Islas del Queguay

The Islas del Queguay Habitat and Species Management Area is a protected area covering 8,327 hectares in the Paysandú Department of western Uruguay, formally established by governmental decree in August 2025. The reserve encompasses nine islands — Queguay Grande, Queguay Chica, San Miguel, San Francisco Grande, San Francisco Chica, Almirón, Sombrerito, Mellizas de Afuera, and Mellizas de Adentro — together with adjacent riverine areas at the confluence of the Río Queguay Grande with the Río Uruguay, which forms the international border between Uruguay and Argentina. The reserve protects an outstanding diversity of aquatic, riparian, and island habitats that support nearly 100 fish species and globally significant nesting colonies of migratory waterbirds. The ecological connectivity with the adjacent Montes del Queguay protected area creates an important conservation corridor in one of Uruguay's most biodiverse river systems.

The Islas del Queguay represents one of the most important nesting areas for colonial waterbirds in Uruguay, with the islands providing undisturbed breeding sites for black skimmers (rayadores), South American terns (gaviotines), and other migratory bird species that travel thousands of kilometres to breed in the Río Uruguay's island habitats. Resident bird species include the yellow cardinal (cardenal amarillo), a threatened species listed on the IUCN Red List, capuchinos (Sporophila finches), and the white-rumped monjita (viudita blanca grande). The Río Uruguay and its associated channels support approximately 100 fish species, with around 50 prioritised for conservation management, including freshwater stingrays and several species of annual killifish (peces anuales) that complete their entire life cycle within a single year in temporary pools. Capybaras are abundant on the islands and along the riverbanks, and river otters are also present in the waterways. The habitat heterogeneity — combining river channels, island forest, floodplain grassland, and wetland — drives the area's exceptional vertebrate diversity.

The vegetation of the Islas del Queguay reflects the transitional character of the Río Uruguay corridor, combining elements of the subtropical Atlantic Forest, the Espinal woodland of the Río de la Plata basin, and the gallery forests typical of large South American rivers. The islands support park-like forests (monte parque) in which native trees including tala (Celtis tala), coronilla, espinillo (Vachellia caven), sarandí blanco, and various willows and poplars create an open-canopied woodland with a grassy understorey. Dense riverine forests (monte ribereño) of willows, poplars, and ceibo trees fringe the water margins, providing nesting cover for colonial waterbirds and roosting sites for raptors. Shrubland communities occupy the drier interior areas of the larger islands. Rare plant species have been documented within the reserve through botanical assessments conducted in preparation for its protected area designation, and the floodplain grasslands support native meadow flora. Historical eucalyptus plantations established in the 19th and 20th centuries are present on some islands but are being gradually managed to allow native vegetation recovery.

The islands of the Islas del Queguay reserve are alluvial landforms deposited over millennia by the sediment-laden waters of the Río Uruguay and Río Queguay Grande. These flat to gently undulating landforms are composed of river gravels, sands, silts, and organic-rich soils accumulated as the rivers slowed and deposited their sediment load at the confluence zone. The Río Uruguay itself is one of the major rivers of South America, draining a large catchment across southern Brazil, northeastern Argentina, and northern Uruguay, and its sediment budget has shaped the island archipelago over thousands of years of fluvial geomorphic activity. The underlying bedrock of the Paysandú region consists of Precambrian basement rocks and Mesozoic sedimentary sequences, but these are deeply buried beneath the river alluvium and are not expressed at the surface within the island reserve. Seasonal flooding during the austral winter and spring reshapes island margins, deposits new sediment, and creates the dynamic floodplain mosaic of habitats that characterises the reserve.

The Islas del Queguay experiences a humid subtropical climate (Köppen Cfa) typical of western Uruguay, with warm, humid summers and mild winters. Average summer temperatures reach 28–30°C between December and February, while winter temperatures in June to August average 12–15°C, with frost possible on the clearest, coldest nights. Annual rainfall ranges from 1,100 to 1,300 mm, distributed fairly evenly across the year without a pronounced dry season, though late autumn and winter tend to be somewhat wetter. The Río Uruguay's seasonal flood pulse, driven by rainfall in the upper catchment in Brazil, creates an annual pattern of rising waters in winter and spring that inundates the lower islands and floodplains, triggering the biological productivity cycle that drives fish breeding and waterbird nesting. Summer drought periods can lower river levels significantly, temporarily exposing sandbanks and mudflats that provide additional foraging and nesting habitat for shorebirds and terns. Thunderstorms are frequent in summer, associated with Atlantic frontal systems tracking south across the Pampas.

