How well do you know the Great Lakes?
The Great Lakes form the largest group of freshwater lakes on Earth. Six questions, from easy to hard, with explanations.
Did you know?
- Strong winds can push Lake Erie's water toward one end of the lake, raising water levels by several feet there while dropping them at the other end. This sloshing effect, called a seiche, can cause sudden flooding along the shore.
- Lake Superior is so cold and deep that it rarely freezes over completely. Its average water temperature stays around 40°F (4°C), and even in summer, deep water remains cold enough to preserve old shipwrecks remarkably well.
- If all the water in the Great Lakes were spread evenly across the lower 48 states, it would cover them about 9.5 feet deep. That comparison shows just how much water the lakes contain.
Inland seas of North America
The Great Lakes — Superior, Michigan, Huron, Erie and Ontario — lie along the border between the United States and Canada. Together they cover about 94,000 square miles, roughly the size of the United Kingdom. They are big enough to produce storm waves taller than a house, surfable swells and weather of their own, which is why they are sometimes called inland seas.
Carved by ice
The lakes formed at the end of the last Ice Age. Massive ice sheets gouged deep basins into the land, and as the ice melted, around 14,000 years ago and later, meltwater filled them. The lakes have changed shape many times since then.
One connected system
Water flows from Lake Superior through the St. Marys River into Lake Huron, joined by Lake Michigan. It then passes through the Detroit River into Lake Erie, over Niagara Falls into Lake Ontario and finally out through the St. Lawrence River to the Atlantic.
Shipping lanes
Since the St. Lawrence Seaway opened in 1959, ocean ships can sail from the Atlantic deep into North America. Special freighters called lakers, some more than 1,000 feet long, carry iron ore, coal, grain and stone between lake ports.
Shared by two countries
Eight US states and the Canadian province of Ontario border the lakes. The two countries have cooperated on the lakes for more than a century, sharing responsibility for water quality, water levels and fisheries.
Invasive species
Some of the biggest changes to the lakes came from animals that arrived from elsewhere. Sea lampreys entered through shipping canals and damaged fish populations, and zebra mussels, discovered in 1988, likely arrived in ships' ballast water.
Shores and dunes
The lakes have thousands of miles of shoreline, with sandy beaches, rocky cliffs, wetlands and huge freshwater dunes. These coastal habitats support migrating birds, rare plants and fish that spawn in shallow waters.