The Hong Kong countryside has experienced centuries of intense human impact, and none of the native climax forest remains. Anthropogenic influences upon Hong Kong freshwaters reflect, on the one hand, pollution and degradation of rivers and wetlands as a consequence of urbanization of rural lowlands. On the other hand, the need to preserve pristine catchments for the supply of water for human consumption has ensured the protection of upland streams which are typically unpolluted. Hong Kong has no natural lakes, limited ground-water reserves, and marked seasonal and inter-year rainfall variation. Most upland streams are impounded, and water is transferred from them into reservoirs by underground tunnels. Hong Kong's 17 reservoirs collect insufficient water from local catchments to meet the territory's needs. To satisfy the shortfall, large amounts of water (1.1 billion m3 in 1994) are piped each year from the Dongjiang (a tributary of the Zhujiang or Pearl River) in Guangdong Province (southern China) into reservoirs in Hong Kong where it mixes with water from local streams. The natural seasonality of flow in Hong Kong streams is heightened by aggressive water extraction during the dry season. No consideration is given to maintenance of the minimum in-stream flows necessary to conserve ecosystem integrity below extraction points and, in extreme cases, surface flow ceases during the dry season. Water extraction also causes dry-season increases in pollution load as flows are reduced and the ability of streams to dilute pollution is diminished. The cumulative impact of such modifications is severe, and lowland freshwaters now support a depauperate flora and fauna of adaptable generalists, including a significant proportion of exotic or alien species.