A new study has found that up to twenty-six billion microplastics are being discharged into the ocean by sewage treatment facilities every day, seriously damaging Hong Kong's marine ecosystem.

The City University said large amounts of microplastics - fragments of plastic shorter than 5 millimetres - are still being discharged into the ocean, even after the treatment process removes most of the pollutant from the water.

The study, conducted last year, found that storm drains are also discharging microplastics into the ocean.

The university's Kenneth Leung says while the government should create treatment facilities to filter drain water, the public also has a role to play in improving the situation.

Leung said the most common form of microplastic was microfibres associated with laundry discharge.

He said that if people simply put a filter on the washing machine discharge pipe, that would help filter out a lot of the microplastic before the water was discharged into the system.