I just watched a episode of River Monsters with Jeremy Wade, he was deep in the Amazon with the natives catching Arapaima fish known to kill people and the largest fresh water fish in the world.
He got sidetracked when the natives told him there was a snake called the Cobra Grande living in the area. Thought to be a myth the snake dwarfs the Anaconda's that can grow to 30 feet long so they went to show Jeremy the spot. They showed the animals sliding tracks and the hole it lives in "huge is the only word for it" and giant scaled snake skin, when the natives saw it previous they shot it with a rifle 3 times that had no effect and found the lead bullets on the ground later.
A whole native settlement had to be moved because they were so afraid of it. It's like a LocNess Monster story but with obvious proof. I tried to find a full episode on youtube but only found this from that episode.
I recommend watching if you can, I believe it's on Animal Planet too.