Why this ominous shadow shut down a packed beach in Sydney

It may look like a simple shadow cast by a cloud, but in fact this dark shape in the water at a popular Sydney beach sparked alarm, with swimmers ordered to head to shore immediately.

Swimmers and surfers at Manly Beach, on Sydney’s northern beaches, were told to flee the water after lifeguards spotted what was actually a giant school of small fish.

Drone photos and video taken by photographer Lee Bollom from Batuti photos showed the size of the group of fish.

A nearby lifeboat seemed small in comparison.

Although the fish themselves posed no danger to swimmers, there was a risk that they would attract sharks that feed on these large schools.

Surf Life Saving NSW general manager Brent Manieri told Daily Mail Australia surf lifeboats can sometimes float smaller bait balls from beaches, but this one was ‘way too big’.

“If bait balls are present, it will often attract predators – larger fish, birds and dolphins, and that can also attract sharks to the area,” Manieri said.

‘People swimming through such a bait ball can lead to an interaction with a shark. It is clearly a higher risk and the precaution is to remove swimmers from the area.”

Bait balls form when small fish gather into a spherical shape, either voluntarily or to protect themselves from predators (pictured is a bait ball at Sydney’s Manly Beach on Sunday)

Mr Bollom, who captured the bait ball on his drone, also used the camera to scan the coastline for sharks but saw none.

The natural phenomenon occurs when small fish gather in a group to protect themselves from predators.

It comes after another drone photographer captured the moment a shark came dangerously close to unsuspecting swimmers on a Perth beach.

The very close call was filmed with a drone at Whitfords Beach in the north of Perth, Western Australia, a spot known for tiger shark sightings.

The shark swam close to a father and his two children in the waves before being startled by a paddleboarder and heading into deeper water.