The metaphor of the Black Swan is of something that does not comply with commonly-held perceptions. We ask if there are any such phenomena in tropical and subtropical southern-hemisphere aquatic ecosystems, and if so, whether they are important for management and conservation. We identify the following phenomena principally from our research in tropical coastal rainforest streams. Each is compared to its action in (well-known) temperate systems: 1. Food-webs based on algae at more shaded and upstream locations; 2. Lower fractionation of carbon stable isotopes in algae at more shaded, smaller, streams (allowing analysis of allochthonous and autochthonous sources in shaded streams); 3. Lack of shredding macroinvertebrates; 4. Prevalence of “macroconsumer” crustaceans and fish; 5. Prevalence of trophic cascades and strong interactions of fauna; 6. Large proportion of non-trophic interactions and bioturbation. These phenomena are quantitative differences of tropical vs temperate systems, and are not “black vs white”. They have not been tested over a large variety of tropical systems and their generality has not been established. Indeed, we have documented interesting diversity of trophic relationships within a small catchment, such that the prevalence of strong interactions is shown, but the exact dynamics between the components appears only after experimental analysis. Other phenomena such as the apparent lack of shredders and shredding have been shown in part to be caused by “unusual” fauna as well as the properties of the terrestrial vegetation. Inasmuch as the phenomena are significant parts of the functioning of stream ecosystems, they are important for stream monitoring, conservation and restoration, with the caveat of always needing local verification.