Marajó is the largest fluvial island in the world, and the second largest island in South America. With a land area of 40,100 square kilometres Marajó is comparable in size to Switzerland. Is is approximately 295 kilometres long and 200 kilometres wide.
Mainitaan yllä olevaan liittyen vielä turhana tietona, että maailman väkirikkain "jokisaari" on Zhongshan Dao, josta löytyy 2,3 miljoonaa asukasta.