Donald Trump has signed an executive order officially changing Lake Ontario's name to Lake America, his latest attack on Canada in an escalating trade war.

'I guess the purpose of this, more than anything else, is we're going to be changing the name of Lake Ontario, effective immediately to Lake America. That's going to take place right now as I sign the order,' the President said.

According to Trump, this official order is effective immediately, as he set his pen to paper.

'We defend Canada for nothing, we don't get anything,' he told reporters in the Oval Office when asked what prompted these changes. 'We love the people of Canada, but their representatives aren't doing an appropriate job.'

Trump says he has been thinking of this name change for a 'long time'.

The President announced the tariff increase after the two countries failed to reach a trade deal on Friday, sparking a tense back-and-forth between Trump and Canada's prime minister Mark Carney.

Trump is set to increase tariffs on cars, trucks, automotive parts and steel from Canada to 50 per cent by 2027.

'On Trade, and in other ways, also, they are among the worst Nations in the World to deal with. They feel entitled, and yet, we don't need Canada, they need us,' Trump said on Truth Social.

The executive order signed today directs Secretary Burgum and the Department of the Interior to update the Geographic Names Information Service to reflect an official name change.

Trump detailed that most of the lake actually sits in US territory.

Lake Ontario straddles the border with New York State, along its southern and eastern shores, and the Canadian province of Ontario to the north. It is not controlled outright by either Canada or the US and has instead been jointly managed under the 1909 Boundary Waters Treaty for more than a century. 

When pressed on the message the move sends to Canada, Trump launched into an attack on Canadian leadership over defence spending and ongoing economic disputes. 

'No message, as you know, Canada has been ripping us off for a long time on trade, very sadly,' Trump said. 'Even the military, you know, we defend Canada for nothing. We don't get anything. They don't pay us to defend Canada, but we defend Canada, and they understand that.'

He pointed to cross-border equipment as an example of Canada's reliance on the United States: 'As an example, we bought icebreakers. They'd like to use them. We have 11 brand new icebreakers coming in. They'd like to use the icebreakers. They don't pay for anything, and they want to be treated like a state, but they're not a state.'

Trump teased that the Atlantic and Pacific oceans could be next on his radar.

'Actually, as you know, we took something called the Gulf of Mexico and we changed it, and now it's very routinely the Gulf of America,' Trump noted. 'So, if you think about it, we have a Gulf and we have a lake. Now, all we need is an ocean. So, maybe we'll have to change the name of the Atlantic and/or the Pacific.' 

Returning to his frustration with Canadian negotiators, Trump branded them the absolute hardest trade partners on the planet.

'Canadian officials have treated us very badly. They're nasty people. They charge our farmers 400 percent tariffs,' Trump blasted. 'People oftentimes they'll ask me who's the worst to deal with on trade, and I said that's easy, Canada. They are the worst to trade, and they feel entitled, and just we can't have that.'

Asked whether a deepening trade conflict could hurt broader economic affordability, Trump dismissed the concern: 'Well, ultimately, it's going to be very good for us because we're losing... 62 billion a year on average with Canada... We can't lose that.'

Mr Carney previously claimed the US had made 'threats' and demands targeting French-language protections and Quebec culture during tariff negotiations.

This signing follows a viral teaser video posted on the President's official TikTok account, where Trump offered a sneak peek at his bold rebranding scheme.

In the clip, the 80-year-old sat behind the Resolute Desk displaying a map of the Great Lake, which straddles the US-Canada border.

'We're gonna make a little change; we're gonna call it something different than Lake Ontario,' Trump said in the video. 'We're gonna call it Lake America. And all it takes is a good pen and some intelligence.'