Crocodiles do not attack people every time an opportunity presents itself, especially when they have other things on their mind, new research suggests.

Queensland scientists used underwater technology to track about 130 Crocodylus porosus crocs, in the Wenlock River and the Ducie River in the state's far north over a three-year period.

The researchers from the University of New England (UNE), the University of Queensland and Australia Zoo were surprised to find despite the crocs being in close proximity to humans between the months of September and December, they did not attack anyone.

UNE's Dr Hamish Campbell said he did not believe that was because the crocodiles were not interested in people but was probably because they had other priorities, including searching for mates and nesting sites, in that period of the year.

"Earlier in the year they remained reasonably sedentary, but come September crocodiles became highly mobile and they would travel through these shallow water areas where people were undertaking water based activities," he said.

"There was no instance of attacks, perhaps that's because these crocodiles are highly mobile, perhaps their minds are on other matters.

"The boys are looking for the girls, and the girls are looking for nests, and they really just want to access these areas to travel through."

Dr Campbell said some of the males travelled up to 50 kilometres a day.

"They would do that repeatedly over one or two weeks, so their movement potential was up to hundreds of kilometres in only a couple of weeks, which was quite remarkable," he said.

New clues over when crocs likely to be lurking

The scientists were also surprised to find that the tide had a large influence on crocodiles' movements.

"The crocodiles would actually move up into these areas with the tide," Dr Campbell said.

"So around periods of high tide, during September to December, shallow watered areas around far north Queensland have a really high probability - it was almost 100 per cent - of a large crocodile being present.

"We also found that the crocodiles moved up in those areas on sunset, and were present throughout the night.

"So accessing these shallow water areas between September and December after sunset, there's a really high probability that crocodiles will be in those areas."