Johnson South Reef, also known as Chigua (Chih-kua) Reef (Chinese: 赤瓜礁; pinyin: Chìguā Jiāo; Wade–Giles: Chih-kua chiao), Gạc Ma Reef (Vietnamese: Đá Gạc Ma), or Mabini Reef (Filipino: Bahura ng Mabini, lit. 'Reef of Mabini'), is a reef in the southwest portion of the 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 and also claimed by the Philippines, Taiwan (ROC), and Vietnam.