The communities of diatoms associated with some aquatic plants in two polluted water courses in the Nile Delta were identified. Three types of hydrophytes, Eichhornia crassipes (Mart.) Sloms, & Pistia stratiotes L. as floating hydrophytes; Ceratophyllum demersum L., and Chara sp. as submerged and Persicaria salicifolia (Willd) (Assenov) as emergent species have been distingushed. Relationship between the microalgae and the present hydrophytes were studied. Forty-six diatom taxa were identified and most of them can be used as indicator of freshwater pollution. Bacillaria paxillifer,  Gomphonema spp.. Nicschia  palea,  N. lorenziana,  Synedra ulna, Navicula viridula, Cyclotella meneghiniana werethe predominant species. Results indicated that pennate forms dominated the centric one. The taxonomic composition of epiphytic diatoms was more or less similar on the different plants during the investigation period. Eichhornia crassipes, Ceratophyllum demersum and Chara sp. hosted higher number of individuals of associated diatoms. However, lower numbers of individuals were recorded on the emergent species P. salicifolia. The physical and chemical characteristics of the water samples were also analysed and correlations between the occurrence of diatoms and the selected plants in relation to the prevailing environmental parameters were performed. Some heavy metals like Cu and Pb exhibit highly positive correlation with the dominant diatom species as well as diversity index. Nevertheless, water temperature and NH₄-N showed high negatively correlation with the total number of diatoms.