Peter Jackson and Phillippa Wearne, from Sydney, Australia, were driving alongside the huge Loch in the Scottish highlands when “something big and fast moving through the water” caught their eyes.
The sighting happened near the ruins of Urquhart Castle – one of the major hotspots for alleged Nessie sightings.
Even Scotland’s official registrar for evidence of the mythical creature has been unable to debunk the photograph, saying there is “no clear explanation as to what the family caught on camera”.
It is only the second reported sighting of the Loch Ness monster this year.
Phillippa, 60, a retired lawyer, said: “I really was just stunned and I thought: ‘what is it?’
“It was pretty big even from 150 yards or more offshore.
“I didn’t know what to think.
“We took photos and showed them to people at a B&B and then showed them to people on a cruise.
“Skipper for the Loch Ness Project, Ali Matheson, said he had not seen anything like it.
“It seemed to be moving fast but in the direction of the current.
“We just figured if he’s worked on here for years and not seen anything like it, then it must be something.”
Peter, 64, a retired engineer, said: “We were dumbfounded but excited.
“We just thought: ‘Wow, what is it?’
“It has been a childhood dream to come here.
“We were just driving along when we spotted it.
“We stopped the car and ran back along the road to get the shots.”
The couple noticed the object moving in the water at 5.18pm about four miles south of Urquhart Castle.
They safely stopped, ran back to find a clearing in the trees and took out their smartphones to take pictures.
Peter said: “I know I saw something and I know it was large so I am keeping an open mind.”
Phillippa said: “We had a lovely feeling between ourselves watching it until it disappeared.”
Gary Campbell, registrar of sightings at Loch Ness, said: “It’s great that once again smartphone technology has allowed visitors to the area to snap something unusual at the loch.
“This makes it much easier to identify known creatures which has led to a drop in recorded sightings over the past few years.
“This is only the second sighting of 2017 to make it on to the official register and we’re already halfway through the year, so we’re delighted that Nessie appears to have popped up again.
“With regard to Peter’s pictures, as with pretty much all Nessie photos, they are just that little bit indistinct. However, the report that he has submitted gives much more detail on the distances and time frames and from this, there is really no clear explanation as to what the family caught on camera.”
He is appealing for anyone else who may have been in the area and seen something similar on June 22 to get in touch.