The park is barely there, geographically speaking, and that is its genius. It stretches some thirty-five kilometers along the Atlantic shore but averages only about a kilometer wide, a thin band caught between two parallel lines of dunes. At its heart lies the Lagoa do Peixe, the Fish Lagoon that gives the park its name, a long, narrow body of water that opens to the sea. The land never rises far, reaching only seventeen meters at its highest. Across its 36,721 hectares the park braids together salt marsh and freshwater lagoon, sandy fields and flood plain, with two freshwater lagoons, Veiana and Pai João, in the north and saline waters elsewhere. This patchwork of habitats, perched right on the ocean's edge, is precisely what makes it irresistible to birds.

Twice a year the sky fills. Lagoa do Peixe sits on one of the planet's great migratory flyways, a resting place for birds traveling between Patagonia in the far south and breeding grounds as distant as the United States and the Arctic. The cast of travelers is extraordinary: red knots and sanderlings, common terns and royal terns, white-rumped sandpipers, two-banded plovers, the tawny-throated dotterel, the rufous-chested plover. They arrive exhausted, gorge on the lagoon's invertebrate riches, and lift off again to complete journeys of thousands of kilometers. To lose a link like this in the chain would be to break the migration itself. That is why protecting one slim ribbon of Brazilian coast matters far beyond its borders.

Among the seasonal travelers, two species stand out in color and in significance. Both the Chilean flamingo and the rarer Andean flamingo visit these waters, and Lagoa do Peixe holds a distinction found nowhere else in the country: it is home to Brazil's only resident population of Chilean flamingos. Their numbers swell through the cooler months of winter and spring and thin in the austral summer, but the lagoon remains their stronghold. To see them is to watch hundreds of long-legged shapes standing in shallow brackish water, the flat coastal light catching their plumage, an unexpected splash of pink against the muted dunes of southern Brazil.

The world has recognized what Lagoa do Peixe protects. In April 1991 it was named an International Reserve of the Western Hemisphere Shorebird Reserve Network, joining a continent-spanning chain of refuges. In May 1993 it became Ramsar Site number 603, registered under the global convention on wetlands of international importance, and in 1999 it was folded into the Atlantic Forest Biosphere Reserve. The Chico Mendes Institute for Biodiversity Conservation administers it as a strict national park. Beyond the birds, the dunes shelter the tuco-tuco, a burrowing rodent endemic to the coastal dunes of Rio Grande do Sul, while protected predators like the cinereous harrier patrol the marshes. It is a small park with an outsized job: keeping open a doorway that countless wings depend on.