What kind of dummy would go out on a boating trip in this weather and get stuck in the ice?
That's exactly what went through the mind of the passer-by who noticed the chap stranded in his ice-bound rowing boat looking in need of a helping hand.
Specialist water rescue teams, an RAF helicopter and two fire engines were scrambled fearing a Christmas tragedy.
Frozen stiff: But rescuers discovered the boatman in distress was in fact a bird scarer deterring cormorants from stealing trout
But when rescuers arrived at the frozen reservoir, they discovered that the marooned 'fisherman' was nothing but a... er... dummy.
In fact, it was a bird scarer dressed in a fluorescent jacket usually worn by a fishery manager to deter cormorants from swooping down and gorging themselves on trout.
It is the second winter running that people have mistaken the water-borne bird scarer for an angler in distress.
'Last winter we had police jumping over the wall thinking there was somebody stuck,' said Stephen Cuthbert, owner of Arnfield Fishery near Glossop, Derbyshire.
'He's out there during the winter and you'd be amazed how many people think "That fella in the lake's looking a bit pale" and get worried.'
Mr Cuthbert admitted that from a distance the figure looked realistic, explaining: 'The dummy wears the fluorescent jacket because that's what I wear when I go out to chase away the cormorant.
'When he's flying, he looks down, sees this man in a bright yellow jacket and thinks he's me so he doesn't come down. It really works.'
Stephen Cuthbert, owner of Arnfield Fishery where his brightly jacketed bird scarer, pictured in the background, is often mistaken for a fisherman in distress
Following Sunday's 999 call, a specialist water rescue team was dispatched while a helicopter was readied to fly down from Boulmer in Northumberland.
But when an officer from Derbyshire Police arrived at the reservoir on the edge of the frozen Peak District, the call was quickly revealed as a case of mistaken identity.
Tony Morgan, watch manager at Glossop fire station, said: 'A helicopter from the RAF was scrambled due to the position of the rowing boat in the middle of the reservoir.
'Both appliances from Glossop and specialist water rescue unit from Buxton were mobilised.
'On the road we were told it was a false alarm and it was actually a dummy which had been put in the boat previously by the gamekeeper.'