A lake is a large body of water contained within a land-based basin. While the majority of lakes are freshwater, a notable number are saltwater. The specific characteristics of a lake’s basin and its surrounding environment determine whether its waters accumulate significant levels of dissolved salts.
Why Most Lakes Are Freshwater
Most lakes contain freshwater due to the continuous movement of water through the Earth’s hydrological cycle. Precipitation, such as rain and snow, provides the primary source of water, which is low in dissolved salts. This water flows into lakes directly or as runoff from surrounding land, carrying only trace amounts of dissolved minerals.
A key factor in maintaining low salinity is the presence of an outlet, typically a river or stream, that allows water to continuously flow out of the lake. As water exits, it carries away dissolved minerals, preventing their accumulation. This continuous flushing ensures that salts do not concentrate over time, keeping the water fresh.
How Lakes Can Become Salty
Lakes become salty when specific environmental conditions lead to the concentration of dissolved minerals. This often occurs in “endorheic basins,” which are landlocked depressions with no natural outflow. Water flows into these basins, but it can only leave through evaporation or by seeping into the ground.
In regions with high evaporation rates, especially arid or semi-arid climates, water rapidly turns into vapor, leaving behind dissolved salts. Over extended periods, this process causes salts to accumulate, leading to progressively higher salinity. Additionally, some lakes are situated in areas with naturally occurring salt deposits or highly mineralized rocks, which contribute dissolved salts. Well-known examples include the Great Salt Lake in Utah, the Dead Sea, and the Caspian Sea.
Characteristics of Freshwater vs. Saltwater Lakes
The primary distinction between freshwater and saltwater lakes is their salinity level, which refers to the concentration of dissolved salts. Freshwater lakes typically have less than 0.5 grams of dissolved salts per liter, while saltwater lakes generally contain at least 3 grams per liter, with some hypersaline lakes exceeding 300 grams per liter. This difference in salt content directly influences water density; saltwater is denser than freshwater, which is why objects, including people, float more easily in highly saline lakes like the Dead Sea.
These differing chemical and physical properties dictate the types of ecosystems each lake can support. Freshwater lakes host a wide array of aquatic life, including diverse fish species, amphibians, and various water plants. Conversely, saltwater lakes support specialized organisms, such as halophilic (salt-loving) bacteria and certain brine shrimp species, that have adapted to high-salinity conditions, with fewer varieties of higher organisms. Freshwater lakes are widely utilized for drinking water, agricultural irrigation, and recreational activities like swimming and fishing. Saltwater lakes are sometimes used for mineral extraction or offer unique recreational experiences like effortless floating due to their buoyancy.