Monster hunter’s delight after sonar picks up large object at bottom of Loch Ness.

The “most compelling” evidence of the existence of Nessie has been recorded more than 500ft below the surface of the loch.

Monster hunters are astounded by the clarity of the image of an object, estimated to be 33ft long – although an expert said it may just be a shoal of fish.

The sonar image was captured by Cruise Loch Ness director Ronald Mackenzie while he was skippering a catamaran on Wednesday afternoon.

The 49-year-old said: “It was a bit of a dreich day and we only had 12 passengers. We were at our halfway point off Invermoriston, where we turn around. The water is 189m (620ft) deep there.

“The passengers were quite excited because we had just spotted a sea eagle, but then I saw on the sonar something more eye-catching.

Loch Ness tour boat skipper Ronald Mackenzie. (Image: Peter Jolly)

“It was right in the middle of the loch at about 170m (558ft) down. It was big – at least 10m (33ft). The contact lasted 10 seconds while we passed over.

“I’ve been on the loch since I was 16 years old and I have never seen anything like it.

“We have real state-of-the-art sonar on the new boat. It doesn’t lie. It captures what’s there.

Sonar image of Nessie (the small white dot). (Image: Peter Jolly)

“All the dots nearer the surface are shoals of Arctic char and deeper down there are ferox trout, so it gives you a good idea of the size of this large crescent shape.

“I believe there’s something in the loch that nobody knows what it is, be it a big eel or a sturgeon or a big fish of some sort – or even Nessie.”

Leading sonar expert Craig Wallace described the image as “100 per cent genuine”.

The marine robotics senior application specialist said: “I do believe large sturgeon do enter Loch Ness. It may be a sturgeon or a small shoal of fish.

Spirit of Loch Ness tour boat. (Image: Peter Jolly)

“But it is certainly a fascinating and interesting contact and without doubt it further adds to the debate about Nessie.”

Nessie expert Steve Feltham, who has set a world record for the longest vigil of looking for the Loch Ness Monster, said Ronald’s sonar image was the “most compelling” evidence of the 
existence of the legendary creature he had seen.

He said: “It is extremely exciting. I have known Ronald Mackenzie for 30 years. He’s a Highland lad who does not seek publicity and shies away from the fanciful Nessie theories.

“He’s not somebody who would cry wolf – or Nessie – but within seven minutes of getting the sonar contact he messaged me.

“I definitely think Nessie is an animal. I think we are getting closer to finding the answer.”

Colonel Robert Kenneth Wilson's famous hoax picture of Nessie, taken in 1934. (Image: Getty Images)

The Official Loch Ness Monster Sightings Register has accepted eight sightings so far this year.

Among the most famous claimed sightings is a photograph taken in 1934 by Colonel Robert Kenneth Wilson, which was later exposed as a hoax.