94-102Variations in salinity, temperature, dissolved oxygen and zooplankton biomass in the backwaters from Cochin to Alleppey are discussed with reference to conditions prevailing respectively in premonsoon, monsoon and postmonsoon periods. Salinity in general decreases from the mouth of the estuary towards the head. The extent of intrusion of saline water depends on the strength of tidal influx and the fresh water efflux which differ with seasons. Higher temperature values observed in premonsoon fall with the advance of monsoon. High oxygen values recorded during monsoon suggest high primary production at surface during this season. Biomass values fluctuate with seasons and they can be correlated with the hydrographical conditions prevailing in the estuary
