Invasive species have an impact on the structure and functioning of ecosystems they occupy. There is an increasing interest in understanding the effect of invasive fishes within the reservoir ecosystem, and models offer an essential tool for assessment. Ecopath with Ecosim (EwE) is modeling software that can be used as a tool in understanding the impacts. Incorporating invasive species into EwE models may be a challenging task. This study measures the effects of two invasive species, African catfish Clarias gariepinus in the food web of the Karapuzha reservoir ecosystem in India. The model we have developed incorporates fifteen functional groups ranging from detritus, produces to apex predators. The findings show that the two invasive species, directly and indirectly, influence several ecosystem elements. The high level of niche overlap (92%) and strong competition for similar resources was exhibited by. gariepinus. The adverse effects of African catfish on all fish and crustaceans in the reservoir were revealed by mixed trophic impact assessed in this reservoir while Oreochromis mossambicus impacts were both positive and negative. O. mossambicus had a beneficial impact on its predator aquatic birds and negative towards minnows.