The Great Lakes¶

Extent: The five-lake basin — Superior, Michigan, Huron, Erie, Ontario — touching eight U.S. states and the Canadian province of Ontario, draining approximately 295,000 square miles into the St. Lawrence River.

Core watersheds: All five lakes form a single cascading system draining northeast to the Atlantic

Keystone species: Lake trout, walleye, lake sturgeon, lake whitefish, lake herring, double-crested cormorant, osprey, bald eagle — and a growing roster of invasive species that have restructured the food web

The Place¶

The Great Lakes are an accident of ice.

They were carved by glaciers advancing and retreating over the last two million years — the most recent major advance, the Wisconsin glaciation, completed its retreat roughly 10,000 years ago. What it left behind was the largest surface freshwater system on Earth: 5,472 cubic miles of water, covering 94,250 square miles. The lakes contain approximately 21% of the world's surface fresh water and 84% of North America's surface fresh water.

To put that in context: if you evenly distributed the water in the Great Lakes across the contiguous 48 states, it would cover the entire country in about 9.5 feet of water.

Lake Superior alone — the largest freshwater lake on Earth by surface area — is cold enough and deep enough (1,333 feet at maximum) that ships sunk in it are often found intact, preserved by the near-freezing temperatures of its deepest reaches. The Edmund Fitzgerald, which sank in a November gale in 1975, lies in 530 feet of water, its contents still visible.

The lakes are geologically new and ecologically dynamic. Their food webs have been radically restructured by human action in ways that make them one of the best-documented case studies in invasive species ecology in the world — for better and worse.

The Water¶

The Great Lakes don't "flow" in the conventional sense. They are more like a chain of inland seas connected by rivers. Water moves from Superior through the St. Mary's River into Lake Huron, which connects to Lake Michigan (hydrologically a single lake), then through the St. Clair River and Lake St. Clair into Lake Erie, then over Niagara Falls into Lake Ontario, and finally down the St. Lawrence.

The entire system has a water retention time of roughly 190 years for Lake Superior — meaning water that enters Superior today will take about 190 years to work its way to the Atlantic. Lake Erie, much shallower and faster-flushing, has a retention time of about 2.6 years. This difference has enormous implications for how pollution accumulates and how long recovery takes.

The lakes do not significantly recharge the way groundwater does. They are a finite resource accumulated over geologic time. The Great Lakes Compact of 2008, signed by eight U.S. states and two Canadian provinces, was specifically created to prevent large-scale water diversion out of the basin — a real threat as water scarcity intensifies across the American West and Midwest.

The Governance Story¶

The Great Lakes Compact is one of the most successful examples of bioregional governance in North American history.

The basic problem was simple: the Great Lakes are politically fragmented across eight U.S. states and two Canadian provinces, but they function as a single ecological and hydrological system. Decisions made in Wisconsin about water withdrawals affect water levels in Ontario. A diversion approved in Illinois changes flows felt in New York.

The compact took decades to negotiate and was finally ratified in 2008. Its core provisions:

Prohibit most diversions of water out of the Great Lakes basin
Require that all new or increased withdrawals meet conservation and efficiency standards
Create a review process for large withdrawals that requires approval from all eight governors

It is imperfect — it allows some withdrawals, it has enforcement gaps, and it doesn't address pollution or invasive species. But it demonstrates that bioregional governance is achievable even across politically complex multi-jurisdictional systems.

The Invasion¶

No ecological story about the Great Lakes is complete without the invasion.

The St. Lawrence Seaway, opened in 1959, connected the lakes to the Atlantic and the world. Ships came in carrying ballast water — and in that water, organisms from the other side of the planet. The result has been one of the most consequential biological invasions in recorded history.

The sea lamprey arrived first, devastating lake trout populations across the upper lakes within a decade. Lake trout catches in Lake Michigan dropped from 6.5 million pounds per year in the 1940s to essentially zero by 1955. A massive lamprey-control program — using targeted pesticides in spawning streams — has suppressed lamprey populations enough for partial lake trout recovery, but the control effort must be sustained indefinitely.

