US President Donald Trump signed an order on Thursday to call Lake Ontario “Lake America” in the United States. The lake lies between Canada and the US state of New York. The US Department of the Interior has 30 days to change the name in US government records. However, Canada does not have to use the new name.

Canadian Prime Minister Mark Carney said Canada will always call it Lake Ontario. Leaders in Ontario, Nova Scotia, and New York also rejected Trump’s new name. The name Lake Ontario is more than 400 years old. There is no world group that controls the names of waters shared by two countries.

The order comes during a serious trade fight between the US and Canada. Talks ended last week without a deal. The US then put a 50% tax on $20 billion of Canadian goods. Canada plans to put the same level of tax on US goods next month. Some US politicians want to stop the name change, but both countries may hold new trade talks later.