Marine waters have experienced heavy pollution since the late 1960s, having been used as a receiving medium for a range of wastes, although measures to treat sewage and other effluents have been progressively introduced to offset an otherwise widening gap between pollutant inputs and the marine environment's ability to assimilate these inputs. Nevertheless, infrastructure to enhance the assimilative capacity may not be sufficient to maintain the capital stock without supporting measures to address the fundamental causes of pollution. A sustainability driven approach to improving the assimilative capacity of marine waters will need to involve a series of responses to deal with the "outputs" of the problem (eg improving wastewater treatment standards and capacities, maintaining flushing capacities of waterbodies and maintaining discharge standards) as well as "input" responses to reduce flows and loads entering the waste stream destined for marine waters. These measures need to include charging schemes (polluter pays), water pricing, extension of sewerage networks to reduce direct discharges to marine waters, better education and strict enforcement of discharge consents and promoting cleaner/eco-efficient technologies.

Assimilative Capacity of Freshwaters - Issues and Trends

• 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 Index (WQI) data for the last 10 years show that river water quality has sustained a territory-wide improvement (in terms of the ranking of water quality at each of the 82 monitoring stations), with fewer than 20% of stations recording 'Bad' or 'Very Bad' water quality in 1998.
• Assimilative capacity of rivers may be ascertained by examining compliance with WQOs. The least compliant rivers overall 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 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.