WHEN Dwight Eisenhower, then president of the United States, and John Diefenbaker, his Canadian counterpart, signed a treaty in 1961 to jointly control the unruly Columbia river, they hailed their collaboration as a model for the rest of the world. Fifty years after the treaty was implemented, in 1964, cracks are appearing. The treaty involved a series of new dams and an agreement to share the power generated as a result. It has worked well. There has been no repeat of the catastrophic flood that wiped out the second-largest city in Oregon in 1948. The United States dutifully hands over Canada’s share of the hydropower generated, worth an average of C$215m ($170m) a year between 1998 and 2013. But the Americans in particular are keen to make changes. Nigel Bankes of the University of Calgary says there is “zero chance” that the disagreements between the two countries can be resolved before September 16th—after which date either country can give ten years’ notice that it wishes to terminate the agreement.

Money is one of two main differences. In return for building three dams—Duncan, Hugh Keenleyside and Mica (see map)—on its side of the border, Canada received an upfront payment from the United States and a guaranteed share of the extra power that could be generated downstream as a result of more dependable water flows. The Americans think Canada has been more than reimbursed for the costs of dam construction, and want to whittle away the annual energy payment known as the Canadian Entitlement. In an open letter to Barack Obama in April, 26 senators and congressmen from the Pacific north-west said a reduction should be part of a renegotiated deal.

Not so fast, say the Canadians. They point out that people were displaced and fertile land flooded to create the dams. That represents a continuing loss. There are also benefits not captured in the treaty, says Bill Bennett, the minister of energy and mines for British Columbia (BC), which implements the treaty for Canada. More dependable water flows lead to improved navigation and irrigation south of the border; BC also co-operates when the United States asks it to spill water over its dams to help meet obligations under endangered-fish-species legislation.

In fact, fish are the other slippery issue. The restoration of salmon migration on the upper reaches of the Columbia river is being pushed by First Nations (native Indian) tribes on both sides of the border. The United States wants salmon on the negotiating table, but the Canadians do not. None of the treaty dams was built with fish ladders and they would be costly to construct today. “Salmon migration in the Columbia river ended 26 years before the treaty was ever ratified,” says Mr Bennett. “It was eliminated by the Grand Coulee dam in 1938, and our position is that’s an important issue but it’s not part of the Columbia River Treaty discussion.”

There is still tremendous cross-border goodwill at the regional level, a product of working co-operatively for 50 years. But relations at the national level are fraying at the edges. The Canadian government has already been riled by the Obama administration’s delays in making a decision on the Keystone XL pipeline, which would take oil from Alberta’s tar sands to refineries in the United States, and by its foot-dragging on financing a customs plaza for a new international bridge between Windsor, Ontario and Detroit. The model friendship is not what it was.