The largest wetland system on Earth is the West Siberian Lowland in Russia, blanketing roughly 2.7 million square kilometres of boreal peat bog. Among tropical wetlands, the Pantanal of South America is the biggest, spreading across 150,000 to 195,000 square kilometres of Brazil, Bolivia, and Paraguay. These waterlogged wildernesses — swamps, marshes, bogs, and floodplains — cover only about 6% of the planet's land yet rank among its most productive and carbon-rich ecosystems.
Wetlands are places where water sits at or near the soil surface for all or part of the year. That simple condition produces some of the most life-filled landscapes on Earth, from peat bogs that lock away ancient carbon to seasonally flooded grasslands teeming with jaguars, caimans, and migratory birds. Below is a complete guide to the world's largest and most important wetland systems, ranked and explained.
What Counts as a Wetland?
Not every soggy patch of ground is a wetland in the scientific sense. Ecologists define wetlands by three features: the presence of water at or near the surface, soils that develop under waterlogged conditions, and vegetation adapted to wet ground. Within that definition lie several distinct types:
- Swamps: Wetlands dominated by trees and woody shrubs, such as mangroves and cypress forests.
- Marshes: Treeless wetlands ruled by grasses, reeds, and sedges.
- Bogs: Waterlogged, acidic systems where dead plants accumulate as peat instead of decaying.
- Floodplains and deltas: Low-lying land along rivers that floods seasonally, depositing nutrient-rich sediment.
The 1971 Ramsar Convention, the international treaty for wetland protection, recognises more than 2,500 "Wetlands of International Importance" worldwide — proof of how seriously scientists and governments take these ecosystems.
1. West Siberian Lowland, Russia
- Area: ~2,745,000 km²
- Type: Boreal wetland and peatland
- Carbon: Stores roughly 70 billion tonnes of CO2
The West Siberian Lowland is the single largest wetland system on Earth, stretching between the Ural Mountains and the Yenisei River. It holds the world's most extensive peat bogs, accumulated over thousands of years in a cold climate where plant material decays too slowly to break down. The result is an immense carbon vault. Climate change is now thawing these peatlands, and scientists warn that their decomposition could release billions of tonnes of greenhouse gases, accelerating warming further.
2. Pantanal, South America
- Area: ~150,000-195,000 km²
- Countries: Brazil, Bolivia, Paraguay
- Flooding: Up to 80% floods during the wet season
The Pantanal is the largest tropical wetland in the world. Each wet season, rains swell the upper Paraguay River and flood as much as 80% of the basin, turning grasslands into a vast shallow sea. As the waters recede, they leave behind nutrient-rich mud that fuels an explosion of life. The Pantanal hosts the highest concentration of wildlife in South America, including jaguars, giant otters, capybaras, and the spectacular blue hyacinth macaw — and it has more jaguars per square kilometre than any other habitat on Earth.
3. Llanos, South America
The Llanos is a sweeping tropical grassland drained by the Orinoco River system. During the rainy months it floods extensively, transforming into a patchwork of marshes and shallow lakes before drying out again in the dry season. This dramatic wet-dry cycle supports enormous populations of capybara, green anacondas, spectacled caimans, and waterbirds such as the scarlet ibis, making the Llanos one of the great seasonal wetlands of the Americas.
4. Congo Swamp Forests
- Area: ~190,000 km²
- Type: Tropical peatland
- Carbon: ~30 billion tonnes
Hidden in the heart of the Congo Basin lies the world's largest tropical peatland, the Cuvette Centrale. Remarkably, scientists only confirmed its full extent in 2017. Beneath its swamp forests sits peat several metres deep, holding roughly 30 billion tonnes of carbon — as much as 20 years of total United States fossil fuel emissions. Keeping this peat waterlogged and undisturbed is one of the quiet priorities of global climate policy.
5. Sudd, South Sudan
- Area: ~30,000-130,000 km² (seasonal)
- River: White Nile
- Type: Freshwater swamp
The Sudd is one of the largest freshwater swamps on the planet, fed by the White Nile as it spreads across the flat clay plains of South Sudan. Its area balloons and shrinks dramatically between wet and dry seasons. So much water spreads out and evaporates here that the Sudd cuts the White Nile's downstream flow by roughly half — a loss that has tempted engineers for a century, though the swamp's ecological importance has kept it largely intact.
