The rapidly advancing technology of distributed acoustic sensing (DAS) has profoundly impacted the field of underwater geophysics. Our study investigates the effectiveness of DAS in underwater geological stability monitoring, with a particular focus on microseismic monitoring in the Xinfengjiang reservoir. The 6.2 km long acquisition setup, covering both land and reservoir bottom, was verified using temporary shore‐based short‐period seismometers to ensure reliable data acquisition in various environments. Higher background noise was observed on the land section compared with the lakebed section during the day, whereas both sections exhibited similar noise levels at night. We confirmed that the DAS system was capable of detecting distant microseismic events, some of which were previously unreported. These detections exhibited temporal and phase consistency with neighboring seismometers. Comparison of signal‐to‐noise ratios indicates that the lakebed section demonstrates higher sensitivity. This system delivers cost‐effective performance through natural settling, negating the requirement for costly embedding methods. Moreover, the DAS system identified “comet‐like” small‐scale signals on the lakebed that had eluded shore‐based seismometers. This exemplifies the exceptional high‐density and high‐resolution capabilities of DAS technology in both aquatic and terrestrial environments. This study underscores the pivotal role of the DAS technology in conducting underwater microseismic monitoring, real‐time seismic monitoring, seismic mechanism research, and earthquake hazard assessment.

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