Yangzonghai Lake is a typical fault-controlled highland lake in China. In this study, we investigated the occurrence and behavior of Arsenic in and around the lake. The As concentrations of lakeside sediment, lacustrine sediment, and soil samples were 20-70 mg·kg^-1. Ascribed to the geochemical accumulation and anthropogenic contamination, soil, lakeside sediment, and lacustrine sediment showed gradually increased correlation coefficients between As and heavy metals. Arsenic in and around the lake was influenced by both groundwater and human pollution. The sinters of groundwater showed high concentrations of As (>150 mg·kg^-1), Sb, and Hg, while the chemical waste and slope deposit samples from the pollution industry exhibited elevated concentrations of all heavy metals (As, 170-370 mg·kg^-1). The enrichment factors (EF) of the samples suggest that the soil and lacustrine sediment samples were relatively unpolluted with As enrichment of <10, while the sinters and chemical wastes showed extremely high EF values of >200. Most samples can be classified into groups 1, 2, and 3 that were affected by groundwater, indicating that the influence of groundwater on the As occurrence was more intensive than that of the pollution industry. The influence of human pollution was quite limited and localized. This study suggests that groundwater is an essential factor that should be taken into consideration when assessing the As contamination in fault-related plateau lakes.