Water quality at Deep Water Bay, Clear Water Bay Second, Golden and Silverstrand beaches has been rated 'good' by the Environmental Protection Department for this weekend.

Silverstrand improved in quality, registering only a 'fair' rating last week. There was no change in grading for the three other beaches.

The four beaches are open year-round, and all are equipped with shark nets. Other beaches are closed for the winter.

Beach grades can also be obtained from the department's homepage or the beach hotline, 2511 6666.

The department warns that many 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.

Two red tides have been sighted in Hong Kong waters over the past few days. Department officers found red tide in Shing Mun River on January 13, which dissipated the following day.

Meanwhile, Agriculture, Fisheries & Conservation officers found another case in the river on January 15, which persists.

The first red tide was formed by Chlamydomonas uva-maris, the other by Teleaulax acuta. Both species are common in Hong Kong waters but seldom cause red tide. Both are non-toxic.