Derna, a coastal city in northern Libya, is characterized by a fluctuating marine environment, which makes its concrete structures highly susceptible to deterioration due to continuous exposure to sea spray containing chlorides, sulfates, and other ionic salts. These salts adversely affect both concrete and reinforcing steel through complex physical and chemical interactions. Chloride ions, in particular, penetrate concrete pores and micro cracks via capillary action and wet-dry cycles, reaching the reinforcing steel and breaking its passive protective layer. This process leads to increased concrete permeability, surface layer degradation, initiation of steel corrosion, and rust formation, thereby reducing the service life of structures and threatening their structural safety. These risks were further exacerbated by the catastrophic floods that struck Derna in 2023, accelerating the deterioration of many existing buildings. The presence of salts intensified the penetration of chlorides into the concrete, weakening the passive layer around the steel reinforcement and hastening the onset and propagation of corrosion. In light of these findings, this study highlights the impact of the coastal environment and sea spray on the accelerated degradation of concrete structures in Derna and emphasizes the importance of implementing effective preventive strategies and routine maintenance programs to preserve the safety and extend the service life of coastal buildings.................... Keywords:............... Sea spray, coastal environment, chloride penetration, reinforcement corrosion