Qualitative and quantitative studies on phytoplankton of the Cochin Backwater showed that about 120 species of phytoplankters (excluding nanoplankton) commonly occur in the estuary. Of the 88 species of diatoms, 74 occur regularly and the rest are rare. These 14, have been recorded for the first time from the Indian waters.

Two peaks of abundance were observed—one during the monsoon months (May to July) and the other in the post-monsoon period (October to December). In the Backwater the enrichment of water with nutrients largely occurs during the monsoon months. This seems to be the most important feature governing the quantitative abundance of the species.