For a moment, the water looks peaceful.
Then someone drops in a hunk of meat.
Teddy Roosevelt wrote about the piranha in 1914, calling it the "most ferocious fish in the world":
"If cattle are driven into, or of their own accord enter, the water, they are commonly not molested; but if by chance some unusually big or ferocious specimen of these fearsome fishes does bite an animal-taking off part of an ear, or perhaps of a teat from the udder of a cow-the blood brings up every member of the ravenous throng which is anywhere near, and unless the attacked animal can immediately make its escape from the water it is devoured alive."
But really, according to National Geographic, piranhas rarely attack people. In this case, they probably hang out in this area because someone nearby feeds them. This makes them gather in numbers they normally wouldn't, which can create a dangerous situation.
"Piranhas can be dangerous if they are trapped in a backwater without food, or [are] somehow concentrated in an area and they are hungry," National Geographic fellow Zeb Hogan told Nat Geo.
Still, this seems like a great place not to fall out of one of those boats into the water.
Check out the full video.
h/t io9