The world’s lakes represent a significant portion of the planet’s liquid freshwater, but determining an exact count is a complex scientific challenge. Lakes vary dramatically in size, depth, and permanence. Advances in satellite technology have provided clearer, though still debated, figures for the number of lakes dotting the Earth’s surface. Understanding the global count requires first establishing what constitutes a lake and then applying those criteria to vast landscapes.
Defining the Boundaries of a Lake
The primary difficulty in counting the world’s lakes stems from the lack of a single, universally accepted definition. Different scientific disciplines use varying criteria, leading to vastly different tallies. For instance, some definitions rely on physical size, with a common minimum threshold being 0.01 square kilometers (one hectare) of surface area. This size threshold is often used in modern inventories to classify a body of water as a lake.
Other limnological criteria focus on depth, specifically the presence of a thermocline. This layer of rapid temperature change prevents the water column from mixing completely, which is characteristic of deeper lakes. A pond, conversely, is typically shallow enough for the temperature to remain relatively uniform. Furthermore, a true lake is generally expected to be a naturally occurring and permanent feature, excluding temporary seasonal pools and artificial reservoirs.
Scientific Estimates of the Global Count
Modern scientific estimates, derived from high-resolution satellite imagery, have scaled the global lake inventory. One widely cited study estimated the total number of lakes to be approximately 117 million. This massive figure results from including the smallest water bodies, as roughly 90 million fall into the smallest size category (0.002 to 0.01 square kilometers). This demonstrates that the vast majority of the world’s lakes are small bodies of water.
Another comprehensive database, using a larger minimum size threshold of 0.1 square kilometers, identified around 1.42 million lakes globally. The enormous difference between these figures highlights the importance of the minimum size cutoff used by researchers. These large-scale inventories sometimes struggle to differentiate natural lakes from artificial reservoirs, which can lead to overestimation.
Geographic Distribution of Lakes
The distribution of the world’s lakes is far from uniform, concentrating heavily in the northern latitudes due to the geological legacy of the last Ice Age. Glacial processes, involving the advance and retreat of massive ice sheets, dramatically reshaped the landscape. This action carved out depressions and left behind millions of water-filled basins. Most of the world’s lakes are situated in the Northern Hemisphere, predominantly between 45 and 75 degrees north latitude.
This concentration is most pronounced in regions like Canada, Russia, and Fennoscandia, which were extensively covered by continental glaciers. Canada alone is home to over two million lakes and holds 60% of the world’s lakes larger than 0.1 square kilometers. The sheer density results directly from glacial scouring. This process created features like kettle lakes, where water pooled easily in the resulting chaotic drainage patterns.
Surface Area and Total Water Volume
While the count of lakes is in the millions, the majority of the world’s freshwater is contained within a small fraction of these bodies. Lakes collectively cover an estimated surface area of about 5 million square kilometers, representing approximately 3.7% of the non-glacier land area. The total volume of liquid freshwater stored is the more significant metric for global water resources. Freshwater lakes are estimated to hold approximately 125,000 cubic kilometers of water, constituting over 80% of the Earth’s liquid surface freshwater.
This immense volume is not spread evenly; a small number of deep, ancient lakes hold the bulk of the water. Lake Baikal in Siberia, the world’s deepest lake, contains about 20% of the world’s surface freshwater volume. Similarly, the North American Great Lakes hold about 21% of the volume. While small lakes provide the sheer numbers, the largest and deepest lakes serve as the planet’s primary freshwater storage tanks.