Phytoplankton diversity and physicochemical parameters are important criteria for evaluating the suitability of water for drinking and other purposes. An assessment of physicochemical parameters and phytoplankton diversity in Anambra River, Anambra State, was conducted for a period of eight months from February 2021-September 2021. Water samples were collected from three sampling stations of the river every month in sterilized containers during the course of the study. The study stations were designated as S1 (Umueri) S2 (Anam) and S3 (Otuocha). The samples were analysed for both physicochemical attributes and plankton diversity. Phytoplankton species were determined following standard procedures. A total of twenty three species of phytoplankton were encountered in Anambra River. Chlorophyceae was the dominant group of phytoplanktons in the river, accounting for 44.8% and 38.3%. The most abundant phytoplankton species was Spirogyra, accounting for 8.9 %. There were 98, 82 and 101 phytoplanktons recorded for Station 1 (S1), Station 2 (S2) and Station 3 (S3) respectively. 14 phytoplankton species cut across the 3 stations in Anambra River while Closterium Spp and Tetraspora Spp were unique to Station 3 (S3) and Station 2 (S2) respectively. A. bisoletiana and Navicula spp were absent in S1; Oscillatoria spp., Nodularia and Zygnema were absent in S2, while Rivularia spp. and Microspora were absent in S3. Anambra River recorded high diversity indices value for Chlorophyceae = 1.26 and least value for Cyanophycaea = 1.23. The physico-chemical attributes of the river was investigated by measuring the degree of correlation with the phytoplankton diversity. The phytoplankton diversity of the river showed significant correlation with physicochemical parameters. The result revealed a deterioration of water quality of the river due to industrial, commercial and anthropogenic activities. The status of plankton diversity of Anambra River was low indicating that the river is highly polluted and the water chemistry has direct effect on plankton diversity. There is need for urgent management and conservation strategies to protect and restore the water quality of the river.