SUMMARY OF ISSUE
Large dams are numerous and varied, and include direct impacts to the biological, chemical and physical properties of rivers and riparian (or "stream-side") environments.The dam wall itself blocks fish migrations, which in some cases and with some species completely separate spawning habitats from rearing habitats. The dam also traps sediments, which are critical for maintaining physical processes and habitats downstream of the dam (include the maintenance of productive deltas, barrier islands, fertile floodplains and coastal wetlands).
Another significant and obvious impact is the transformation upstream of the dam from a free-flowing river ecosystem to an artificial slack-water reservoir habitat. Changes in temperature, chemical composition, dissolved oxygen levels and the physical properties of a reservoir are often not suitable to the aquatic plants and animals that evolved with a given river system. Indeed, reservoirs often host non-native and invasive species (e.g. snails, algae, predatory fish) that further undermine the river's natural communities of plants and animals.
WHY THIS ISSUE IS IMPORTANT
This issue is important because dams block movement of fish and other species, change river habitat to pond-like habitat, degrade water quality, change the flow of the river, and can impact downstream users. All of these terrible environmental issues are being created for the trade off of an energy source. In many aspects this seems like an unfair trade but it is impossible to know if the damage is irreparable.
Large dams are numerous and varied, and include direct impacts to the biological, chemical and physical properties of rivers and riparian (or "stream-side") environments.The dam wall itself blocks fish migrations, which in some cases and with some species completely separate spawning habitats from rearing habitats. The dam also traps sediments, which are critical for maintaining physical processes and habitats downstream of the dam (include the maintenance of productive deltas, barrier islands, fertile floodplains and coastal wetlands).
Another significant and obvious impact is the transformation upstream of the dam from a free-flowing river ecosystem to an artificial slack-water reservoir habitat. Changes in temperature, chemical composition, dissolved oxygen levels and the physical properties of a reservoir are often not suitable to the aquatic plants and animals that evolved with a given river system. Indeed, reservoirs often host non-native and invasive species (e.g. snails, algae, predatory fish) that further undermine the river's natural communities of plants and animals.
WHY THIS ISSUE IS IMPORTANT
This issue is important because dams block movement of fish and other species, change river habitat to pond-like habitat, degrade water quality, change the flow of the river, and can impact downstream users. All of these terrible environmental issues are being created for the trade off of an energy source. In many aspects this seems like an unfair trade but it is impossible to know if the damage is irreparable.