Lake Dianchi is severely polluted with nitrogen (N) and phosphorus (P). The effects of implementing environmental policies and technologies on future lake quality are not well understood. We analyse effects of environmental policies and technologies on future river export of nutrients into Lake Dianchi. We develop scenarios for 2050 and analyse these with the existing MARINA-Lakes model (Model to Assess River Inputs of Nutrient to lAkes). The scenarios differ in assumptions about future nutrient management in agriculture, sewage systems and mining. In the SSP3 (Shared Socio-economic Pathway 3) scenario, river export of nutrients to Lake Dianchi is projected to increase 1.4–4.4 times between 2012 and 2050. In the Current Policies scenario, rivers may export fewer nutrients than in SSP3, but this may not avoid eutrophication. Effects of improved nutrient management on river export of nutrients differ among nutrient forms, sub-basins and sources (e.g., urbanization in the north, agriculture in the middle and south). Pollution levels can be reduced below the 2012 level in an Optimistic scenario assuming advanced wastewater treatment, improved nutrient management in agriculture and no mining. However, even this may not completely prevent eutrophication. Preventing eutrophication requires even more efforts, for example, in implementing circular-oriented management options.