Discovery this week goes in search of the Gangetic River Dolphin, an extraordinary creature which inhabits the muddy waters of the Ganges and Brahmaputra rivers.
Not long ago, the dolphin was a common sight for people along these mighty water ways, but now it's one of the world's rarest freshwater mammals.
Andrew Luck-Baker joins Indian biologists studying the dolphins and the threats to them along the stretch of the Brahmaputra in the state of Assam.
In a joint project between Aaranyak, an Indian conservation organisation, and the Zoological Society of London, the scientists are also mobilising local communities to protect this special animal and the ecosystem they share with it.