It's hard to tell with nothing for scale and the water not moving in a still picture, but this boulder has probably eaten some boats in its day. The main current funnels anything coming from above down a fast, narrow chute right smack into this thing.

Caption

It's hard to tell with nothing for scale and the water not moving in a still picture, but this boulder has probably eaten some boats in its day. The main current funnels anything coming from above down a fast, narrow chute right smack into this thing.
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