The alteration of corrosion mediums in the salt and freshwater confluence area is poorly understood, with low concentrations complicating matters further. This significantly changes the corrosion patterns of concrete structures, rendering the chloride diffusion models developed for marine environments inaccurate for predicting the lifespan of concrete structures in such salt and freshwater confluence areas. Additionally, the deterioration mechanisms in the salt and freshwater confluence area differ from those in marine environments. Hence, applying marine protective measures to these areas would lead to substantial resource wastage. To address this issue, this study leveraged the Nansha Bridge project, employing field tests, laboratory tests, and theoretical analyses to investigate the durability of concrete structures in the salt and freshwater confluence area. First, the carbonation and chloride corrosion of the concrete structure under different corrosion environments at Nansha Bridge were analyzed. Subsequently, the pore distribution, chemical composition, and microstructure of the concrete were characterized by mercury intrusion porosimetry (MIP), thermogravimetric (TG) analysis, and scanning electron microscopy (SEM). This study may have potential for the life prediction, repair, and reinforcement of concrete structures in the salt and freshwater confluence area.