We present an independent assessment of the health and water sustainability of the East River (Dongjiang) in South China, which is the source of nearly 80% of Hong Kong's water supply. Field measurements show that the water quality in the upper and middle reaches is generally good and well exceeds the drinking quality standard, with high bio-diversity. The streamflow of the East River Basin is satisfactorily simulated using both the distributed MIKE-SHE model and the lumped HSPF model. With an average streamflow of 760 m3/s, the River is able to satisfy the current water demand. Using the HSPF model, the water quality is found to have deteriorated in recent years. In addition to water supply, the River also supports a variety of needs such as hydro-power generation, waste assimilation, navigation, habitat for aquatic life, and expulsion of sea water intrusion. Using the projected need of 150 m3/s for water supply, the instream flow requirement based on hydrological and water quality simulation is estimated to be 467 m3/s in 2010. This suggests that the water sustainability of the East River requires alternative strategies, which may include integrated water resources management, provision of better wastewater treatment, and water and soil conservation.

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