A population assessment survey of the endangered Ganges river dolphin was made between February and Apil 2005 in the Brahmaputra River starting from Assam-Arunachal border to the India-Bangladesh border. One hundred and ninety seven dolphins were recorded in the entire 856 km river stretch with an encounter rate of 0.23 dolphins per km.

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Ganges River dolphins (Platanista gangetica gangetica) occur in the Ganges-Brahmaputra River system primarily in India and Bangladesh. They are listed as Endangered by the IUCN due to a probable population decline of at least 50% over the last 50 years and projected future population declines. No quantitative estimates of abundance are available for the Ganges River