The Singapore Zoo formerly known as the Singapore Zoological Gardens and commonly known locally as the Mandai Zoo, occupies 28 hectares (0.28 km²) of land on the margins of Upper Seletar Reservoir within Singapore's heavily forested central catchment area. The zoo was built at a cost of S$9m granted by the government of Singapore and opened on 23 June 1973. It is operated by Wildlife Reserves Singapore, who also manage the neighbouring Night Safari and the Jurong BirdPark.
From the beginning, Singapore Zoo followed the modern trend of displaying animals in naturalistic, 'open' exhibits, i.e. with hidden barriers, behind moats and shrubbery etc. It also houses the largest captive colony of orangutans in the world.
The conception of the Singapore Zoo dates from 1969. At the time, the Public Utilities Board (PUB) decided to use some of its land holdings around reservoirs for parks and open recreational facilities. The then Executive Chairman of PUB, Dr Ong Swee Law, set aside 88 hectares of land for the construction of a zoological garden.
In 1970, consultants and staff were hired, and in 1971, the construction of the basic 50 enclosures started. Animals were collected from dealers and donated by sponsors. The Director of the Colombo Zoo in Sri Lanka, Lyn de Alwis, was hired as a special consultant to work out problems inherent in tropical zoos.
On 23 June 1973, the Singapore Zoo opened its gates for the first time with a collection of 270 animals from over 72 species, and a staff of 130. By 1990, 1,600 animals from more than 160 species lived in social groups, housed in 65 landscaped exhibits with boundaries conceived to look as natural as possible.