Hunter Swim Club competitors Lexi Sutherland, Lara Morgan and Alice Spadari qualify for Australian open water swimming championships

But taking on an open water five-kilometre race was new to each.

Sutherland, 14, said it was "harder mentally" than the 200-metre, 400m and 800m distances she was more accustomed to in competition.

Morgan, 13, was keen to test herself over a longer distance.

Spadari, also 13, described it as "painful".

The trio were part of a strong Hunter Swim Club contingent who competed at the Penrith Marine & Mercury Marathon and Open Water Series event held at the Sydney International Regatta Centre (SIRC) on October 22.

Competing in the 12/13-years girls' 5km event, Sutherland finished second, Morgan third and Sparadi seventh.

All three qualified for their first Australian Open Water Championships in the process.

"My older sister did it last year and she really liked it so I tried it this year," Sutherland said.

"It was pretty good. You kind of just had to stick with other people and work with them. It was harder moreso mentally, just being able to get through the race.

"I didn't really know how I was going to go because it was my first race at that distance, but I was aiming for the national time."

In all, 320 swimmers took part in the Penrith event, which included a 1km, 2.5km or 5km open water option.

"Last year I swam the 2.5 kilometre at NSW titles," Morgan said.

"I liked it more than the shorter stuff so I did it again. I'm really excited about going to nationals.

"I'll see how state and nationals is and go from there. I'm aiming to try to get top 10."

Next up is the NSW open water championships, also at SIRC on December 18 and 19.

The Australian championships will be staged in Busselton, Western Australia from January 25 to 28.

Hunter Swim Club finished top of the pointscore at Penrith with a host of strong results.

Xander Murdoch won the 10-years girls 1km and Cassandra Fayers finished first in the 16-19 years girls 5km. Dolcie Blackwood was second in the 12-years girls 2.5km and Aaleyah Tolar in the 14-years girls 2.5km.

Top-10 results were also recorded by Eleanor Judd 7th (12-years girls 2.5km), Claudia Morgan (12 years girls 2.5km), Teo Bendonelli (11 years boys 2.5km), Hannah Morris (13 years girls 2.5km), Estella Bonsor (14 years girls 2.5km), Rose Donnelly (14 years girls 2.5km), Harvey Lusis (12 years boys 2.5km), Molly Breasley (16-19 years girls 5km), Lara Clack (14-15 years girls 5km) and Stella Sutherland 14-15 years girls 5km).

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