How long can the US and Canada keep sharing the Great Lakes?

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This is the script for my video posted on August 7, 2026. Watch it on TikTok.

What if the Great Lakes had US and Canadian warships circling each other for control of the largest freshwater system on earth? There's no structural reason they shouldn't. What stops it is a series of agreements that have made these lakes arguably the most successful binational commons on the planet. But you probably don't know that those treaties are now under tremendous stress. So how do the Great Lakes fit into geopolitics, and how are their dynamics evolving?

The Great Lakes, including Ontario, Erie, Huron, Michigan, and Superior, hold about a fifth of the world's surface fresh water, and nine-tenths of the US’s. That comes to roughly 5500 cubic miles of water.

On average, less than 1% of that water is renewed annually through precipitation, runoff, and groundwater. Almost all of the lakes’ volume is meltwater left behind by ancient glaciers. That's why what goes into these lakes tends to stay in them, and why they’re often treated as a non-renewable resource.

The basin and its massive shoreline are home to about 30-40m people who are dependent on the lakes for drinking water and other uses. But Canada is far more reliant on this in general than the US is.

If the Great Lakes and St. Lawrence region were its own country, it would rank third or fourth in the world economically, at roughly six trillion dollars. A great deal of that has only been possible because of the lakes themselves.

They've been important since long before the US and Canada existed, though. By the time Europeans arrived, the region was dominated by the Anishinaabe of the upper lakes and the Haudenosaunee Confederacy to the east. The French and British built their fur trade on Indigenous routes and alliances, then steadily sidelined the peoples who built them.

In the 1836 Treaty of Washington, tribes ceded nearly 14 million acres, or over a third of modern Michigan. But they reserved their fishing rights in the treaty itself, and those persist to this day through a series of consent decrees.

Ever since, the lakes have needed arms control and boundary enforcement to stay stable. In 1794, the US proposed demilitarizing them entirely, though Britain refused at the time.

In 1817, the Rush-Bagot Agreement capped each side at a handful of vessels: one on Lake Ontario, two on the upper lakes, none over a hundred tons, and each carrying a single cannon. It is very likely the oldest arms control agreement still in force anywhere in the world. Interestingly though, it says nothing about armed non-naval vessels, which has caused complications when it comes to coast guard ships.

In the 19th and 20th centuries, both countries reshaped the lakes to serve their own interests. New York State built the Erie Canal between 1817 and 1825 without using any federal money, after President Madison vetoed funding on constitutional grounds. The canal bypassed the St. Lawrence River, which ran through British territory, and pulled the entire interior's trade toward New York City instead of Montreal.

In 1900, Chicago finished its sanitary and ship canal, reversing the Chicago River to send the city's sewage away from its drinking water intake on Lake Michigan and into the Mississippi instead. The city acted alone, permanently redirecting water out of a shared basin. Neighbors sued and won, and the Supreme Court has rationed Chicago’s diversion ever since. It remains the only major permanent outflow from the basin, and it’s grandfathered past every rule written afterward to prevent another one.

That same canal connected the Great Lakes with the Mississippi, and through it to the Gulf of Mexico. The Atlantic connection took far longer, because the US spent decades blocking it due to the threat a seaway would pose to US railroads, coal interests, and ports.

Canada threatened to build an all-Canadian seaway, and that threat to US economic and national security finally pushed Congress to pass the Wiley-Dondero Act in 1954. The timing was truly terrible though, because the first container ship sailed in 1956. The Seaway opened in 1959, but it was too small for modern container ships, most of which still can't fit through its locks.

Chicago exposed the problem that shapes everything here. Water belongs to states and provinces, but the basin is one connected system. Any single actor can reach into it, and everyone else absorbs the consequences. That gap has to be closed across two federal governments, eight states, two provinces, and dozens of tribes and First Nations whose treaty rights predate all of them.

The 1909 Boundary Waters Treaty was the first serious attempt to fix this. It created the International Joint Commission, a standing binational body that can approve or block projects in shared waters but cannot force either government to do much else. Around it grew the Great Lakes Fishery Commission, the Water Quality Agreement, and the 2008 Great Lakes Compact, which bans most new diversions out of the basin.

Since 2010, the US has poured billions into cleanup through the Great Lakes Restoration Initiative, though that one is unilateral. It's a US program on a US budget, with Canada funding its own parallel effort.

But there are problems you've probably never heard about. The Canadian firm Enbridge operates a pipeline called Line 5 that crosses the Straits of Mackinac, where Lake Michigan and Lake Huron meet, through a 4.5-mile twin segment on the lakebed. It has been there since 1953, but gaps in its protective coating and an anchor strike in 2018 have provoked real conflict between the two governments, in part because a 1977 treaty guarantees Canada uninterrupted transit of hydrocarbons across American soil, and this guarantee bends only for genuine emergencies. Canada has invoked it twice. But the situation faces persistent litigation and has yet to be resolved.

Growing water stress in the American Southwest keeps reviving speculation that Great Lakes water could be piped out of the basin, which is exactly what the Great Lakes Compact was built to prevent. Nobody actually knows how vulnerable the Compact is, because while some say that Congress could revisit its consent, others argue that it's a binding contract among eight states and far more difficult to undo. This has never actually been put to the test.

The current US administration has talked openly about turning what it called a "very large faucet" of Canadian water southward. That was about the Columbia River, not these lakes. But it has also reportedly considered walking away from the 1909 Boundary Waters Treaty itself, the instrument the entire order surrounding the Great Lakes is built on. In 2025 the US disinvited Canadian mayors from Great Lakes Day two days before the event, and federal cuts have hit the effort to keep the invasive sea lamprey from collapsing Great Lakes fishing again. But Canada is far more sensitive to this because of how much it relies on the basin.

Water levels are swinging harder than they used to, from a record low on Lake Michigan-Huron in 2013 to record highs by 2019. Scientists tie the swings partly to climate change, though natural variability still drives a great deal of it. On Lake Erie, the warmest and shallowest of the lakes, farm runoff feeds toxic algal blooms every summer. In August 2014, one of them shut off water for half a million people in Toledo for three days. A decade of trying to reduce phosphorus output hasn’t clearly bent the trend of accumulation downward, and PFAS and microplastics are worsening too.

The governance surrounding the US and Canada’s relationship in the Great Lakes region was successful for a long time because it was simply the rational move on both sides. Their economies were so deeply entwined that cooperation was in many ways the only option. But growing contention and rivalry and shifting environmental dynamics have produced a fundamentally different situation.

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