Variation in salinity, temperature and dissolved oxygen of the five experimental ponds adjoining to the sea near Mandapam from November 1979 to December 1980 were studied. The temperature, salinity and pH decreased during Northeast Monsoon while dissolved oxygen was high. Large seasonal variation in salinity was observed. The low salinity during November to December (19.02 to 20.94 %o) mainly due to rainfall during Northeast Monsoon. Higher salinity in July-August was due to evaporation and seepage. Salinity values of the ponds were compared with the adjoining sea.