Start with the gateway, not with the panic
The first useful truth about Marajo access is that most travelers do not need a complicated arrival plan. They need a clear one. Belem works as the main gateway because it concentrates the arrival logic for both Brazilian and international visitors. Once you reach Belem, the remaining question is not whether Marajo is possible, but which route best supports the kind of trip you are building.
That perspective is important because travelers often search for transport details before deciding what side of the island they actually want to experience. In practice, it is more efficient to define the base, then build the transfer around it. This reduces redundant searching and helps the traveler feel like the journey is manageable instead of obscure.