The Great Salt Lake, located in northern Utah, is the largest saltwater lake in the Western Hemisphere and one of the saltiest inland bodies of water globally. Its salinity often measures several times that of the ocean, earning it the nickname “America’s Dead Sea.” This extreme salt concentration is the result of a unique combination of geography, geology, and hydrology that has been at work for millennia. Understanding why the Great Salt Lake is so intensely saline requires examining the mechanics of its water balance and the origin of its dissolved minerals.
The Geographic Trap
The primary reason for the lake’s high salinity is its status as a terminal lake, which sits in a closed basin without any outlet to the ocean. Water enters the lake via the Bear, Weber, and Jordan Rivers, carrying dissolved minerals and salts into the basin. Since water cannot flow out, the only way for water to leave is through evaporation. As the water evaporates, pure water molecules ascend as vapor, but the dissolved solids are left behind, concentrating the minerals in the remaining lake volume over vast stretches of time.
The Geological Source of the Minerals
The tremendous volume of salt originated from the surrounding mountains and soil that make up its drainage basin. As rainwater and snowmelt run over rocks in the Uinta Mountains and Wasatch Range, they naturally dissolve minerals, including sodium and chloride. These mineralized waters flow into the lake, transporting about 2.2 million tons of dissolved solids each year. The modern lake is also a remnant of Lake Bonneville, a much larger freshwater body that existed during the Pleistocene Epoch. When Lake Bonneville began to shrink, it left behind the dissolved mineral content, which the Great Salt Lake inherited and has continuously concentrated through evaporation ever since.
Variations in Salt Concentration
The salinity of the Great Salt Lake is not uniform; it varies dramatically between different sections of the lake, a phenomenon largely driven by human engineering. The construction of the Lucin Cutoff, an earthen railroad causeway built in the late 1950s, divided the lake into two distinct hydraulic systems: the North Arm (Gunnison Bay) and the South Arm (Gilbert Bay). Since the three major freshwater rivers flow exclusively into the South Arm, it receives the majority of the inflow, resulting in a lower salinity that typically ranges between 6 and 17 percent. The causeway restricted water flow and mixing, isolating the North Arm from this freshwater input. Consequently, evaporation dominates the North Arm, causing its salinity to skyrocket, often reaching concentrations near 29 percent.
Life in Hypersaline Water
The intense salinity creates a unique and specialized ecosystem populated by organisms known as extremophiles. The high salt concentration is too extreme for most aquatic species, including fish. The most visible macro-organism is the brine shrimp (Artemia franciscana), which has evolved a highly efficient osmoregulation system to expel excess salt. Brine shrimp thrive in the moderately saline conditions of the South Arm. However, the hypersaline North Arm is often too salty even for brine shrimp, leaving the environment almost exclusively to microscopic life, such as halophilic bacteria and algae.