Every bird, fish and bear knows that rivers don’t stop at an international boundary, but it’s taken awhile to convince human governments of that fact.

Now the U.S. Geological Survey has released a “harmonized” set of maps of the watersheds that cross the U.S.-Canada border. The set includes 120 areas from the Alaska-Yukon to the Maine-New Brunswick border edges. They range in size from the Great Lakes to Montana’s little Milk River.

“Any time you have a seamless map across a border, that’s a pretty unique contribution to science,” said Erin Sexton, a University of Montana research scientist at the Flathead Lake Biological Station. “That’s rare at this point. So many maps of wildlife activity or human use footprints just stop at the international border. Those of us who live and work here know that’s not true.”

The Milk River is rare in that it originates in Montana, flows into Alberta, and then comes back into Montana, giving both nations a stake in its comings and goings. Compare that with the more common North Fork of the Flathead River, which has its headwaters in the mountains of British Columbia leading to a one-way trip into the United States at the northwestern corner of Glacier National Park.

The maps include each nation’s collection of flow gauges, water quality monitors and other data-gathering devices, according to USGS physical scientist Pete Steeves, who worked on the maps. That’s important to model how much water is flowing through a river system that’s been dammed, such as the gigantic Columbia River watershed that covers British Columbia, Washington, Idaho and parts of Montana.

“These maps allow somebody to build time-of-travel models,” Steeves said. “For example, if there was a cross-border spill, like what recently happened in West Virginia, you could create a time-of-travel test to see at what point downstream public water supplies are affected.”

The United States and Canada are currently renegotiating a multiyear treaty governing hydropower and irrigation flows on the Columbia River system. Montana and British Columbia have a memorandum of understanding that’s nearing federal confirmation to protect the North Fork of the Flathead from energy development. And there’ve been ongoing disputes about the Elk and Kootenai rivers’ degradation due to Canadian coal mining operations near their headwaters that flow into Lake Koocanusa.

Canadian Ambassador to the United States Gary Doer told the Calgary Herald “five years from now, we will be spending a lot of our time diplomatically and a lot of our work on dealing with water.” He noted the Columbia River Treaty, the transboundary Flathead River and the Missouri River diversion were all ongoing debates between the two nations.

“We’re blessed with a lot of water, but we cannot take it for granted,” Doer told the Herald. “We have to manage it more effectively and that means waterflows south to north and north to south. There will be pressure on water quality and water quantity.”

Reporter Rob Chaney can be reached at 523-5382 or at rchaney@missoulian.com.

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