Marshes, mires, swamps, wetlands, bogs, fens; there are many words for the intriguing places where land and water mix until the two become inseparable.
These last great wildernesses still mystify humans but such watery worlds create some of the most complex and vibrant ecosystems on earth.
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Rich in food, they provide shelter and spawning grounds for fish and amphibians, and fuelling stations for migrating mammals and birds. But, for humans, they are hard to navigate, with sinuous, ever-changing channels and treacherous mud. It is not a natural home for us and can be life-threatening: from diseases and myriad biting insects to large, dangerous predatory animals.
Deadliest swamps on the planet
Everglades
Covering 8100 sq km, the Everglades is an immense area of flooded grassland in Florida, US. It is described as a slow-moving 'river of grass' and encompasses sawgrass marshes, pine flatwoods and vast areas of coastal mangroves.
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It is home to hundreds of animals including 350 species of birds such as the roseate spoonbill and the endangered snail kite. Other star attractions include snapping turtles, manatees on the coast and the super-rare Florida panther, a subspecies of mountain lion of which just 100 individuals survive.
For humans, the biggest dangers are getting lost or drowning in this wild and beautiful place. However, there are several creatures to be wary of – not least the venomous eastern diamondback rattlesnake and the cottonmouth snake, though very few people are bitten and fewer still become ill. More threatening are the American crocodiles and American alligators that live here – though numbers have declined due to human persecution and habitat loss.
The crocodiles are mostly found in saltwater, preferring the coastal mangrove swamps. Alligators are more likely to be encountered as they inhabit deeper channels of freshwater (called sloughs) but move out onto the wet prairies to dig holes for their nests. Since WW2, there have been about 30 fatalities due to alligator attacks in the Everglades.
Okavango Delta
This extraordinary place is the world's largest inland delta where, instead of flowing to the sea, the Okavango River and its tributaries drain into a great shallow basin in the Kalahari Desert of Botswana. Seasonally, up to 15000sq km of land floods to become a huge marshland, though much of the water eventually evaporates during the drier seasons.
But when there is water, the region teems with extraordinary life – over 70 species of fish can be found in the waters and 400 bird species have been recorded here. Meanwhile, herds of elephants and grazing herbivores including giraffes, plains zebras and white rhinos enjoy the fresh grass growth and are followed by predators such as lions, hyenas, wild dogs and leopards. The most abundant large animal is the lechwe – some 90000 of these antelopes may gather in the delta.
Visiting humans are most at risk if they stray on to the water. Hippos and crocodiles have been known to capsize boats and even kill the occupants. On land, lions and territorial elephants can pose a danger.
But the biggest threat to life in the region are diseases carried by insects. Malaria is spread by mosquitoes that breed in the floodwaters while sleeping sickness (a paralysing illness known as trypanosomiasis) is caused by a parasite spread by the tiny tsetse fly.
The Great Vasyugan Mire
The true definition of a swamp is a wooded wetland and, at 53000sq km and growing, this is the largest swamp in the Northern Hemisphere. Located in Central Russia, it accounts for two per cent of the world's peat bogs.
The swamp comprises wetlands, lakes, wet forest and is threaded by rivers, notably the Ob and the Irtysh. During the short, hot summers, the wetlands produce a phenomenal biomass of insects, which attract insect-eating bird species but also dozens of Odonata species (dragonflies) that catch mosquitoes and flies on the wing. There are also immense populations of rodents, including mice, voles and squirrels.
Larger animals such as elk, lynx and sable are common here but the one to watch out for is the brown bear, which is numerous due to abundant berries, fish and small mammals that it eats. There have been over 300 documented brown bear attacks on humans in Russia over the past 80 years.
Perhaps more dangerous are the numerous tick species that thrive here and happily attach themselves to passing humans, drinking blood and passing on serious pathogens such as Lyme's Disease. And worse still are the long, unrelenting winters here where temperatures drop to an inhospitable -20°C.
Pantanal
South America's Kingdom of Water is the world's largest tropical wetland and covers 171,000 sq km of Brazil, Bolivia and Paraguay. From October to March, floodwaters fill the Pantanal like a giant reservoir and it becomes a network swamps, flooded savannahs and forests - as vital to the biodiversity of South America as the great Amazonian rainforest to the north.
These waters drain out slowly between April and September. Home to 650 species of birds, including rare hyacinth macaws, as well as giant otters, tapirs and the world's greatest concentrations of South America's big cat, the jaguar, it is a region under threat.
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Climate change has altered the Pantanal's river systems and some waterways are silting up. Meanwhile forest fires, unheard of until recently, turned vast areas to ashes in 2020 with a loss of 17 million vertebrates.
And these natural threats are the biggest dangers to human visitors (an estimate one million people visit every year). On the wildlife side, there have been occasional isolated jaguar attacks on people but more are affected by spider or snake bites or stings from scorpions.
The World Wildlife Fund estimates there are 10 million black caimans – a species of crocodile – living in the Pantanal. Swimming is inadvisable.
Al-Sudd (The Sudd)
As the young White Nile and various tributaries meander across the flat plains of southern Sudan, they seasonally overflow their banks creating a wetland area 57,000sq km. It is called Al-Sudd and is one of the world's largest but least-known freshwater systems.
Tall papyrus, water hyacinth and aquatic grass slow the flow, creating a myriad of channels, lagoons and dead-ends – and making the rivers un-navigable. In some areas, trees have established, creating true swamp woodland.
Thousands of buffalos and antelopes – including the endemic Nile lechwe, white-eared kob and tiang (topi) – make seasonal journeys through the region. Millions of birds either breed here or stop off on migration, including the great white pelican and the black tern.
Most striking is the shoebill, a species of stork with an enormous bill that it uses to scoop up amphibians and small mammals. The Sudd is also home to important numbers of African elephants and abundant fish populations.
