If you're planning on heading out on the water this summer please make sure you are wearing a correctly fitted lifejacket at all times.

This plea follow in the wake of an incident at Lake Rotoiti near Rotorua where a 48-year-old man dived into the water from his boat and moments later disappeared under the surface on Wednesday.

The search for the man's body has now entered its third day, with police's national dive squad scouring the waters of the lake and their search and rescue team searching the shoreline.

It is understood the man had been wearing a lifejacket at the time of the incident but it has somehow slipped off him when he hit the water.

'This very unfortunate incident emphasises the importance of having a properly fitting lifejacket and wearing it when out on the water,” says Waikato Regional Council maritime service team leader Richard Barnett.

'Lifejackets should fit snugly without being too tight. If you can't make your life jacket fit snugly, then it's too big.”

Maritime New Zealand's website says crotch straps are also recommended in situations other than very calm water as lifejackets, even when tightly secured, have a tendency to ride up if there's any wave action.

Crotch straps are also mandatory for all child-sized lifejackets and in some yacht racing situations.

'Most drownings in boating accidents involve craft under six metres. Everyone on board boats under six metres should wear a lifejacket, unless the skipper has assessed this is not necessary, due to the low risk at the time.

'We recommend that non-swimmers and children wear lifejackets at all times.”

The search for the 48-year-old man who went missing in the water without a lifejacket at Lake Rotoiti, just north of Rotorua, on Wednesday was changed to a recovery operation on Thursday. Photo: Benn Bathgate/Fairfax NZ

It is understood the missing man, his partner and primary school-age son had travelled to Rotorua for a family getaway on Wednesday.

Speaking to Fairfax, Rotorua Lakes Coastguard president Barry Grouby says the family launched their boat at Otaramarae Road boat ramp on the northern side of the lake, and were heading to the popular lakeside thermal pools on the southern shore which is only accessible by boat.

But about halfway across the lake the man somehow ended up in the water.

Police were called at 2.10pm and told the man's lifejacket came off when he entered the water and he didn't resurface – exactly how this happened is still not clear.

'I don't think he had one on and I think his partner threw him one, but it got caught in the wind and didn't make it to him, he couldn't get to it,” says Barry.

A search operation involving Coastguard, the Rotorua Harbourmaster, the Bay Trust rescue helicopter, police and ambulance was activated soon after the man was reported missing, but was suspended for the night shortly before 9pm.

Police, Coastguard and the rescue helicopter resumed the operation, which was changed to a recovery operation and involved police's dive squad, on Thursday morning and spent more than eight hours scouring the waters of Lake Rotoiti with no luck.

The search continues today.

The man's family is currently being supported by other family members, friends, police, Victim Support and local residents.

- Additional reporting: stuff.co.nz