The Great Salt Lake (GSL) in northern Utah is the largest inland body of salt water in the Western Hemisphere. As a terminal lake, water flows in from rivers (like the Bear, Weber, and Jordan) but has no natural outlet. When the water evaporates, dissolved minerals remain, creating a hyper-saline environment. Salt concentrations fluctuate but are typically much higher than the ocean’s 3.5% salinity. This immense salt content acts as an ecological filter, severely limiting the types of organisms that can inhabit the main body, allowing only specialized extremophiles to thrive in a simple but productive food web.
The Microbial Foundation of the Lake
The base of the Great Salt Lake’s food web consists of microscopic life forms called halophiles, or “salt-loving” organisms. These include bacteria, archaea, and algae that manage the intense osmotic stress of the salty water. The primary producer is the single-celled green algae Dunaliella salina, which thrives in highly concentrated brine. This algae produces beta-carotene, a red-orange pigment that protects it from intense radiation.
This pigment causes the lake’s distinct coloration, often appearing vivid pink or red in the highly saline North Arm. The less concentrated South Arm supports a wider diversity of algae and cyanobacteria, resulting in a greenish hue. Halophilic archaea also contribute to the intense pink color in the saltiest areas. These microorganisms provide the foundational energy source for the entire ecosystem.
The Primary Inhabitants: Brine Shrimp and Brine Flies
The two macro-invertebrates linking the microbial base to larger wildlife are the brine shrimp (Artemia franciscana) and the brine fly (primarily Ephydra hians and E. cinerea). Brine shrimp are small crustaceans, up to half an inch long, that consume suspended algae and bacteria. They adapt to extreme salinity using specialized gills that actively excrete salt, maintaining their internal water balance.
Brine shrimp reproduce prolifically, either giving birth to live young or producing dormant, hard-shelled eggs called cysts. These cysts are resilient, surviving decades of desiccation and extreme temperatures until conditions allow hatching. Brine fly larvae live on the lake bottom, grazing on algae and microorganisms that form dense microbialite mats. Larvae densities can reach 25,000 individuals per square meter on the shallow lakebed.
Adult brine flies emerge after pupating in air-filled casings, often forming massive swarms along the shoreline. The adults do not possess functional mouthparts and do not feed; their sole purpose is reproduction, and they live for only a few days. The total biomass of these invertebrates is staggering, creating an enormous, accessible food source for visiting birds.
Millions of Migratory Birds
The Great Salt Lake is a globally recognized destination for avian life and a vital stopover point on the Pacific Flyway migration route. Each year, an estimated 8 to 12 million migratory birds from over 330 species use the lake for feeding, resting, and breeding. The abundance of brine shrimp and brine flies provides a concentrated, high-calorie food supply with virtually no aquatic predators.
The lake supports a significant portion of North America’s Eared Grebe population, with up to 90% descending in late summer and fall to molt and feed. These birds consume an estimated 30,000 brine shrimp daily to build fat reserves for migration. The lake is also a crucial staging area for the Wilson’s Phalarope, where up to 60% of the global population stops to feed on the abundant invertebrates.
Other species include the American Avocet, which sweeps for invertebrates in shallow mudflats, and the California Gull, which maintains large nesting colonies on the islands. The lake’s vast open water and surrounding wetlands offer diverse habitats. This irreplaceable link in the migratory chain supports species like Northern Pintails, Green-winged Teals, and Snowy Plovers.
Why Fish and Other Aquatic Life Are Absent
The hyper-salinity of the main body of the Great Salt Lake prevents the survival of most fish and aquatic vertebrates. Freshwater fish cannot tolerate salt concentrations much higher than 1.5%. The GSL typically ranges between 5% and 27% salinity, depending on water level and location. This high salt content destroys the cellular mechanisms fish use to regulate water balance, leading to fatal dehydration.
Consequently, the vast, open waters are devoid of fish, amphibians, and reptiles. Fish populations are restricted to less saline areas, such as bays and wetlands, where inflowing rivers (like the Bear, Weber, and Jordan) dilute the water. These areas, including Farmington Bay and Bear River Bay, support species adapted to brackish water, but they cannot survive in the highly concentrated brine of the main lake.