There are concerns about the safety of a number of humpback whales that have strayed into crocodile-infested rivers in Australia.

At least three whales have been spotted in the East Alligator River in the Kakadu National Park in the Northern Territory, about 12 miles (20 km) from the mouth of the Timur Sea.

It is believed that three whales initially entered the river and it remains one, although it is not yet clear whether the others have actually gone or are merely staying underwater.

Unprecedented sightings have stunned locals and authorities, with scientists suggesting that whales could make a “wrong turn” during their annual migration to Antarctica.

Recorded sightings of whales in a World Heritage-listed park on the East All Tihiabhai River have never been seen before.

Yet it is not clear how the animals became accustomed to living with the clear sea, penetrating deep into a river with very little visibility.

Marine ecologist Jason Fowler said he spotted three whales on Sept. 2 while traveling with friends.

Mr Fowler said: “We jumped into some big whales that blew me away.

“The water is incredibly weak. It’s got zero visibility. So you can see the whales right at the bottom.”

He estimated that there were two adults and a small whale, which was about 10 meters (33 feet) to 12 meters (39 feet) long.

Their size makes it impossible for any crocodile to try to attack them.

“The population of Western Australian humpback whales has completely exploded. This is a great success story in marine conservation,” Mr Fowler added.

“There’s a lot of humpbacks on the WA (West Australian) coast right now, they’re forced to end up in new places. Incredibly surprising is the fact that they’ve created a raw, shallow river filled with crocodiles – that’s not heard,” he continued.

Despite the name of the river, there is no alligator in Australia. European explorers named it after many crocodiles who clearly could not tell the difference.

Carol Palmer, a whale and dolphin scientist, said there was still at least one whale in the river during the weekend.

“We don’t know what happened, but obviously it turned out to be a mistake and ended up in the East Alligator River,” Mrs. Palmer said.

“It’s very tidal. It’s quite shallow and we’re all eager to try to get this guy out,” he added.

Options to persuade a whale to leave the river include using recorded whale calls or making noises tied to boats.

Mr Fowler said: “We spoke to the indigenous elders who spoke on behalf of the country in Kakadu and they said that the whale has no name. It is not recorded in their cultural history. They have never heard of it before.”

Several whales have entered the River Thames in London Last year two.