The sediment deposition in Phewa Lake has been the subject of perennial challenges in the conservation of the lake and its ecosystem. Thousands of tons of sediment flow into the lake annually from its catchment, reducing its capacity. Climate change has an impact on the soil erosion process in the Phewa watershed. The Adheri Khola sub-watershed makes a significant contribution to the sediment source, transportation, and deposition in Phewa Lake. This study analyzes potential soil erosion using the revised universal soil loss equation (RUSLE) model and quantifies the sediment deposition caused by four active landslides in the Adheri Khola sub-watershed. The impact of climate change and adaptation measures was studied using a questionnaire survey for the targeted stakeholders. The result showed that 48,015 tons per hectare of soil were eroded annually. Additionally, 31,370 m3 of sediment was deposited in four active landslides that formed inside the watershed. Furthermore, climate change had a negative impact on crop yield. It is important to mitigate soil erosion and sedimentation in the Andheri Khola sub-watershed so that the sediment load in Phewa Lake can be reduced. The mitigation plan, based on the risk map developed here, can concurrently address the possible climate change impacts. The erosion and transportation of sediment over Phewa Lake are key factors in reducing the water area of the lake and its aesthetic value in the future.