XN000022-1995-08-03 — Page 11

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It gives an estimate on the risk of contracting some minor skin or gastrointestinal illnesses resulted from swimming at a beach with some degree of pollution. The estimate is based on a large scale epidemiological study carried out in Hong Kong in the past bathing seasons.

The grading of some beaches fluctuates during the summer. In most cases, this represents a natural fluctuation in the bacteriological quality of bathing waters as rain and tides bring more or less pollution to the beaches.

Beaches with highly developed hinterlands are likely to be more polluted than the grades suggested during and after heavy rain.

Principal Environmental Protection Officer, Dr Daniel Lau said: "Bathers should avoid swimming at such beaches for two to three days after a storm, or even longer if the weather remains overcast, shorter if there is strong sunshine". However, the biweekly grades give a general picture of the most recent water quality at bathing beaches at the time of reporting and form the best available forecast for the immediate future.

The system for grading beach water quality is as follows:

Grade "1" indicates that the water quality is good. The E coli count is no more than 24 per 100 millilitres at each beach so graded, and the expected risk of minor illness to swimmers is undetectable.

Grade "2" indicates that the water quality is fair. The E coli count is no more than 180 per 100 millilitres at each beach so graded, and the expected health risk is no more than 10 cases of minor illness per 1,000 swimmers.

Grade "3" indicates that the water quality is poor. The E coli count is no more than 610 per 100 millilitres at each beach so graded, and the expected health risk is no more than 15 cases of minor illness per 1,000 swimmers.

Grade "4" indicates that the water quality is very poor. The E coli count is more than 610 per 100 millilitres at each beach so graded, and the expected health risk is more than 15 cases of minor illness per 1,000 swimmers.

The decision whether or not to close a beach to swimmers is based on a judgement of what degree of pollution is acceptable.