Majuli or Majoli (pron: ml) ) is a river island in the Brahmaputra River, Assam and in 2016 became the first island to be made a district in India. It had an area of 880 square kilometres (340 sq mi) at the beginning of the 20th century, but having lost significantly to erosion it covers 352 square kilometres (136 sq mi) as at 2014. Majuli has shrunk as the river surrounding it has grown. Majuli is currently listed as world's largest river island in Guinness book of world's record.

Answer this question based on the passage: world's largest riverine island formed by brahmaputra river? Okie... think carefully first, then make a decision:
The important part for answering this question is: Majuli is currently listed as world's largest river island in Guinness book of world's record. So, the answer is Majuli.