The Boatettes swept aside Avalon Beach Chanels, Mona Vale Beast Mode, Maroubra Sealettes, Mollymook Mookie Rookies and Collaroy on Sunday at Collaroy's north Sydney beaches.

Under-19 girls sweep Steve Monaghan said the win was momentous and well earned by members Lucy and Grace Monaghan, Emma Eggins and Jess Willis.

"The girls rowed particularly well that day, against some pretty stiff competition," he said.

"They made the finals, won the semi and won the final.

"It was challenging, wasn't that big (surf) but there was a southerly breeze and a big gutter, a lot of water moving around to negotiate."

Mr Monaghan said most of the crew had been together for two seasons, with a new crew member joining this year.

"Everything went our way on the day, the girls had trained well and fitness levels were good - (they've) been doing extra crossfit training which definitely paid off, they felt stronger in the boat," he said.

"(In) the final we were coming second or third behind Avalon, the Australian champs, about the last 100m of the beach we said 'its up to us to win this, let’s have a go'

"They put the hammer down, won the day".