Fatigue and drifting into shipping lanes were the main concerns facing 100 brave people who swam from Waiheke to Auckland in aid of charity.
The gruelling 20km Westpac Chopper swim kicked off from the island's Matiatia Bay ferry terminal at 10am on Monday.
The fastest swimmer made it to the finish line at Mechanic's Bay in just over four hours.
Swimmers were told to simply "aim for the Sky Tower" in the distance.
Before the swim started, organisers held a moment of silence for those who lost their lives in the Christchurch mosque shootings.
"Today we come together to do good. We will swim to Auckland in support of an organisation that saves lives. In all the grief and confusion, this is pretty much the most constructive and positive thing that anyone can do right now."
Kirwan and Adam Clark raised upwards of $7,000 between them for the Westpac Rescue Helicopter.
The swim featured a range of swimmer abilities, from All Black legends Ian Jones and Sir John Kirwan to teenage swim star Caitlin O'Reilly, who recently swam 40kms across Lake Taupo.
The were up against seasoned endurance swimmers Roger Soulsby, who swam 1000kms in a year, and Kathy Snowden who swam 100kms in 10 days.
Sir John said he swam like a "plodder".
Most swam the distance wearing a wetsuit.
"When some people see me swim against other people, they say it's like seeing a Ferrari and a Lamborghini, then a diesel tractor out the back".
He and his buddy Adam Clark were planning on doing 10kms each in a relay and had raised about $7,500 between them.
"You just want to get into a rhythm and enjoy the moment - we live in a beautiful country."
Roger Soulsby and his FurSeals team hoped to cross the finish line together.
Soulsby was swimming with a group of four called the FurSeal Flyers, but was aiming to do the whole distance by himself.
"For me it's about making sure the arms keep turning over and I'm feeling relaxed."
Instead of an entry fee, swimmers were asked to raise money for the Auckland Rescue Helicopter Trust.
The swimmers were supported by people in kayaks.
By midday, more than $142,000 had been raised for the life-saving service, which costs around $5000 per rescue.
The fundraising had already smashed 2018's results, where 75 swimmers raised $115,000 for the trust.
Swimmers had the choice of tackling it solo or in teams, and all were required to have their own dedicated kayaker and support crew in a nearby boat.
Ian Jones said the race was raising money for a great cause.
The event organiser taking the briefing told swimmers they should simply aim for the Sky Tower in the distance.
"If you ever cross a yellow marker to the right, you are in a shipping lane."
He encouraged swimmers to help out their fellow competitors if they got into trouble: "This is not a race - we are not competing."
"Know your limits and be sensible - we are swimming for the chopper, we don't want to call them."