THE last time Canada and the United States sat down to hammer out a deal over controlling the flow of the Columbia river, Dwight Eisenhower was president and John Diefenbaker prime minister. In those days, the two governments were eager to work together: they built the St Lawrence Seaway and set up the joint North American Aerospace Defence Command around the same time. Public acrimony like the insults Donald Trump has hurled at Canadian negotiators—he has called them “very difficult to deal with” and “spoiled” for refusing his demands for changes to the North American Free-Trade Agreement—would have been unthinkable. The result of their talks was the Columbia river treaty, signed in 1961 and ratified three years later. The pact required Canada to construct three dams on the 1,954km (1,214-mile) long river. It also allowed the reservoir behind a dam that would be built in Montana in 1975 to extend into Canada.

In exchange, the United States agreed to pay $64.4m to Canada for improved flood control—in 1948 a flood had wiped out Vanport City, Oregon—and to return half of the additional electricity made possible by the smoother flow of the river. From 1973 to 2003, American utility companies bought back that power, called the “Canadian Entitlement”. Since that deal expired, they have sent the electricity instead, worth anywhere from $120m-335m a year.

Not everyone benefited: the creation of one reservoir in Canada forced an estimated 2,500 people to move. On the whole, however, both sides have been pleased with the treaty. Whether it will remain in effect is up to Mr Trump—who in the past year has withdrawn from the Paris climate agreement and the nuclear deal with Iran.

The river treaty’s current rules extend only until 2024. And in 2014, both sides gained the ability to terminate it outright with a ten-year notice period. As a result, following years of preparation, discussions began on May 29th to revise it.

Even before Mr Trump took office, the United States planned to seek a reduction of the Canadian Entitlement. The American side says that Canada has already been paid enough for building the dams, and that the deal raises electricity costs in north-western states. In 2013 America also said it wanted the treaty to have ecosystem protection as a third aim, alongside power generation and flood management. That could force Canada to do costly work on its dams to allow fish to pass.

The Canadians politely disagree. They note that the treaty delivers myriad benefits to America, such as more predictable river navigation and supply of fresh water, and inflicts costs on Canada. Frequent adjustments of water levels reduce fish and bird populations, erode waterfront land and cause dust storms when reservoir bottoms are exposed. “We never know whether we’ll have a swimming area,” says Karen Hamling, the mayor of the village of Nakusp, who wants her town’s reservoir level fixed and compensation paid to its 1,600 residents. The formula used to calculate the entitlement does not take account of these effects. As for migrating fish, Canada argues that America had already blocked them with a dam built in 1942, and should thus have to pay for their reintroduction.

The floodgates will not open if the talks fail. If no changes are made, Canada’s automatic flood-management duties would end in 2024. Afterwards, it would only have to act to prevent flooding if America requests aid, proves that its own storage facilities are full and provides compensation. If either party does pull out, the withdrawal could not take effect before 2028.

Nonetheless, if Canada and the United States can no longer work together on river management, the prospects for collaboration on more contentious subjects look dim. Just as talks on the original Columbia river treaty, which began in 1944, marked the beginning of a warm era in their relations, so too might those on a successor deal indicate the end of one.