The raft was made up of a trampoline, a basketball hoop and an awning.

A lazy day on the Waikato River turned into a schemozzle for police after more than about 20 people ended up in the drink.

Hamilton police sent boats on to the river after the raft briefly capsized, throwing most on board into the water near the Pukete boat ramp on Saturday.

Some were wearing lifejackets, others were not, Waikato police Senior Sergeant Ray Malcomson said.

DOMINICO ZAPATA/FAIRFAX NZ The 20 people were rafting down the Waikato River.

There was no immediate concern for the rafters' safety. They were being monitored by a police officer who got aboard a person's boat, he said.

"Looks like most were drifting towards the bank at the Pukete boat ramp, north of Church Road."

Malcolmson said most if not all of the rafters, aged between 18 and 50, managed to make it to the shore unaided.

They swam to the side and scrambled out of the shallow water on to the riverbank.

"The next thing is to go and rescue the raft," Malcolmson said.

Leaving it posed a hazard to any other river users, he said.

At 4.30pm, police were seen to be towing in a large raft consisting of a trampoline and basketball hoop to the side of the river.

A scattering of people remained on board.

There were a number of smaller rafts attached to the craft by rope.