A humpback whale has found its way back to sea weeks after it got lost in a murky, crocodile-infested river in northern Australia.

There have been no previous recorded sightings of whales in remote East Alligator River in the Northern Territory’s World Heritage-listed Kakadu National Park, and no one can explain why at least three of the blue water mammals ventured so deep inland in a river with little visibility.

The last of the trio managed to navigate its way through shallow channels at the broad river mouth and back into Van Diemen Gulf over the weekend, Kakadu National Park manager Feach Moyle said on Monday.

“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,” Moyle said.

Humpbacks follow the western Australian coast in their annual migration from the tropics to Antarctica.

A group of recreational sailors first spotted the lost trio on Sept. 2 more than 20 kilometers (12 miles) from the river mouth.

Two of the whales had disappeared before wildlife authorities arrived a week later.

Northern Territory government whale and dolphin scientist Carol Palmer said it was a mystery why a whale would stray so far up a shallow river full of crocodiles.

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

Despite the river’s name, there are no alligators in Australia. It was named after the river's many crocodiles by European explorers who apparently couldn’t tell the difference.

Authorities thought the whale was too big to be attacked by crocodiles, unless it became weak or sick.