How did the Mackenzie river get its name?

The name 'Mackenzie' was given to the river during Alexander Mackenzie's 1789 exploration to its mouth in the Arctic Ocean; it was named in honour of Mackenzie by British Prime Minister William Pitt the Younger after Mackenzie returned to Britain.

Prior to that time, different parts of the river bore differing names in various aboriginal languages such as "Deh Cho" in Slavey or "K'ahsho Got'ı̨né" in Hare.