SWIMMERS have been advised to stay away from 19 beaches until the weather improves because the heavy rains have raised pollution levels so high bathers could get sick. The warning came from the Environmental Protection Department, which said yesterday that weeks of rainy weather had washed pollution from the land and was also causing some septic tanks to overflow into the sea. People should wait until several days after the rain has stopped before returning to the affected beaches because it took time for the pollution bugs to die off, the department said. Special attention was called to Stanley Main Beach, Turtle Cove and Hairpin beaches on Hong Kong Island, Clearwater Bay 2nd Beach in Sai Kung and Tung Wan on Cheung Chau, where water quality was usually good or fair, but has deteriorated in recent weeks. Principal environmental protection officer Dr Malcolm Broom said people generally were advised not to swim at beaches with poor water quality, but a special warning was required because of the impact of the rainy weather. ''We're trying to draw people's attention to the fact that beaches which have always been good bets may not be such good bets [at the moment],'' he said. This time last year only 11 beaches had poor water quality, most of them in the Tuen Mun and Tsuen Wan districts. Sixteen beaches had good water, compared with seven now. The department grades 45 beaches on a four-grade system: good meaning there is no detectable health risk; fair meaning the health risk is to 10 or fewer swimmers per 1,000; poor meaning a risk to 15 or fewer swimmers; and very poor meaning a risk to more than 15 swimmers per 1,000. The health problems that could be encountered include minor skin or gastro-intestinal problems and eye problems. Dr Broom said they were investigating the causes of the water quality decline but it was usually related to how much development there was behind the beach. Sewage from homes, offices, farms and industries pollute the water. Hong Kong Island has been hit particularly hard by the water quality decline and has intensive development around many of its beaches. Another pollution source is septic tanks which might overflow if the rain water entered them, as happened at Ma Hang Prison and is contributing to the pollution problem at Stanley Main Beach. Dr Broom said the Correctional Services Department was looking at the problem. Four beaches are closed permanently to swimmers because their pollution levels are so high, Rocky Bay on Hong Kong Island, Old Cafeteria and Castle Peak in Tuen Mun, and Anglers' in Tsuen Wan. Hong Kong South: Big Wave Bay - poor, Chung Hom Kok - fair, Deep Water Bay - fair, Hairpin - poor, Middle Bay - fair, Repulse Bay - fair, Shek O - poor, South Bay - good, St Stephen's - fair, Turtle Cove - poor, Stanley Main - very poor, Rocky Bay - closed, To Tei Wan (non-gazetted) - fair. Tuen Mun District: Old Cafeteria - closed, New Cafeteria - poor, Castle Peak closed, Kadoorie - poor, Butterfly - poor. Sai Kung District: Campers - good, Clear Water Bay 1st Beach - poor, Clear Water Bay 2nd Beach - poor, Hap Mun Bay - good, Kiu Tsui - good, Pak Sha Chau - good, Silverstrand - poor, Trio (Hebe Haven) - fair. Islands District: Cheung Sha Upper - good, Cheung Sha Lower - fair, Discovery Bay (non-gazetted) - fair, Hung Shing Yeh - fair, Kwun Yam Wan - fair, Tong Fuk - fair, Lo So Shing - good, Pui O - fair, Silvermine Bay - poor, Tung Wan, Cheung Chau - poor, Tung O (non-gazetted) - fair. Tsuen Wan District: Anglers - closed, Approach - very poor, Casam - poor, Gemini - poor, Hoi Mei Wan - very poor, Lido - poor, Ting Kau - very poor, Tung Wan, Ma Wan - fair.