Waterfalls have unique physical characteristics and harbour highly specialised macroinvertebrate communities, but have been the subject of very few ecological studies. There are no previous studies of trophic structure of waterfall assemblages. It was hypothesised that because of the steep gradient of waterfalls and low retention of terrestrial-based resources, the abundant basal food resources would be periphyton. In addition, because of the frequent scouring flood events, it was predicted that periphyton would be a significant source of food for filter feeders. Waterfalls in the Ulu Temburong National Park (Brunei Darussalam) were used in the present case study. Methods included stable carbon (C)- and nitrogen (N)-isotope analyses (SIA; δ13C and δ15N of leaf litter and periphyton) and gut-content analysis (GCA) of the most the abundant macroinvertebrates. With δ15N values ranging from -1.9 to 5.5‰, literature suggests that this indicates that herbivores (Heptageniidae and Blephariceridae), omnivores (Simuliidae and Hydropsychidae) and predators (Buccinidae) live in the waterfalls. Apart from Buccinidae, the taxa had δ13C signatures ranging from -33 to -26‰, with a high dependence on periphyton, which is similar to other tropical-stream biotopes. The present study suggests that despite scouring velocities, waterfalls support animals with a range of diets, based on grazing or scraping, filter feeding and predation.