Water quality at 20 beaches will be 'good' this weekend, according to the Environmental Protection Department's latest gradings. Thirteen will be 'fair'.

Compared with last week, Middle Bay Beach has been changed from 'good' to 'fair'.

The changes are generally within the normal range of fluctuation of the bacteriological water quality of the beaches.

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.

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