The fact that freshwater whales actually exist on our planet deserves far more fanfare — especially considering how their populations are declining.
Many species of river dolphins, specifically, live in waterways spanning multiple continents and countries around the globe. Their unique habitats correlate with strange attributes and extraordinary behaviors not found in marine dolphins and other cetaceans.
But, as the world's major rivers change under human development, river dolphins seem to be paying a price.
The International Union for Conservation of Nature Red List now categorizes all species of river dolphins as endangered or worse, with populations declining rapidly or disappearing completely in recent years.
Fresh Water Dolphins
While these (mostly) freshwater mammals share many general features and a common ancestor with ocean dolphins, they are hardly new to the evolutionary tree.
Research suggests that the river dolphin’s marine counterpart made its way into fresh water more than 5 million years ago.
This was likely during the Miocene epoch, when global sea levels were much higher than today. Species such as those in the Amazon and the Ganges River now live exclusively in fresh water.
Read More: Just How Intelligent Are Dolphins?
River Dolphin Features
Compared to the more popular bottlenose or spinner species of the sea, most river dolphins are immediately recognizable by unusual head and facial features, which seem to have evolved for optimum survival in their habitat.
Set behind a protruding forehead, the eyes of these creatures are generally smaller and less effective. In fact, some populations are virtually blind; as such, these species exhibit echolocation abilities (and a unique inner ear) unlike any other cetacean.
Globally, other key features include a low triangular dorsal fin, broad and “visibly fingered flippers” and a flexible neck, as one 2020 study in PNAS put it.
The latter characteristic allows them to turn their heads significantly, sometimes creating the appearance of a wrinkled double chin below the head.
Fresh Water Dolphin Snout
Perhaps the most obvious and recognizable attribute of the river dolphin is its long and toothy, beak-like snout.
This nose, along with its echolocation, likely serves as a hunting asset in the murky, silty waterways the dolphins inhabit.
The Amazon river dolphin is also uniquely known to have molars among its 100-plus teeth, which can help crush snails, turtles and other crustaceous prey. This chewing differs from most dolphins who use their teeth to grip and catch food before swallowing it whole.
Boto Dolphin Myth
Perhaps due to their novelty and odd features, multiple cultures developed myths and lore surrounding these freshwater whales.
Groups within the Amazon River basin of Peru long held that the river dolphin, or boto, could shape-shift into a seductive person and lure people to their death by drowning. One version of an encounter tells of a boto coming to a woman at night disguised as her husband; after a sexual encounter, the woman became pregnant and bore a child.
Similarly, in China, the Yangtze River dolphin was said to be the reincarnation of a fabled princess who was drowned in the river after she refused to marry.
Many South American Species
More than half a dozen species of river dolphins have been identified worldwide. Growing up to 350 pounds and nearly 9 feet long, the pink dolphins of the Amazon are the largest and most widely recognizable.
Similar species in South America include the Araguaian boto, named after a river it inhabits in Brazil, and the Bolivian river dolphin.
The tucuxi, also found in the Amazon, looks the most like a bottlenose dolphin (though smaller), and uniquely exhibits more playful and social qualities.
A smaller, gray-and-pale species called the la plata or franciscana river dolphin is the only kind to live in salt water. It occupies estuaries and coastal waters of Brazil, Uruguay and Argentina.
Reports in the past two decades have shown a rapid decline among most of these species, including some populations “halving every decade,” according to a Mongabay report.
Freshwater Dolphins of Asia
Another well-established species in the Eastern Hemisphere calls the Ganges River home in parts of India, Bangladesh and Nepal.
These blind river dolphins, or susu, have lost their vision altogether, perhaps due to the murkiness of the water, and possess extraordinary echolocation abilities for hunting. A similar species, the Indus River dolphin in south-central Pakistan, has been called one of the world’s most endangered cetaceans.
As of 2014, a study in Ambio also revealed that populations of the susu in the Ganges had decreased from roughly 4,000 to 5,000 in the early 1980s to about 3,500.
In addition to the above groups, a pale blue-gray dolphin known as the baiji also long occupied the Yangtze River of China. But this species is now believed to be extinct.
The last confirmed evidence of a sighting occurred in 2002, though unconfirmed claims of baiji dolphin encounters still surface from time to time.
Read More: How Do We Know When a Species Is Extinct?
Threats to the Species
Amidst climate change with expanding human development and urbanization, a mix of several forces seems to be killing off river dolphins.
A few of the top threats include hydroelectric development (with dams), pollution and declining water quality and fishing practices (such as incidental bycatch).
To preserve these rare creatures in the present day, the World Wide Fund for Nature and other organizations have spearheaded various conservation efforts.
Advocates emphasize that the best practices and solutions to protect river dolphins should be customized according to each unique population in the respective habitat and region it calls home.