The kayaker had been gliding along the Amazon River, in Brazil when a horde of blob-like creatures appeared in the water beneath him.
The shock clip captured the moment when one of the mystery creatures appears to touch the kayak.
The water suddenly splashes and foams violently all around the kayaker – who somehow manages to keep his cool.
The shocked man posted the video to Instagram, alongside the caption: “Someone explain to me what this is.”
One social media user joked in the comments: “I would be the first man in the world and in history to run on top of the water if that happened to me.”
Another remarked: “Like the lake part of Resident Evil 4.”
A third praised the man’s bravery, adding: “The guy doesn’t even flinch. I would have c*apped myself.”
And a fourth said: “After millions and millions of years, the great Cthulhu was free once again.”
Others gave their thoughts on what the uncanny sea beasts could be.
One user speculated: “I think they could be manatees. What surprises me is the speed at which they move because, according to my knowledge, they are not that fast.”
While a second added: “I think it was a herd of manatees that were resting in shallow water and thought there was a predator.”
It’s not the first time a kayaker has been startled by threatening sea animals.
Last year, kayaker Scott Haraguchi was in a kayak just off the coast of Hawaii when a massive tiger shark suddenly leapt out of the water.
He had been using a GoPro to film his fishing antics when the shark made a beeline for his boat.
Heart-stopping footage shows the shark thundering towards the kayak before launching itself at Scott.
The shark can be seen opening its jaws as it crashes into the boat while Scott screams.
Luckily, Scott was able to kick the shark away.
A few years prior, a kayaker had a similarly miraculous escape after a great white shark attempted to attack him off the coast of Monterey Bay, California.
Heart-stopping footage of the close encounter shows the kayaker waving his arms frantically in the air to attract attention from the shore.
The shark then moves to within a few yards of the terrified man before disappearing beneath the water.