This study aims to investigate the phytotoxic effects of both Punica granatum peel extract directed copper oxide nanoparticles (CuONPs) and copper nitrate on Elodea canadensis. The CuONPs were characterised by UV-visible spectroscopy (UV-Vis), Dynamic Light Scattering (DLS), X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), and Fourier Transform Infrared (FT-IR) Spectroscopy. The ratio of photosynthetic pigments, total soluble protein, malondialdehyde (MDA), catalase (CAT), ascorbate peroxidase (APX), and copper accumulation in the E.canadensis was determined to evaluate the phytotoxicity of the CuONPs and copper nitrate on E.canadensis. The significant improvements were observed in the growth rate of E.canadensis, chlorophyll a and b, carotenoid contents, and total soluble protein in the E.canadensis when it was exposed to the CuONPs. Additionally, CAT and APX activities and MDA contents were enhanced by accumulation of the CuONPs into the E.canadensis. These results suggested that oxidative stress was alleviated, owing to the result of an increase in the antioxidants such as CAT and APX, with an increase in the concentration of the CuONPs. Finally, the findings of this study show that copper nitrate has many negative effects on E.canadensis compared bio-synthesised CuONPs.