A video has emerged which appears to show a 30ft creature moving through the water at Loch Ness, reigniting monster rumours.
The two-and-a-half minute clip seems to show humps emerge above the surface of the water with something swimming and turning below.
Experts have described it as the most compelling footage from the past two decades years spent looking for the Loch Ness Monster.
Gary Campbell, who celebrated 25 years of recording Nessie sightings, acknowledged the footage and said it was the best he has seen in 22 years.
"In terms of video evidence, there’s been two or three really good videos in the past but this is certainly up there with the best of them," he told Mail Online.
"When something like this comes along which is genuinely inexplicable then it is great."
A couple in their 50s filmed the apparent sighting while on holiday in the Scottish Highlands and hope it will be analysed in efforts to help solve rumours about the monster.
The clip shows a mysterious creature swimming just below the surface of the water around 150 yards from the shore, with a strong wake of water behind it.
"I really don’t know what it was in the water. It was something large... It was propelling itself with something. It wasn’t how a fish would do it," the woman said.
She captured the eerie moment on the loch after waking up early on Monday and heading out with her camera as the water was so still, when she spotted a large creature moving.
"What on Earth is that?" she is heard saying as she captures the moment on her iPhone.
Pictures were also taken from the couple's holiday cottage less than half a mile from the loch and opposite Urquhart Castle.
The husband and wife claim the creature was between 20 and 30ft long and had at least one fin or limb which moved "like an oar" beneath the surface.
They described seeing something weird under the water which "rushed forward and turned around."
A local expert in video and photography said what the couple had captured was "clearly animate" and came out of the water before going back in, and was "definitely larger than a bird."
It is one of four sightings so far this year which have been approved on the Official Loch Ness Monster Sightings Register which is run by Mr Campbell.
The first was logged on March 30 when documentary maker Jamie Huntley visited the loch at around 11.15am with his colleague Warren Speed.
Mr Huntley, from Tyne and Wear, told how they were driving past Boleskine Cemetery when he saw a "large object or creature" in the loch which he mistook for a big boulder.
He recalled saying "what's that it's huge" after seeing movement in the water and said the beast's skin was wet and comparable to whale skin.
Five days later, another sighting was reported by Tom Ingram onboard the Spirit Of Loch Ness cruise.
Mr Ingram, who was visiting from Portsmouth, took a picture of a large mass in the water after contact was made on the boat's sonar near Invermoriston at around 1.30pm.
On April 15, a third sighting occurred near Aldourie Castle at around 9.30am.
Local Glenn Blevins was working on the banks of the loch when he saw "a large animate object in the water."
He told the register: "It was dark in colour and stayed there for around 20 seconds before sinking into the water.
"It was difficult to estimate the size but it was definitely larger than a seal and given the angle, there may have been two, one behind the other.”
