The ability of graphene oxide (GO) to function as a flocculant capable of mediating the removal of algae and associated extracellular organic matter (EOM) from water was assessed. GO was demonstrated to mediate the dose-dependent removal of algae via flocculation, with 40 mg/L GO being sufficient to remove 100% of chlorophyll-a (chl-a) and 99.1% of the UV₂₅₄. Diatomite addition failed to enhance GO flocculation efficiency or to reduce the necessary GO dosage, although it did result in a significantly reduced settling time, with denser floc and a corresponding increase in supernatant ratio. GO-mediated algae flocculation was primarily achieved via netting and bridging mechanisms, with diatomite addition leading to the conversion of a subset of two-dimensional GO nets into threedimensional nets containing a diatomite core. Flocculation efficiency was comparable under acidic and neutral conditions but declined significantly with rising pH when pH≥7, with just 13.8% of chl-a being removed at pH of 10. At pH of 5, more than 60% of EOM and 57.6% to 90.1% of the disinfection byproduct formation potentials were reduced following the GO/diatomite flocculation process, and following flocculation the solution always had a final pH of 7.4±0.4 regardless of the starting pH.