Over the past two years of my soft fascination with the Great Lakes, there are many facts and statistics I have either learned or revisited. But one fact stands out: The Great Lakes and their connecting waterways make up the largest surface freshwater system on earth.

Why this matters: The Great Lakes are actually one system, and it is this interconnectedness that also makes them ecologically fragile.

The Great Lakes are the result of glaciers that built up over North America starting about 500,000 years ago. About 14,000 years ago, temperatures began to warm, and the glaciers shrunk and retreated. As they did this, they carved new landforms, including massive depressions. Some of these depressions filled with the melting glacial ice, creating the early Great Lakes. 

The lakes and connected rivers have changed shape and form over the past 14,000 years, but today, water flows through the system more or less eastward. It starts in the deep, cold, expansive waters of Lake Superior (the largest lake by surface area and deepest with an average depth of 489 feet). It flows into the St. Mary’s River and then into Lakes Huron and Michigan. I say “Lakes” because Huron and Michigan are actually one body of water, appearing like two lungs, connected at the Straits of Mackinac. Lake Huron waters flow into the St. Clair and Detroit Rivers before moving into the western basin of Lake Erie. On the eastern basin of Lake Erie (the shallowest of the lakes with average depth of 62 feet; much more on the impact of this shallowness in future posts), the water flows into the Niagara River, over Niagara Falls, and into Lake Ontario (the smallest lake by surface area). From there, water moves into the St. Lawrence River and eventually flows into the Atlantic Ocean.  

This interconnectedness is what enabled a multisectoral economy to emerge on the Great Lakes. Manufacturing, agriculture, mining, energy services and tourism all thrive with ships moving between the US, Canada and further global reaches. A notable example: the history of the automobile industry in the US is interdependent with the history of the Great Lakes. But the interconnectedness is also what makes the lakes vulnerable to environmental threats, notably invasive species, which have had dramatic impacts I will discuss more in future posts. Chemicals, plastics, toxins and warming temperatures also upset the balance of the lakes as they flow through the system.These threats create an interlocking and cascading range of issues for the plants and animals in the lakes, and those that live on lands surrounding the lakes – including humans. Approximately 40 million North Americans get their drinking and household water from the Great Lakes. Affirming this tremendous natural resource while simultaneously recognizing its fragility is critical to protecting the lakes for the very near and distant future.