Mulcahy began his career at Wellington's Lyall Bay Surf Lifesaving Club and spent time as a volunteer and professional lifeguard on the Gold Coast in Australia before moving to Titahi Bay.
He says each club tries to manage the pressure by having senior lifeguards responding to the more critical incidents but there is a lasting impact for everyone involved.
Each year, hundreds of new volunteers join Surf Life Saving New Zealand (SLSNZ) to help patrol the 80 locations around the country. Right now 4000 active lifeguards are on duty, including 567 new recruits.
Last Sunday, a group of off-duty junior lifeguards - some as young as 14 - were waiting to be collected by their parents at the end of the day at Hot Water Beach in the Coromandel when they went to the rescue of a group who had gone into the water and were caught in a rip.
With help from bystanders on the beach, the young lifeguards managed to save three of the adults. But 24-year-old Aucklander Hiva Peaulu Lavaka died, despite the teens performing CPR to try to save him.
Mulcahy, who was named ¬Instructor of the Year for 2015, says those situations are always difficult for all involved. "You see it pop up around New Zealand regularly.
Lifeguards going above and beyond to do what they can to assist people. Obviously that has a considerable impact."
He says it clearly influences, first and foremost, the family and friends of the deceased - "and obviously our condolences always go out to those people" - but he says it also has an impact on the lifeguards.
The guards make life-changing decisions in an instant. The decisions can haunt them and everyone reacts differently. A counselling service is available to everyone.
"The last thing we want to have is people keeping these things inside and it chewing them up inside."
He says the first decision - whether¬ to respond or not - is always difficult. "It is definitely a hard decision to make and you have to weigh that up at the time - your ability and your physical fitness and skills against the conditions, because the surf is very unforgiving."
He says people might be aware of the hazards but in the sea things can happen quickly.
"You could be standing at a beach in knee-deep water and if a large wave or set of waves come in, that knee-deep water could change to chest-deep and you could be swept off your feet and pulled out beyond your depth.
"If you don't have the ability in the water, or ability to float or make it back to shore, obviously things can go wrong quickly."
There were 113 drowning deaths last year compared to 90 in 2014. Surf Life Saving New Zealand rescue data gives an indication of the hotspots. Between July 2014 and June last year the most rescues were at Mt Maunganui in the Bay of Plenty, Muriwai on the west coast of Auckland, Omanu Beach near Mt Maunganui, Whangamata in the Coromandel, and Raglan.
Others with a high number of rescues were Mangawhai Heads in Northland and Piha on Auckland's west coast .
In all, there were 1328 rescues across the country.
Reliable data is not yet available for this summer. There have been at least 200 rescues since July last year, but SLSNZ says that figure will be far higher.
Last week, the close-knit community of lifesavers lost one of their own. Mt Maunganui club member Hamish Rieger was with friends after a day on patrol when he was swept out to sea. SLSNZ manager Allan Mundy said the entire organisation was mourning the loss. "Losing a life is always a tough part of life-saving and when it involves one of your own, the tragedy is that much closer to home."
Mulcahy says surf lifesaving is a close-knit organisation and everyone felt the loss.
"We wear the same thing - the red and yellows - and it's really one big family."
This week, surf lifesavers called for more resources and funding to keep swimmers safe.
Chairman of Hot Water Beach Surf Life Saving, Gary Hinds, told One News more resources were needed to keep swimmers and tourists, in particular, safe.
"I don't see the beaches being a problem or danger. I see the people we attract being the problem -because they have no understanding," he said.
Hinds said it was about getting more funding to put more lifeguards on the beaches for longer.
"And having paid guards on beaches, especially on beaches that are big tourist destinations for New Zealand."
This season at Titahi Bay there were 14 new recruits, including SLSNZ chief executive Paul Dalton.
Dalton - who was commercial manager for the New Zealand Rugby Union before moving to SLSNZ - says going through the qualifying process, and now spending time patrolling the beach at Titahi Bay, gave him a special insight into the service he is running.
"You get a first-hand appreciation of the decisions you make, that's for sure.
"It has been interesting because you're sitting there in a tower and you feel that responsibility.
"People are 100m either side of where you're sitting and you're trying to keep an eye on them and think, 'well, if I miss somebody in trouble, they could die'. That suddenly sinks home - how important it is to be on your game."
Dalton says extra funding would have a big impact on surf lifesaving, especially as it would allow the paid mid-week lifeguards during the holiday period to increase their shifts.
Most of these mid-week paid ¬patrols started just before Christmas and finished on Friday - the end of school holidays.
"From the professional side, obviously the more funding we can get from councils to extend that period of mid-week coverage, then we know that we can do a better job for some of those beaches," he says.
"Some of it is to do with the number of days and also it's the hours. You tend to find, as we saw at Hot ¬ Water Beach last week, after 5pm people are still at the beach and things happen.
"So if we can extend the coverage longer during the day and for more weeks then we can definitely do a better job in the parts of the country where summer is longer than ¬others."
It also cost an average surf life-saving club about $100,000 to run a year, Dalton says.
At Titahi Bay, Mulcahy will be back on patrol today.
It has been a quiet season there so far - "but you never really know when things are going to happen," he says.
"We're still only half way through the season so I guess we're just hoping that people continue to swim within their limits, use the beach within their limits, make sure they swim between the flags and go out with a friend."
Funding might be the elephant in the room but for Mulcahy and thousands of others like him on the front line, it is about prevention.
"If we see people down the beach, going into rips, we go and talk to them and encourage them to move ¬between the flags because we have some strong rips at either end of the beach."
Mulcahy, who also runs a coastal science and risk management consultancy business, says people -become lifeguards because it is ¬exciting fun, and it means you are part of the community.
"And it's a great organisation to be involved with. You can give back to your community and enjoy the beach at the same time."
