Three mangrove species anchor the lagoon's ecosystem. Black Mangrove, White Mangrove, and Buttonwood form dense thickets along the channel and the inner lagoon, their submerged root systems functioning as nurseries for reef fish and crustaceans that depend on the shelter those tangled roots provide. Above the waterline, the branches serve double duty as breeding colonies and roosting sites for migratory and resident birds alike. Ospreys circle the bay and plunge for fish, hitting the water with enough force to send spray glittering in the Caribbean sun. Sandpipers, egrets, and herons work the shallows at low tide, picking through the mud with surgical patience. The lagoon is divided into two connected bodies of water -- a channel open to the sea and a more sheltered inner lagoon -- and this dual structure creates a gradient of salinity and current that supports an unusually wide range of species for such a compact area. What looks like a single body of water is really two distinct habitats working in concert.

Beyond the mangroves, tidal mudflats extend inland, flooded daily by the rhythm of the Caribbean tide. Bird species congregate here during daylight hours to forage, but the mudflats' most charismatic residents are nocturnal. Aruban Burrowing Owls dig their nests into the drier sections of the flats, a subspecies found nowhere else on earth. During the rainy season, land crabs cross the exposed mud in search of water to deposit their eggs, their sideways march one of the stranger spectacles the lagoon offers. The mudflats connect to three dry river creeks, called rooi in the local Papiamento language. Rooi Bringamosa and Rooi Taki reach all the way to Arikok National Park on the island's northeastern coast. The third, Rooi Frances -- known in English as Frenchman's Pass -- carries water only after heavy rains, but its fertile soil and high water table support fruit trees, cottontail rabbits, dragonflies, and the Colombian Four-eyed Frog.

Walk northeast from the lagoon and the landscape shifts abruptly. Volcanic rock and sediment from the Aruba Lava Formation replace the soft mud, bringing with them a different cast of inhabitants: cacti standing in stiff columns against the dry sky, the critically endangered Aruban Rattlesnake coiled in the shade of boulders, and flocks of Brown-throated Parakeets chattering through the low scrub. This terrain belongs to the same geological formation that defines Arikok National Park further along the coast. Swing the other direction and limestone cliffs and terraces ring the lagoon on nearly every side, their dry, xeric surfaces dominated by aloe plants -- remnants of the plantations that once formed a cornerstone of the island's economy before tourism eclipsed everything else. Crested Caracaras perch on the cliff edges, scanning for prey with the focused stillness of raptors everywhere. The contrast is striking: within a few hundred meters, the landscape transitions from salt-soaked mangrove to volcanic desert to bleached limestone terrace. Few places this small contain this many geological chapters written in such different stone.

Spaans Lagoen sits halfway between Queen Beatrix International Airport and the town of San Nicolaas, which made it a natural corridor for road infrastructure. In 2016, the Green Corridor project built a bridge over the lagoon to improve access to San Nicolaas. Construction damaged a section of the mangrove forest -- an uncomfortable irony for a Ramsar-protected site. Engineers responded by creating an S-shaped canal designed to restore water flow and encourage mangrove regeneration. The intervention reflects a tension familiar across the Caribbean: small islands need development, but their most valuable ecosystems occupy precisely the land that development covets. Whether the S-canal succeeds as a long-term remedy remains to be seen. The mangroves, at least, have been growing back.