With the gradual implementation of the Lishui tail channel project，the water level and flow in the lower reaches of the Lishui River have changed greatly. The low flow of the lower reaches increased due to the regulation and storage of the Three Gorges Hydro-junction and two upstream reservoirs，while the low water level showed a slight downward trend. Moreover，the relationship between the water level and flow at the Jinshi Hydrological Station also decreased. To determine the lowest navigable water level downstream from the ship lock of the Yanzhou Hydro-junction at the end cascade of the Lishui River，this paper employs methods such as calculating the water surface slope in the dry season to analyze the causes and main trends of the above phenomena in consideration of channel regulation and sand mining activities. It then proposes a method of determining the short-term and long-term lowest navigable water levels downstream from the Yanzhou Hydro-junction and demonstrates the rationality of the reserved long-term water level drop.