Researchers investigated pollution sources in Fuxian Lake to understand and manage its deteriorating water quality. They studied pollution from rural areas, cities, phosphate chemical sites, and tourism. The main pollution in the lake came from rural sources, especially farm runoff. A high percentage of pollution (COD, nitrogen, phosphorus) in the lake was due to rural non-point sources, mainly from farms. Farmland runoff was the biggest contributor to this pollution. Checkbox: Researchers identified rural non-point sources, particularly farm runoff, as the major pollution source in Fuxian Lake, affecting water quality due to high levels of COD, nitrogen, and phosphorus.