River Soan is one of the important aquatic systems of the Punjab province in Pakistan and flows into Indus River near Kalla Bagh (District Mianwali). In order to measure the quality of water and to evaluate planktonic community, an integrated monitoring system was applied from May to December 2001. During the study period total of 202 genera were observed of which 134 were of phytoplankton present in various phylums including Cyanophyta (22), Cyarophyta (7), Xanthophyta (5), Bacillariophyta (22), Euglenophyta (5), Chlorophyta (62), Chrysophyta (8), Pyrrophyta (1) and Cphryrotophyta (2). 53 genera of zooplankton were observed including Protozoa (33), Rotifera (8), Cladocera (7), Copepoda (4) and Aquatic insecta (1). In addition to phyto and zooplankton 3 genera of Charophyta and 11 genera of Macrophyta were observed. Diversity index of phytoplankton ranged from 4.6 to 13.5 and of zooplankton from 1.94 to 5.90. Water samples were collected on monthly basis for estimation of various physical and chemical water quality parameters i.e., water temperature (9-31 0C), light penetration (1.2-22.3 cm), viscosity (0.8570-1.0572 mNS m-2), conductivity (7-19 mv), surface tension (69.28-72.63 dynes cm-1), density (0.980-1.022 mg l-1), specifi c gravity (0.796-1.025), boiling point (95-98 0C), turbidity (0.02-0.48 mg l-1), pH (8-9), dissolved oxygen (4.6- 9.3 mg l-1), alkalinity (19-36 mg l-1), acidity 1.0-1.8 mg l-1), carbonates (0), bicarbonates (19-36 mg l-1), total solids (0.56-4.24 mg l-1), total dissolved solids (0.53-4.83) and total dissolved volatile solids (0.05-0.29). Among elements, sodium (22.50-168.75 ppm), potassium (3.94-12.31 ppm), calcium (2.75-34.25 ppm), strontium (0.00-0.47 ppm), magnesium (0.00 ppm) and zinc (0.00 ppm) were detected through atomic absorption while seasonal variation in planktonic diversity was analyzed by calculating the frequency of occurrence, relative abundance and diversity index of planktonic life. The overall water quality of the study site remained within safe limits throughout the study period
