How salty is the Great Salt Lake?

The Great Salt Lake in northern Utah is one of the saltiest bodies of water in the Western Hemisphere, and its salinity is a defining feature of its ecology and global significance. Unlike oceans, whose salinity averages around 3.5%, the Great Salt Lake’s salinity can range from 5% to over 27%, depending on location, water level, and inflow. In some parts of the lake, the salt concentration is so high that only a few extremophilic organisms like brine shrimp and halophilic bacteria can survive.

Why Is the Great Salt Lake So Salty?

The Great Salt Lake has no outlet to the ocean. It is a terminal lake, meaning water flows in via rivers and streams but can only leave through evaporation. As water evaporates, it leaves behind salts and minerals that accumulate over thousands of years. This process creates an environment where salinity can increase dramatically when water levels fall.

The primary sources of water — and dissolved minerals — are:

• Bear River
• Weber River
• Jordan River

These rivers carry salts and minerals from the surrounding mountains into the lake. Over time, these substances concentrate in the water, leading to hypersaline conditions.

Salinity Variations Across the Lake

The Great Salt Lake is not uniform in salinity. It’s effectively divided into two major parts by a man-made railroad causeway built in 1959, which restricts the flow of water between the north arm (Gunnison Bay) and the south arm (Gilbert Bay). This separation has led to a stark difference in salinity levels.

1. Gunnison Bay (North Arm)

• Salinity: 25–27% (sometimes exceeding 30%)
• Appearance: Deep pink or red due to halophilic (salt-loving) bacteria and algae like Dunaliella salina
• This area receives very little freshwater, so evaporation is the primary water loss, and salinity remains extremely high.

2. Gilbert Bay (South Arm)

• Salinity: 5–15%, depending on water level
• Receives most of the freshwater from the rivers
• Home to brine shrimp and brine flies, which can tolerate high salinity but require slightly less saline water than the north arm

3. Bridger Bay and Farmington Bay (Peripheral Areas)

• These shallower regions can be influenced by seasonal inflow and may exhibit lower salinity (near brackish water) during wet periods.
• The salinity here can fluctuate between 1–5%, supporting wetland vegetation and aquatic life in nearby marshes.

Factors Affecting Salinity

Salinity in the Great Salt Lake isn’t static—it changes with climatic and human-induced factors:

1. Drought and high evaporation: Decrease lake levels, increasing salinity
2. Snowpack and river inflow: Increase water volume, diluting salinity
3. Water diversion for agriculture and urban use: Reduces inflow, causing higher salinity
4. Climate change: Intensifies fluctuations in precipitation and evaporation

In 2021 and 2022, the lake reached record-low levels, exposing large lakebeds and concentrating salts. Some sections of the south arm reached salinity levels above 18%, pushing the limits of survival for even brine shrimp.

Comparison to Other Saline Lakes

The Great Salt Lake is often compared to other hypersaline environments:

• Dead Sea (Israel/Jordan): ~34% salinity
• Lake Urmia (Iran): Up to 31% when water levels are low
• Mono Lake (California): ~8–12%

Although not quite as salty as the Dead Sea, the Great Salt Lake is still among the saltiest large lakes in the world.

Ecological Importance of Salinity

The lake’s hypersalinity plays a crucial role in shaping its unique ecosystem. Fish cannot survive in the lake, but brine shrimp, brine flies, and halophilic microbes thrive. These organisms form the base of a vital food web for over 10 million migratory birds, including:

• Eared grebes
• American avocets
• Wilson’s phalaropes
• Snowy plovers

Maintaining appropriate salinity levels is essential for the survival of these species.

Conclusion

The Great Salt Lake's salinity is both its defining feature and a delicate balancing act. Ranging from about 5% in the fresher southern arms to over 27% in the isolated north arm, the lake’s salt content has created a highly specialized and globally important ecosystem. As water levels fluctuate due to climate change and water management, the future of this saline giant and its dependent wildlife remains uncertain—but its uniqueness in the natural world is undisputed.