More than 800 Canadian wildfires are burning as air quality alerts extend into the US.

The air quality in the Midwestern city of Detroit is currently the worst in the world, according to the Swiss air quality tracker IQAir, followed by Minneapolis and Toronto.

Republican legislators in the state of Michigan wrote An open letter, External For the third year in a row, Canadian Prime Minister Mark Carney expressed frustration with calls for better control of the country’s wildfires.

“A year has passed, the season has come again, and nothing has changed except that our patience has run out,” said the letter, signed by four of the council’s representatives in the US state.

Pete Hoekstra, the US ambassador to Canada, in a statement on Wednesday praised the wildfire fighting from both countries and struck a more diplomatic tone.

“This challenge knows no borders. The United States will continue to coordinate closely with Canada, just as we have faced more than four decades of joint wildlife emergencies,” he said.