On August 3, three people died when a vessel capsized while crossing a bar in Riverton.
On Saturday, two weeks later, a man died when a boat overturned at the Catlins River bar near New Haven.
Water Safety New Zealand chief executive Daniel Gerrard said crossing a bar was among the most hazardous manoeuvres a skipper could undertake.
"The recent tragedies in the Catlins and Riverton highlight the deadly potential of these natural barriers, even for experienced boaties."
Since 1980, 153 people have drowned in bar-crossing incidents across New Zealand, Mr Gerrard said.
While the North Island had more bar crossings than the South, the frigid conditions and rough waters meant when things went wrong, they could go very wrong.
"Anywhere exposed to that strong southern swell means water incidents are much more impactful, such as what you see in the Catlins and other places along the southern coasts", Mr Gerrard said.
"There’s two types of bars — there’s dangerous bars, and really dangerous bars. Never take it for granted, there is no such thing as an expert on the bar.
He said before setting out, boaties should check the conditions, seek local knowledge, bring communication tools and tell people where they were going.
Boaties should not cross bars at low tide.
"It’s down to knowing your own limits and your boat’s limits. A good rule of thumb is if you’re standing there thinking ‘can I or can’t I?’, you should go home and come back another day."
Mr Dryden said when crossing a bar, only do so at high tide.
"A bar is a buildup of sand near the entrance to a river or an estuary where water [is] pushing out and the swell is pushing in, creating a sand hill of sorts under the water.
"The bar is always moving, always changing.
"When you’re on the water look for the safe zone, which will be a spot where the water is deep and the waves aren’t forming.
"Stop and assess, and take your time."
He said people should take two forms of communication, such as a personal locator beacon, or a mobile phone in a waterproof pouch.
People should always wear lifejackets and turn back if the weather took a turn, even if when you set out everything was fine.
"When something goes wrong, it’s catastrophic."
The annual bar-crossing seminar hosted by Coastguard, ORC, Surf Lifesaving, Maritime NZ and others will be held in October.
The exact date and location will be announced at a later date.
