I wish to thank the following officers of the Inland Fisheries Division, Ministry of Fisheries, for their fruitful discussions and comments: the former Director, Mr. K. Thayaparan, Deputy Directors Messers D.E.M. Weerakoon and K.S.B. Tennakone. Mr. H.G.K. Sirisena's cooperation in the field is much appreciated. My gratitude is also due to Dr. Tomi Petr of the FAO for his invaluable suggestions; Ms. P.A. Wickremaratne for patiently typing the manuscript; Mr. K. Gunadasa for drawing some of the maps; Mr. K.D.W. Senaratne for his help in the word processing; Dr. Celine de Silva, my wife, for reading the draft; Natural Resources, Energy and Science Authority (NARESA) of Sri Lanka, International Foundation for Science (Sweden), and the Swedish Agency for Research Cooperation in Developing Countries (SAREC) for funding my reservoir research over the last decade.