But the strange shape on the horizon was a hi-tech submarine hired by a Japanese television company to make a 90-minute documentary on the "monster" at Bala Lake in North Wales.
Sightings of "Teggie" - whose name derives from the lake's Welsh name, Llyn Tegid - have been reported since the 1960s, with claims it has reared more than 10ft out of the water.
The company, TVS, has captured footage of "monsters" such as "Migo" in New Guinea and a creature in the Congo, Africa, where they filmed "something very large moving through the water".
Jason Priestly, research and project co-ordinator, said: "Going by those past successes, I think we have some chance of getting something on film here."Reuse content