Donald Trump has signed an executive order renaming Lake Ontario, the major body of water separating the United States and Canada, to 'Lake America' within the US.

Announcing the move from the Oval Office, President Trump declared that the name change was "effective immediately". The signing took place at the Resolute Desk under a banner bearing the slogan 'Making the Great Lakes even Greater'.

The decision comes amid renewed friction between Washington and its northern neighbour, with both countries currently locked in a bitter trade war.

Tensions had recently ramped up after Mark Carney announced that the Canadian province of Ontario would match Washington's economic measures by imposing 50 per cent tariffs on key exports.

Speaking from the White House, Mr Trump insisted that all the legal and formal procedures for the renaming had already been completed.

"We filed all the necessary papers, documents, everything else," Mr Trump said. "We notified all the people we have to notify. So we've done everything that you have to do. This is official, effective immediately."

Explaining why he chose to issue the executive order, Mr Trump pointed directly to the defence relationship and his dissatisfaction with Canadian leadership. "We defend Canada for nothing; we don’t get anything," he told reporters. "We love the people of Canada, but their representatives aren’t doing an appropriate job."

To put the geography into perspective, the lake lies directly between the US state of New York and the Canadian province of Ontario, from which the body of water originally took its name.

Both nations share control of the water. Joint management of the lake dates back more than a century, established when the United States and Canada signed the Boundary Waters Treaty in 1909.

What we do not know yet is how this domestic executive order will interact with existing bilateral agreements, or how Canadian officials will respond to Washington's unilateral renaming of shared waters.

With 50 per cent tariffs already announced on key exports and diplomatic relations strained, this dispute is developing quickly. I'll be tracking what happens next — check back for updates as more details emerge.