US President Donald Trump signed an executive order on Thursday to rename Lake Ontario as Lake America, a change he said would take effect immediately.
A White House aide said the order directs the Department of the Interior and Secretary Doug Burgum to make the change.
One of the five Great Lakes of North America, Lake Ontario borders both the Canadian province of Ontario and the US state of New York.
Prime Minister Mark Carney's office did not immediately respond to a request for comment.
Trade talks between the US and Canada collapsed last week with each side blaming the other for derailing three days of intensive negotiations.
Trump claims Canada has been ripping off the US for decades
Trump claimed this week in a flurry of social media posts that Canada had been “ripping off the US for decades” by charging US farmers more than 400% in tariffs, driving companies out of business, and causing the US to lose an average of $60 billion a year.
This is not the first time Trump has renamed a body of water. On January 20 last year, shortly after beginning his second term, the Interior Department renamed the "Gulf of Mexico" the "Gulf of America."
Carney responds to Trump's renaming of lake
Canadian Prime Minister Mark Carney said on Thursday Lake Ontario will continue to be called by that name after US President Donald Trump said he was renaming it as "Lake America."
"The name is more than 400 years old, predating both the Confederation of Canada and the Declaration of Independence of the United States of America," Carney said on X/Twitter.
"Canadians also know that naming reality means calling it Lake Ontario – then, now and always."
Ariella Roitman contributed to this report.