Navy sonar equipment may be the last hope of solving the disappearance of two fishermen on a Waikato lake.
James Roberts, 45, of Pukeatua, and Jordan Pooley, 21, of Tokoroa, have been missing since Sunday last week, when they went fishing in a small boat on Lake Arapuni, west of Putaruru.
The search has been widening, with about 10 boaties and a private helicopter aiding police yesterday, but by last night there was still no trace of them.
On Saturday, two kayakers paddled from one end of the 25km-long lake to the other as well as searching small tributaries. A jetboater familiar with the area also found nothing.
Police have been searching one area, about 8km from where the men embarked, where members of the Tokoroa Sports Fishing Association found rope, a spool from a fishing line and footprints that may belong to Mr Roberts' dog, which returned home alone almost 10km away on Wednesday, causing the alarm to be raised.
"If they can prove that it was his dog's footprints, that narrows down the search area pretty significantly," said club captain Tony Baldwin.
Taupo area police commander Inspector Steve Bullock told RadioLive the lake was too large for divers to search every centimetre.
"We've got a couple of options available to us but we'll probably use police divers or else the navy have some sonar equipment," he said.
"But without a narrowed area of focus, we are unable to use either of those."
Cambridge man Mike Southward, who made an hour-and-a-half-long flight over the lake in his helicopter yesterday morning, said the lack of clues had left searchers baffled.
"It's kind of strange. People always put stuff in their boats and you'd expect something would be floating on the surface, whether it's a cushion or a fuel tank. Everybody's got lots of theories."
Mr Southward said the length of the lake was flanked by farmland, and the two men would not have had to walk far to seek help if they had made it to shore.
"It's just very unusual that there's no conclusion. We've now exhausted everything that we can do and it's up to using sonar. That will then find the boat or it won't."
Police have been speaking to local residents and the search team will re-evaluate the situation today.