A fruitless search of Lake Wakatipu after the sighting of a flare cost thousands, Marty Black said.
Two boats and a helicopter searched the lake for several hours on Thursday night after a red distress flare was spotted by a member of the public from the suburb of Fernhill.
Whoever set off the flare might not realise the effects of what might have seemed like ''a bit of fun'', Mr Black said.
The use of the helicopter would have cost more than $4000.
''The coastguard and a helicopter pilot were out for almost two hours, searching for a boat in trouble on the lake in the middle of the night.
''That's a big ask of volunteers who have already done a full day's work and have to be up again in the morning.''
Senior Sergeant Paula Enoka, of Queenstown, said they had spoken to a group of people on the Walter Peak side of the lake, but it was unclear if they were responsible.
''We weren't able to identify anyone who set off the flare, or any evidence of it, but we've still got further investigation to do.
''It's a big area - to be seeing it from this side of the lake to that side - it could've been anywhere in that area.''
Coastguard volunteer skipper Tim Buckley said a Coastguard boat with four volunteers, a commercial vessel and a helicopter with night vision equipment searched the lake for about two hours after the alarm was raised about 10.45pm.
Police called off the search about 1am.
''As far as we're aware, nobody was reported overdue or in distress. There was no radio signal.
''You can make your own assumptions, given it was fireworks night.''
Walter Peak Station manager James Clouston said he was unaware of any flares or fireworks being set off in the area.
Tourism operator Real Journeys spokeswoman Tsehai Tiffin said a group of staff had set off fireworks on the beach as its steamship TSS Earnslaw departed for Queenstown Bay about 9.20pm, and had continued to set off fireworks intermittently afterwards.
Mr Black said flares and fireworks looked completely different, and the witness had been clear about what they saw.
