From Manaus to Novo Airão is an overland trip of about 200 kilometers on a paved road, a route that still feels like an Amazon frontier despite the asphalt. Novo Airão is a small riverside town that serves as the management base for the park, with its local unit accessible by phone - +55 92 3613-3094 for the main office. From Novo Airão, flyer boats make the run to the park entrance in about three hours. Most travelers do not arrange their own trip. They book with a Manaus-based tour operator, which handles the fees, the permits, and the logistics of food, lodging, and guide. The park is not structured for casual tourism. To visit on your own, you need to contact the management authority - extension 229 at +55 92 3613-3277 - at least a month in advance.

IBAMA, the Brazilian environmental agency that oversees the park, charges a maintenance fee of three reais per person per day. There is an additional boat fee ranging from 16 to 64 reais, charged by vessel rather than by passenger and scaling with the size of the boat. Most tour packages include these fees. If you see an operator asking for much more - some claim official visitor fees of 100 reais or more - you are being overcharged. Damage to the park's flora or fauna is a federal crime, and the military police conduct regular patrols looking for poachers. The rules here are enforced, and they matter. The park's purpose is preservation, and casual tourism comes second to the ecosystem it protects.

Once inside, everything moves by water. Motor boats for the main rivers, canoes for the side channels, sometimes nothing more than a light wooden hull that can float over tree roots and duck under low branches. When the water is high, especially from December to April, boats can reach places that in the dry season become mudflats. In the drier months from July to September, many of the smaller tributaries become impassable except to very light craft. Daily temperatures sit between 22 and 32 degrees Celsius year-round. The humidity is constant. December through April is the rainiest stretch of a generally wet climate - plan for afternoon downpours that turn the river surface to static and then pass as quickly as they came.

Wildlife in the Jaú is abundant but quieter than along the main Amazon channel - the fauna is less dense here than in the more productive waters of the Solimões. Still, what moves through is the full cast of Amazonian biodiversity. Pink river dolphins, or botos, surface in the channels. Jaguars pad through the flooded forest. Tapirs browse riverbanks at dusk. Armadillos scuffle in the understory. Monkeys call from the canopy and crocodilians - mostly caimans - slip off sandbars as your boat approaches. Fish of hundreds of species fill the water, some of them new to science when first catalogued. Birds of every description wake before dawn and go quiet through the middle of the day when the heat builds. The Jaú is not a zoo. Animals appear on their own schedule, often briefly, and a patient eye is rewarded more than a loud one.

There are no hotels inside the park. Lodging options are in Novo Airão or further upstream in Barcelos, where hotels accommodate travelers before and after the boat trip. Inside the park, you sleep on the boat - either in a hammock strung between posts under a covered deck or, on larger vessels, in a cabin. There is a visitors' center at the park entrance and some facilities for researchers who have government permission to stay. Food is what you bring. Unless you are content with fish for every meal, stock up in Manaus or Novo Airão before the trip. The local diet is organized around what the river provides, and the river provides mostly fish. That constraint is part of the honesty of the place. You are not in a serviced destination. You are in a working ecosystem that tolerates visitors on its terms.