Kayaking between Auckland and Waiheke Island allowed Rotorua's Henk Greupink time to reflect on events since last Friday's terror attack in Christchurch.
The swim coach was supporting friend and master's swimmer David Blackmore who, with two others, swam the distance to raise funds for Auckland's rescue helicopter.
"When you're out on the water for that long you start thinking," Greupink said.
"I was trying to come up with something personal to support the people of Christchurch but also something that would allow people taking part to grieve, or get rid of anger."
He came up with the 50x50 at 50. That's 50 lengths of 50 metres at 50 second intervals.
"It's not rocket science but it represents the 50 lives lost in Christchurch. After each swimmer completes the challenge, they will write a message on a whiteboard and I will post it to the United Aquatic Sports Facebook page."
Greupink said initially the idea was to get the groups he coaches to take on the challenge but it has taken on a life of its own.
"I approached the team at the Rotorua Aquatic Centre and they have agreed to have the centre open from 6 – 9pm on Thursday night so anyone can take on the 50x50 at 50."
Entry will be via a gold coin donation with all proceeds going to the victims of the Christchurch shootings.
"Then I challenged every coach, player or participant I know from around the country from swimming, water polo and surf lifesaving, to come on board."
He said the response had been swift and overwhelming.
"I've had about 40 messages from people saying they [as individuals] or their club was on board. If people want to donate then they can, if they don't they don't.
"As a person who spends a lot of time in the water, I know how therapeutic it can be. For some who take part, the swim may simply be a way of letting go of grief or of anger."
Greunpick encouraged everyone to get involved.