Interim Report on River and Marine Water Quality in Hong Kong in 2000
(ACE Paper 28/2001)
For information
Introduction
The Environmental Protection Department publishes two water quality reports each year to inform the public about the health status of Hong Kong's river and marine environment. The river and marine reports for 2000 are scheduled to be published in November this year. For the advance information of ACE members, this paper provides a brief summary of the water quality data from representative monitoring stations, and a 'snapshot' of the general condition of rivers and marine waters in 2000.
River water quality
2. The rivers in Hong Kong have shown steady improvement since the late 1980s in terms of the Water Quality Index (WQI) (Figure 1) which reflects the river's organic pollution level and its ability to support aquatic life. This improvement continued in 2000 with an increase in the percentage of monitoring stations recording a WQI grading of 'fair', 'good' or 'excellent' (89.7% in 2000 vs 83.2% in 1999). For the first time since regular monitoring began, none of the monitoring stations was in the 'very bad' category.
3. Figure 2 shows the locations of 12 major rivers in the territory and their most downstream monitoring stations. In 2000, Mui Wo River continued to maintain an 'excellent' WQI grading; while Shing Mun Main Channel and Tuen Mun River both remained 'good'. Sam Dip Tam Stream, Lam Tsuen, Tai Po and Ho Chung Rivers were upgraded to either 'good' or 'excellent' (Figures 3 a-b). Although the overall water quality of Deep Bay rivers remained unsatisfactory, Yuen Long Creek, River Ganges, River Beas, River Indus and Kam Tin River have shown some improvement in 2000 (Figure 3c).
4. Improvement in bacteriological quality was observed in six rivers i.e. Lam Tsuen River, Tai Po River, Ho Chung River, River Beas, River Ganges and Yuen Long Creek. However, the overall E.coli levels in the major rivers in 2000 remained high, ranging from an annual geometric mean of 2,500 cfu/100 mL in Shing Mun River to 1,100,000 cfu/100 mL in Yuen Long Creek.
Marine water quality
5. A summary of the long-term water quality from representative marine monitoring stations located roughly in the middle of the 10 Water Control Zones (Figure 4) is plotted in Figures 5a. to 5j. The E.coli and total nitrogen levels in the marine waters in 2000 were similar to those in 1999. A slight increase in dissolved oxygen (DO) level was found. In addition the low DO situation frequently observed in Inner Deep Bay during summer months, continued to improve.
6. In general, the water quality of Port Shelter and Mirs Bay continued to be the best in the territory with very low levels of sewage bacteria and nutrients and high levels of DO. On the other hand, the water quality in Victoria Harbour remained poor with relatively low levels of DO and high levels of E.coli in 2000. The situation, however, is expected to improve upon full commissioning of the HATS towards the end of 2001.
7. Figure 6 shows the frequency of red tides in Hong Kong waters from 1980 to 2000. Most red tides occurred in the eastern and southern waters of Hong Kong. Red tide incidents increased significantly in the 1980s, reaching a peak in 1988, and remained relatively stable in the 1990s. In 2000, a total of 45 red tides was reported, there was no red tide-associated fish kill during the year.
Conclusions
8. In 2000, the river water quality has shown a general improvement in comparison with the previous years. None of the rivers was in the 'very bad' category. Although the bacterial contents of the major rivers remained very high, many of them showed a noticeable reduction in E.coli.
9. The overall marine water quality in 2000 was largely similar to that in 1999 with Port Shelter and Mirs Bay being the best and Deep Bay and Victoria Harbour the poorest. There was a general increase in dissolved oxygen in the marine water in 2000.
Water Policy and Planning Group
Environmental Protection Department
July 2001
