed and the lake shrank dramatically into the shallow, hypersaline body we know today.2Sedimentology. The lacustrine microbial carbonate factory of the successive Lake Bonneville and Great Salt Lake, Utah, USA The transition was not gentle. Around 14,500 years ago, Lake Bonneville catastrophically breached its northern rim at Red Rock Pass in Idaho, sending a massive flood down the Snake River and dropping the lake level by about 100 meters in a geologically brief period. What remained continued to shrink as the region dried, eventually settling into the shallow configuration the Great Salt Lake has maintained for roughly the last 11,000 years.
This history matters for understanding depth because the lakebed itself was shaped by Bonneville. The broad, flat basin is what you get when a massive lake evaporates and leaves behind its sediment-filled floor. The Great Salt Lake does not sit in a deep geological depression; it sits in the leftover footprint of its much grander predecessor.
The Railroad Causeway and Two Different Lakes
Since 1959, a solid-fill railroad causeway has divided the Great Salt Lake roughly in half, creating a north arm and a south arm that function almost as separate water bodies. The three major rivers feeding the lake (the Bear, Weber, and Jordan) all empty into the south arm, so the south arm receives the vast majority of freshwater inflow. The north arm, largely cut off from those rivers, became far saltier over time.
This division affects depth in practical ways. The south arm, with its greater inflow, has historically maintained higher water levels and more volume. The north arm, starved of fresh water, has at times been reduced to a shallow brine so concentrated that salt crusts form across exposed portions of the lakebed. The causeway has small openings that allow some water and salt to exchange between the two arms, but the flow is limited enough to sustain major differences in salinity and water level on either side.
One of the more scientifically interesting consequences of this exchange is the “deep brine layer” in the south arm. When dense, extra-salty water from the north arm flows through or under the causeway into the south arm, it sinks to the bottom and forms a distinct layer of heavy brine beneath the lighter surface water. This deep brine layer is ecologically important because it creates low-oxygen conditions near the lakebed that affect nutrient cycling.3SN Applied Sciences. Historic low stand of Great Salt Lake, Utah: I Researchers have documented that this layer is intermittent: it only forms when causeway exchange supports enough flow from north to south.4Water. The Salinity of the Great Salt Lake and Its Deep Brine Layer When the lake is very low and the causeway exchange diminishes, the deep brine layer can disappear altogether, altering the chemistry of the lake bottom.
Why the Lake Keeps Getting Shallower
The Great Salt Lake hit its modern high-water mark in 1986 and 1987, when flooding pushed levels well above the long-term average. Since then, the trend has been almost relentlessly downward. By the early 2020s, the lake had reached historic lows, with surface elevation dropping below 1,278 meters, roughly two meters below the long-term average. In a lake this shallow, losing two meters of depth means losing a substantial fraction of total volume and exposing hundreds of square kilometers of lakebed.
The decline has two intertwined causes. The dominant one is human water consumption. The rivers that feed the Great Salt Lake pass through heavily irrigated agricultural land before they reach it, and agricultural activities account for about 67 percent of total water withdrawals in the basin.5Journal of Rural Studies. “We live in an agricultural death zone”: A post-growth approach for ensuring farmer and lake livelihoods in the Great Salt Lake Basin Every gallon diverted for crops or livestock is a gallon that does not reach the lake. Municipal and industrial use adds to the deficit. The second cause is rising temperatures driven by climate change, which increase evaporation from the lake surface and evapotranspiration from the surrounding landscape. Together, these forces have been steadily depriving the lake of the water it needs to maintain its already modest depth.
The lake has no outlet. Like all terminal lakes, the Great Salt Lake loses water only through evaporation. This means its level is entirely determined by the balance between inflow and evaporation. When more water is pulled from the feeder rivers upstream, or when warmer air increases evaporation, the lake shrinks. There is no downstream valve to close or overflow channel to redirect. The lake simply gets smaller and shallower.
