Planning is underway for an extremely dangerous rescue operation to help a baby whale entangled in a fishing trap off Sydney.
A National Parks boat crew wants to cut the calf free, but its protective 45 tonne mother makes it incredibly risky.
The female humpback whale and her calf were spotted with about 30 metres of rope, just off Sydney Heads, at one stage thrashing in circles trying to break free.
It's believed to be a fish trap snagged around the calf's left flipper.
Typically, the trap will have a steel cage at one end and three floats at the other.
Whale watchers looked on in horror as the calf tried to free itself.
“It was just going up and down pretty fast, usually it'd dive for three, top six minutes," Whale Watching Sydney’s Jonas Liebschner said.
The pair was first spotted about 700 metres off Dover Heights around midday.
The humpbacks ventured into Sydney Harbour before heading south on the return leg of their annual migration.
Water Police and National Parks headed out to organise a rescue. The plan was to send a crew in a small, fast boat to pull alongside and cut the rope. But a sudden storm over Sydney made it too dangerous.
Experts warned the mother would be highly protective of her calf. And, at around 45 tonnes, highly dangerous.
“In all likelihood we'll get an aircraft up in the morning to assess the current status of the animal, and its location," Geoff Ross from National Parks and Wildlife said.
Mothers and calves usually hug the coast for protection, this time however it placed them in danger.
Spotters will attempt to keep an eye on the pair overnight.