Dense mats of invasive free-floating freshwater plant species tend to reduce native species biomass and diversity by altering habitat characteristics and competitively pre-empting resources. However, the ongoing environmental and climate change may modify competitive interactions between them and co-occurring native species. We investigated the effect of CO2 and nutrient enrichment on competition between two free-floating fern species that co-occur in south-eastern Australia - native Azolla filiculoides and invasive exotic Salvinia molesta. The species were grown in monoculture and competition in a glasshouse experiment where the nutrient medium was replaced weekly to simulate a dynamic system. We hypothesised that resource enrichment will enhance relative growth rates (RGR) of both species. We further hypothesised that although RGR of both species will be suppressed under competition relative to their counterparts grown in monoculture, S. molesta will be the dominant species in the competition treatment. We found that the relative growth rate (RGR) of both species was greater under high resource conditions as hypothesised. However, neither of the species showed a suppressive response due to competition. On the contrary, A. filiculoides had a facilitative effect on S. molesta. In addition, A. filiculoides gained more biomass under high resource conditions relative to S. molesta and the opposite was true under low resource conditions. We conclude that CO2 and nutrient concentration did not mediate competition between the species but instead influenced RGR independent of competition. These findings suggest that species composition in dynamic water bodies under future conditions may be determined by the species’ responses to environmental changes rather than by changes in competitive interactions.