This paper proposes replacing Ordinary Portland Cement (OPC) with Geopolymer material (GP) comprised of Fly Ash (FA) along with activator solution as a binding material. The efficacy of FA geopolymer concrete (GPC) in aggressive media, Qaroun lake conditions (sea water), is examined. First, GPC and OPC samples are prepared as well as preserved for 28 days and subsequently submerged (for 90 days) in aggressive media or potable water. Consequently, energy-dispersive X-ray spectroscopy (EDX) analysis, scanning electron microscopy (SEM), and compression testing are utilized to determine the durability of samples. The technique of Linear Polarization Resistance (LPR) is also used to measure the steel corrosion rate embedded in concrete samples. According to the comparison, raising GPC's FA content enhances its technical characteristics. In addition, GPC (based on FA) has the greatest compressive strength (CS) in comparison with OPC concrete. In aggressive media, the CS of GP increases nearly threefold compared to potable water. Furthermore, the steel corrosion rate (in GPC samples) in the medium is nearly reduced. In addition, the microstructure of the GPC matrix exhibits greater stability in aggressive media than in OPC. In contrast to OPC, the GPC exhibits a substantially more stable mineral composition formation following seawater media exposure, as determined by microstructural analysis.