RESUMO
Seasonal and topographical variations of abundance and quality composition of periphyton at up and down stream of Imphal, Thoubal and Khuga rivers were studied from 1999-2002. It was found that periphyton population was high (3,055-53,450 u cm-2) and fluctuated in a wide range. Upper stretches (3053-53,450 u cm-2) of the rivers have higher periphyton population and showed definite seasonal fluctuation than the middle and lower stretches (3,276-16,320 u cm-2). Species richness was also higher in upper stretches in comparison to lower stretches of all the rivers. Bacillariophyceae dominated the periphyton population and contribution of Cyanophyceae was nominal. Shannon and Weaver species diversity index was within the favorable range and evenness value for all the rivers were near unity and reflected a stable and unpolluted aquatic environment of the rivers.