Dozens of lakes around the world contain salt water, ranging from slightly brackish to nearly ten times saltier than the ocean. The largest is the Caspian Sea, and the most famous include the Dead Sea, Great Salt Lake, and the Aral Sea. But salt lakes exist on every continent, including Antarctica, and they vary enormously in size, salinity, and the life they support.
How Salt Lakes Form
Salt lakes form in basins that have no outlet to the ocean. Rivers and groundwater carry dissolved minerals into the basin, but the only way water leaves is through evaporation. As water evaporates, the minerals stay behind and concentrate over thousands of years. The key requirement is that evaporation exceeds rainfall, which is why most salt lakes sit in arid or semi-arid regions. Many form in the rain shadow of mountain ranges, where surrounding highlands funnel water into a low-lying basin that bakes under dry conditions.
These closed drainage systems are called endorheic basins. Every continent has them. The chemistry of any given salt lake depends on the types of rock in the surrounding watershed, the balance between surface water and groundwater flowing in, and how long the basin has been accumulating minerals. Some lakes are rich in sodium chloride (common table salt), others in sodium carbonate (soda), and still others in magnesium, potassium, or lithium compounds.
The Largest Salt Lakes
The Caspian Sea, bordered by Iran, Russia, Kazakhstan, Turkmenistan, and Azerbaijan, is by far the world’s largest salt lake at roughly 378,000 square kilometers. Despite its name, it is technically a lake because it has no connection to the ocean. Its salinity sits around 13 grams per liter, about a third of ocean salinity, yet its massive volume means it holds more than 85% of all the salt contained in Earth’s saline lakes combined.
After the Caspian, the next largest salt lakes historically included the Aral Sea in Central Asia, Lake Balkhash in Kazakhstan, and the Great Salt Lake in Utah. Lake Chad in central Africa also appears on this list, though its salinity fluctuates with seasonal rainfall and it is only mildly saline in most conditions.
The Dead Sea
The Dead Sea, sitting on the border of Israel, Jordan, and the West Bank, is one of the saltiest large lakes on Earth at roughly 340 grams per liter. That makes it about ten times saltier than the ocean. Its mineral profile is unusual: it contains extremely high concentrations of magnesium, calcium, and potassium compared to ordinary seawater. The magnesium content alone is roughly 44 grams per liter, compared to just 1.27 grams per liter in the ocean.
This extreme chemistry is what makes the Dead Sea so buoyant and so inhospitable to fish and most aquatic life. The lake’s surface sits at one of the lowest elevations on land, and it has been shrinking for decades as the Jordan River’s water is diverted for agriculture and drinking water upstream.
Great Salt Lake, Utah
The Great Salt Lake is the largest salt lake in the Western Hemisphere. A railroad causeway divides it into two distinct arms with very different salinity levels. The north arm, called Gunnison Bay, averaged around 296 grams per liter between 1966 and 2020, making it comparable to the Dead Sea. The south arm, called Gilbert Bay, is far less salty, averaging about 134 grams per liter over the same period. Overall, the lake’s salinity ranges between 5% and 27% depending on location and water levels.
The Great Salt Lake supports enormous populations of brine shrimp and brine flies, which in turn feed millions of migratory birds. The brine shrimp industry harvests cysts (eggs) that are sold globally as feed for aquaculture operations.
The Aral Sea’s Collapse
The Aral Sea in Kazakhstan and Uzbekistan was once the world’s fourth-largest lake. Beginning in the 1960s, Soviet irrigation projects diverted the rivers feeding it, and the lake has since split into separate bodies of water. Before the diversion, its salinity was around 10 grams per liter, less than a third of ocean salinity. The South Aral Sea now exceeds 100 grams per liter, roughly three times saltier than the ocean, and continues to shrink. The North Aral has stabilized somewhat after a dam was built to retain its water, but the southern portion is largely considered an ecological disaster.
Other Notable Salt Lakes
Lake Van in eastern Turkey is the world’s largest soda lake, with a salt content of about 22 grams per liter and highly alkaline water dominated by sodium carbonate. Its chemistry is so unusual that scientists have used it as a model for what Earth’s early oceans may have looked like.
Lake Natron in Tanzania is one of the most hostile lakes on the planet. Fed by volcanic mineral springs, its pH can reach 10.5, nearly as alkaline as ammonia, and the temperature of its shallow mud flats can hit 50°C (122°F). Despite these conditions, it is the primary breeding ground for East Africa’s lesser flamingos, which feed on the cyanobacteria that thrive in the caustic water.
Australia is home to numerous pink salt lakes, including Lake Hillier on Middle Island. These lakes are roughly ten times saltier than the ocean, and their striking bubblegum-pink color comes from salt-loving bacteria and microalgae that produce beta-carotene, the same pigment that gives carrots their orange color. The pigment protects the microbes from ultraviolet radiation. These pink lakes are fragile: heavy rainfall can dilute the salt enough to wipe out the pigment-producing organisms and turn the water back to blue or green.
The Saltiest Water on Earth
The title of saltiest body of water belongs to Don Juan Pond, a shallow pool in Antarctica’s McMurdo Dry Valleys. Its salinity exceeds 40%, so concentrated with calcium chloride that it remains liquid even at temperatures well below freezing. For comparison, the Dead Sea sits at about 34%, the Great Salt Lake tops out around 27%, and ocean water averages 3.5%. Don Juan Pond is too small and too extreme to support any known complex life.
Life in Salt Lakes
Salt lakes are not lifeless. They support specialized communities of microorganisms called halophiles, organisms that require high salt concentrations to survive. At the highest salinities, archaea (a domain of single-celled organisms distinct from bacteria) tend to dominate. At moderate salinities, bacteria and algae like Dunaliella thrive. These microbes are collectively responsible for the vivid pink, red, and purple colors seen in many salt lakes and commercial salt ponds around the world.
At lower salinities, salt lakes can support brine shrimp, brine flies, and even fish. The Caspian Sea, with its relatively mild salinity, supports sturgeon populations famous for producing caviar. As salinity climbs, biodiversity drops sharply until only the most salt-tolerant microorganisms remain.
Why Salt Lakes Matter Economically
Salt lakes are significant sources of industrial minerals. Common salt has been harvested from them for millennia. Today, many salt lakes are also mined for potash (used in fertilizers) and, increasingly, lithium. The growing demand for electric vehicle batteries has made lithium-rich salt lakes, particularly those on the Tibetan Plateau and in South America’s “Lithium Triangle,” strategically important. Extracting lithium from brine is generally cheaper and less energy-intensive than mining it from hard rock, making these lakes central to the global energy transition.