Lotic ecosystem monitoring is important to avoid pollution risks, safeguard biodiversity, and maintain ecosystem health. In this essence, it is impossible to ignore the involvement of epiphytic microalgae in riverine monitoring. Two host plants, such as the common reed, Phragmites australis, which is primarily found in marsh grasses, and the submerged, free-floating hornwort, Ceratophyllum demersum, were chosen for this study. The estimation of various biodiversity metrics, including Brillouin, Dominance (D), Equitability (J), Evenness (e^H/S), Margalef, Menhinick, Shannon (H), and Simpson (1-D), were conducted in Diyala River, Diyala province, Iraq, using data covering the four seasons. One hundred and forty-four taxa of epiphytic algae on both host plants were recorded. Among them, diatoms (Bacillariophyta) were the predominant group of algae on both plants comprising 84% and 92% of C. demersum and P. australis, respectively, followed by Cyanophyceae (3- 25%) and Chlorophyceae (3- 42%). Preferences of algae on particular host plants were observed. A spatial and temporal of epiphyton algae was observed on the plants. Some epiphyton species, such as Gomphonema paravalum, Ulnaria acus, Cyclotella meneghiniana, Navicula gregaria, and Nitzschia amphibian arerecorded in the river and are considered bioindicators for determining the water quality. (By applying the recommended indices as mentioned in the text you have to recognize the trophic, saprobic, and halobic status of the investigated area based on the identified species) Based on the overall outputs of this study it is anticipated that the  Diyala River is getting a  pollution load. the level of pollution must be determined (beta-mesosaprobic, alpha mesosaprobic, polysaprobic) that needs to be overcome.  [D1]Check for changes as there are missing informations that need to be addressed.