BACKGROUND: In the current scenario, the synthesis of nanoparticles (NPs) using environmentally benign methods has gained significant attention due to their facile processes, cost-effectiveness, and eco-friendly nature. METHODS: In the present study, copper oxide nanoparticles (CuO NPs) were synthesized using aqueous extract of  algae as a reducing, stabilizing, and capping agent. The synthesized CuO NPs were characterized by X-ray diffraction (XRD), UV-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), and field emission scanning electron microscopy (FE-SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). RESULTS: XRD investigation revealed that the biosynthesized CuO NPs were nanocrystalline with high-phase purity and size in the range of 4.26 nm to 28.51 nm. FTIR spectra confirmed the existence of secondary metabolites on the surface of the synthesized CuO NPs, with characteristic Cu-O vibrations being identified around 600 cm, 496 cm, and 440 cm. The FE-SEM images predicted that the enhancement of the algal extract amount converted the flattened rice-like structures of CuO NPs into flower petal-like structures. Furthermore, the degradation ability of biosynthesized CuO NPs was investigated against Amido black 10B (AB10B) dye. The results displayed that the optimal degradation efficacy of AB10B dye was 94.19%, obtained at 6 pH, 50 ppm concentration of dye, and 0.05 g dosage of CuO NPs in 90 min with a pseudo-first-order rate constant of 0.0296 min. The CuO-1 NPs synthesized through algae exhibited notable antibacterial efficacy against with a zone of inhibition (ZOI) of 22 mm and against with a ZOI of 17 mm. CONCLUSION: Based on the findings of this study, it can be concluded that utilizing algae for the synthesis of CuO NPs presents a promising solution for addressing environmental contamination.