The agency that mediates disputes between Canada and the United States over shared waters is pleading with the federal Liberals to join an investigation into contamination from British Columbia coal mines before the Americans move on their own. In a May 13 letter, the International Joint Commission asked Prime Minister Justin Trudeau to commit Canada to collaborating with the U.S. on studying and finding a solution to selenium from Teck Resource’s Elk Valley mines that ends up in rivers and lakes south of the border.