Due to Global Climate Change (GCC), temperatures are rising, and heatwaves will reoccur more frequently in aquatic ecosystems. These events have been shown to influence the toxicity of chemicals (e.g., pesticides) in the environment by complex mechanisms not yet fully understood. If at all considered in standard ecotoxicological testing, elevated temperatures are usually incorporated as a fixed constant temperature, not representing heatwaves or daily fluctuating scenarios. As a result, there is a lack of studies evaluating the possible combined effects of pesticides and realistic warming conditions. The aim of this study was to assess the single and combined effects of an herbicide and GCC warming scenarios (fluctuating elevated temperatures and extreme heatwave events) on four different macrophyte species (submerged and free-floating). For this purpose, we used the herbicide Terbuthylazine (TBA) and tested it on aquatic macrophytes under both an ecologically realistic set up (outdoor mesocosms) and a controlled single-species laboratory test. In both experiments, a fully factorial design was applied, combining three temperature scenarios (ambient, elevated temperature (+4°C) and recurring heatwaves (+8°C for 1-week intervals)) with different concentrations of TBA (0 – 100 µg/l). Single and combined effects were evaluated on the growth of two submerged species (Elodea nutalli and Myriophyllum spicatum) and two free-floating species (Spirodela polyrhiza and Salvinia natans). Preliminary results show clear effects from the highest concentration of TBA by significantly decreasing the growth of all four macrophytes species and drastically dropping dissolved oxygen levels. Warming (elevated temperatures and heatwaves) seemed to affect growth in controls of all species. While, at mid to high TBA concentrations, effects seem to be antagonistic, particularly at elevated temperatures. This depended, however, on the species. Nonetheless, further analyses must be conducted. The results from this study provide a better understanding of the interactions of these omnipresent stressors allowing for a more accurate aquatic risk assessment for pesticides in the future.