YOU have been warned. With more than half Hong Kong's public beaches unfit for swimming, you brave the waters this long holiday weekend at your peril, if the rain lets up. But we are a brave and perhaps foolish lot. When the long spell of wet weather breaks, thousands of swimmers and sunbathers are expected to take their chances and make the most of what's left of the summer holiday. That's despite the fact that the Government has warned swimmers to stay away from 19 of the territory's 45 bathing beaches until the weather, which has lowered water quality by flushing pollution from the land to the sea, improves. But the health risks and problems that can spoil a day out aren't confined to the water. Sharp objects such as barbecue forks, even syringes, lurk in the sand, as do animal faeces. Shark nets in three beaches can't completely eliminate the risk of attack by a killer from the deep and although there are many patrolled areas, there are always those who insist on swimming alone, cutting their chances of being rescued if they're in trouble. The average beach attendance rates recorded by the two municipal councils last year, show Repulse Bay, Shek O, Butterfly, Stanley Main, Lido, Deep Water Bay and Clear Water Bay's second beach are swimmers' top choices. But the recent downpours have left only Repulse Bay and Deep Water Bay fit to pass the Government water quality test. Both are now graded fair in the fortnightly report issued on Thursday last week. All the other top beaches are also rated hazardous to swim at. Even Stanley Main, where water quality was usually good or fair, is now very poor, meaning more than 15 out of every 1,000 swimmers risk their health by swimming there, the Environment Protection Department (EPD) warns. But the potential health risks don't end there. One angry Shek O regular protested: ''People litter the beach with barbecue forks and broken glass bottles after the holiday. To make matters worse, we don't have enough people cleaning the mess up. It's so dangerous.'' Lisa Hopkinson of Friends of the Earth (FoE), said: ''I'm sure people who litter the beach are those who want to enjoy it, why pollute their own backyards?'' But they do. The territory also has a track record of shark attacks. Two swimmers were killed by sharks last year at Silverstrand Beach and neighbouring Sheung Sz Wan. Sharks had not been sighted this summer, until late this week when two possible sightings were reported at Silverstrand in Clear Water Bay and warnings were issued, although this later proved to be a false alarm. Then there are the beach thieves. The police say there is generally an upsurge of thefts on beaches during the swimming season and they warn the public not to leave their valuables unattended. But it is Hong Kong's poor water quality that is the prime area of concern - a problem that is not confined to the territory. A two-year survey conducted by the Tidy Britain Group revealed earlier this month that 31 beaches surveyed failed the quality test and that 19 were of particular concern. The beaches were not only badly managed and unsightly but had poor and potentially hazardous bathing waters. The survey showed beaches in some of Britain's most popular holiday resorts was contaminated by sewage. In Hong Kong, surveys conducted by the EPD last year show that our beach water quality has deteriorated in recent years. The number of beaches graded poor and very poor has increased gradually over the past four years from 10 in 1990 to 15 last year. BUT you don't really need official studies to realise what a sorry state our beaches are in. ''Anyone who goes down to the beaches notices the deterioration in recent years, especially Stanley Main where the smell of sewage is so strong,'' Ms Hopkinson said. ''Because of the high population density of Hong kong and because we have minimal sewerage infrastructure, the waters of many beaches are contaminated with sewage containing human and animal faecal waste. ''This waste contains large numbers of bacteria and viruses, many of which are disease-causing, for example, the bacterium vibrio cholere and the virus hepatitis A.'' A large-scale epidemiological study conducted by the EPD and Hong Kong University in 1987 found that the symptom rates for the swimmers were significantly higher than non-swimmers. They included gastrointestinal symptoms such as vomiting and diarrhoea, stomach ache, eye and ear complaints, skin complaints and respiratory symptoms such as sore throats. But the findings indicated that Hong Kong has a much lower symptom rate than the United States. ''This suggests that either Hong Kong people do not report themselves sick as readily as the Americans or that we may be more immune to bacteria through eating seafood,'' Ms Hopkinson said. ''So take comfort that while you may get sick eating the seafood, at least its developing your immunity for when you go swimming.'' The EPD's principal environmental protection officer (waste and water service group), Dr Malcolm Broom, agreed that Hong Kong beach water was becoming more polluted. ''Back in 1987, we all wondered whether, unless we had a continuing commitment like putting in comprehensive new sewers in all the areas around all the beaches, we would see a gradual decline [in the water quality],'' Dr Broom said. ''That doesn't mean the sewers are not being put in place, they are, but it's taking a long time. ''The first scheme of new sewerage that got underway was the Hong Kong Island South scheme. At the end of this year, there will be a new sewerage treatment works open in an underground cavern at Stanley. ''Once the new sewers are brought into operation, we'll then need to make sure that the various properties which at the moment rely on septic tanks are all connected up to a new sewer.'' When the project is finished Dr Broom believes the decline of beach water quality will come to a halt and the territory will start to see permanent improvement in the southern part of Hong Kong island. But the bad news is that the rest of the waters will have to wait for the larger, multi-billion sewage disposal project to be completed - and there is no guarantee on when that might be. A review is underway to determine the scheme's future. Dr Lee Cho-key, spokesman for the Hong Kong Association of Dermatology and Venereology, reassured the public, saying Hong Kong water did not normally carry any viruses which affect our skin. HE said his clinic generally had more out-patients visiting during summer but they were not sick because they swam in contaminated water. ''Their problems are not normally caused by polluted sea water,'' he said. ''Rather we get the odd patients coming in for jellyfish sting treatment. ''It is unfair to exaggerate the danger posed by beach water. Unless there is an epidemic like cholera going around, Hong Kong beach water is quite safe. Besides, it's more common that swimmers hurt themselves by walking on sharp objects like sea-urchins buried in the water and on the beach.'' Both Urban and Regional Councils say bathers getting injured by sharp objects is not a serious problem. Each beach has its own team of cleaners who clean up the beach before it opens at 8 am during the peak season. The Regional Council's chief amenities officer (operations), Shum Hing-hay, said so far this summer there had been only a few complaints about the cleanliness of its 27 beaches. The Urban Council boasts that just one complaint has been received regarding the discovery of sharp objects on its 12 beaches. ''Every UC gazetted beach is raked and litter-picked manually at least twice a day,'' said Olivia Chan, amenities manager, Hong Kong West. A first-aid room is standard at all council beaches and all lifeguards possess first-aid certificates. ''All our lifeguards are fully qualified,'' Mr Shum said. ''By that I mean they have to pass eye and physical tests. They have to be under the age of 35 and have a valid Bronze Medallion awarded by the Royal Life Saving Society.'' The same applies to lifeguards employed by the Urban Council. All council beaches also provide showers for bathers to wash away the sea water. And with the two possible shark sightings this week, the councils say they remain vigilant: the Regional Council has begun a two-year $8.9-million experiment with shark prevention nets at Clear Water Bay Beach, Silverstrand Beach and Kadoorie Beach. The Urban Council says its beach staff maintain close surveillance of the water beyond the boomlines. It is also in touch with the police and Regional Council on reports of shark sightings in other parts of Hong Kong. Jo Ruxton, senior conservation officer at the World Wide Fund for Nature (WWF) says August is not really the season for sharks, but no one can be 100 per cent sure that they are no longer a risk to swimmers. ''It will be a small risk,'' she said. ''If people are concerned, they should either go to a swimming pool or beaches with shark nets.''