Overview

The Great Lakes -- Superior, Michigan, Huron, Erie and Ontario -- and their connecting channels form the largest fresh surface water system on earth. If you stood on the moon, you could see the lakes and recognize the familiar wolf head shape of Lake Superior, or the mitten bounded by lakes Michigan, Huron and Erie. Covering more than 94,000 square miles and draining more than twice as much land, these Freshwater Seas hold an estimated 6 quadrillion gallons of water, about one-fifth of the world's fresh surface water supply and nine-tenths of the U.S. supply. Spread evenly across the contiguous 48 states, the lakes' water would be about 9.5 feet deep.

The channels that connect the Great Lakes are an important part of the system. The St. Marys River is the northernmost of these, a 60-mile waterway flowing from Lake Superior down to Lake Huron. At the St. Marys rapids, the Soo Locks bypass the rough waters, providing safe transport for ships. The St. Clair and Detroit rivers, and Lake St. Clair between them, form an 89-mile long channel connecting Lake Huron with Lake Erie. The 35-mile Niagara River links lakes Erie and Ontario, and sends approximately 50,000 to 100,000 cubic feet of water per second over Niagara Falls; the manmade Welland Canal also links the two lakes, providing a detour around the falls. From Lake Ontario, the water from the Great Lakes flows through the St. Lawrence River all the way to the Atlantic Ocean, about 1,000 miles away.

This system greatly affects our way of life, as well as all aspects of the natural environment, from weather and climate, to wildlife and habitat. Yet for all their size and power, the Great Lakes are fragile. In the past, this fragile nature wasn't recognized, and the lakes were mistreated for economic gain, placing the ecosystem under tremendous stress from our activities. Today, we understand that our health and our children's inheritance depend on our collective efforts to wisely manage our complex ecosystem.

Invasive carp threatens Great Lakes

Fish and wildlife officials will poison a 6-mile stretch of water near Chicago on Wednesday in a last-ditch effort to keep one of the most dangerous invasive species of fish, the Asian carp, out of the Great Lakes. The Asian carp, a voracious eater that has no predators and negligible worth as a commercial or sport fish, now dominates the Mississippi and Illinois rivers and their tributaries.

The fish has entered the Chicago Sanitary and Ship Canal — a man-made link between the Mississippi River system and the Great Lakes — and is knocking on the door of Lake Michigan. Once inside a Great Lake, the carp would have free rein in the world's largest freshwater ecosystem, imperiling the native fish of the lakes and a $7 billion fishing and recreation industry.

"We've got a chance to beat this thing, but we've got to do everything right," says Joel Brammeier, acting president of the Alliance for the Great Lakes, a conservation group.

The poisoning will kill an estimated 100 tons of fish, which will be removed by crane and hauled to a landfill. The five-day fish kill will provide time for the Army Corps of Engineers to perform routine maintenance on an electrical barrier that has been placed in the canal to block Asian carp from entering Lake Michigan.

No Asian carp have been found on the Great Lakes' side of the electrical barrier. However, recent DNA samples taken from water indicate the carp may have gotten past the barrier.

"We feel confident that our barriers repel the fish," says Chuck Shea, the Army Corps of Engineers' project manager. The barrier consists of low voltage sent through steel cables, electrifying the water enough to stop the fish but not enough to kill them or humans.

The Great Lakes have struggled for decades from more than 150 invasive species brought in by ocean-going vessels dumping water from around the world. The Asian carp is the first major threat to come from the other direction, upstream from the Mississippi River.

The results are potentially devastating for the Great Lakes and the rivers that flow into it