The study explored the lake as mesotrophic. Inflow streams to Phewa lake, lake itself and its outflow stream were sampled in monsoon and post-monsoon. Nine different sampling sites were chosen and physico-chemical parameters like pH, temperature, dissolved oxygen, electric conductivity were recorded at the spotand rest of the parameters (total nitrogen, total phosphorus and total suspended solids) were analyzed in the laboratory. The observed concentrations were compared with Standard of Surface water quality for sustaining aquatic life. There was no significant difference in DO level, pH, TSS whereas EC, TN and water temperature showed significant difference with respective seasons. The electric conductivity of Phirke khola (inflow stream to lake) was found high that means it was putting nutrient load to the lake. The total suspended solids were much higher (176 mg/l) at Harpan khola (inflow stream) in monsoon and maximum at the middle point of lake (11 mg/l) in post-monsoon. This showed that the TSS carried by Harpan khola are maximally deposited at middle point of lake and shortening the life of the lake. The study finally recommends controlling the discharge of pollution load and periodic surface water quality monitoring and vertical (depth wise) monitoring is necessary.