The main pier of a large bridge is located in the Pearl River. Locked steel pipe piles were used as the enclosure structure for the cushion cap foundation pit of the main pier, with C30 underwater concrete used for bottom-sealing. After bottom-sealing was completed, the confined water level was too high, leading to water kick-in at the bottom of the foundation pit during the cofferdam drainage process. Two solutions were discussed afterwards: the first option was internal dewatering of cofferdam and the second was external dewatering of the cofferdam. After comparison, the second solution was chosen. External dewatering of the cofferdam eliminated successfully the incident and ensured the smooth construction of the pile cap, proving that it is feasible to lower the confined water level in the river. Dewatering is one of the important means to ensure the