In 2000, the first global survey of dams showed that their overall impact was negative leading to the loss of forests and wetland ecosystem services. In Africa, the Middle East and Europe, dams and other hydrological structures are a threat to nearly 10% of the region’s Important Bird Areas, the majority of which are Ramsar sites.
Large dams cause major ecological changes in river basins. The first global survey of these showed that, despite some positive effects, their overall impact was distinctly negative (World Commission on Dams 2000). Large dams have led to:
A high proportion of the world’s river basins (61% of a large sample) are highly or moderately fragmented by dams (World Commission on Dams 2000). For example, in Africa, the Middle East and Europe, dams and other hydrological structures are considered to pose a threat to nearly 10% (304) of the 3,701 globally Important Bird Areas (IBAs) in this region (analysis of data held in BirdLife’s World Bird Database 2004). The great majority (87%) of the 304 potentially affected IBAs contain areas that qualify as wetlands of international importance (Ramsar Sites), according to the criteria of the Convention on Wetlands (see figure). In Asia, actual or planned dam projects are likely to have significant impacts on at least 10 globally threatened birds. Waterbirds of lowland floodplains, such as Masked Finfoot Heliopais personata and Indian Skimmer Rynchops albicollis, are affected particularly badly.
BirdLife International (2004) Large dams and barrages are an increasing threat to wetland-dependent birds. Presented as part of the BirdLife State of the world's birds website. Available from: http://www.birdlife.org/datazone/sowb/casestudy/150. Checked: 29/11/2014