AN impressive field, including former Olympian Daniel Kowalski, took to the water on Sunday to compete in the Big Bay Swim.

All eyes were on Kowalski as he set the pace early and looked set to win the gruelling 3.2-kilometre race.

But Olympic hopeful Andrew Roberts, 18, from Avondale Heights, swam a brilliant tactical race to overtake Kowalski 400 metres from the finish line to power home in 35 minutes, 21.2 seconds.

His mother Leanne said her son had planned the race to perfection.

"Andrew knew Daniel was his toughest competition and his plan was to sit off the leaders and conserve energy for the end.

"He sat back and about 400 metres out he started to accelerate and powered through the final stage."

Roberts has been swimming since he was seven.

"He trains at the Maribyrnong Aquatic Centre and has his eyes firmly set on representing Australia at the 2012 Olympics," Ms Roberts said. "Andrew just missed out on qualifying for the Australian championships. He finished seventh in the 10km swim but is determined and gained a lot of experience."

About 140 swimmers competed in the Big Bay Swim, which started in Port Melbourne and finished at Williamstown.

The event raised more than $10,000.

■ Placegetters: Second: Daniel Kowalksi, 35 min 38.86 sec. Third: Max Thorn, 35 min 56.27 sec. First female was Hannah Tuohey (37 min27.57sec).