6. Vasyugan Swamp, Russia
- Area: ~53,000 km²
- Type: Peat bog
- Age: ~10,000 years
Lying within the West Siberian Lowland but distinct enough to count on its own, the Vasyugan Swamp is among the largest peat bogs in the world. It began forming around 10,000 years ago, at the close of the last Ice Age, and continues to grow today — expanding by roughly half a percent each year as smaller bogs merge. It stores billions of tonnes of carbon and supplies fresh water to much of western Siberia.
7. Okavango Delta, Botswana
- Area: ~20,000 km²
- Type: Inland delta and wetland
- UNESCO: World Heritage Site
The Okavango Delta is one of nature's great paradoxes: a lush, water-laced delta that floods in the middle of the arid Kalahari. Unlike most deltas, it never reaches the sea — its water evaporates or is swallowed by desert sand. The annual flood, born of rains far away in the Angolan highlands, takes about four months to travel down into Botswana, arriving in the dry season just when wildlife needs it most. Elephants, hippos, lions, and vast flocks of birds converge on this oasis, which UNESCO named a World Heritage Site in 2014.
8. Everglades, United States
- Area: ~12,000 km²
- Type: Subtropical wetland
- Nickname: "River of Grass"
The Everglades is a vast, almost imperceptibly slow-moving sheet of water that drains southern Florida — famously described as a "river of grass" rather than a true swamp. Sawgrass marshes, mangrove forests, and cypress stands shelter an extraordinary mix of species, and it remains the only place on Earth where wild alligators and crocodiles live side by side. Decades of drainage for farms and cities shrank the system dramatically, prompting one of the world's most ambitious wetland restoration projects.
Why Wetlands Matter
Wetlands punch far above their weight ecologically. They filter pollutants from water, buffer coastlines and river valleys against floods, recharge groundwater, and serve as nurseries for fish and breeding grounds for birds. Crucially, they are powerful carbon stores: although wetlands cover only about 6% of the land surface, their waterlogged, oxygen-poor soils trap an estimated 30% of all terrestrial carbon. When drained, they flip from carbon sinks to carbon sources, which is why their protection is now central to fighting climate change.
Key Facts
- Largest wetland overall: West Siberian Lowland, Russia (~2.7 million km²)
- Largest tropical wetland: Pantanal, South America (~150,000-195,000 km²)
- Largest tropical peatland: Congo Basin Cuvette Centrale (~190,000 km²)
- Carbon storage: Wetlands cover 6% of Earth but hold about 30% of terrestrial carbon
- Unique delta: The Okavango floods the Kalahari Desert and never reaches the sea
- Hidden giant: The Congo peatlands' full extent was only confirmed in 2017
- Protection: Over 2,500 sites are listed under the Ramsar Convention worldwide
Frequently Asked Questions
What is the largest wetland in the world?
The West Siberian Lowland in Russia is the largest wetland system on Earth, covering roughly 2.7 million square kilometres. Its vast peat bogs store about 70 billion tonnes of carbon, making it both an ecological giant and a key player in the global climate system.
What is the difference between a swamp and a marsh?
The main difference is vegetation. Swamps are dominated by trees and woody shrubs, such as cypress or mangroves, while marshes are treeless and ruled by grasses, reeds, and sedges. Both are types of wetland with water at or near the soil surface.
Why are wetlands important for the climate?
Wetlands store enormous amounts of carbon in their waterlogged soils — about 30% of all carbon held in land ecosystems, despite covering only 6% of the planet's surface. They also filter water, control floods, and provide habitat for huge numbers of species. When drained, they release stored carbon, so protecting them helps limit climate change.
Which wetland has the most wildlife?
The Pantanal in South America has the highest concentration of wildlife in the Americas, including the densest jaguar population on Earth, alongside giant otters, capybaras, caimans, and hyacinth macaws. Africa's Okavango Delta and the Llanos of Venezuela and Colombia are similarly rich in animal life.