The South American ocellate river stingray, Potamotrygon motoro, was reported from an artificial reservoir in Singapore in 2009, but there have been no further studies since. We aimed to investigate the distribution and ecology of this species, and surveyed 12 reservoirs with multiple methods, capturing 34 adults (1♂:1.32♀) that included several pregnant females, and 24 juveniles from three reservoirs (two new reservoirs plus the original locality). Gut content analyses reflected a varied diet that mainly comprised macroinvertebrates (e.g., gastropods). This was supported by stable isotope analyses, which found the benthopelagic P. motoro to be in a distinct trophic guild from other pelagic carnivores in the reservoir. As Singapore remains the only place outside South America with established populations of non-native P. motoro, and in view of its popularity in the international aquarium trade, we conducted Species Distribution Modelling (SDM) to estimate its potential to establish in other parts of the world. Our SDMs revealed that P. motoro could become established in a range of countries including China, Japan, USA, Taiwan, and Malaysia. Issues surrounding its introduction pathway in Singapore and potential spread into natural forest streams that are important refugia for native species will also be discussed.