The Amazon river dolphin: size, range and the river it lives in

Ask what the pink dolphins in the Amazon are and the answer is a single animal, the boto, Inia geoffrensis. The IUCN gives it the English names Amazon River Dolphin and Pink Dolphin, while in Brazil it goes by boto-vermelho, boto-cor-de-rosa, boto da Amazônia or plain boto.^6,7 It is the largest of the river dolphins, a true dolphin of fresh water, and it lives its whole life in rivers, lakes and flooded forest rather than in the sea.⁸

The Amazon basin is home to 2 dolphins that look and behave very differently. Besides the boto there is the smaller tucuxi, a grey dolphin of the same rivers that reaches about 1.5 m and nearly 60 kg.^9,10 Keep the pair apart by size and colour: the boto is the bigger, pinker animal and the tucuxi the smaller, greyer animal. If you see a pink back with a long snout and a low ridge instead of a tall fin, you are looking at a boto. A small grey dolphin that leaps clear of the water is usually a tucuxi.

Scientists still argue about how many species the boto group holds. ICMBio recognises 3 subspecies, spread over the Orinoco basin, the Amazon basin and the Bolivian rivers above the Madeira rapids, while the IUCN assessment follows a list with a single species and 2 subspecies and notes a separate species described from the Araguaia and Tocantins rivers.^11,12 For a traveller this means the dolphin of Manaus is the Amazon-basin form, which the Brazilian assessment calls Inia geoffrensis geoffrensis.¹¹

The boto's body is designed for tight spaces, and each feature has a job in a river full of obstacles. The 7 neck vertebrae are not fused, which lets the head move in every direction, and the gaps between the other vertebrae make the whole body unusually flexible for a dolphin.²¹ That flexibility matters when the river floods the forest and an animal has to weave between roots and trunks in search of fish.¹⁴ Its dorsal fin is a long, low ridge shaped like a boat keel, which also helps it slip under branches.²²

The teeth tell a feeding story. Each half of the lower jaw holds 28 teeth of 2 kinds, 10 pairs shaped like molars at the rear and 18 pairs of big cones at the front.⁵ A mouth with both sharp and crushing teeth can handle fish of different shapes and, as the diet guide on this site explains, even the hard armour of some prey.²³ The eyes are small, but the animal sees well both in and out of the water.²⁴

In murky water, sight is only part of the picture, and the boto relies on another sense as well. Both Amazon river dolphins use biosonar to find fish and to orient themselves under water.²⁵ The result is an animal that hunts by sound in rivers where a human swimmer cannot see their own hand. Its skin carries marks as well: intense encounters between individuals leave scars, and researchers can use the scars to tell dolphins apart in photographs.²⁶

The boto's days follow the river. The IUCN says its biology and ecology are strongly tied to the seasonal rise and fall of the water.³⁸ At low water, dolphins often gather below channel confluences, where fish are easier to meet.¹³ For a boat trip, that makes the margins and the mouths of side channels the first places to scan. As the river rises, their interest in confluences fades, because the animals move into side lakes and the flooded forest.¹⁴

At high water the sexes spread out. Females with dependent calves stay longer in the flooded forest, lakes and small tributaries, while most adult males are in the main rivers.¹⁵ Nursing mothers favour lakes probably because the current is weak, small fish are plentiful and large sharks pose less of a threat to a calf there.⁴⁴ Once the water starts to fall, the animals abandon lakes and shallows, perhaps to avoid being trapped.¹⁶

Breeding follows the same calendar. Reproduction is concentrated between July and October and is busiest in September, while births cluster as the water falls and fish are squeezed into less space.¹⁷ Despite all this movement the boto does not migrate in the usual sense of a seasonal journey to a breeding ground. Some animals keep to a home stretch all year, while others wander across tens to hundreds of kilometres of the river system.⁴⁵

For a visitor from Manaus the options are a river tour, a lodge stay or a day trip with a dolphin stop. The day tour sold on this site runs 12 hours and counts a swim with pink river dolphins at a dolphin protection project among its highlights, alongside a jungle trek and a night ride for caimans. A shorter listing runs 4.5 hours on the Rio Negro and lists the chance to swim with the dolphins. A 9-hour listing includes time at a pink river dolphin research base.

Be aware of how these meetings are managed. ICMBio says that in several places in Amazonas state botos are being attracted and tamed for use as a tourist attraction, and that a state normative instruction on managing tourism with botos already exists.^53,40 In 2015 INPA said that 4 other floating platforms offered contact with botos, none with set hours or information, and opened a platform in Iranduba, 80 km from Manaus, meant to set low-impact rules.^54,28

Choose a guide who explains the rules before the boat stops, and treat the dolphins as wild animals that happen to share a river with the boat. The swim and feeding questions have their own page, and the ethics page covers what the IUCN says about feeding.³⁶ The calculator further down prices the 3 listings by length and from-price, and it pays to read each listing's own highlights before you book, because a dolphin stop can be a swim, a platform visit or a sighting from the boat.