Bristol Water staff inspecting a Somerset reservoir have spotted what appeared to be an alligator.
The reptile was spotted near to Chew Valley reservoir by Bristol Water staff.
They caught the two-foot-long animal with a net and put it in a box.
John Harris, fisheries and recreation officer at Bristol Water, says the animal hissed when approached.
Experts now believe that the animal is in fact a caiman, which can grow to 15 feet - bigger than their alligator relatives.
The caiman is one of the largest predators in the Amazon basin.
It is not known how the exotic reptile has found its way to the West country.
Bristol Water say the alligator is now safe.
The RSPCA says it is experiencing a 'worrying number' of reptiles being abandoned by negligent owners.
It also says caimans are not suitable pets.
WATCH footage of the running reptile below: