Water levels in the Great Lakes have fluctuated since 1860. Over the last few decades, water levels have declined slightly for most of the Great Lakes (see Figure 1).
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Climate change's hotter temperatures and society's diversion of water have been shrinking the world's lakes by trillions of litres of water a year since the early 1990s. A close examination of nearly 2,000 of the world's largest lakes found they are losing about 21.5 trillion litres a year.
The Great Lakes are struggling under the combined weight of many ailments, from invasive species and toxic chemicals to the nutrient runoffs that fuel Lake Erie's chronic algae problem. And in many cases, climate change is making it worse.
Those findings are consistent with a study from Michigan Technological University. That study found Lake Superior is expected to rise on average by 7.5 inches while levels on the Lake Michigan-Huron system is projected to increase 17 inches by 2050 due to climate change.
Pollution from over a century of intensive development remains in the sediment of many Great Lakes tributaries, harming fish and wildlife and leaving water unsafe for people. These sites are being cleaned up through the Great Lakes Legacy Act by the U.S. EPA in partnership with local, state, and private organizations.
Threats & ConservationThe source of toxic pollutants includes decades of industrial waste, raw sewage overflows, runoff from cities, and mining operations. Excess nutrients that throw the ecosystem out of balance enter the lakes from agricultural runoff and untreated sewage.
Current pressures on the Lake Michigan ecosystem include increasing use of groundwater by a growing basin population, disruption of the aquatic food web, and habitat alteration.
Geology of Lake InferiorLake Inferior is an underground lake that is located beneath Lake Superior. It is believed to be formed by a process known as karstification, which is the dissolution of limestone and dolomite rock. This process creates sinkholes, caves, and underground rivers and lakes.
In winter, the precipitation amounts decline in the colder air. A loss of water level basically comes down to more water flowing out and evaporating than falling as precipitation.
The Great Lakes are freshwater ecosystems. Traditionally, Lake Michigan, for example, has been a very low-salt lake, with levels around one milligram of chloride per liter of water. Over the years, due to our increased salt use, that level has steadily but gradually climbed up to 15 milligrams per liter.
Lake Erie is the shallowest, warmest, and most productive of the Great Lakes. Three distinct basins provide a variety of offshore habitats. The Detroit River, Maumee River, and smaller tributaries drain into the western basin, which averages 24 feet deep and contains extremely nutrient-rich water.
The most dangerous predator in the Great Lakes is the sea lamprey, which was actually introduced as an invasive species. Primarily, it goes after a sports fish called the lake trout, often wounding them as they kill them off. It is also attracted to the blood and bodily fluids of any creature.