Concrete plant worker Tony Young claims to have discovered a mysterious sight in the water of the outer basin at Preston Dock, off Lockside Road.
Tony, from Ashton, enjoys walks round the area when he is on breaks from work and first spotted the creature on March 23.
He said: "I was walking on the dock at about 8.15am and I saw it.
"There was a lad there who goes round doing the lifeboat rings.
"He was just coming up to me and I said 'What does that look like to you?' He said it was a log."
But Mr Young thinks it was the body of an animal – possibly a big cat.
He took several photographs and showed them to friends and colleagues and his 23-year-old son Richard.
He said: "They said it does look real.
"My son keeps trying to go down and see it at the dock but it's always full of water.
"The face of it looks like a big cat, like a puma or a panther.
"It doesn't look like a soft toy because a soft toy would have a friendly face, this had a really mean face and a short snout."
Big cats include tigers, lions, leopards, jaguars, cheetahs and snow leopards.
The Dangerous Wild Animals Act, introduced in 1976, made it illegal to keep certain types of animals meaning hundreds of people released animals into the wild.
Tony said: "There was a big cat quite a while ago round this area.
"Since then they have been dregging up the dock and unloading all the waste land and I just wonder whether they have disturbed it."
"One thing I did notice was its eye was white and looked fleshy.
"On the end of its nose, it looked like a bit had been chopped off and it was pink underneath."
"I'd like somebody to go and have a look and see if it's real."
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