"But a lot of the time you don't see it until the last minute. It's deemed to be dangerous if there's a lot of people in the water and we want to get them out of the flagged area because he might be turning around and swimming around."
Only about 10 people were swimming between the flags at Papamoa when the shark was spotted yesterday.
Lifeguards were not allowed to enter the water to chase off the sharks, Mr Smith said.