Researchers are racing against the weather as they try to fit satellite transmitters to 21 Top End crocodiles.
The Federal and Northern Territory Governments are working with crocodile specialists in an attempt to learn why and how far the crocodiles move.
Transmitters have been attached to 10 crocodiles so far and researchers hope to fit another 11 before the rains begin.
Zoologist Dr Adam Britton of Wildlife Management International says of the crocodiles already fitted, those in tidal rivers are starting to move around now the build-up is in full swing.
"The record holder at the moment is a crocodile on the Mary River. We caught this animal downstream on the tidal section and it then moved south upstream to Shady Camp, and it actually moved into the freshwater area of the barrage," he said.
"It was moving at about five kilometres an hour while it was doing that and now it's turned around and it's gone all the way back up to the mouth."
Dr Britton says trapping the crocodiles before the wet is proving tricky.
"It does take a lot of time and effort to actually go out there and catch these animals," he said.
"At the moment Gary Lin and his team in Kakadu National Park are doing all the legwork. They're actually setting traps out at billabongs every single day and they're also going out on the river at night with a spot light and they just caught another one, number 10, a couple of days ago."