Every year in New Zealand there are about 700 rescues related to rip currents and about five people die in these incidents every year.
So what is a rip and how do you identify one?
We ask the University of Canterbury's Dr Seb Pitman who recently published new research on water-safety education.
Photo: Keepa Digital
We can think of a rip as a narrow river of water that starts at the beach and heads offshore - taking with it whatever is in the water, Pitman tells Kathryn Ryan.
"[Rips are] just driven by waves coming into the beach. If you think of all that water rolling into the beach it has to go somewhere, and the way it can move offshore is through these narrow channels. We're talking a water flow that can be up to 2 metres a second sometimes."
The most common kind are channel rips which flow out to sea through deep channels carved out by sand bars. Most sandy beaches have these every couple of hundred metres.
Less common - and perhaps most dangerous - are flash rips which are driven by a certain set of waves. These are very unpredictable and come and go in ten minutes.
Most rescues from rips occur because a person has expended their energy panicking, Dr Pitman says.
If you're alone and caught in a rip, follow the Three Rs:
Relax (and float)
"This is really getting at controlling that panic response, understanding that you're not being pulled under. Yes, you might be being moved but as long as you're happy to tread water or lay on your back you're going to be fine."
Raise (your hand)
This is a universal signal to other people on the beach and in the water that you need help.
Ride (don't fight) the current
Then either wait to be rescued or wait till the current stops and dissipates, Dr Pitman.
"If you've conserved your energy you can then use that to swim across the breaking waves towards the shore."
Any bystander attempting a water rescue should have some experience, he says.
"If you're confident and competent of your ability in the water, you're looking to approach somebody from behind and drag them on their back away from the current. But you just have to be so mindful that the panic respo9nse will be for them to plunge you underwater to help get their breath."
A survey of beachgoers at Muriwai confirmed most people don't know how to identify a rip - either in person or in a photograph.
Rips generally can be seen as calmer patches of water or gaps between breaking waves. You might also see plumes of sediment being carried offshore.
Education about how to stay safe in a rip is quite ad hoc, Dr Pitman says, and video is the best way, Dr Pitman says.
He hopes VR headsets with 360-degree footage of a rolling surf taken from water level.
