The waters of the Great Lakes are, for the most part, a nonrenewable resource. They are composed of numerous aquifers (groundwater) that have filled with water over the centuries, waters that flow in the tributaries of the Great Lakes, and waters that fill the lakes themselves. Although the total volume in the lakes is vast, on average less than 1 percent of the waters of the Great Lakes is renewed annually by precipitation, surface water runoff, and inflow from groundwater sources.
Because the Basin is a nonrenewable resource, water diversions (especially diversions out of the basin) are hot political issues. Here’s a look at current water diversions.
The Chicago diversion from Lake Michigan into the Mississippi River system is the only major diversion out of the Great Lakes Basin.
The Longlac and Ogoki diversions into Lake Superior from the Albany River system in northern Ontario are the only major diversions into the Basin. The Longlac and Ogoki diversions represent 6 percent of the supply to Lake Superior.
At present, more water is diverted into the Great Lakes Basin through the Longlac and Ogoki diversions than is diverted out of the Basin at Chicago and by several small diversions in the United States.
- Longlac and Ogoki diversion = 3.6 billion gallons per day into Lake Superior
- Chicago diversion = 2.1 billion gallons per day out of Lake Michigan
In addition to these diversions in and out of the Great Lakes Basin, the Welland and Erie Canals divert water between subbasins of the Great Lakes and are considered intrabasin diversions.
Aside from these major diversions, there are also a few small diversions:
- Forrestport, New York diverts waters of the Black River into the Erie Canal and the Hudson River watershed
- Portage Canal diverts Wisconsin River waters (Mississippi Basin) into the Great Lakes Basin.
- London, Ontario, and Detroit take water from Lake Huron for municipal purposes. London and Detroit discharge their effluent to Lake St. Clair and the Detroit River, respectively
- The Raisin River Conservation Authority in New York takes water from the international section of the St. Lawrence River to maintain summer flows in the Raisin River
- The communities of Pleasant Prairie, Wisconsin, and Akron, Ohio, which lie outside the Great Lakes Basin take water from the Great Lakes on the condition that they return an equivalent volume of water over time to the Basin
- Haldimand, Ontario takes water from Lake Ontarioa