page_title: Great Lakes
section_title: Water levels
hierarchical_section_title: Great Lakes / Geography / Water levels
caption_attribution_description: English: Monthly water levels were downloaded from the US Army Corps of Engineers, and then seasonally detrended using the R language detrend() function to provide an estimate of average annual water levels.
context_page_description: The Great Lakes or the Great Lakes of North America, are a series of large interconnected freshwater lakes in the upper mid-east region of North America, that connect to the Atlantic Ocean through the Saint Lawrence River. In general, they are on or near the Canada–United States border. They are lakes Superior, Michigan, Huron, Erie, and Ontario. Hydrologically, there are only four lakes, because lakes Michigan and Huron join at the Straits of Mackinac. The lakes form the basis for Great Lakes Waterway.
  The Great Lakes are the largest group of freshwater lakes on Earth by total area, and second-largest by total volume, containing 21% of the world's surface fresh water by volume. The total surface is 94,250 square miles, and the total volume is 5,439 cubic miles, slightly less than the volume of Lake Baikal. Due to their sea-like characteristics the five Great Lakes have also long been referred to as inland seas. Lake Superior is the second-largest lake in the world by area, and the largest freshwater lake by surface area. Lake Michigan is the largest lake that is entirely within one country.
context_section_description: In 2009, the lakes contained 84% of the surface freshwater of North America; if the water were evenly distributed over the entire continent's land area, it would reach a depth of 5 feet (1.5 meters). The source of water levels in the lakes is tied to what was left by melting glaciers when the lakes took their present form. Annually, only about 1% is "new" water originating from rivers, precipitation, and groundwater springs that drain into the lakes. Historically, evaporation has been balanced by drainage, making the level of the lakes constant.
  Intensive human population growth only began in the region in the 20th century and continues today. At least two human water use activities have been identified as having the potential to affect the lakes' levels: diversion (the transfer of water to other watersheds) and consumption (substantially done today by the use of lake water to power and cool electric generation plants, resulting in evaporation).
  The physical impacts of climate change can be seen in water levels in the Great Lakes over the past century. The United Nations' Intergovernmental Panel on Climate Change in 1997 predicted: "the following lake level declines could occur: Lake Superior −0.2 to −0.5 m, Lakes Michigan and Huron −1.0 to −2.5 m, and Lake Erie −0.9 to −1.9 m."  In 2009, it was predicted that global warming will decrease water levels. In 2013, record low water levels in the Great Lakes were attributed to climate change.
  The water level of Lake Michigan–Huron had remained fairly constant over the 20th century, but has nevertheless dropped more than 6 feet from the record high in 1986 to the low of 2013. In 2012, National Geographic tied the water level drop to warming climate change., as did the Natural Resources Defense Council. One newspaper reported that the long-term average level has gone down about 20 inches because of dredging and subsequent erosion in the St. Clair River. Lake Michigan–Huron hit all-time record low levels in 2013; according to the US Army Corps of Engineers, the previous record low had been set in 1964. By April 2015 the water level had recovered to 7 inches (17.5 cm) more than the "long term monthly average".
caption: Water levels of Lakes Michigan and Huron in the United States, 1918 to 2019.
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