Abstract: In order to investigate the environmental degradation risks in tidal rivers and downstream aquatic environments induced by the construction of the Jiaojiang River estuary hydraulic hub, a two-dimensional hydrodynamic-water quality coupled model (Mike 21) was developed for the Jiaojiang River. The model dynamically integrated gate operation rules with tidal-riverine interactions to systematically elucidate the alterations in pollutant transport mechanisms and eutrophication dynamics driven by tidal gate construction in a macrotidal estuary. The results showed that the operation of the hub obstructed the bidirectional transport of tides, and weakened the dilution and self-purification capacity of the water body, thereby leading to the accumulation of pollutants upstream of the gate. The dilution effect of water flow in wet periods suppressed the increase in concentration, keeping it lower than during dry periods. Additionally, due to differences in runoff and tidal changes in different river sections, the concentration generally increased along the river. However, when the flow was less than 10 m³/s, the increase in concentration was greater in river sections with significant external pollution. The research shows that the construction of the gates can increase eutrophication risk, mainly concentrated downstream of the dam.