The Río Uruguay and its islands have been inhabited since pre-Columbian times by indigenous groups including the Charrúa and Guaraní peoples, who exploited the river's abundant fish resources and the island forests for hunting and gathering. The Portuguese and Spanish colonial powers contested the Río Uruguay as a border zone, and the establishment of the town of Paysandú on the Uruguayan bank in the 18th century made the river one of the key frontiers of the colonial era in the Southern Cone. The islands of the Queguay system were used during the colonial and early independence period for charcoal production and timber harvesting, exploiting the native forests of tala, coronilla, and willows for fuel and construction material. Eucalyptus plantations were established on some islands during the 19th and 20th centuries as a commercial timber resource. Artisanal fishing has been practised by riverside communities for generations, exploiting the diverse fish fauna of the Queguay confluence. The city of Paysandú, one of Uruguay's major inland cities, lies across the river from the Argentine city of Colón, connected by an international bridge.

The conservation significance of the Islas del Queguay was championed for decades by the local Uruguayan NGO Gensa Paysandú, which worked to document the islands' biodiversity and raise awareness of the threats posed by unregulated use and habitat degradation. In 2018, the Seacology Foundation funded expert botanical and zoological assessments required to support the formal application for inclusion in Uruguay's National Protected Areas System (SNAP), providing the scientific basis for the reserve's designation. Warning signs were installed at waterbird nesting colonies, educational materials were developed for local schools, and community tour guides were trained in responsible wildlife observation practices as part of the pre-designation groundwork. The Uruguayan Ministry of Environment formally incorporated the Islas del Queguay into SNAP as a Habitat and Species Management Area by decree in August 2025, recognising the area's outstanding value for migratory waterbirds, threatened fish species, and the yellow cardinal. The reserve maintains ecological connectivity with the adjacent Montes del Queguay protected area, together forming a significant conservation complex in the Paysandú region.

The Islas del Queguay offers exceptional wildlife watching opportunities, particularly for waterbirds during the nesting season when black skimmer and tern colonies assemble on the island beaches and sandy margins. Boat-based exploration of the nine islands and their surrounding channels is the primary means of accessing the reserve, with local guides from Paysandú able to navigate the river system and locate nesting colonies while minimising disturbance. The yellow cardinal, a striking and increasingly rare bird of the subtropical woodlands, is a sought-after sighting for birdwatchers visiting the island forests. Fishing in the Río Uruguay and Queguay channels is a traditional activity, and the spectacular freshwater stingray is an unusual and memorable encounter for those exploring the riverine habitats. The forested island interiors provide pleasant walks through riparian woodland, with views across the broad Río Uruguay toward the Argentine bank. The nearby city of Paysandú offers cultural and historical attractions including the city's historic centre and the Basílica Catedral de Paysandú.

The Islas del Queguay is accessed by boat from Paysandú city, one of Uruguay's principal cities located on the Río Uruguay approximately 380 kilometres north of Montevideo. Paysandú is reached by Route 3 from Montevideo or via the international bridge from Colón, Argentina. Boat tours and fishing excursions depart from the Paysandú waterfront, with local operators and the NGO Gensa Paysandú providing guided visits for birdwatchers and ecotourists. Visitor facilities on the islands themselves are minimal — there are no permanent structures, accommodation, or food services — so day trips are the standard format. The Ministry of Environment's SNAP programme provides management oversight, and visitors should contact local conservation groups for the latest information on access arrangements and nesting colony locations. Paysandú city offers comprehensive accommodation, restaurants, and services. As a recently designated protected area, visitor infrastructure is still developing, and guided tours through knowledgeable local operators are the recommended approach.

The Islas del Queguay's designation as a Habitat and Species Management Area reflects its primary conservation purpose: protecting the critical breeding habitat of migratory waterbirds and the rich fish fauna of the Queguay-Uruguay confluence. Black skimmers, South American terns, and associated colonial nesting species depend on undisturbed island sites for reproductive success, and disturbance from unregulated boat traffic, dogs, and recreational use has historically threatened nesting colonies. The yellow cardinal, listed as Endangered by IUCN due to trapping for the cagebird trade and habitat loss, finds protected habitat within the reserve's island woodlands. Conservation of approximately 50 priority fish species, including endemic freshwater stingrays and annual killifish, requires maintaining the natural flood-pulse dynamics and water quality of the Río Uruguay. Ongoing threats include illegal fishing, poaching of capybaras, solid waste entering the river system from upstream sources, and pressure from unmanaged tourism. Community engagement programmes developed by Gensa Paysandú and the Ministry of Environment support local awareness and voluntary stewardship. The ecological corridor connecting Islas del Queguay with the Montes del Queguay protected area is being strengthened to maintain habitat connectivity for wide-ranging species across the Paysandú conservation landscape.