The kei wai (JfilS) is essentially a device for exploiting the nutrient-rich waters of an estuary. As they exist in the region of Mai Po (N.W. New Territories) kei wais consist of ponds about 1 metre deep and some 10 hectares in area. Each kei wai is separated from the adjacent Deep Bay (Hau Hoi Wan /uifiilf) by an embankment or bund, but communicates with it through a sluicegate. Seawater is allowed to enter on the high tide, carrying with it the fry and larvae of potential produce (fish, shrimps, crabs), and the gate is then closed to prevent outflow of water. Individual kei wais are also separated from one another by bunds.
There is an obvious similarity in managing the kei wais to that used to control the exchange of water in commercial shrimp ponds in Hong Kong, namely the opening and closing of the gates as the tidal level changes. However, an important characteristic of kei wais is that no artificial fertilizer or food is added to the water. This paper consists of two parts: I which describes the actual mode of operation of the kei wai and may be of interest to the general reader, and II which reports an investigation into factors affecting productivity of the kei wai.