The Hoogly-Matlahestuarine system, the major portion of which is characterised as a positive mixohaline estuary, is divided into five zones, each presenting different physico chemical and biological zonation in this estuarine system are temperature, salinity, turbidity and freshwater drainage.  As regards the flora and fauna of the estuary, most of the data so far gathered are on the plakton and biology of commercially important fishes salient features of which are presented and discussed. The biological characteristics  of (i) he marine fishes which use the estuary as nursery ground (ii) the species which migrate into the mouth of the estuary to form important local fisherie, and (iii) freshwater fishes which come into the estuary, are discussed. Prominent features of the fisheries potential of the estuarine system have also been given.