Arsenic (As), which ranks 20th in abundance in the earth's crust, is a ubiquitous and toxic element in the environment. The impact of As pollution on ecosystem and human health has become one of the major environmental concerns in the world. Large amount of As from both geogenic and anthropogenic sources have entered into the waters such as groundwater, rivers and lakes, resulting in adverse effects on human health. This paper reviews the literature regarding As in freshwater lake ecosystem with some comparison to the marine ecosystem. As contents and speciation in various biological and environmental media as well as their influencing factors were extensively discussed. Complex factors have caused the large regional differences of As in global freshwater lake ecosystem, e.g., As ranges from 1.0 to 15000 μg/L in lake water and 1.0 to 2000 mg/kg in lake sediments. Generally, As contents in aquatic organisms are in the descending order of zoobenthos > phytoplankton > zooplankton > fish. As contents in lake sediments play a significant role on the natural habitats of benthos, and even bring about changes to the ecological zone of benthic fauna. In contrast, fish, the higher trophic organisms in the lake, usually has effective mechanisms for absorption, detoxification and excretion of As through the metabolism processes. As in fish tissues is generally in the range of 0.1 to 10 mg/kg DW. In macrophytes, As contents generally followed the order of roots > stems > leaves, with bioacaccumulating factors generally in a descending order of submerged plants > floated plants > emerged plants. Nevertheless, there is lack of comprehensive study on the role of As in the lakes in China. The mechanisms for As migration and transformation in lacustrine ecosystem have partially been elucidated, However, little efforts have been made to incorporate such mechanisms into the ecological risk assessment of the lake ecosystem and adjacent areas. Finally, this review proposed some ideas and schemes for future studies on As in the lake ecosystem.