Johnson South Reef (Chinese: 赤瓜礁; pinyin: Chìguā Jiāo; Vietnamese: Đá Gạc Ma), also known as Chigua Reef in China, Gạc Ma Reef in Vietnam and Mabini reef in Philippines is a reef in the southwest portion of Union Banks, in the Spratly Islands of the South China Sea. It is controlled by the People's Republic of China (PRC), but its ownership is disputed by the Philippines, Brunei, Taiwan, and Vietnam.