What Lives in 14 Feet of Water
The extreme shallowness and high salinity of the Great Salt Lake severely limit what can survive in it. There are no fish. The lake’s ecosystem runs on two primary invertebrate groups: brine shrimp (the species Artemia franciscana) and brine flies (the species Ephydra gracilis). These organisms are the food base for millions of migratory birds that depend on the lake as a stopover or breeding ground.
Depth and salinity are tightly linked in the Great Salt Lake, and both affect these creatures directly. When the lake is deeper, salinity tends to be lower because there is more freshwater dilution. When the lake shrinks, salinity concentrates. Experiments simulating these salinity ranges found that brine shrimp nearly disappear at both very low and very high salinities, and their biomass drops roughly fourfold as salt levels climb from moderate to extremely high concentrations.6Canadian Journal of Fisheries and Aquatic Sciences. The effects of salinity on plankton and benthic communities in the Great Salt Lake, Utah, USA: a microcosm experiment Brine fly biomass also drops substantially under saltier conditions. As the lake gets shallower and saltier, the base of the food web shrinks.
The consequences ripple upward to birds. The Great Salt Lake hosts one of the largest breeding colonies of American white pelicans in North America, along with huge populations of eared grebes, Wilson’s phalaropes, and other species. When lake levels drop, islands that once protected nesting colonies from land-based predators like coyotes and foxes become connected to the mainland by exposed lakebed. Research on breeding colonies at the lake has found that these low levels, which allow terrestrial predators access to nesting sites, are a probable driver of recent colony declines.7PubMed. Scale-dependent population drivers inform avian management in a declining saline lake ecosystem Depth, in other words, is not just a number on a bathymetric chart. For the birds, it is the moat that keeps predators away.
Dust from the Exposed Lakebed
When the lake shrinks and its bed dries out, the exposed sediment becomes a source of windblown dust that reaches populated areas along the Wasatch Front. This is not ordinary dust. The lakebed has accumulated metals and other elements over millennia, and when those sediments dry and get picked up by wind, they carry contaminants into neighborhoods, schools, and farmland. Among the metals measured in Great Salt Lake dust, zinc, copper, and lead had the highest total concentrations, while cadmium, lead, and arsenic showed high bioaccessibility in simulated stomach-acid tests, meaning they are readily absorbed if swallowed.8Atmospheric Environment. Metal mobility and bioaccessibility in Great Salt Lake dust and exposure risks for humans and food crops
Arsenic in particular drives the estimated health risk from accidentally ingesting this dust, with children facing higher risks than adults due to hand-to-mouth behavior and lower body weight. Greenhouse experiments have also shown that the dust can transfer metals into food crops: cabbage grown with exposure to Great Salt Lake dust accumulated lithium, arsenic, strontium, antimony, uranium, and other elements in its leaves.8Atmospheric Environment. Metal mobility and bioaccessibility in Great Salt Lake dust and exposure risks for humans and food crops The concern is not just breathing in particles but also eating produce grown in affected areas.
Dust monitoring near the lake has found that the highest dust fluxes occur closest to the exposed lakebed, particularly northeast of Farmington Bay. The chemical fingerprint of the dust varies by location: some sites show signatures consistent with lakebed sediment, while others near more urbanized areas like Bountiful reflect contributions from industrial and anthropogenic sources as well.9PubMed Central. Contributions of Great Salt Lake Playa- and Industrially Sourced Priority Pollutant Metals in Dust Contribute to Possible Health Hazards in the Communities of Northern Utah Thallium, arsenic, lead, cobalt, and chromium contributed most to the estimated non-cancer health hazard, and among those, arsenic and sometimes lead appear to come specifically from the lake’s exposed playa. The practical implication is straightforward: suppressing dust from the lakebed by keeping it underwater, which means maintaining lake depth, could reduce health risks for children in northern Utah.
