The Cochin Backwater is a system of lakes and estuaries along the west coast of South India. The hydrographical conditions depend on the influence of the sea and the rivers. The Cochin Backwater is connected with the sea by the inlet of the Cochin harbour and some minor entrances. The land and islands are of alluvial origin. Meteorologically three seasons can be observed:

(1) Pre-monsoon season from January to May, dry and hot.

(2) Monsoon season from June to August, moistand cool, with much rain and wind.

(3) Post-monsoon season from September to December, moist, constantly becoming hotter and dry. The seasons can also be traced in the hydrographical situations in the Cochin Backwater. The north-east monsoon can seldom be traced in Kerala, and it is usually not considered as a separate season. During the pre-monsoon season the Cochin harbour area, which has been investigated by the author, shows no salinity stratification. During the SW monsoon the conditions change very quickly in accordance with the freshwater influx from the rivers. The stratification built up during the monsoon season persists throughout the post-monsoon season until at the beginning of the new year the influence of the sea grows and the river output decreases to small amounts.