... This has a statistically significant impact on the growth of both Atlantic Salmon (Salmo salar L.) and trout (Salmo trutta L.) (Saltveit, 1990) Below the Cow Green reservoir, UK, small changes in trout growth are attributed to lowered summer temperature peaks (by 1 -28C), reduced diel fluctuations, and the delayed rise in spring temperatures and fall in autumn temperatures (Crisp et al., 1983) The Hume dam on the Murray River, Australia, alters the thermal regime of the river and its effect is still discernible 200 km downstream (Walker, 1979) Water chemistry Lake Guiers, fills by flooding from the Senegal River. Since construction of the Diama and Manantali dams on the river, average salinity in the lake has reduced from 360 mg l 21 to 240 mg l 21 , and temporal variability is considerably reduced (Cogels et al., 1997) Increased salinity, across a wide range of flows, downstream of the Massingir dam on the Elefantes River, Mozambique, is attributed to high evaporation from the reservoir (Suschka, 1986) Field and laboratory experiments suggest that, in the first 21 months after flooding, accumulated nutrient loads originating from the topsoil of the area (655 ha) inundated by the Nanhua reservoir, Taiwan, were 124 kg of nitrogen and 7.2 kg of phosphorous per hectare. Furthermore, if it had not been cleared, complete decay of the terrestrial vegetation (monsoon rain forest and farmland) would have contributed an additional 243 kg of nitrogen and 37 kg of phosphorous per hectare (Chang & Wen, 1998) In the period immediately following impoundment, water abstracted from the Volta reservoir, Ghana, had to be treated with potassium permanganate to remove 'high' concentrations of iron and manganese, neither of which was present prior to dam construction (Kumi, 1973) Sedimentation Dams constructed on the Rhone River, France, have reduced the annual quantity of sediment transported to the Mediterranean from 12 million tons in the 19th Century to only 4 to 5 million tons today (Balland, 1991) Prior to construction of the Aswan High Dam, floods deposited on average 12 million tonnes of silt on land along the Nile each year. ...
