IT looks like a monster from the deep, something that would not have been out of place in Loch Ness – and it gave Hampstead Heath rangers the fright of their lives at the weekend.

This huge European eel, a member of a critically endangered species, was spotted basking in sun-warmed waters in Highgate Number One pond by the rangers, and the species has never been spotted alive on the Heath before.

Ranger Justin Walsh was wearing waders and doing oxygen testing in the pond’s shallows when he caught sight of the beast, which was well over a metre in length. 

He said: “It was quite a sight – it was a big old thing, thicker than my arm and it certainly mustered an expletive or two.”

The only time an eel has been seen before by rangers was a dead one that had been found partly eaten last year – but at the time, it was believed it had probably been dumped.

The European eel has a remarkable life: spawned in the Sargasso Sea, they drift to Europe in a migration that takes the best part of a year. When they hit the coast, they turn from larvae into eels and go from salt water into fresh, swimming upstream. 

How the eel could have got into the pond is a mystery. 

The pond has a drain that feeds down into the River Fleet, and then into the Thames, so there is a chance the eel wriggled its way for miles along underground culverts and emerged into the Highgate chain of ponds.