A mystery monster is lurking in the River Nene - and terrifying fishermen.
Two local anglers say the white six-foot beast came close to tipping them out of their boat.
It was so big one of them mistook it for a dolphin - although it could be a huge sturgeon, which were once bred in the area.
The pair are now warning fellow fisherman to be on their guard as they go on the Nene in Cambridgeshire.
And they are planning a return trip to hunt the creature which they spotted at Whittlesey.
One of them described their frightening encounter to BBC Radio Cambridgeshire.
He said: “I enjoy going out on my boat. One day we were on our boat going up towards Whittlesey and the boat suddenly juddered as if there was something large in the water.
“My friend and myself looked at each other and I looked down to see what we had hit.
“I saw the most extraordinary thing. I saw the biggest fish I have ever seen in my life.
“I like boating and I like wildlife, but I had never seen a fish like this before. It was absolutely huge - it was over six-foot long.
“It was swimming alongside us and our boat had struck it and it was as if it was showing us the side of itself where the propeller had hit it and we could see the white flesh.
“My friend saw it and exclaimed ‘blimey is that a dolphin?’
“It was so big. We’re going to go out again this year and see if we can see it.”
The pair - who have asked to remain anonymous - did some research when after getting home and found that someone used to breed sturgeon in the area before the war.
He added: “We are wondering if it was one of these sturgeon. They can grow to enormous lengths.”
Sturgeon can grow as long as 20ft and are known to live between coasts and rivers, moving to the river to breed.
They used to be common in the UK.
The Marine Conservation Society has wild sturgeon on a ‘do not eat’ list.
Sturgeon are bred in captivity for their roe which is sold on as caviar. Most sturgeon farming in Europe takes place in France.
The Environment Agency said the men probably saw a seal or otter which often swim in the River Nene as it is linked to the sea.
Fish in the river include zander, pike, eel, bream and carp fish which grow to large sizes, but have never been known to reach six-foot long.