An injured baby humpback whale found earlier this week off Sydney's coast has been euthanized, Radio Australia reported on Friday.

The calf, nicknamed Colin, was abandoned by its mother and was unable to feed himself.

After vain attempts to save the animal's life, wildlife rescue workers decided to kill it to stop its suffering.

The whale had been attempting to suckle yachts, which it apparently mistook for its mother.

It was given a lethal dose of an anesthetic as its condition deteriorated.