Abagaitu Islet (simplified Chinese: 阿巴该图洲渚; traditional Chinese: 阿巴該圖洲渚; pinyin: Ābāgāitú Zhōuzhǔ; Russian: Большой остров, Bolshoy Ostrov) is an islet in the Argun River (Asia) divided between the People's Republic of China (Inner Mongolia Autonomous Region) and Russia (Chita Oblast). Its area is 58 square kilometres (22 square miles). The island was occupied by the Soviet Union in 1929, a move not accepted by China, resulting in a border dispute that lasted more than seventy years.