The 12-year-old is quickly building the resume of a future one as well.

Oldershaw won 10 medals at last weekend's Canadian Age Group National Swimming Championships in Montreal, leading the Oakville Aquatic Club (OAK) to a second-place overall finish at the event.

The daughter of Dean Oldershaw, who competed in kayaking at the 1972 and 1976 Olympic Summer Games, and the granddaughter of three-time Olympian canoeist Bert Oldershaw, Marni collected five gold and three silver in individual competition. She also added a pair of relay golds, winning the 12-and-under girls' 4x50-metre medley and freestyle events with teammates Bridget Jordan, Emily Hunt and Mika Spencer.

Oldershaw sets the bar high for herself, according to OAK head coach Christy Yaremczuk.

"This season, her goal was to achieve some top-10 all-time Canadian times for 12-year-old girls, in a range of events," Yaremczuk said. "She was just off a top-10 time in the 400m individual medley, and in the 200m backstroke she did manage to accomplish that. You're talking about (being on a list with) swimmers like (former Olympian) Joanne Malar. She's always looking at what she needs to do next."

Yaremczuk said Oldershaw has "all the tools" needed to continue to develop as an elite swimmer, including a strong support system from her family as well as the club.

"She doesn't take anything for granted. When she's training, she's always trying to improve technically," said Yaremczuk, noting that Oldershaw has greatly improved her breaststroke this season with the help of coach Alex Wallingford. "She has that high-performance mindset that you need to have."

While Oldershaw was OAK's leading medal-winner at the age group nationals, she was not the only one to make a major medal haul.

Mack Darragh (three gold, four silver) and Spencer (three silver, two bronze and two relay gold) reached the podium in seven events each, while Cam Cummings -- a gold medalist in the 200m backstroke at last year's nationals -- earned another gold, a silver and two bronze.

Yaremczuk was impressed with the way OAK swimmers responded to swimming at the Parc Jean Drapeau outdoor facility, which hosted the World Championships in 2005. She was also pleased with how the young competitors, particularly Darragh and Spencer, were able to perform well in the national championship environment.

"When you race in Ontario and you're one of the best kids in Ontario, you're racing against the same people on a regular basis and you get almost comfortable in that racing environment," she said. "It's quite different from racing people from across the country. It was great how (Mack and Mika) were able to stay focused on what their racing goals were."

Other OAK swimmers contributing to the club's 30-medal total included Curtis Samuel (silver), Clara Armstrong (silver) and Zack Chetrat (two bronze). OAK finished the four-day meet with 1,486.5 points, behind only the Etobicoke Swim Club (2,410).

The second-place showing was OAK's best-ever, following an 11th-place effort last year. The club finished 60th in 2005.

"Swimmers from all the different age groups contributed to the point scores, from relays to individual in every age group in male and female. That shows the depth, but also that, in all coaching levels and all age groups, everyone's doing a great job," said Yaremczuk, crediting the club's other coaches -- Laura Nichols, Kathy Pardy, Dave Judd, Melanie MacKay and Wallingford.