Hong Kong has a unique wetland habitat, the gei wai, in which delicious gei wai ha are cultivated. Gei wais are shallow ponds found in mangrove areas. These are used for shrimp and fish culture. Gei wais are constructed by excavating along the boundary of the mangrove areas. The mud is heaped up on the boundary to form bunds which impound a shallow pond. A gate is then built in the coastal bund, connecting with a channel that leads to the sea. During the high tide, the gate is opened and the sea water rushes into the gei wai, bringing in masses of shrimp and fish. These creatures then feed on the plankton already present in the water and on litter from the mangroves. This 'natural' process makes it cheaper to run a gei wai than fish and shrimp cultivation methods which require artificial feeding. During harvest periods - between April and October every year - the gei wais are drained and reflooded daily, synchronising with the tides. At each draining and reflooding, shrimps and fish are caught in a net placed across the sluice gate. They are then transported to the market to be sold. However, there has been a decrease in commercial productivity because the sea is becoming more polluted and the mangrove habitat is being destroyed. The only gei wais still in operation are found in Mai Po Nature Reserve. WWF HK is a local charity environmental organisation established in 1981. It aims to build a future in which people can live in harmony with nature. For further information, please call 2526-1011 or e-mail to http://www.wwf.org.hk .