Although featured in many international zoo collections for decades, little was known about the natural history of Sunda gharial Tomistoma schlegelii until recently. Zoos rarely keep large individuals and breeding success has been low. As late as 1998, even though most conservationists regarded the conservation status of the species as Endangered, the reality was that over most of the range the actual status of the Sunda gharial was Data Deficient. Beginning with surveys of the species by international and local scientists in Indonesian Sumatra and, later, in Kalimantan, Indonesian Borneo, supported by the International Union for Conservation of Nature/Species Survival Commission Crocodile Specialist Group, more details on the broad distribution of this crocodilian came to light. Ironically, rediscovery of a large and healthy population of T. schlegelii in East Kalimantan arose from an oil-palm company accessing the area to develop a site called Danau Mesangat. Subsequently through a cooperation agreement with the oil-palm company’s conservation department and a local foundation, a group of dedicated zoos in Europe and America, and the Tomistoma Task Force set up by the Crocodile Specialist Group, provided funding for three consecutive years of field studies by a research group. These studies investigated the ecology of T. schlegelii and of a sympatric population of the Critically Endangered Siamese crocodile Crocodylus siamensis. The role of the zoos, including their role in the development of the research programme, is described. Accounts are given of the characteristics of the Mesangat habitat, some new details about the distribution and abundance of Sunda gharial and Siamese crocodiles in the habitat, and information about reproduction in T. schlegelii. In summary, an overview of threats and suggestions for conservation actions needed at the Mesangat site are provided.