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The natural assimilative capacity of Hong Kong's rivers and streams is influenced by their physical, chemical and biological characteristics, as well as by the level of polluting inputs received by the waterbody and physical impacts such as river course modifications and abstraction of water for irrigation. River water quality is monitored by EPD and rivers are graded using the Water Quality Index (WQI). Index data for the last 10 years show that river water quality has sustained a territory-wide improvement, with fewer than 20% of stations recording 'Bad' or 'Very Bad' water quality in 1998 (Figure 5.2a).
Figure 5.2a: River Water Quality Trends in Hong Kong, 1988 - 1998
Assimilative capacity of rivers may be ascertained by examining compliance with W1ater Quality Objectives (WQOs). The least compliant rivers in Hong Kong occur within the Deep Bay WCZ where many watercourses continue to receive high organic pollutant inputs from sewage, livestock waste and industrial effluents, despite recent initiatives such as the Livestock Waste Control Scheme which have significantly reduced organic loadings.
Phased implementation of the Sewerage Master Plans will help to reduce sewage discharges to rivers, particularly in rural areas, by connecting formerly unsewered premises to sewers and by increasing the level and coverage of sewage treatment. Nevertheless, organic and faecal pollution of several watercourses remains of concern not only for the amenity and ecology of the river but also for its downstream effects such as pollution of coastal waters and beaches.
Continued physical and infrastructural development which affects catchment regimes (such as channelisation and new drainage) also exerts impacts on the ecology of the catchment for example through changes to the hydrological regime of sensitive wetland areas.
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