Experts failed to pour cold water last night on reports a crocodile is alive and well and living in a Welsh lake.

Crocodile hunters are heading for Swansea after it emerged one of the reptiles has been spotted patrolling the 20ft deep pool in the middle of a city business park.

The creature is normally the preserve of warmer climes such as Africa, Asia and Australia, but fisherman Steve Jenkins is convinced he saw a specimen in Morfa Enterprise Zone's Pluck Lake.

Mr Jenkins, who lives nearby, was on Sunday walking his dog around the lake, which is the size of four football pitches, when he saw what he first thought was a log in the water.

He said yesterday, "It was definitely a crocodile. There was a white van submerged in the water and it swam over the top of it so I had a good look. It was a metre long and had a long tail.

"I've been ribbed mercilessly since I reported it to the police - people whistle the tune of Crocodile Shoes when they see me. But I don't care what people think, I know what I saw."

Natural history expert Professor Paul Brain of Swansea University, said it was possible for a crocodile to live in a relatively cold climate.

He said, "If this is not a mistaken sighting, the crocodile would simply slow down or even shut down for a while during cold weather then spring back to life when the water gets warmer.

"There are a lot of exotic pets out there and this could be one which outgrew its tank and the lake may have been a suitable place to dump it."

The shores of the lake were busy yesterday with potential croc-watchers, including Gwilym Games from the Fortean Zoology Centre.

Parallels were drawn with the Loch Ness Monster, which is worth around £20m a year to Scotland's tourism industry.

Geoff Haden, vice-chairman of Tourism Swansea, said: "If we have the Loch Pluck Monster in our midst then it could be the start of a massive influx of tourists.

"Loch Ness has made an incredible amount of money from its monster - having one here can only be a good thing for the Swansea economy."

A spokesman for Visit Scotland said the Nessy legend would take a lot of beating.

He said, "While research has been conducted at many lakes, Loch Ness is the icon for monsters and Nessie, the Loch Ness Monster, is without doubt the grand daddy of them all. It is to Loch Ness where myriad researchers, professional and amateur, from all walks of life, have flocked with their cameras and sonars, hopes, fears and aspirations to solve the greatest mystery on Earth, Nessie, the Loch Ness Monster.

"Loch Ness investigations have included lures, fish baits, exploding light bulbs, submarines, scanning sonars, echo sounders, telephoto cameras, underwater cameras with strobe flashes, movie cameras, video and, now, digital cameras too."

A spokesman for Swansea Police said yesterday officers had visited the lake but had not seen anything. RSPCA officials have also visited Pluck Lake but have not reported seeing anything like a crocodile.

But Leicestershire-based Beastwatch UK says the number of sightings of non-indigenous, exotic animals in Britain has rocketed this century. The group has received more than 10,000 sightings of everything from wallabies to dangerous spiders, crocodiles and even a penguin since 2000.

Carpenter Chris Mullins, the founder and co-ordinator of Beastwatch UK, attributes the surge to climate change, zoo thefts and exotic pet escapes.

He said, "Our figures show that in the last eight years 51 wallabies, 13 spiders including a tarantula and a black widow, 13 racoons, 10 crocodiles, seven wolves, three pandas, two scorpions and one penguin have been spotted."

There were also reported sightings of 5,931 big cats and 332 wild boars roaming the countryside and 3,389 sharks in British waters.

In the 1990s, after the craze prompted by the film Teenage Mutant Ninja Turtles, more than 100 terrapins were found in Cardiff's Roath Park Lake.

When the pets grew to the size of dinner plates the novelty wore off and they were often placed in the nearest watercourse. The National Terrapin Project's 1997 survey revealed that Roath Park contained 125 of these unwanted pets - more than any other urban lake. When they demonstrated a liking for chick eggs, small animals and birds - not to mention biting human fingers - many were rounded up and sent off to a terrapin centre in Italy.

Having a monster here can only be a good thing for the economy.