Bukit Timah Nature Reserve (BTNR) holds the largest remnant patch of primary rainforest in Singapore and its hill streams supports many native and threatened freshwater fauna. As the last comprehensive survey of freshwater fishes in BTNR was published nearly two decades ago, a series of surveys was carried out at 12 streams permeating BTNR and the Singapore Quarry to update the status of the fishes. Of the 27 species documented, 16 are native to Singapore and 11 are introduced. Two native species known from other parts of the Central Catchment Nature Reserve are recorded for the first time in BTNR. Species distribution, richness and abundance have been qualitatively assessed in relation to habitat characteristics. Potential threats and mitigation measures are discussed, which are important in the formulation of conservation and management strategies to safeguard the current diversity of freshwater fishes, many of which are threatened in rapidly developing Singapore.