保护水的生态系统对于可持续发展具有重要意义，因为系统提供宝贵的经济和社会服务，例如纯净水质，供鱼类产卵以及保护生物多样性资源。最近一项研究的结论指出，由于江河流量减少和流量形态变化、水质下降以及建造基础设施和土地转为他用，生态系统受到沉重打击。因此，全球依赖水生态系统的水生物多样性和渔业都在衰退。

  目前水的消费模式正在对水生物多样性以及依赖水生态系统的民众产生危害。在一些大的江河流域，例如澳大利亚默累-达令河流域、南非奥兰治河流域和中国黄河流域，几乎现有全部水量都被人类使用。在黄河下游，低流量时期从20世纪90年代初期的40天延长到1997年的200天，有时候根本无水流入大海。这种现象给黄河流域一亿多民众产生极大的压力，破坏了他们种植庄稼的能力，而且对淡水物种和生态造成危害。

  在过去半个世纪中，全世界一半的湿地已经不复存在，许多淡水物种的种群数量急剧减少，或者面临绝种。咸海是世界上最严重的生态灾害之一，其面积从6.5万多平方公里缩小到1998年的大约2.85万平方公里，含水量减少75%，盐碱度大为提高。在许多国家，陆地产生的污染对沿海地区产生了深远影响，造成藻类大量繁殖，破坏礁石，伤害渔业。世界上大多数鱼类都生长于内水，仅对大约10%的鱼类进行了评估，其中30%被列为受威胁鱼种。即使在经合组织国家中，近几十年来做出的重大水资源管理努力也未能保护和恢复水质和水生态系统。

  尽管这些趋势令人担忧，但是有大量事实表明，许多国家正在发生令人振奋的变化。根据《生物多样性公约》提交国家报告的72个国家中，大多数国家指出，它们正在收集关于内水和生物多样性的信息，采取行动保护和可持续使用内水生态系统，并且采取能力建设措施。

  在环境政策中，“为环境服务付费”原则日益得到重视，并在许多国家试行。哥斯达黎加的“为环境服务付费”系统——这是发展中国家最详尽的系统之一——向有些土地拥有者支付费用，因为他们管理的森林提供水流管制和水质纯净等服务。在哥伦比亚，许多水的用户团体支付流域服务费——有时是购买一部分上游水域。

原文如下：

Protecting aquatic ecosystems

Protection of aquatic ecosystems is critical to sustainable development because such systems provide valuable economic and social services such as water purification and fish spawning, as well as protecting biodiversity resources. A recent study concludes that freshwater ecosystems have been hit hard by reduced and altered river flow patterns, by deteriorating water quality, by infrastructure construction and by land conversion. As a result, aquatic biodiversity and fisheries dependent upon aquatic ecosystems are in global decline.

Current water consumption patterns are harming aquatic biodiversity and the people whose livelihoods depend on the services that aquatic ecosystems provide. In some major water basins, for example the Murray-Darling basin in Australia, the Orange River basin in South Africa, and the Huang He basin in China, almost all the available flow is being withdrawn for human use. In the case of the Huang He River, the duration of low-flow periods in the lower parts of the river increased from 40 days in the early 1990s to 200 days in 1997, and at times no water reaches the sea at all. That has placed enormous stress on more than 100 million people in the basin, undermining their capacity to grow crops, as well as taking a toll on freshwater species and habitats.

Half the world's wetlands have been lost in the past century, and many freshwater species are facing rapid population declines or extinction. The Aral Sea has been one of the world's worst ecological disasters - its area reduced from more than 65,000 square kilometres to about 28,500 square kilometres in 1998, with a 75 per cent decrease in volume and greatly increased salinity. In many countries, the impact of land-based pollution on coastal areas has been far-reaching, triggering algal blooms, damaging reefs, and hurting fisheries. Of the world's fish species, most of which are from inland waters, only about 10 per cent have been assessed, and 30 per cent of those are listed as threatened. Even in OECD countries, the considerable water management efforts of recent decades have not been enough to safeguard and restore water quality and aquatic ecosystems.

Despite these worrying trends, there is considerable evidence of promising changes in many countries. Most of the 72 countries submitting national reports under the Biodiversity Convention indicate they are gathering information on inland water biodiversity and undertaking actions towards conservation and sustainable use of inland water ecosystems, and capacity-building measures.