For the first time, humpback whales have been spotted in the East Alligator River in the Northern Territory's remote Kakadu National Park.
Kakadu National Park staff have monitored the animals since they arrived early in the week and as of Thursday just one whale remained in the river.
Authorities have moved to put an exclusion zone in place from the mouth of the East Alligator River to a point about 30 kilometres upstream for the welfare of the whale and the safety of people who may have been considering going to the area by boat.
In a statement, Parks Australia said they were "working with NT government authorities to gather data on this unusual event".
"As far as we're aware, this is the first time this has happened," the statement read.
"An expert working group has been set up to monitor the whale and prepare plans for intervention if required.
"The last thing we want is a collision between a boat and whale in waters where crocodiles are prevalent and visibility underwater is zero.
"We also don't want boats to inadvertently force the whale further up the river.
"The whale is not in distress at the moment and it is not an emergency situation.
"The best-case scenario is for the whale to make its way back out to sea."
Kakadu National Park and NT Government scientists will continue to monitor the whale in the coming days.
