Extant animals size

[Catherine]

Quote: The green anaconda is probably the heaviest extant species of snake or squamate in the world, perhaps only rivaled by the Komodo dragon. Reports of 9 - 12 m (30-40 ft) anacondas exist but such claims have never been scientifically verified.  A $50,000 cash reward is offered for anyone who can catch an anaconda 30 ft (9.1 m) or longer, but the prize has not been claimed yet. The longest and heaviest verified specimen encountered by Dr. Jesús Antonio Rivas, who had examined thousands of anacondas, was a female measuring 5.2 m (17.1 ft) long and weigh 97.5 kg. 

People are always claiming to have seen something really big that is actually nowhere near as big as they claim it is. 
A 5m anaconda is a big snake. Possibly a really old female could reach 5.5m. I have never heard of it, but it is possible because snakes do keep growing slowly all their lives. I really doubt anyone has seen a 9-12 m anaconda because they don't exist.
I actually held a green anaconda once. It was a female and she was only 2m at the time. She was still a pretty big snake.
And she was a pretty snake.