Boaties are being warned of rough conditions at the Maketu bar after two men plunged into cold water when their boat overturned in rough conditions.

Maketu station officer Shane Gourlay says the two men were trialling a new motor on their 14 foot tinny when the incident occurred at about midday, Thursday.

'They were going out to try a new motor and it stopped and they got swamped and tipped over,” says Shane.

One man, aged 81, was taken to Tauranga Hospital with minor injuries after sustaining lacerations to both his arms.

'We just assisted with first aid – we did not have to get them out of the water they were already out,” says Shane.

'And a local boatie was pulling their boat out of the water for them.”

Shane says it has been some time since a boat overturned at the bar.

'That bar can be quite dangerous when it's rough weather and big waves.”

The other man involved is believed to be in his 60s; both men are from Little Waihi.

Coastguard New Zealand is investigating dangerous bars around the country where new traffic lights can be used.

The lights will signal to boaties if conditions are safe.

A green light will indicate safe conditions, an orange will indicate hazardous and red dangerous.