Water quality at 11 beaches has been rated 'good' for this weekend, 19 'fair' and one 'poor', while Ma Wan Tung Wan and St Stephen's Beach have been downgraded to 'very poor', according to the Environmental Protection Department's latest grading.

Compared to last week, Clear Water Bay Second has been upgraded from fair to good, Middle Bay and Silverstrand from poor to fair, while Cheung Chau Tung Wan, Discovery Bay, Kwun Yam and Turtle Cove have changed from good to fair, Big Wave Bay from fair to poor, with Ma Wan Tung Wan and St Stephen's Beach dropping from fair to very poor.

The department said the very poor water quality of Ma Wan Tung Wan and St Stephen's Beach is due to heavy rain which flushed pollutants from their nearby areas into the water, while changes in other beaches are generally within the normal range of fluctuation of the bacteriological water quality.

Anglers', Approach, Ting Kau, Casam, Gemini, Hoi Mei Wan and Lido beaches are closed to swimmers year round because of poor water quality.

As many beaches are likely to be more polluted than their grades suggest during and after periods of heavy rain, bathers should avoid beach swimming for up to three days after a storm or heavy rain.