Authorities issue shark warning over whale that swam 11km upstream in Clarence River and later died

Authorities have warned against swimming in areas surrounding the dead whale after it was towed out to sea from the Clarence River. Photograph: Jessica Hromas/The Guardian

While the case of a whale found 11km upstream in a New South Wales river this weekend was unusual, it was not unprecedented, experts say.

The juvenile humpback, which swam into the Clarence River on the state’s mid-north coast and later died, was towed out to sea on Sunday, according to NSW authorities.