Diurnal variations in phytoplankton pigments in the water on 3/ 4 September, 1969, at 3 stations in the Vellar estuary were investigated. The peak values of pigment content of the water were:

Chlorophyll a                          .. 19.CO µg/l

Chlorophyll b                          .. 16.CO µg/l

Chlorophyll c                          .. 35.80 µg/l

Carotenoids                             .. 5.34 MSP/M³

The yellow:green pigment ratio was generally between 2.50 to 3.50 and the range of variation was from 1.60 to 4.40 ( with an occasional 7.50). The plankton settlement volume varied between 25 to 130 c³. The peak values in pigments usually occurred during morning and late evening hours.