Three whales were initially spotted in the river, after two escaped, the remaining one made its way back to sea on the weekend.
A humpback whale that made a wrong turn and entered a crocodile-infested river in Australia has managed to escape back to sea.
The whale was first spotted in the East Alligator River in the Northern Territory’s Kakadu National Park last week.
Feach Moyle, Kakadu National Park manager, said: “It made its way out on the high tides and we’re pleased it appeared to be in good condition and not suffering any ill effects.”
Officials had been monitoring the whale after it was spotted just over 18 miles inland.
A further two whales were also seen in the river last week, however they managed to return to the sea after a short time.
Scientists have suggested that the whales may have made a “wrong turn” while on their annual migration where they follow the western coast of Australia to get from the tropics to Antarctica.
It is the first time there have been any recorded sightings of whales in the East Alligator River.
Despite the river’s name, Australia does not have any alligators – it was named by European explorers who did not know the difference between crocodiles and alligators.
The whales were considered unlikely to disrupt any crocodiles unless they became stranded.
Authorities also considered the chance of them being attacked by crocodiles was slim due to their size, unless they became weak or sick.
Marine ecologist Jason Fowler said he initially spotted three whales on 2 September while sailing with friends.
Mr Fowler said: “We happened to bump into some great big whales which completely blew me away.
“The water’s incredibly murky. It’s got zero visibility. So you can only see the whales when they’re right on the surface.”
He added: “There are so many humpbacks heading up the WA (Western Australia state) coast now, they’re bound to end up in new places. What’s incredibly weird is the fact that they’re up a muddy, shallow river full of crocodiles – that’s unheard of.”