A video shared online appears to show swimmers at Leighton beach, near Perth in Australia, approaching a humpback whale that was swimming “dangerously close” to the shore.
In the footage, the whale can be seen straying into shallow waters and attracting the attention of beachgoers.
The whale later managed to swim back into deeper waters, before heading back out to sea.
Marine biologist Dr Natalie Sinclair told the BBC that the whale could have been at risk of stranding, and that this kind of behaviour is “unusual and perilous”.
She also warned that people swimming that close risk disorientating the whale, and that the best thing to do in this situation is to “leave the whale alone” and leave any rescue attempts to professionals.
“The proximity of individuals to the whale poses risks not only to the animal but also to the people involved,” she added.