Water quality at 16 beaches has been rated 'good' for this weekend, with 17 'fair'.

Compared with last week, Big Wave Bay, Chung Hom Kok, Clear Water Bay First and Second, Discovery Bay, Hap Mun Bay Middle Bay and Shek O Beaches have been downgraded from good to fair.

Seven gazetted beaches - Anglers', Approach, Ting Kau, Casam, Gemini, Hoi Mei Wan and Lido - are closed to swimmers year-round because of poor water quality. Swimmers are advised not to swim at these beaches.

Many beaches are likely to be more polluted than their grades suggest during and after heavy rain. Bathers should avoid swimming at beaches for up to three days after a storm or heavy rainfall.