Surface water resources have played an important role throughout history in the development of human civilization. About one third of the drinking water requirement of the world is obtained from surface sources like rivers,canals and lakes. But, these sources serve as the best sinks for the discharge of domestic as well as industrial wastes. This unscientific disposal of wastes has caused immense problems not only to human beings but also to the aquatic environment world wide. In Sri Lanka, this problem started long back but intensified during the last few decades and now the situation has...