My story is set in a small Idaho town called Serpent's Yard, named after the cryptid they believe lives in the lake up in the mountains above the town. The town is built around a river, known as Serpent's Road, that flows out of this lake, which then goes into a waterfall just past the town limits on the other side. An important plot point of the story is that this river has a notoriously strong current that has a penchant for drowning people who fall into it and, crucially, the bodies are very rarely ever seen again.
I heard this characteristic about other rivers somewhere, but I don't know what aspects of the river might have allowed for that, or if it's even possible for my specific river as I understand it. So I thought I'd check here to see if there are any changes to my setting's geography I need to make in order for this deadly river to be possible.
What needs to be true about my river that makes it difficult to impossible to find the bodies of those who drown in it?