Whale in croc-infested NT river confused

Scientists hope to get a whale back to the ocean after it ended up in a crocodile-infested NT river.
Scientists hope to get a whale back to the ocean after it ended up in a crocodile-infested NT river.

Scientists monitoring a whale that took a wrong turn into a crocodile-infested Northern Territory river will search for a path out of the shallow waterway.

It's the first time a humpback whale has been spotted in Kakadu National Park's murky East Alligator River, with one report placing it 30km inland.

NT government scientist Carol Palmer said the whale appeared healthy at the moment but could be confused and unable to find a way back to the ocean.

She plans to return to the river with wildlife officers on Friday to quietly observe the animal in a bid to figure out what's going on.

"We're also going to map the sandbars and the depths for a channel out to be able to potentially move the whale downstream out into the Van Diemen Gulf and sea," she told AAP on Thursday.

"We're all very keen up here in the NT and Kakadu to try and get it out," she said.

Experts aren't sure why the humpback swam up the muddy tidal river and didn't migrate south to Antarctica for its annual feed.

"It could have been chased up by some big sharks or maybe it was just a wrong turn," Dr Palmer said.

It's currently safe but risks becoming unhealthy when wet season rains start dumping fresh water into the waterway.

"That change to the saltwater can affect their skin and health," she said.

If it does become unwell or stuck on a sandbar the whale could become a meal for the hundreds of saltwater crocodiles in the river, marine biologist Jason Fowler said.

He initially spotted three humpbacks in the remote river about two weeks ago.

It's not clear if the other two have left to head south for the summer or are staying under the water.

Dr Palmer hopes Friday's trip will clear up exactly how many humpbacks are still in the river before any plans are made to intervene.

If the Kakadu team does decide to shepherd the whale back to the ocean the best opportunity may be in a few weeks when the highest tide of the year is expected.

Australian Associated Press