On an overcast day in early August, a flotilla of five canoes pushed away from a jetty in Astoria, Ore., near where the Pacific breaks on Desolation Point, at the mouth of the Columbia River.

Eight weeks later, the Sea to the Source expedition is approaching the last leg of a 2,000-kilometre trip that is taking the paddlers across dramatic landscapes and past more than 14 hydro dams to the river’s headwaters in British Columbia.

The expedition was planned not to promote tourism or retrace the routes of explorers, but to focus attention on the environmental health of the largest river in the Pacific Northwest – and on an international water treaty that is set to expire. With 10 years’ advance notice, either Canada or the United States can terminate the Columbia River Treaty in 2024, which means the deadline to renegotiate or abandon one of the most important water agreements in North America is fast approaching. And debate on it is heating up on both sides of the border.

Fifty years ago, the linked waterways that rise in the Rocky Mountains, near Invermere, B.C., were viewed as forces to be controlled, commodities to be developed. But as B.C. gets a second chance to negotiate the future of a crucial water resource, the values today are more complex: This time around, interested parties are talking about navigation, recreation, agriculture, fisheries, First Nations rights and climate change – the latter a preoccupation of the politically attuned paddlers.

Aligned against a powerful array of U.S. stakeholders, B.C. is seeking to defend a dominant source of the province’s energy supply, as well as the dividends that have delivered billions of dollars to government coffers.

Premier Christy Clark will be talking about the treaty when she is in Washington, D.C., next week, as will a delegation from 15 tribes in the Pacific Northwest on hand to lobby the U.S. Congress.

“I’m pretty confident we’ll be able to get a good deal for British Columbia,” said Ms. Clark, who believes B.C. has a strong case. “Because here is the thing: ‘No deal’ is terrible for the United States. … Yes, there is a lot of financial interest in it for us, but if there is no deal for the United States, it will be an environmental and economic mess south of the border. So we have every interest in working together.”

While officials are talking in Washington, Adam Wicks-Arshack and his four colleagues on the Sea to the Source expedition are working the grassroots, drumming up interest on the banks of the Columbia. “We’ve talked to thousands of people,” he said.

The expedition, which wants environmental issues included in any treaty talks, launched on Aug. 2 and will end sometime next month in Canal Flats, B.C., where the great river begins. Along the way, the canoeists will have retraced the route that migrating salmon once took up the Columbia – until they were stopped by a series of impassable hydro dams.

“Near the ocean, salmon are present the whole time. Just constantly along the banks there are people fishing, native people netting as we were going by, so we were with salmon and the salmon culture the whole way,” Mr. Wicks-Arshack said. But about 800 kilometres upstream from Astoria, the salmon disappear from the river, blocked by Chief Joseph Dam in central Washington State.

“You could feel it change,” he said of the river above the dam. “Suddenly there just aren’t any salmon.”

When the treaty was ratified, environmental matters were an afterthought. The driving interests for governments were flood control, power generation and profit sharing. As part of the deal, BC Hydro built a series of dams to hold back water that is released to facilitate power generation in the U.S.

At a Vancouver signing ceremony in 1964, then-U.S. president Lyndon Johnson had a full honour guard as his treasury advanced the first cheque to B.C. – $253,929,534.25 to cover the initial 30 years of the agreement. “You Canadians went for that last 25 cents,” he said, joking about the hard bargain Canadians drove.

B.C. premier W.A.C. Bennett would later call the signing the happiest day of his career. Since then, the treaty has delivered billions of dollars in revenue through annual payments that range from $120-million to $300-million, reflecting a yearly share of the additional downstream power that is generated in the U.S.

The deal was seen as a good one at the time, but both sides appear to be heading toward a modified, modernized treaty.

With its concentration on developing liquefied natural gas projects in B.C., the Clark government has not made the treaty a major talking point. But that is changing. The file now sits on the desk of Energy Minister Bill Bennett, whose Kootenay East riding lies in the Columbia River Basin, where constituents still recall the good land and small communities that disappeared when reservoirs filled. Across the border he faces an array of four states, 11 federal agencies and representatives for 15 tribal governments. And the U.S. interests are expected to push hard to reduce the annual power payments to B.C. by more than half – with some parties saying B.C.’s entitlement should be slashed by 90 per cent.

Mr. Bennett is dismissive of that position: “They can’t substantiate that.” But he also knows he is in for some tough negotiating. “Sure we have differences of opinion. There are folks that wish they didn’t have to pay as much to B.C. for benefits. They are tough, they are smart – but there is goodwill on both sides.”

Nancy Stephan is the program manager for the treaty review at the Bonneville Power Administration, which together with the U.S. Army Corps of Engineers, operates the system south of the border.

“In 1964, it was a win-win for both countries,” she said in an interview. But the concepts that guided it are now out of date and “we really think it is important to modernize it.”

The idea of forecasting has changed much in 50 years, too. While the signatories in 1964 had confidence about how to promote development, today there is less certainty about what the future holds. With climate change promising more unreliable weather patterns, and a recognition that a nation’s water supply is a more complex and fragile resource, Ms. Stephan suggested there is little appetite for another treaty that would lock the two countries in for half a century or more.

“The treaty has given us a lot of experience, and we’ve learned that sometimes our energy forecasts are not that great,” she said.

In B.C., the Columbia Basin Trust has consulted with some 2,500 residents in 22 information sessions and has drafted a report summarizing issues of concern. The report notes people identified “managing eco-systems … in a comprehensive manner across the border” as a key area of interest.

Last week, the Army Corps of Engineers and the Bonneville Power Authority released draft recommendations that call for “ecosystem function” to be added to the treaty as a key, third component along with flood control and power generation.

Pat Ford, special adviser on Columbia River Treaty to Save Our Wild Salmon, a U.S. group that has been lobbying to have the agreement renegotiated, said the environment just wasn’t on the agenda when the deal was first done.

“I think it came near the end of a period where ignoring environmental issues was acceptable behaviour,” Mr. Ford said. “It would not have happened in the 1970s, but in 1964 it did.”

Mr. Ford said dams were built without fish ladders, destroying salmon runs, and water was released in ways that dramatically changed the natural flow of the river.

“The overwhelming impact … has been a tremendous deterioration, destruction of what used to be the largest and most productive salmon watershed in the world,” said Mr. Ford, part of a delegation that recently met with Matthew Rooney, deputy secretary of the U.S. State Department. “We made plain in our presentation that in the Pacific Northwest, ecosystem function is economic function. If you don’t have a healthy river, you are hurting all the users.”