A family swim on a hot day at a popular Mid North Coast waterfall has ended with a teenager falling to his death.

Manning Great Lakes Police Inspector Nick Seddon said the boy and his family had been enjoying a day cooling off in the water.

"They were swimming in the waterhole and jumping from the rocks, which is very popular," Inspector Seddon said.

"The 14-year-old ... was seen to slip and hit his head on the way down and hasn't resurfaced."

Alarm raised

The boy's family and other swimmers attempted to find him, but called emergency services at around 3pm when he couldn't be found.

Police, ambulance and fire and rescue attended the scene, which is only accessible by foot.

Police divers were later flown from Sydney and they located the boy's body in the water at 8:40pm.

"It's incredibly tragic for the family and very heartfelt by the police and emergency services," Inspector Seddon said.

"Our hearts really go out to that family."

Dangers away from the beach:

Police said the incident was a timely reminder of the dangers of swimming in rivers and waterholes away from the coast.

"Inland waterways … are unpatrolled and there are a lot of inherent dangers because you don't always know what's underneath the water and how slippery the rocks are and help can be some distance away," Inspector Seddon said.

The boy's death was the second at a NSW waterhole on Sunday.

A seven-year-old boy died after being found unconscious at the bottom of the Jellybean Pool in the Blue Mountains National Park at Glenbrook after being missing for 30 minutes.

He died shortly after arriving at Nepean Hospital.