Lakes are an important source of freshwater to sustain human and natural systems. Only 2.5 % of the earth’s water is fresh, and almost 99 % of that freshwater is locked up in glaciers and icecaps or in underground aquifers. Slightly more than 1.2 % of the earth’s freshwater is located on its surface, but a large share of this surface freshwater is locked up in permafrost or ground ice. This makes the 21 % of surface freshwater stored in lakes (a mere 0.007 % of all the water stored on earth) extremely valuable for sustaining life, and it is the large lakes of the world that hold the vast majority of that life-sustaining water.
Large lakes occur on all of the earth’s continents except Antarctica. There are over 250 natural lakes worldwide that are over 500 km2 in size (roughly the size of Lake Tahoe in California/Nevada and larger). Of these, 189 are fresh and the remainder salt (saline or fresh to salt variation). The northern hemisphere contains a majority of the world’s large lakes, in large part formed as a result of the scouring action of Pleistocene glaciers. Tectonic movement is responsible for the rift valleys that are home to the great lakes of East Africa and Siberia.
The greatest of the world’s large lakes, the great lakes of North America (Superior, Michigan, Huron, Erie, and Ontario), Africa (Victoria, Malawi, and Tanganyika), and Siberia (Baikal) hold a staggering amount of valuable freshwater. The Laurentian Great Lakes hold 21 % of the world’s readily available (not frozen) surface freshwater, the African Rift Lakes 27%, and Siberia’s Lake Baikal nearly 20%.
These lakes are critically important not only as sources of freshwater, but also for the abundance of life they support and the economic, social and environmental benefits they provide to the millions of people who reside in the surrounding areas. They support some of the most diverse freshwater ecosystems and fisheries in the world and draw millions of visitors annually to their shores.
Each great lake has unique features and species, however they all share similar challenges to future health ranging from impacts of invasive and introduced species, pollution from industry and agricultural runoff, population growth and urbanization, impacts from a changing climate, and potentially increasing demands for water diversion to a thirsty world.