The zebra mussel arrived in the late 1980s, almost certainly in ballast water from a European cargo ship. It spread with stunning speed. Zebra mussels are phenomenally efficient filter feeders — a single mussel can filter up to a liter of water per day — and they have clarified the lakes dramatically, increasing light penetration and fundamentally restructuring the food web. Native mussels, which they outcompete for attachment surfaces and food, have been nearly eliminated from large portions of the lakes.

The quagga mussel, zebra mussel's larger cousin, followed. Together they have rerouted energy pathways throughout the lake system in ways that are still being mapped.

Asian carp — specifically bighead and silver carp, introduced to Southern fish farms in the 1970s — have been advancing up the Mississippi and Illinois River systems toward Lake Michigan for decades. ⚠️ The status of carp barrier infrastructure and prevention efforts is actively evolving; verify current conditions. Their arrival in the lakes would be catastrophic for the existing food web.

Lake Erie's Warning¶

Lake Erie is the shallowest and warmest of the Great Lakes, and it is the system's canary.

In the 1960s, Lake Erie was declared "dead" — a massive algal bloom, fed by phosphorus runoff from farms and sewage, had consumed the oxygen in its central basin and killed most of its fish. The Clean Water Act of 1972 and aggressive phosphorus controls in the following years produced a remarkable recovery by the 1980s. Lake Erie's revival became a model for the environmental movement.

Then the blooms came back. Agricultural phosphorus runoff — particularly from the Maumee River watershed in northwest Ohio — has driven a resurgence of harmful algal blooms in the western basin of Lake Erie. In August 2014, a bloom contaminated the water intake for Toledo, Ohio, leaving 400,000 people without safe drinking water for three days.

The Maumee watershed is some of the most intensively farmed land in the country — flat, tile-drained, planted in corn and soybeans. Phosphorus applied as fertilizer runs off during spring rains into drainage tiles and then into the river. The political fight over agricultural runoff regulation in Ohio has been ongoing for years, pitting farm interests against cities that depend on Lake Erie for drinking water. ⚠️ Regulatory status is contested and evolving.

The People¶

The Great Lakes basin has been inhabited for at least 10,000 years. The Anishinaabe people — including the Ojibwe/Chippewa, Ottawa/Odawa, and Potawatomi — are most closely associated with the lakes and have managed their fisheries and forests for millennia. The Haudenosaunee (Iroquois Confederacy) held the southern and eastern portions of the basin. The Menominee, Ho-Chunk, and others occupied portions of the western basin.

The Anishinaabe oral tradition contains accounts of the Great Lakes that span thousands of years and encode ecological knowledge of the lake systems that Western science is only recently catching up to. Their treaties with the U.S. and Canadian governments explicitly reserved fishing rights that have been subject to legal battles into the present day.

Industrialization transformed the basin starting in the mid-1800s. Detroit, Cleveland, Chicago, Milwaukee, Buffalo, Toledo — the industrial heartland of North America — all sit within the basin. Steel, automobiles, chemicals, paper: all of these industries used the lakes as both a resource and a dump. The legacy contamination from this era — mercury, PCBs, dioxins, PAHs — remains in the sediments of harbors and river mouths across the region. Forty-three "Areas of Concern" were formally designated under the Great Lakes Water Quality Agreement; some have been remediated, some remain severely impaired. ⚠️ Current remediation status varies by site.

What to Know Here¶

If you live in the Great Lakes basin:

You are in one of the most water-rich places on Earth — and that resource is under persistent threat from diversion, contamination, and invasive species
The lakes are not bottomless; they do not recharge quickly; they retain pollutants for decades
The food web you inherited is already heavily restructured by invasive species — the "natural" baseline is gone; what matters now is managed stability
Agricultural runoff from your county flows to your watershed and eventually to the lakes; this is a political issue with a local face
The Great Lakes Compact is a governance achievement worth understanding and defending