While many of us were enjoying the warm weekend weather supping on a cool beverage, young Auckland-based marathon swimmer Caitlin O'Reilly was doing what she does best, swimming - to one end of Lake Taupō and back again.

Starting from the Lake Taupō Yacht Club at 1.03pm on Saturday, O'Reilly arrived at the opposite end of the lake around 3am, she then turned around and swam back to where she started, finishing her epic swim at 5.05pm on Sunday evening.

She completed the 82km round trip in 28 hours and 2 minutes and did it not only for herself, but as part of a fundraising effort for the Westpac Rescue Helicopter's Chopper Challenge.

The 17-year-old is only the third person to have made a double-crossing of Lake Taupō. The previous two swims were completed by legendary marathon swimmers Philip Rush in 1985 and Sandra Blewett in 1986.

Last year she completed the New Zealand Triple Crown for marathon swimmers by swimming across Cook Strait, Lake Taupō and Foveaux Strait.

She said her accomplishment was yet to sink in, and she was still “totally knackered”.

"At the end I was just exhausted, but I felt really good as I was still running on adrenalin and caffeine, and it was great having so much support there when I got out of the water."

O'Reilly said she knew she had it in her physically but the hardest part was the mental side of the challenge.

"You think about a lot of different things and staying focussed is hard.

"I was laughing at my coach sitting in the IRB with all of his warm clothes on, things like the war in Ukraine, all sorts of stuff.

"It hasn't quite sunk in yet but I'm really stoked with how it went, parts of it were really enjoyable.

"During the night was rough because I knew I had to turn round and do it all again and mum had a motel booked so I knew there was a nice warm bed waiting for me.

"I had to get out and clear the water. I sat on the jetty and ate some lasagne and rested for about five minutes and got back into it, that was hard."

She knew she couldn't let her supporters down and that all of them would be waiting for her to finish.

She said every half hour her support crew would prepare snacks such as endurance gels and watching them being readied helped her concentration.

Most weekdays she's up at 4.30am and heading to the pool to train with her friends at the North Shore Swim Club and the weekends usually see her competing in a long distance swim or sprint race.

"I guess I just like pushing myself, and I really enjoy it and want to do it. I also like to set goals, and the sport teaches you how to set goals."

Philip Rush is O'Reilly's open water swimming programme manager and said it was a special effort, especially for someone so young.

"The mental ability she has to do that is just phenomenal.

"She's a solid swimmer and a very determined young lady. She swims very well and is really consistent, she sat on 3kmh for almost the whole 28 hours."

Rush said the hardest part of the swim was at night as there was no moon and the water was pitch black.

"She just kept working hard and I couldn't be happier with her performance.

"It was fantastic to watch when we got back, all her swimming friends were on the beach waiting for her.

"To see someone so young be able to conquer her mind and that piece of water was just awesome."

O'Reilly and her team are now planning to complete the Oceans Seven - the seven greatest ocean swims in the world - and are hoping to get to Japan in July to conquer the Tsugaru Strait, a 20km swim between the Japanese islands of Honshu and Hokkaido.

"Cook Strait is one of the hardest of those swims and she's already ticked that one off," Rush said.

"The sea has difference challenges, such as the sea life and tides, but in a lake you are sitting lower in the water, so it has its own challenges."

Only 21 people have completed the Oceans Seven and if O'Reilly finishes them in the next few years she would be by far the youngest person to complete the feat after 29-year-old Thomas Pembroke from Australia finished them in 2018.

"Hopefully we can get it done in the next couple of years, if we can travel again,” she said.

"This year we want to get to Japan and Los Angeles and then the rest before 2024."

The Oceans Seven:

The North Channel: between Ireland and Scotland, 34 km

The Cook Strait: between New Zealand’s North and South islands, 26 km

The Moloka’i Channel: between Moloka’i and O’ahu in Hawaii, 44 km

The English Channel: between England and France, 34 km

The Catalina Channel: between Santa Catalina Island and Los Angeles, 32 km

The Tsugaru Strait: between the Japanese islands of Honshu and Hokkaido, 20 km

The Strait of Gibraltar: between Spain and Morocco, 16 km

Credit: Stuff.co.nz