Wildlife experts in Australia's Northern Territory are monitoring a humpback whale that has travelled 18 miles (30km) up the East Alligator river.
It is the first time a whale has been recorded swimming so far up a river in Australia. Two other whales that were originally seen in the river have returned to the ocean. The whales are thought to have got lost while migrating from their breeding grounds warmer waters to Antarctica where they spend the austral summer feeding.
Kakadu is a World Heritage Site famed throughout the world for its wildlife and the East Alligator river is home to a population of saltwater crocodiles. It is not thought the crocodiles pose a threat to the 16m whale unless it becomes stranded.
Boats have been banned from the are while a plan is devised to encourage the whale to head back downstream to the sea.