An international team of researchers published a study in the journal, Ecology and Evolution, which highlights the complex impacts of introducing an exotic species. This case showed that Eucalyptus has lethal and sublethal effects on the larvae of aquatic insects, which in turn affects various organisms that inhabit fluvial ecosystems with eucalyptus plantations on their banks. The study explains how the larvae affected by eucalyptus are mainly found in rivers, as they prevail in environments that have had less external intervention (small headwater rivers). In these environments, in addition to being food for native fish, they break up the leaves that fall from the forest, which is a key process in the functioning of these ecosystems.
See an article (in Spanish) at this link: http://www.naturalesudec.cl/estudio-demuestra-impacto-negativo-del-eucalipto-en-ecosistemas-acuaticos-dulceacuicolas/
And the study here: http://onlinelibrary.wiley.com/doi/10.1002/ece3.3094/full