-LRB- CNN -RRB- -- The Irrawaddy , one of the world 's rarest species of freshwater dolphins , have been found in surprisingly large numbers deep in the waterlogged jungles of Bangladesh . The Irrawaddy is considered to be one of the world 's rarest species of freshwater dolphin . Conservationists thought the Irrawaddy had dwindled in number to just a few hundred , but they have now counted almost 6,000 of them in the Sundarban mangrove forests and the adjacent waters of the Bay of Bengal . The forests of the Sundarban -- Bengali for `` beautiful forest '' -- lie at the delta of the Ganges and two other rivers on the Bay of Bengal . Until now , little mammal research had taken place in the area . `` Every time we had done a study to look into the population -LRB- elsewhere -RRB- , they came out critically endangered , '' said Brian Smith of the New York-based Wildlife Conservation Society , who led the study . `` It was a very pleasant surprise and a shock to find that Bangladesh supports such a large number -LRB- of dolphins -RRB- . '' The discovery is noteworthy because scientists do not know how many Irrawaddy dolphins remain . The next step , they say , is to ensure the mammal 's survival . One rare dolphin species -- the Yangtze River dolphin , or baiji -- is extinct . Another , the Ganges River dolphin , is critically endangered . Some of the threats affecting the Irrawaddy are man-made . The construction of dams has reduced the flow of fresh water in many parts of Bangladesh . And the population is dwindling because the dolphins sometimes get caught in fishermen 's nets . The dolphin , which has a large , rounded head , can grow up to 8 feet in length and is related to the orca , or killer whale . It is found in large rivers , estuaries and freshwater lagoons in south and southeast Asia . In Myanmar , the dolphins help herd schools of fish toward fishermen 's boats and nets . In Bangladesh , fishermen hold them in high regard , Smith said . `` There is no market for dolphin products , '' he said . `` In a country like Bangladesh , with protein deficiency and where food is scarce , there is a real cultural prohibition against harming them . It gives us hope because it means fishermen are very receptive to working with us . '' The results of the study were shared Wednesday at a conference for marine mammal protected areas in Hawaii , and published in the winter issue of the Journal of Cetacean Research and Management . Conservationists are now working with the Bangladesh government to establish a protected area for the dolphins . `` There are so many bad news -LRB- stories -RRB- coming out of the conservation community that this is a real sort of positive story , '' Smith said .