Canada's retaliatory tariffs on billions of dollars' worth of American imports took effect on Tuesday, deepening a trade dispute between US president Donald Trump and Canadian prime minister Mark Carney. The counter-measures, ranging from 15% to 50% on $20bn (£15.7bn) of US goods, respond to Trump's earlier decision to impose 50% tariffs on Canadian products. The row matters because it has spilled beyond trade into wider diplomatic friction, with Trump making symbolic gestures such as renaming Lake Ontario "Lake America" and threatening to block US sales of Canadian planemaker Bombardier.

Canada's tariffs target sectors including steel, dairy, appliances, agricultural equipment, pulp and paper, and electronics, and exclude US goods already in transit. Talks between the two governments broke down on 21 August, with Carney citing unacceptable US demands over trade deals with third countries and threats to French-language protections in Quebec. Polls suggest Carney retains strong domestic support, while only 20% of Americans approve of Trump's tariffs on Canada, though analysts warn Carney's backing could erode as the trade war's economic effects take hold. US media reports indicate no negotiations are currently under way.