Pictures of the creepy discovery has sparked a viral frenzy as online commentators debate what lurks beneath Britain’s lakes.
The images have been shared more than 200 times in a bid to clear up the peculiar find.
Shocked walkers came across the carcass on the banks of Hollingworth Lake in Rochdale, Greater Manchester, yesterday.
Some have named the creature the “Roch Ness Monster” – with the lake 400 miles from Loch Ness.
The strange five-foot fish still had a mouth full of razor-sharp teeth.
One walker claims he could fit his entire fist inside the animal.
Sales worker Jonny Beckett, 32, said: “I was just on a romantic walk with my partner Suzanne and I was stunned when I saw it.
“I thought it was a crocodile or some ancient creature and I immediately took a photo of it.
“It looked huge – about 5ft in length.
“A group of kids saw me taking the photo and looked horrified.”
Myron Szymanskyj, who also shared his photos of the beast, said: “I eyeballed the deceased monster.
“I turned it over and boy did it stink.”
Many online users are downplaying the discovery, insisting the ‘ancient beast’ is simply an ordinary pike.
Pikes are regularly found in the 130-acre reservoir and have been known to grow up to 4ft.
However, the creepy creature has been enough to put off regular visitors.
Local resident Carole Ann Gleeson said: “It’s bloody horrible. I won’t paddle in the lake again, that’s for sure.”
Emma Lorraine Mitchell added: “Some pike that is. That looks lethal, I wonder if thats the only one or if there are more or if its ancient.”
Emma Meredith said: “Aww I was going to have a drive up weekend with the kids. I think I’ll pass now.”