Abstract: In order to reveal the characteristics of layered changes, influencing factors, and water quality effects of Bo'ai Reservoir,the vertical physical, chemical, and water quality parameters of the Reservoir water body were measured in October 2023. The results showed that a significant thermocline layer was formed at a depth of 30-40 meters underwater in the Reservoir during the monitoring period. The vertical dissolved oxygen, COD, BOD₅, permanganate index, total phosphorus, and oxidation-reduction potential exhibited a layered phenomenon consistent with the water temperature. The formation of the thermocline hindered the exchange of substances and energy in water. COD, BOD5 and permanganate index showed a vertical decrease in the water above the thermocline, while the water below the thermocline showed a vertical increase. Ammonia nitrogen, total nitrogen, and total phosphorus showed a vertical upward trend, but decreased slightly as they approached the bottom of the reservoir. The oxidation-reduction potential exhibited a significant abrupt change near the thermocline, with the water above the thermocline exhibiting oxidizing properties and the water below exhibiting reducing properties. The changes in water quality indicators were closely related to the thermocline. The identification and monitoring results of dominant algal species showed that the distribution of algae was mainly concentrated in the surface to 10m deep, and the surface filamentous blue-green algae had an absolute advantage in quantity,with the vast majority being Planktothrixagardhii.