While most teenagers spend their spare time checking their Facebook updates, Yasmine Dai has been more interested in staring into murky tanks of sea water.

Not so strange, as the 18-year-old hopes her investigation into the filtering power of the green-lipped mussel could aid ecologists as they look to the molluscs as tools to help clean up the Hauraki Gulf.

Her project, which beat more than 230 students to scoop the top prize at the Niwa Auckland Science and Technology Fair, involved hauling 200 litres of seawater up to her third-floor classroom at Diocesan School for Girls.

There, she spent hours adding silt to the water to see how the mussels' filtration systems responded, taking new samples every 45 minutes.

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Her interest in the cleaning power of mussels was piqued by the restoration project Revive Our Gulf, an ambitious project headed by The Mussel Reef Restoration Trust proposing the use of wild mussel beds to restore the polluted water of the gulf.

"I was interested to find out whether, if we did put a lot of mussels back in the gulf but it turned out the water was too polluted, would this affect the filtration rate of the mussels and would it have any adverse effect on the mussels themselves?

"I thought that mussels would filter slower as the silt increased - but actually they were more effective the murkier the water got - up to a point."

In awarding Yasmine the contest's top prize, the judges described her experiment as "innovative, purposeful and topical".

Her school's head of science, Sarah Boasman, was proud of the way Yasmine "took ownership" of the investigation and worked her way around obstacles. "Her win is a testament to the many, many hours she spent on this project."