Lagoa do Açu

Lagoa do Açu State Park protects a significant coastal lagoon system and associated restinga and wetland ecosystems on the northern coast of Rio de Janeiro state, between the municipalities of São João da Barra and Campos dos Goytacazes. Created on March 20, 2012 by State Decree No. 43,522, the park covers 8,251 hectares and encompasses the Lagoa do Açu—a coastal lagoon 13 km in length—alongside the Banhado da Boa Vista wetland and sections of the Lagoa Salgada. ^[1] The surrounding restinga vegetation, freshwater marshes, and transitional coastal habitats support considerable biodiversity adapted to the dynamic coastal zone. The park's establishment was driven by the need to protect this important wetland system from agricultural conversion, drainage for industrial development, and recreational encroachment. The area plays important roles in coastal hydrology, fisheries productivity, and migratory bird movements along the South American Atlantic coast.

Lagoa do Açu is an important wetland for waterbirds along the Atlantic coast of Brazil, with over 500 bird species documented in the region—130 of which are listed as threatened. ^[1] The lagoon supports large populations of herons, egrets, ibises, and shorebirds throughout the year, with migratory species including sandpipers and lesser yellowlegs making the lagoon a stopover point. The lagoon's fish community supports populations of snook, mullet, and tarpon that sustain recreational and artisanal fishing in the region. Caimans inhabit the freshwater sections of the lagoon and adjacent marshes. The restinga scrubland bordering the lagoon provides nesting habitat for restinga-endemic lizards and colonial waterbirds. The aquatic invertebrate community, including diverse crustaceans and mollusks, supports the productivity of the entire wetland food web.

The vegetation of Lagoa do Açu State Park is dominated by the coastal wetland and restinga plant communities characteristic of the northern Rio de Janeiro lowland coastal plain. Restinga scrubland covers the sandy substrates surrounding the lagoon, with native species adapted to nutrient-poor, well-drained sandy soils and salt-laden coastal winds, including clúsia, pitangueira (Eugenia uniflora), araçá, aroeira (Schinus terebinthifolia), bromeliads, and orchids. ^[1] Freshwater marsh vegetation borders the lagoon shallows, with bulrushes (Typha, locally known as taboa), sedges, and water lilies (Nymphaea) forming extensive beds that provide habitat for aquatic birds and fish. Mangrove patches occur where saltwater influence from the coastal inlet penetrates the lagoon system. The botanical collection includes aquatic macrophytes that regulate nutrient dynamics in the lagoon water column.

Lagoa do Açu occupies a coastal plain composed of Quaternary sedimentary deposits—sands, silts, and organic material—accumulated over thousands of years as sea levels fluctuated with glacial cycles and the coastline migrated. ^[1] The lagoon itself formed as a coastal depression isolated from the sea by the accumulation of barrier beach ridges (restingas) built by longshore drift and wave deposition. The alternating sand ridges and intervening swales that characterize the northern Rio de Janeiro coastal plain create the topographic framework within which the lagoon system sits. The underlying Precambrian crystalline basement lies at depth below the thick sedimentary sequence of the coastal plain. The active coastal geomorphology of the barrier beach and lagoon system means that the park's physical landscape continues to evolve in response to storm events, sea level change, and modified sediment budgets.

The northern coast of Rio de Janeiro state experiences a tropical climate (Köppen Aw to Am) with a moderately distinct dry season from June to September and a wet season from October to May when orographic rainfall from the Serra do Mar lifts moist South Atlantic air masses. Annual rainfall in the coastal lowlands ranges from 1,000 to 1,400 mm. ^[1] Temperatures are tropical throughout the year, averaging 23–27°C, with only modest seasonal variation. The coastal position moderates summer heat and winter cold relative to the interior, with sea breezes providing relief during the hotter months. The lagoon and wetland system is sensitive to rainfall variability, with high rainfall years producing expanded wetland areas, while drier years can lower lagoon water levels and concentrate aquatic wildlife in the remaining water bodies.

The Lagoa do Açu area has been inhabited since pre-colonial times by indigenous coastal peoples who exploited the lagoon's fish and shellfish resources, as evidenced by shell middens (sambaquis) found in the archaeological record of the northern Rio de Janeiro coastal plain. ^[1] Portuguese colonization established agricultural settlements in the region from the seventeenth century, with sugarcane cultivation dominating the coastal lowlands of the Campos dos Goytacazes area—one of the most important sugar-producing regions of colonial Brazil. The lagoon and associated wetlands were exploited for fish, hunting, and agricultural irrigation. The twentieth century brought increasing pressure from sugar agribusiness, then from petroleum industry infrastructure—the Port of Açu, one of Brazil's largest private ports, was constructed immediately adjacent to the park area, profoundly affecting the surrounding landscape.

Lagoa do Açu State Park was established by State Decree No. 43,522 of March 20, 2012, to protect the lagoon system and associated coastal habitats from escalating development pressures in the northern coastal zone, particularly from the Port of Açu complex and the broader Campos Basin petroleum industry infrastructure. ^[1] The park's establishment was contentious given the proximity of large-scale industrial development and competing interests in land use for the coastal zone. Environmental impact assessments associated with the Port of Açu development contributed to defining the conservation values at stake. Management has since focused on monitoring the ecological health of the lagoon in relation to surrounding industrial activities and maintaining the integrity of restinga and wetland habitats within the park boundary. In 2022, the park celebrated its tenth anniversary, with management coordination led by the Universidade Estadual do Norte Fluminense (UENF). ^[2]

Lagoa do Açu State Park's principal attractions center on the lagoon and wetland environment and the exceptional birdwatching opportunities it provides. ^[1] The lagoon shallows are accessible by boat for guided birdwatching excursions, with dawn and dusk offering the best opportunities to observe large aggregations of herons, egrets, and migratory shorebirds. Observation platforms positioned along the lagoon margin provide terrestrial viewpoints over the wetland habitats. The restinga vegetation trails offer botanical interest and the opportunity to observe lizards, small mammals, and the nesting activities of colonial birds in the scrubland habitat. Artisanal fishing culture is evident in the communities bordering the park, and visits to working fishing villages provide insight into the traditional use of the lagoon's resources.

Lagoa do Açu State Park is accessible from the city of Campos dos Goytacazes, approximately 50 km to the south via BR-356 and coastal access roads, or from São João da Barra to the north. ^[1] Regular bus services connect these municipalities to Rio de Janeiro city, approximately 300 km to the south via BR-101. The park entrance provides basic visitor orientation facilities, and guided visits by boat and on foot can be arranged through the park administration. Accommodation options are available in Campos dos Goytacazes and São João da Barra. The park can be combined with visits to other natural features of the northern Rio de Janeiro coastal zone.

Conservation at Lagoa do Açu State Park operates in the challenging context of one of Brazil's most active industrial development zones, requiring vigilant monitoring of water quality, sediment dynamics, and wildlife populations in relation to activities at the Port of Açu and surrounding petroleum industry infrastructure. ^[1] Water quality monitoring tracks parameters including salinity, nutrients, and potential industrial contaminants that could affect the lagoon's ecological function and fisheries productivity. Shorebird and waterbird monitoring contributes data to the broader South American Atlantic coast conservation network, tracking population trends of migratory species that depend on the lagoon as a critical stopover and wintering site. Restinga restoration in disturbed areas within the park boundary uses native species propagated at the park nursery. Engagement with fishing communities through participatory management approaches ensures that traditional artisanal fishing knowledge informs management decisions.