Feltham gave up his girlfriend and his home to move closer to the Scottish loch to better investigate the sightings, according to the Scotsman.
He had good, admirable reasons: "This is an explainable phenomena," he told the Scotsman. "There is something to be explained in Loch Ness."
The Loch Ness monster's existence has been bandied around for decades. But virtually every sighting of the creature — including the original, infamous 1934 "surgeon's photo" — has turned out to be a fake.
Even this one:
That photo previously fooled Feltham, who once told the Telegraph it was the best image of the monster he'd ever seen.
But as the Telegraph reported in 2013, a man by the name of George Edwards, who operates a cruise boat on the loch, staged the photo, saying the picture was "just a bit of fun."
"He has admitted," the Telegraph reported, "that 'Nessie' was nothing more than a carbon fibre hump that starred in The Truth Behind the Loch Ness Monster, a 2011 National Geographic documentary."
That brings us to the Wels catfish, a truly terrifying creature in its own right.
Known for their voracious appetites, they grow to be about 16 feet long — whiskers and all. The fish is native to Europe, but was introduced into Scottish waters by Victorians looking for sport, according to Reuters.
Feltham is struggling to explain some unusually large objects showing up on sonar — objects that, he said, "are far bigger than any fish that should live in this body of water."
So far, he's turned up nothing.
Nothing, except for the possibility that Nessie is probably an ideal specimen of the third-largest freshwater fish in the world.
"I'm not saying the mystery's solved," Feltham told Sky News of his Wels catfish theory. "I'm still looking for a better explanation than that."
As for the quarter-century he spent Nessie-hunting, Feltham said was all worth it.
“I have to be honest; I just don’t think that Nessie is a prehistoric monster," he told the Scotsman. "However the monster mystery will last forever and will continue to attract people here — monster or not."
"I certainly don’t regret the last 24 years," he added.
This post has been updated.