Ang Trapeang Thmor is a human-made reservoir built by forced labour during the Khmer Rouges regime along an ancient causeway constructed in Angkorian times. In 1998, Sam Veasna (a pioneering Khmer conservationist and ornithologist) discovered a population of the eastern race of Sarus crane at Ang Trapeang Thmor. The species is on The IUCN Red List of Threatened Species as Vulnerable, but the eastern race, Grus antigone sharpii, is so threatened that it would merit a higher category of threat. Ang Trapeang Thmor turns out to hold the largest non-breeding population in Cambodia, which now number over 400 individuals in the dry season. This is fully 40% of the global population of this sub-species. Following this, and with the support of the International Crane Foundation and the Wildlife Conservation Society, the reservoir and surrounding wetlands and forest were declared a Sarus Crane Conservation Area by Royal Decree in 2000. The protected area totals 12,500ha and is one of the few protected areas in Cambodia under Royal Decree.