River Dolphins
As opposed to oceanic dolphins, river dolphins do not live out in the open oceans but instead in freshwater inland rivers, and coastal estuarine rivers.
There are only five species (two of them are subspecies) of them in the world, four of which live in the fresh water and one in estuarine (brackish) water. They all belong to different families within the superfamily Platanistoidea.
Iniidae
The family Iniidae contains the only genus Inia, and the only species Amazon or Pink River Dolphin or Boto (Inia geoffrensis). It has got a long thin beak and a blunt head. It can be 1.7-3 metres long and weigh up to 160kg. The ventral and lateral body parts of it can be pinkish, particularly in older individuals, which is why it is often called pink. It surfaces to breathe every 30 to 60 sec. It is restricted to fresh water and it is only found in the Amazon river basin. It may migrate to freshwater lakes during the wet season floods and get trapped there until the next wet season. But it can survive there because a lot of fish get trapped too.
Pontoporiidae
The family Pontoporiidae contains the genus Pontoporia and the only species La Plata Dolphin (Pontoporia blainvillei). This is the other species in South America. As opposed to Boto, it is found in coastal rivers. This is the only species that can handle estuarine water.Platanistidae
Platanistidae contains one genus - Platanista, and two subspecies: Indus (Platanista gangetica minor), found in Indus river valley, and Ganges River Dolphin (Platanista gangetica gangetica), which is found in Ganges river valley. Both are endangered and it has been controversial whether they should be the same, or two different species.Lipotidae
The family Lipotidae contains one genus - Lipotes, and one species - Chinese or Yangtze River Dolphin or Bajij (Lipotes vexillifer), which is found in Chang (Yangtze) River in eastern China.
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