A healthy ecosystem is important to the water quality of a natural river. Therefore, creating a healthy reservoir ecosystem can help improve the water quality, and further safeguard our drinking water. The ecological function is complementary to the reservoir's water supply function. The number and health of aquatic organisms can also act as biological indicators in monitoring water quality.
Although a reservoir is built in a natural valley and is surrounded by woodland and natural streams, its ecological value is not high, because we lack the pioneer species that can adapt to deep freshwater habitat for succession in Hong Kong. Officials can investigate ways to improve hydrological conditions at specific locations, and introduce suitable aquatic plant species to enrich a reservoir's overall aquatic plant community.
Currently, the reservoir banks are mostly steep and smooth mud surfaces, without complicated micro-habitats for different species. If some locations, such as where streams enter the reservoir, can be modified into gentler banks and natural rocks of various sizes introduced, more complex micro-habitats are created. In addition, terrace-stepped banks can also be created, to provide micro-habitats of another type to attract more species (for example, frogs).
Catchwaters fragment the natural river habitats and disconnect the upper and lower courses. Catchwaters have gentle gradients, slow flows, and simpler structures than natural streams, making them unsuitable for survival of stream creatures. In fact, slight modification to a catchwater can make it closer to the structure of a natural stream. Allowing part of the stream to follow its natural path and maintain a base flow, while diverting the remaining flow and extra flow during rainstorms to the catchwater, can minimise damage to the river ecology.