The Parnaíba River runs 1,400 kilometres and spends most of that distance being a border, separating the states of Maranhão and Piauí. At the end it does something unusual for a Brazilian river: instead of arriving at the sea through a single mouth, it splits into five arms and scatters itself across a maze of channels enclosing 73 river islands. Locals call the result the Delta das Américas, a nickname the neighbouring town of Araioses has adopted outright — though geographers are quick to point out that the phrase does not hold up as a technical claim. Ilha do Caju sits in that maze, on the Maranhão side. It belongs administratively to Araioses, a municipality of about 39,000 people spread across 1,782 square kilometres of the Baixo Parnaíba, which also counts the Ilha das Canárias and the Ilha dos Poldros among its territory.

Almost the whole delta falls inside the Área de Proteção Ambiental do Delta do Parnaíba, created by federal decree on 28 August 1996 and covering 313,800 hectares across three states — Maranhão, Piauí and Ceará. It is administered by ICMBio, the federal conservation institute, and ten municipalities lie at least partly within it, Araioses among them. The vegetation inside those boundaries is a strange, layered mix that reflects exactly where the delta sits: coastal caatinga on the dry margins, restinga on the sand, extensive stands of mangrove along the channels, and flood zones dense with carnaúba palms. It is recognised as an Important Bird Area, and the protected species list includes the red-handed howler monkey and the smalltooth sawfish, a ray so heavily fished elsewhere that surviving populations are now a matter of serious concern. Scarlet ibis and rufous crab hawks work the mangroves.

What visitors come to see is the arrangement of those elements at close range. The reserve is a place of mangrove and dune and open river channels, with birds as the dominant wildlife encounter — the delta puts saltwater, freshwater and sand within a few hundred metres of one another, and the birdlife sorts itself accordingly. Getting around the island is done on horseback. This is not an accident of charm: there is no road network to speak of, and horses handle the transition from firm ground to soft sand better than anything with wheels. Tutóia, further west along the Maranhão coast, offers an alternative point of departure to Parnaíba, though the boat arrangement is the same either way.

The entire tourist infrastructure of the island amounts to three lodgings, built next to each other, running at around R$200 a night whether you are one person or two, with a single restaurant beside them. That is the whole list. There is no village to wander into, no strip of competing pousadas, no second option if the first disappoints. The booking requirement that keeps day visitors out is the mechanism that keeps the island in this condition — a privately held nature reserve rather than a destination, with the number of people on it at any given moment capped by the simple arithmetic of how many beds exist. It is a deliberately inconvenient place, and the inconvenience is the point.