She told her brother's story at school assemblies to help raise support and awareness for the event and said Jed would have been right behind the idea.
"I reckon I could have weaseled him into it. He did that kind of weird stuff."
Year 13 student Juanita-Louisa Karora said the water was freezing but the cause made it worthwhile.
"You couldn't feel your feet. It's so cold," she said. "It's support for our friend and her family and support for the leukaemia foundation."
Prize for the best dressed went to Laura Rowland, also Year 13, who was dressed in a bright orange one-piece outfit with a matching fedora.
"You stay in there quite a while and you start to get warm so it's not so bad. I thought it was going to be much colder."
The bravest, or craziest , few students were eventually asked by lifeguards to get out to avoid the risk of hypothermia. Despite not being as cold as expected, the hot sausages and Milo handed out afterwards were snapped up by shivering students.
Claudia Colenso, one of the sports leaders who organised the dip, said she was pleased with the turnout.
"It was amazing. It was really good.
"The water wasn't as bad as we thought it would be."