In an age in which explorers are running out of wildernesses and life has been street-mapped to the ends of the earth, it is a rare moment indeed: the discovery of uncharted waterfalls on a river in a G8 country.

Adam Shoalts was canoeing along a section of the Again river in northern Canada when he found himself hurtling down 12 metres (40ft) into swirling white water. The tumble ruined his boat but piqued his curiosity. The waterfall could well be the largest discovered in Canada in 100 years. Shoalts went on to discover six other falls on the river.

"It's a pretty big deal that you still have unexplored territory in this day and age," said Shoalts, who is now planning to revisit his inadvertent discovery to plot and measure the falls. With financial backing from the Royal Canadian Geographical Society (RCGS), his work will be used to update maps for one of the least explored and most remote areas in the world.

"Many organisations are just sponsoring athletic contests, like going to the north pole … routes and journeys that have been done many times before," he said.

Since his first canoe expedition in 2004, Shoalts has uncovered petroglyphs (rock carvings) in British Columbia; spent 40 days cataloguing amphibians in the Amazon; and dodged polar bears on a newly paddled Again tributary that he hopes to name.

"Given the documentation of these waterfalls, we clearly still have gems to be revealed," said Michael Schmidt, the vice-chair of the RCGS expedition committee. "Perhaps it's not to the magnitude of what explorers would have seen 150 years ago. [But] there is still much to be discovered."

Returning to the falls he found last year will be a harrowing one-man journey for Shoalts, harking back to treacherous wildernesses faced by early explorers. The Hudson Bay lowlands are roughly the same size as Britain but with a population density of fewer than one person per 50 sq km.

Adam Shoalts in front of another waterfall he discovered. Photograph: Adam Shoalts

Without adequate landing for float planes, reaching the Again's headwaters means skirting the dangerous Kattawagami river, which claimed a canoeist's life in 2006, paddling upstream against Shoalts's unnamed tributary and carrying a boat through the world's third largest wetland.

"I used to say that canoeing the river is the easy part because you have to go through such a nightmare to actually reach the thing," he said. "I guess that's the reason these areas … have been passed over or skipped."

But old mapping techniques share the blame, Schmidt explained. Our knowledge of the Again's topography, like that of much of Canada, relies on aerial photographs from the 1960s. The Geological Survey of Canada, responsible for topographic updates, will add Shoalts's plotted waterfalls pending verification from Spot satellite imagery.

"There's still a lot of work left to be done. That's reality," said Shoalts. "Canada's so vast. Even if I do this the rest of my life, all my work would still only be a drop in the bucket.

"We don't know the world nearly as well as we think we do."