Photosyntetic rates and nutrient concentrations in water samples at various depths from four stations of Sungai Ibai in Terengganu revealed high photosynthetic rates and nutrients during low tides and vice versa during high tides. Low photosynthetic values during high tide could be due to a sudden increase in seawater volume going into the estuary from the open sea (i.e. South China Sea) and to corresponding increase in salinity. There is a possibility of inorganic nutrient dilution due to incoming seawater from the open sea into the estuary. The ammonium nitrogen concentration exceeds that of either nitrate nitrogen or reactive phosphorus. Throughout the study period, the occurrence of high nitrate nitrogen could be attributed to increased nitrification while that of ammonium nitrogen to bacterial mineralisation or decomposition.