This is the terrifying moment an ungrateful anaconda sinks its giant fangs into a rescuer as he tries to save it from a river dam.

Local in rural Formoso do Araguaia, in the state of Tocantins, Brazil, had called in wildlife experts when they spotted the monster 10-foot snake trapped in the waterway.

But video footage of the painful encounter on 10th May shows how the anaconda was far from happy about the plan.

As one rescuer reaches down trying to free it, the snake's head shoots out of the water clamping its jaws around his wrist.

The wildlife expert, not named in local media, whips his hand away and later footage shows the snake being captured safely and transferred to a carrying crate.

Finally, the anaconda is released into a nearby river and swims away.

The rescuer said later: "Before it closed its jaw completely I managed to pull my hand away.

"It was very fast and I had some injuries because the snake's fangs are long and scraped down my hand."

Although anacondas are non-venomous, their huge fangs and powerful jaws can inflict serious injuries and are used to pin their prey while they suffocate it with their coils.