Pensioner Paul Smith was enjoying his monthly fishing trip when he spotted the mysterious creature lurking on the other side of the bank.
"I watched it go all the way round from one side of the lake to the other," he told the News.
"It was definitely a big black cat without a doubt.
"It was the size of a labrador and was very graceful.
"I was rather surprised, it was a bit eerie," said Mr Smith of Spilsby Road.

This is one of many sightings of the big black, panther-like cat in Lincolnshire and specifically The Wolds over the years.

A cloud of mystery surrounds the creature and, despite some people considering it to be mythological, there continue to be many sightings in the area in and around Horncastle.

Back in 2003, big cat watchers Mark Fraser and Brian Murphy from the Scottish Big Cats Society and Chris Mullins from Beastwatch UK visited Hemingby and managed to get footage of a large black cat grooming itself next to a caravan.

Speaking at the time, Mr Fraser said: "In the 15 years I have been investigating sightings I have never before seen anything like this in the wild - it was very exciting.
"I believe it is a hybrid which is a mixture of panther and domestic cat after wild cats were let out in the area and bred with something. Farmers see them in the wild all the time and know they are there, and I definitely believe it is a hybrid."

Sightings have also been recorded at Spilsby, Sotby, Ludford and Louth in recent years.
And last year two youngsters claimed to have seen the animal in woods at Woodhalll Spa

There are theories that the big cats may have been released into the Lincolnshire countryside after the Dangerous Animals Act came into force in the late seventies forcing the closure of many zoos.
Have you spotted the black cat? Email alison.sandilands@jpress.co.uk