Exposure to sewage can cause diseases such as gastroenteritis and diarrhoea, as well as enteric fever, hepatitis and kidney infection. Those with weaker immune systems, such as children and the elderly, may also be susceptible to viral respiratory infections. In some rare cases, exposure can be fatal.

But it's not all bad news. To keep Hong Kong's beaches as healthy and safe as possible, the Environmental Protection Department has a comprehensive monitoring programme in place. It grades beaches on a scale of one (good) to four (very poor), based on the bacterial (E coli) level in the water from the five most recent samples that have been taken.

This initiative, known as the Water Quality Objective, was implemented 25 years ago. Last year, the department monitored all 41 gazetted beaches and found that, for the first time, every one complied with the objective. It is a remarkable improvement from the 93 per cent recorded in 2009, and the 83 per cent recorded between 2003 and 2008.

These protocols for monitoring beach water quality are similar to those used overseas in coastal cities such as Miami, Los Angeles, Sydney and Melbourne. 'In terms of bacteriological water quality, [Hong Kong's] is comparable with those cities,' says an Environmental Protection Department spokesman.

'The government continually takes measures to improve the beach water quality by improving the sewerage infrastructure.'

This includes extending the network to cover villages without sewage systems, building new sewage treatment plants, and diverting polluted storm water discharge away from the catchment areas of the beaches.

Volunteer group International Coastal Cleanup says better co-ordination and an overall strategy between the different government departments in charge of cleaning up designated areas are needed to prevent rubbish from ending up in the sea.

Meanwhile, take the plunge at the city's top five cleanest beaches.

Hap Mun Bay

Sharp Island, Sai Kung, tel: 2796 6788

This idyllic piece of Hong Kong has consistently been ranked as one of the city's cleanest beaches - along with most of the beaches in Sai Kung district except for Silverstrand. The wild and island-studded east coast is not as densely populated as other parts of the territory, and pressure from human habitation has thus been lower. Weekdays are quiet but on weekends and public holidays attendance can hit the thousands. So if you want a good spot, make sure you go early. With plenty of lifeguards along the 99-metre-long beach and a shark net set up, you can soak up the sun in safety. Work up an appetite by renting a raft, then book a pit in the barbecue area and fire up a sunset feast. The rocky shores make this a popular fishing spot.

Getting there: take a kaido (a small ferry) to Kiu Tsui or Hap Mun Bay at the Sai Kung bus terminus.

Lo So Shing

Sok Kwu Wan, Lamma Island, tel: 2982 8252

Looking for a beach paradise? Crystal clear waters? This 214-metre-long beach is as close as it comes in Hong Kong. The tranquil spot sits between the villages of Sok Kwu Wan and Yung Shue Wan. It has showers and changing facilities, as well as a solar-powered floodlight on the edge of the bay. Because of its remote location and lack of public transport, there are rarely any crowds.

Getting there: take a ferry from either Central or Aberdeen to Sok Kwu Wan, then walk down the marked path for about 40 minutes.

Hung Shing Yeh

Yung Shue Wan, Lamma Island, tel: 2982 0352

This 55-metre-long beach is Lamma Island's most popular, attracting up to 600 people on weekends. As with most beaches in the Islands district (except Silvermine Bay), its distance from Hong Kong's main urban centres means it generally enjoys good clean water. Head there in the early morning if you want it to yourself. It is well known for its clear waters and smooth sand, and is complete with a barbecue area, showers, changing facilities and a shark net for protection. First-time visitors may find the huge power station nearby a bit daunting, but you will soon get used to the view.

Getting there: take the ferry to Yung Shue Wan from Central, then follow the signs from the village's main street for about 20 minutes.

South Bay Beach

South Bay Road, Repulse Bay, tel: 2812 2468

Just walking distance from Repulse Bay Beach, this 126-metre-long beach is a popular spot at weekends. It has a barbecue area and a fast food kiosk. It is fully equipped with changing rooms, shower facilities, a bathing shed and rafts for use. Chill out at the South Bay Beach Club with a drink in hand, listening to a DJ. Its fellow Southern district beaches are all in good shape, thanks to years of strict pollution control legislation and well-developed infrastructure that diverts storm water and treats sewage.

Getting there: take the No 6 bus from Exchange Square in Central to Repulse Bay Beach and follow the marked signs to South Bay. This should be a 10-minute walk.

St Stephen's Beach

Wong Ma Kok Path, Stanley, tel: 2813 1872

Located a stone's throw from Stanley's main beach, this 120-metre-long beach is a must-visit for water sports lovers. The summer season brings strong southwesterly winds, making it a popular spot for windsurfing and canoeing. The St Stephen's Beach Water Sports Centre (tel: 2813 5407) offers equipment and training courses to get you started. Despite the water sports attraction, the beach tends to remain quiet throughout the season.

Getting there: take the 6A bus from Central's Exchange Square to Stanley Market and walk for 15 minutes following the signs from the bus stop.