Strange Geology on the Shrinking Shoreline
As the lake has dropped to historic lows, some unusual geological features have appeared along its retreating margins. Beginning in the fall of 2019, when lake elevation fell below roughly 1,278.6 meters, crystalline mounds began forming on the southeastern shore near Great Salt Lake State Park and on nearby Antelope Island. These mounds are made of mirabilite, a hydrated sodium sulfate mineral that forms when sulfate-rich spring water seeps up through newly exposed lakebed and hits cold winter air.10Chemical Geology. Sulfate-rich spring seeps and seasonal formation of terraced, crystalline mirabilite mounds along the shores of Great Salt Lake, Utah The resulting formations are striking, with terraced, crystalline structures that look almost sculpted.
These mounds exist because the lake is too shallow to cover the springs that feed them. At higher lake levels, the spring discharge points would be underwater, and the mirabilite would dissolve as fast as it formed. The mounds are, in a sense, geological symptoms of the lake’s depth problem. Deeper beneath the shoreline, a layer of this same mineral acts as a semi-confining barrier for groundwater. Seepage measurements along the south shore found fresh groundwater pushing up through an oolitic sand layer that sits atop the buried mirabilite at a rate of about 0.8 centimeters per day, delivering dissolved selenium and other elements into the lake.11Journal of Hydrology. Quantity and quality of groundwater discharge in a hypersaline lake environment Groundwater is a minor but real contributor to the lake’s water budget and chemistry.
The Lakebed’s Hidden Landscape
Beneath the shallow water, the Great Salt Lake floor is not the featureless flat pan you might imagine. Much of it is covered with microbialites, reef-like structures built by communities of microorganisms that trap and bind carbonate minerals over time. These formations, called bioherms, occupy an estimated area of more than 700 square kilometers in the south arm and more than 300 square kilometers in the north arm.12The Depositional Record. Characteristics and controls on the distribution of sublittoral microbial bioherms in Great Salt Lake, Utah: Implications for understanding microbialite development Some of these structures rise more than 1.5 meters above the surrounding lake bottom, which is a substantial feature in a lake that averages only a few meters deep.
These microbialites are scientifically significant well beyond the lake itself. They are among the best modern analogs for ancient microbial reefs found in the fossil record, and the two-phase history of the Bonneville Basin, from deep freshwater Lake Bonneville to shallow hypersaline Great Salt Lake, has produced distinct generations of microbial carbonate deposits that help researchers understand how such structures form under different conditions.2Sedimentology. The lacustrine microbial carbonate factory of the successive Lake Bonneville and Great Salt Lake, Utah, USA The microbialites also play an ecological role, providing habitat and surface area for the algae and bacteria that sit at the very bottom of the lake’s food chain. As the lake gets shallower, more of these structures become exposed to air, potentially killing the microbial communities on their surfaces and further degrading the ecosystem.
Economic Stakes of a Shallow Lake Getting Shallower
The Great Salt Lake’s depth is not just an environmental metric. It underpins a regional economy tied to mineral extraction, brine shrimp harvesting, and recreation. Companies pump lake brine into evaporation ponds to extract salt, magnesium, potassium, and lithium, an industry worth hundreds of millions of dollars annually. The brine shrimp harvest, sold internationally as aquaculture feed, depends on maintaining the salinity range where the shrimp thrive: too fresh and fish outcompete them, too salty and their biomass collapses. Both industries need water in the lake to operate.
Bioeconomic modeling of the lake system has examined how prolonged drought, mimicking a drying climate’s effect on the lake’s nutrient pool, ripples through the regional economy and even affects international trading partners through supply-chain connections.13Natural Resource Modeling. Measuring the bioeconomic impacts of prolonged drought on a lake ecosystem: The case of the Great Salt Lake, Utah The feedback loops are complex: less water means higher salinity, which means fewer brine shrimp, which means less harvest revenue, which changes economic incentives across the basin. The modeling suggests the system can eventually reach a new equilibrium, but that equilibrium represents a diminished economy adapted to a diminished lake.
Recreation also suffers as the lake shrinks. Marinas built for one water level find themselves stranded far from the waterline. Beaches become mud flats. The smell of exposed organic sediment deters visitors. State parks along the shore have periodically closed access points when the receding water made them unusable. For a metropolitan area of over a million people within an hour’s drive, the lake’s depth has tangible effects on quality of life and tourism revenue that extend well beyond the shoreline.