Al-Sudd has become home to hundreds of thousands of human refugees fleeing conflict in this war-torn country. The growing human population puts pressure on the natural resources and comes into conflict with larger, more dangerous mammals such as Nile crocodiles, elephants and hippos. But as ever in sub tropical regions, malaria spread by swamp-loving mosquitos is the biggest threat to life.
Atchafalaya Basin
This unique habitat of forested wetland in the old floodplain of the Mississippi River witnesses the mixing of fresh and sea water, creating a brackish estuary covering 5700 sq km of southern Louisiana. It is the largest river swamp in the USA, far bigger than the Everglades.
Some 70 per cent of the area is known as cyprus-tupelo – a blend of bald cypress and various tupelo tree species that create a complex habitat rich in biodiversity. The swamp is best characterised by the cyprus trees with their wide buttressed trunks and feathery canopies festooned with Spanish moss.
The murky waters around the trees' feet are home to over 100 species of fish including catfish, which attract an unusually dense concentration of breeding bald eagles as well as other fish hunters such as pelicans, herons and egrets. Meanwhile, healthy populations of beavers, otters and muskrats ply the waterways.
The swamp's rivers and deep muds are treacherous and hard to navigate and sudden floods can take the unwary by surprise. With a thriving population of alligators, black bears and venomous copperhead and cottonmouth snakes, the Atchafalaya is no place to explore without local guides. But the greatest threat is from habitat destruction and pollution caused by human actions.
Congo's Swamp Forests
The world's second largest tropical rainforest after the Amazon, the Congo is a mosaic of swamp and forest twice the size of Alaska and said to hold one in five of Earth's living species.
The Western and Eastern Congolian Swamp Forests, which flood seasonally, cover 130000sq km along the banks of the Congo river and its tributaries and are among the least explored terrestrial habitats on the planet, being exceptionally difficult to penetrate.
Comprising dense close canopy broad-leaved evergreens and raphia palms, they are most famously home to western lowland gorillas, bonobos, African forest elephants and numerous monkey species.
There are also enduring stories of mokele-mbembe, a water-dwelling dinosaur-type creature, hiding out in the waters of Lake Tele and its surrounding forest. As logging continues to eat away at the forest and poaching remains a menace, local people are coming into contact more with large unfamiliar forest animals and this may be source of recent stories of 'monsters' in the forest.
The greatest danger of visiting the swamp forest (after getting lost), is contracting a disease. Ebola, malaria, measles, tuberculosis and monkeypox are endemic in the scattered human populations of the region.
Asmat Swamp
Called the biggest river swamp in the world, Asmat Swamp in Indonesia's Southern Papua province may cover as much as 31000 sq km. Dominated by mangrove forest where it meets the Arafura Sea, the swamp is more diverse further inland – comprising wet grassland, forest and threaded by many rivers.
Still relatively isolated from the modern world and only accessible by boat, the swamp is home to a vast range of fish, invertebrates, reptiles and amphibians and it is thought there are many species still to be discovered. Orchids abound here and the canopies echo to the calls of parrots, cockatoos and birds of paradise.
One notable predator is the crocodile monitor, one of the longest lizards on Earth, which hunts in the coastal forests, catching birds, mammals and other reptiles. It is harmless to humans however. Meanwhile, mammal inhabitants include marsupials such as tree kangaroos, and a monotreme (an egg-laying mammal) known as the long-beaked echidna.
The biggest danger in the Asmat Swamp is getting lost or ill. The region is sparsely settled – by the Asmat people – and so help is very far away if you need it. Beyond that, there are the usual dangers of malaria and other diseases. Highly venomous sea snakes can be found among the mangroves.
Polesia
Europe's largest wetland – and one of the world's largest – can be found in Belarus, Ukraine and parts of Poland. Also known as Pripyat Marshes, this 175000 sq km region focuses on the river Pripyat, one of the last great rivers of Europe not to be straightened, diverted or canalised. Instead, its countless meanders and tributaries form naturally and have created a labyrinth of pools, lakes, islands, marshes and flooded forests.
Millions of migratory birds pass through here each year and millions more stay to breed, including declining species such as the greater spotted eagle and Eurasian curlew. It is a vital spawning ground for the beleagured European eel. There are also lynx, European bison, mink and otters as well as wolves and brown bears.
Though populations of these predators are at good levels and visitors should always be cautious, they are mostly shy and encounters are rare. The greatest danger to human visitors is the Chernobyl Exclusion Zone around the nuclear power station that exploded back in 1985 and still emits dangerous radiation. Therefore humans have largely abandoned much of this wilderness. Although wildlife is also affected by radiation, the lack of human exploitation has meant that populations of many species are thriving.
Amazon Wetlands
The largest area of wetland in the world covering over two million sq km, the Amazon wetlands comprise a vast network of seasonally and tidally flooded forest, flood plains and deep peat swamps dominated by the aguaje palm.
This extraordinary ecosystem houses at least 10 per cent of the world's biodiversity and large areas are still little explored. That said, industrial logging and clearance for farming has meant that nearly 20 per cent of the entire Amazon basin forest has been lost in the last 50 years. There are still thought to be 390 billion trees in the entire Amazon region.
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Countless invertebrates, birds, reptiles and amphibians inhabit the watery forests including many species found nowhere else. Of larger mammals, tapirs, jaguars and giant otters are still relatively common. More dangerous to humans are the largest local predator, the black caiman, a species of crocodile.
The Amazon is also famous for the anaconda, a snake up to 6m long that kills prey through constriction. Though capable of killing and eating a human, there a no documented cases of this occurring. The biggest threat to humans in the Amazon swamp is the deep water, the seemingly bottomless mud and diseases contracted from tiny mosquitos...
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