The robot, belonging to Norwegian offshore oil company Kongsberg Maritime, is drawing up the first high-resolution map of the 230-metre deep lake in a project named "Operation Groundtruth".
"Although it is the shape of Nessie, it is not the remains of the monster that has mystified the world for 80 years," Scottish tourism agency VisitScotland, which is backing the project, said today.
The agency's statement said "Nessie found" with an asterisk at the bottom reading "replica model".
"It is thought the model sank after its humps were removed (the buoyancy was in the humps) never to be seen again," VisitScotland said in a statement.
Also Read
The monster was actually a submarine in the film.
The mapping is being carried out by a robot called "Munin", which resembles a missile-shaped drone.
It also found a 27-foot long shipwreck, which is still being investigated, and worked out that there is no "Nessie trench" in the loch bed in which a creature could be hiding, as previously believed.
Previous discoveries made in Loch Ness include a crashed World War II bomber plane, a 100-year-old fishing boat and the remains of a speedboat used in a 1952 speed record attempt which killed its pilot.
The lake has been notoriously difficult to survey due to its depth and steeply sloping side walls.
VisitScotland estimates the revenue generated by tourists hoping to catch a glimpse of "Nessie" at 60 million pounds (76 million euros, USD 85 million) a year.