The results of investigations conducted on the plankton fluctuations in the Hoogly-Matlah estuarine system during the period January, 1959 to December, 1967 are presented. The upper zones of the rivers Hooghly and Matlah have been found to be rich in phytoplankton. Taking the entire estuarine system, generally two peaks of phytoplankton abundance, with yearly variations in their magnitude are observed, the diatoms playing the most important part in determining the pattern of seasonal variations. Among the zooplankters, copepods form the dominant group. Two annual peal been observed in the case of zooplankton abundance also.

The surface water temperature of the estuarine system varied between 19.0°C and 32.5°C, with the annual range of variation between 7.7° C and l2.08 ⁰C. The salinity varied from traces to 32.77 %o in different zones. Informations so far gathered on the plankton ill this major estuarine system, in relation to salinity and temperature fluctuations, is reviewed and discussed, with special reference to the fisheries potential of the area.