Mannegishi

According to the folklore of the Cree nation, the Mannegishi (singular and plural) are a mysterious race of small humanoids which live among the rocks in the river rapids and are infamous for their habit of capsizing canoes. They're also known to create pictographs on the rocks.

Biology
Mannegishi are strange-looking creatures. They possess skinny limbs, large heads with flat nose-less faces and large eyes, and notably have six fingers on each hand. In spite of their seemingly feeble physique, they're strong enough to tip over canoes with people inside.

Other North American cultures also have tales about small, semi-aquatic humanoids which are similar to the Mannegishi, but usually covered in hair.