Low Water Levels in the Great Lakes

Back to Map Page   The watershed of the Great Lakes. (Image source: U.S. Environmental Protection Agency.) Shipping on the Great Lakes becomes more expensive as water levels fall. (Image source: U.S. Environmental Protection Agency.)   April, 2000 United States After a mild, dry winter in the North American Midwest, the Great Lakes approached record low levels in the spring of 2000. As water levels in the lakes dropped, many people in the region wondered if low lake levels are proof of global warming or simply natural, periodic fluctuations in rainfall and lake levels. In addition to the general concern over possible long-term trends in lake levels, low water is a serious economic problem. The Great Lakes are major shipping routes, with tankers carrying grain, iron ore, coal, and other resources from as far inland as Duluth, Minnesota, to the Atlantic Ocean. Shallow water means tankers cannot be loaded as heavily, so each trip is less profitable. Shallow water also threatens pleasure boating and tourism; some marinas are becoming too shallow, and dredging is necessary to keep them in use. Perhaps most worrisome are city water intakes and outlets, which could be left high and dry if the water continues to drop. Cities are being advised to consider lengthening water intake pipes. They are also being told to look into lengthening wastewater outlets. Treated effluent from sewage systems is usually diluted by lake water, but if the water becomes too shallow, there are serious risks of pollution from these outlets. Precipitation keeps the Great Lakes full. During the mild winter of 2000, snowfall and rain were unusually slight in most of the Great Lakes watershed. Spring came early to much of the region, allowing runoff to start early and providing warm weather to evaporate water in the tributaries as well as in the lakes themselves. At the same time, high temperatures drastically reduced ice cover on the lakes. Ice normally covers large regions of the lakes in mid-winter, reducing evaporative loss of water. With warm, dry weather and little water storage on land, lake levels were unusually low in early spring 2000---when they should be at their peak. The shallower lakes, Huron and Erie, showed the greatest change in lake levels, nearly 3 feet below long-term averages by early April. The deeper lakes, especially Superior and Michigan, dropped more slowly because their volume is so great relative to their surface area. These lakes were only a few inches below normal as of April. All lakes fluctuate from year to year, and water levels in the Great Lakes have changed a great deal since monitoring began more than a century ago. It is not clear whether these recent low levels are part of a serious trend. The rate of water loss looks especially bad because water levels were unusually high just 3 years ago. Lake levels were even lower in the 1960s. Periodic low water has environmental benefits too, since occasional drying can allow new vegetation to become established in coastal wetlands. Therefore, the larger implications of the summer's low water levels remain to be seen. Meanwhile, many lakeshore cities and businesses scramble to avoid economic strains over the summer months. To learn more, see these related websites: Great Lakes info sources (go to environmental Resources Links) Great Lakes Atlas and Resource Book, Government of Canada and USEPA Great Lakes Atlas and Resource Book, Government of Canada and USEPA Private site with Great Lakes links Nature Conservancy's Great Lakes program To read more, see: Environmental Science, A Global Concern, Cunningham and Saigo, 6th ed. Climate change, pp. 384-89 Water resources, pp. 422-29 Drought cycles, p. 431 Environmental Science, A Study of Interrelationships, Enger and Smith, 7th ed. Industrial use of the Great Lakes, pp. 12-14 Water resources and the hydrologic cycle, pp. 275-77 Back to Map Page feedback form | permissions | international | locate your campus rep | request a review copy digital solutions | publish with us | customer service | mhhe home Copyright ©2001 The McGraw-Hill Companies. Any use is subject to the Terms of Use and Privacy Policy. McGraw-Hill Higher Education is one of the many fine businesses of the The McGraw-Hill Companies.