Migratory fish (born in rivers, migrate to the sea or ocean to mature and go back to rivers to reproduce and in most cases die after that)
Some dams do not have the so called fish ladders (or other constructions) which allow migratory fish, for example salmon, to reach the upstream of the river and the ocean
Grand Coulee Dam on the Columbia River in Washington has no fish passage facilities and thus it kills salmon worth 250 000 $ a year
But even if there are fish ladders in most cases only adult fish can pass through them, while their offspring finds it very difficult and it costs them time
The time is extremely important, because when the migration is delayed, the whole life cycle of the fish is behind schedule and fish can lose their ability to switch from fresh to salt water or to swim downstream
Example: It took salmon from the Snake River in Idaho less than 3 days to get to the sea before the dams were built compared to the 39 days it needs now
Dams tend to collect pollutants and toxins with the sediment and water behind dams is extremely dangerous for any species downstream
Deeper dams do not allow the current to mix the water and the water near the surface is hotter than it should be, and the deeper water is vey cold, but with almost no oxygen circulation
During the warm season, great amounts of water evaporate, because dams increase the water surface directly exposed to sun rays
170 cubic kilometers water evaporates every year, which is more than 7% of the all used by humans freshwater (all activities)
Example: 10% of the storing capacity of the High Aswan Dam in Africa evaporates every year and these 11.2 cubic kilometers are roughly the same amount of water as that used for both residential and commercial use on the continent
The high level of evaporation (e.g. 1/3 of the Colorado River!!) leads to increase in salinity which is poisonous to all aquatic organisms and causes great damages to the machinery and pipes (corrosion)
Example: Millions of dollars per year is the cost of the increased salinity in Colorado River
Has the purpose to irrigate previously forested areas
Due to its building the habitat of seven endangered and two threatened animals was turned into agricultural land
The two threatened species are the purple-faced langur and the toque macaque (both monkeys) live only on the island Sri Lanka
800 elephants live in this area and this specie is endangered. They migrate and the reservoirs and canals are an obstacle in on of their migratory routes. That is why they go through the farmland causing much trouble to the farmers and to other animals in the area.
The Victoria Dam, part of the Mahaweli mega scheme http://stonehouselodge.lk/pix/victoria-dam.jpg
Parana River, Itaipu Reservoir http://www.leonardo-energy.org/files/root/EPQU/Images/unsorted/itaipu.jpg
"Impacts of Dams on Rivers." FAO Corporate Document Repository . Food and Agriculture Organization of the United Nations, n.d. Web. 5 June 2010. <http://www.fao.org/docrep/005/y3994e/y3994e0i.htm#TopOfPage>.
McCully, Patrick. "Dams and Migratory Fish." International Rivers . Creative Commons, 1 Jan. 2001. Web. 5 June 2010. <http://www.internationalrivers.org/en/node/1639>.
McCully, Patrick . "Dams and Water Quality." International Rivers . Creative Commons, 1 Jan. 2001. Web. 5 June 2010. <http://www.internationalrivers.org/en/node/ 1638>.
McCully, Patrick. "Rivers No More: The Environmental Effects of Large Dams." International Rivers . Creative Commons, 1 Jan. 2001. Web. 5 June 2010. <http://www.internationalrivers.org/en/node/1636>.
Smith, S. E. "Why are Dams Potentially Harmful to Fish?" Wise Geek . N.p., 12 Apr. 2010. Web. 5 June 2010. <http://www.wisegeek.com/ why-are-dams-potentially-harmful-to-fish.htm>.