Believed to live in swamps, the ninki-nanka appears in the folklore of many parts of West Africa.
It is described as having a horse-like face, a long body with mirror-like scales and a crest of skin on its head.
Team leader Richard Freeman said evidence was sketchy as most people died soon after seeing it.
Mr Freeman, a cryptozoologist from the UK-based Centre for Fortean Zoology, admitted that the ninki-nanka's existence was "very far-fetched indeed".
Second-hand accounts varied wildly from it looking like a crocodile or a snake to having wings and spitting fire, he said.
But he disputed a suggestion that the hunt was a waste of time and money.
"We didn't know any of this before we came. We have to look into everything to see if there is a possibility that there's a real creature there," he told the BBC's Focus on Africa programme.
Cryptozoology is the search for animals whose existence is disputed or unsubstantiated, such as the Loch Ness monster.
A park ranger from the Kiang West National Park lived to tell the tale of his encounter three years ago.
He described an immense animal 50 metres long by one metre wide that he watched for more than an hour before being taken ill.
He put down his survival down to a herbal potion given to him by an Islamic holy man, Mr Freeman said.
After being shown pictures of various reptiles and mythical animals, the ranger said the creature's face most resembled that of a Chinese dragon.
"We've heard very similar stories all over The Gambia but mostly not first hand eyewitnesses... there seems to be this thing when you see the ninki-nanka you will die usually within a few weeks," Mr Freeman said.
"We haven't discounted the possibility that there is a flesh and blood ninki-nanka in the swamps of West Africa, it's just at the moment the evidence is pointing to something more folkloric," he said.
The 2006 Gambia Expedition blog is still available.
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The team of British cryptozoologists from the Centre for Fortean Zoology released a film, documenting their expedition into the swamps and jungles of West Africa, in search of a dangerous dragon-like monster known as the Ninki-Nanka.
The six person team visited the Gambia and Senegal in the summer of 2006, to investigate the legend of a monster so awful, locals believe that to look upon it is death. The Ninki-Nanka is said to resemble a gigantic crested serpent and provokes terror in the locals even to this day.
"One man was so frightened of the monster he refused to enter a swamp where, years before, a sighting of the beast had caused a whole village to be abandoned. We had to speak to him from behind a bush, where he was hiding in terror," said Richard Freeman, Zoological Director of the Centre for Fortean Zoology.
The beast was also blamed for causing a lorry to crash, as it slithered out on to a rural road. The team visited the crash site, where the lorry is still on the side of the road.They spoke with keepers at a sacred crocodile pool, who recount an ancient song to keep the monster at bay, and were even given a supposed Ninki-Nanka scale for examination.
The team also investigated two other unrelated mysteries; a supposed sea serpent carcass - buried on a beach by an amateur naturalist - and the continued existence of a tiny lizard known only from five museum specimens.
Just as tangled as the African forests, are the jungles of the mind, where legend, and superstition, are entwined with natural history. The film goes some way towards exploring both of these shadowy places. - CFZTV
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