Wetlands are ecosystems saturated with water, either permanently or seasonally, providing numerous benefits from supporting diverse wildlife to regulating water cycles. Among the world’s various wetlands, one stands out as the largest tropical wetland: the Pantanal. This vast South American region holds global significance due to its immense scale and rich ecological characteristics.
Identifying the World’s Largest Tropical Wetland
The Pantanal is the world’s largest tropical wetland. It spans an immense area, estimated to be between 140,000 and 195,000 square kilometers (approximately 54,000 to 75,000 square miles). This vast floodplain is situated primarily within the Brazilian state of Mato Grosso do Sul, extending into parts of Mato Grosso, Bolivia, and Paraguay.
Its size is remarkable, covering an area larger than many countries, including England, Austria, Hungary, Greece, and Ireland combined. It is also more than 20 times the size of Florida’s Everglades wetland system.
A Haven of Biodiversity
The Pantanal is one of Earth’s most biologically rich environments. It is home to over 4,700 species of flora and fauna, including approximately 463 species of birds, 269 species of fish, 236 species of mammals, and 141 species of reptiles and amphibians. This life thrives due to the Pantanal’s diverse habitats, including savannas, grasslands, forests, and numerous rivers and lagoons.
The region is known for its wildlife. It boasts the world’s largest concentration of crocodilians, with an estimated 10 million caimans. The Pantanal also supports one of the largest and healthiest jaguar populations, as these large cats find ideal conditions for hunting prey like capybaras and tapirs. Other notable residents include giant river otters, marsh deer, tapirs, and the hyacinth macaw, the largest parrot in the world.
Seasonal flooding creates rich food sources and varied niches for these species. Aquatic vegetation thrives during the wet season, providing abundant food and breeding grounds for fish, birds, and mammals. As waters recede in the dry season, diverse microhabitats emerge, supporting a wide array of life and allowing animals to disperse and recolonize the landscape.
The Rhythmic Waters
The Pantanal’s landscape is shaped by an annual hydrological cycle of alternating wet and dry seasons. The rainy season occurs from October to April, during which rivers overflow their banks, transforming up to 80% of the floodplains into a vast inland sea. This inundation lasts for several months, with water depths ranging from a few centimeters to over 2 meters.
The Paraguay River basin is central to this cycle, with the Pantanal acting as a reservoir. Water from surrounding upland areas, known as the Planalto highlands, slowly drains into the sloped basin. The low gradient of the land, less than 1.5 cm per kilometer, contributes to the slow movement and extensive spread of water across the floodplain. This water retention and slow release into the Paraguay River help regulate downstream flow, delaying maximum flows to the Paraná River by up to six months and minimizing potential flooding in those areas.
As the dry season progresses from May to September, the floodwaters gradually recede. This process leaves behind moist valleys, depleted floodplains, and shallow lakes and rivers. The continuous interplay of flooding and receding waters not only dictates the rhythm of life for the region’s flora and fauna but also aids in nutrient cycling and groundwater recharge.
Pressures and Protection
The Pantanal faces increasing pressures from human activities. Deforestation and land use changes in the surrounding highlands contribute to increased sediment flow and water discharge into the lowlands, potentially altering flood dynamics. Agricultural expansion, particularly cattle ranching and soy cultivation, is a significant threat, with over 3,000 wildfires registered in the first half of 2024, mainly on private lands, representing a 22-fold increase compared to the same period the year before. Large-scale infrastructure projects, such as dams and waterways, further impact the region’s hydrological balance.
Climate change also poses a challenge, with the Pantanal experiencing its driest period in the last four decades since 2019. In the first four months of 2024, the average area covered by water during the flood season was smaller than that of the dry season in 2023, indicating an increasingly severe drought and a heightened risk of large wildfires.
In response to these threats, various conservation efforts are underway. The Pantanal has received international recognition, with parts designated as UNESCO World Heritage Sites and Ramsar Sites of International Importance. While only approximately 5% of the Pantanal is currently preserved in federal protected areas, initiatives are working to increase this coverage. Sustainable tourism is emerging as a protective force, offering economic incentives for landowners to preserve natural habitats rather than converting them for agriculture. These initiatives also support scientific research, wildlife monitoring, and empower local communities to participate in conservation efforts, balancing economic needs with environmental protection.