"While the level of the lake is lowered, we will be undertaking water, land and aerial searches of the area."
Clothing which may belong to the missing men may have been recovered by search teams, Mr Bullock said.
"If so, this could help us to narrow down the search area."
Mr Bullock earlier 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.