The First Nations people of British Columbia were so sure it existed that they wouldn't pass by without offering a live sacrifice, reported Yahoo News.
And scientists and TV stations have sent submarines deep into the Okanagan Lake to try and find proof of its existence.
Legend says it's between 10 and 20 meters long, with a snake-like body and horse-shaped head.
Peer closely at the latest video to emerge of the fabled Ogopogo - Canada's answer to Scotland's Loch Ness monster - and you'll see... well, not much.
The grainy footage, shot by British Columbia local Richard Huls, shows what some claim is a 12-meter sea serpent.
Or it could just be a log.
Huls says there were no boats around when he shot the video a few weeks ago at Okanagan Lake, which made him think the mysterious disturbance couldn't be due to waves.
He told the Vancouver Sun:
“It was not a wave, just a darker colour. The size and the fact that they were not parallel with the waves made me think it had to be something else.
"It proves something is down there. Whether it’s Ogopogo or not, it is a different story but there is something at least down there."
Just over half the local people surveyed by local TV station CHBC believe Ogopogo is real.
Not everyone's convinced, however. Various alternative explanations have been offered for what the strange ripples seen in Huls' video could be, for example a standing wave caused by temperature variation in the lake water.
Then again, as Benjamin Radford of Skeptical Inquirer science magazine suggested:
"Perhaps not coincidentally, Lake Okanagan has tens of thousands of logs harvested by the timber industry floating just under the lake's surface."
Huls' video has also prompted some more obvious fakes, such as this clip titled "Ogopogo ate my wife's dog":