The team faces its greatest challenge yet - exploring the 90-metre-deep trench of the legendary Rio Negro. Using an underwater robot to examine the depths proves trickier than anticipated when a storm brews, and as the machine struggles, Mike deGruy heads for the jungle in search of the three-toed sloth. He eventually ventures into the water - only to come face to face with a predatory fish determined to make him its next meal. First shown in 2005
Join Mike de Gruy, Kate Humble and an international team of scientists and divers in search of some of the Amazon's most incredible creatures. The awesome Amazon is wider and deeper at some points than the English Channel, flowing 6,500km across South America. It's famous for the surrounding rainforest, which can take visitors by surprise because it is not all thick tropical jungle. Watch what dive cameraman, Mike de Gruy, thought after his first trip to the river for the Amazon Abyss expedition.
The waters too are home to incredible creatures. Here are some of the most amazing featured in the programmes.
Giant otter Pteronura brasiliensis
The Amazon's rarest large mammal now lives only in the most remote parts of the region. It's an intelligent, social animal and at 1.8m long when fully grown, is one of the top predators of the region's freshwater fish. Partial to shellfish and crabs, the giant otter carries a favourite rock around to help it break open shells. The world's biggest species of otter faces very high risk of extinction, according to the World Conservation Union (the IUCN). No longer hunted for its fur, the giant otter's survival now depends on protection of the areas in which it lives from destruction and pollution.
Boto (Amazon river dolphin)
This is the largest species of freshwater dolphin. Some people think the boto can stun prey with a burst of sound, produced in its distinctively bulbous forehead. The dolphin's body colour changes through its lifetime. Beginning dark grey, it turns pale or vivid pink before fading almost to white. The neck bones are more flexible than in most other dolphins, so it can move its head independently of its body. This helps with echolocation in the murky Amazon waters.
Other adaptations for river life include sharp hearing and a long beak. Distinctive whisker-like hairs around the mouth aid foraging for food in mud.
Green anaconda Eunectus marinus
This is the world's largest snake and can grow to 10m long and 130kg in weight. It hunts birds, reptiles and mammals in and out of water. The snake coils around its prey, crushing it until it can no longer breathe. There are reports of anacondas eating people. The anaconda doesn't need to feed very often though – perhaps not for three months after a sizeable kill. Unusually for a snake, the anaconda does not lay eggs; females give birth to live young. It is not officially registered as threatened, but it is protected by CITES, the Convention on International Trade in Endangered Species.
Thirty-four varieties of catfish make up the Siluriformes order of ray-finned fish. The Amazon is home to incredible catfish with specialisms to help them survive the tough conditions.
# Wood eating
Panaque fish have spoon-shaped teeth which they use to rasp at submerged wood. Bacteria in their guts convert plant cellulose into nutritious chemicals.
# Air breathing
The water in slow-moving parts of the Amazon river system is often low in the dissolved oxygen that fish need. Some types of catfish supplement the oxygen their gills absorb by swallowing air and breathing with their intestines.
# Land living
The phraetobius catfish has taken air-breathing to an extreme. It lives out of water, in the leaf litter on stream banks. Blood vessels all over its skin mean its entire body is capable of gaseous exchange. It has no eyes and uses touch to detect its insect prey.
# Fisherman frightening
The jaú (Paulicea lutkeni) is notorious among native people. It grows to 1.5m and can weigh over 100kg. Immense strength gives rise to its reputation for dragging fishermen down into the depths.
In the murky river waters of the Amazon basin, sight and smell can be of limited value. Some fish have turned to using electricity instead.
The blind tubesnout lives in deep water, 30m or so down. It uses low voltages to sense its surroundings.
Finding a mate is made easier for the glass knifefish, Gymnotus rosamaria, by its ability to send electrical advertisements to potential partners. At 30–45cm in length when fully grown, the long, thin shape and transparency of this fish is reflected in its name.
The electric eel, Electrophorus electricus, is not a true eel: it has no teeth and doesn't migrate out to sea. It uses electric fields of up to 500 volts to kill prey. Up to 2.5m long and 35kg in weight, the eel breathes air, as the waters it lives in are often low in oxygen.
Candirus are parasitic fish known to feed on other fish and mammals.