There are no roads here in any sense a driver would recognize. The town is a lattice of wooden walkways raised on posts above tidal mud, with houses on stilts branching off them — palafitas, painted in the hard candy colors that hold up against equatorial sun. Residents call the place the Venice of Marajó, and the comparison is less about grandeur than about geometry: a settlement organized around water rather than around ground. Below the boardwalks the mud shines and then disappears, twice a day, as the tide pushes back up the channels. The bay's high water lifts the Afuá, Charapucu, and Jurará rivers along with it. Nothing in this town was built on the assumption that the ground would stay put. The stilts are not a quirk of style; they are the design response to a floodplain that reclaims itself every year.

Afuá owns roughly one bicycle for every resident, and the traffic on those narrow plank streets is dense enough to feel choreographed. The bicitáxi is the workhorse — a cycle rickshaw with a canopied bench that seats up to three, ferrying shoppers, schoolchildren, and luggage from the port. Freight moves the same way, stacked and strapped to cargo frames. What a visitor notices first is not the absence of cars but the absence of the noise cars make: bicycle bells, conversation, the slap of sandals on wood, the diesel thrum of a boat somewhere out in the bay. The decision that produced all this was not originally ideological. There was simply nowhere on the island to put a car. What began as a constraint of geography hardened into an identity, and then into legislation.

The municipality sprawls across 8,373 square kilometers of the Amazon delta, most of it water and islands rather than town — Serraria Island is the largest of them. All of it falls inside the Marajó Archipelago Environmental Protection Area, a nearly 60,000-square-kilometer sustainable-use reserve established in 1989, and Afuá also contains the 65,181-hectare Charapucu State Park, strictly protected since 2010. Afuá belongs to the Marajó mesoregion and the microregion known as the Furos de Breves — furo being the local word for the narrow channels that thread between islands, and the only highways this region has ever had. Getting here is its own commitment: roughly 27 hours by boat from Belém. There is an airstrip in town, but the water regularly takes it back. When the seasonal floods come, families lift their furniture onto blocks and treat the rising water less as a disaster than as an appointment they have kept for generations.

Odimar Wanderley Salomão, mayor for years and universally called Mazinho, argued that his town was a template. "Afuá is an example for the Amazon and Brazil, and maybe for the world," he said, and in 2010 he turned down a tractor offered by the state governor, trading it for a riverboat instead. The net-zero framing has drawn international attention. It also sits uneasily beside how people actually live here. Afuá is not connected to Brazil's hydroelectric grid, so diesel generators keep the lights on. Fewer than three in ten residents have running water, sewage service, or garbage collection, and the town ranks 655th out of 772 Amazon municipalities on the Social Progress Index. A place can be genuinely low-carbon and genuinely underserved at the same time. Afuá is both, and the second fact is not a footnote to the first.