Rivers at risk: dams and the future of freshwater ecosystems

What are the impacts of dams on freshwater ecosystems?

This report analyses the construction and planning of dams on a river basin scale, examining the risks of dams to freshwater ecosystems. It identifies 21 river basins at severe risk of ecological degradation as they have six or more dams over 60 m high planned or under construction, in addition to existing dams.

The report highlights that top of the list is the Yangtze River Basin in China with 46 dams, followed by the La Plata River Basin in South America with 27 and the Tigris and Euphrates River Basin with 26. Of particular concern are the cumulative impacts of large numbers of dams in the same basin, especially in smaller basins such as the Salween/Nu River in Myanmar and China.

Dams are both a blessing and a curse, the author argues. While they provide water and power, they also cause serious damage to freshwater ecosystems, affecting both nature and people. Already, in 60% of the world’s major rivers flows are interrupted by dams, canals and diversions.

Many freshwater habitats and species have been lost, the paper notes, with dams and their associated infrastructure, such as irrigation systems, a major culprit. Dam construction has mainly shifted from the developed to the developing world, with countries such as China and India implementing large dam construction programmes, including inter-basin transfers. While water and energy requirements in developing countries are real and need to be addressed, the risk to ecosystems is acute and unique species and habitats are threatened.

The author recommends that to avoid large-scale damage, decision-making needs to be informed by a comprehensive assessment of all options, alternatives and impacts. This should include careful site choice, a cumulative assessment of dams by river basin, as well as extensive mitigation measures for those dams that are given the go-ahead.

The report singles out river basin management (IRBM) in providing the tools to assess and avoid basin wide impacts and meet the needs of a range of stakeholders. The World Commission on Dams has provided a set of recommendations to improve decision-making on dam development, but these are still not implemented in most countries the author notes.

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Rivers at risk: dams and the future of freshwater ecosystems