Coastal reservoirs are a possible solution to water supply and management issues in coastal zones. However, salinization can degrade the utility of such reservoirs. Two related major challenges affecting the operation of a coastal reservoir are desalinization and seawater intrusion. The former arises mainly during the period following reservoir construction, while the latter is ongoing. This review discusses the salt dynamics of coastal reservoirs under the influence of surface-water flows, river inflows, reservoir water level, and tides. Various salt transport processes are examined in relation to water salinity changes in coastal reservoirs. The methods and limitations of existing numerical models for coastal reservoirs are also discussed. Given the difficulty in reproducing realistic boundary conditions for laboratory experiments, further research needs to focus on investigations that consider salinization in real coastal reservoirs. More broadly, there remains a need to unravel the impacts of coastal reservoirs on the surrounding environment, as they can significantly change the hydrodynamics and chemical transport pathways in coastal waters. A comprehensive understanding of coastal reservoir salinization will improve water management and thus contribute to alleviating overexploitation of water resources in coastal zones.