Considering Türkiye's morphological structure and river beds, it can be seen that it has not yet reached its equilibrium profile. This profile is an ideal structure for installing hydroelectric power plants (HPP). After renewable energy sources, the most environmentally friendly energy source for the ecosystem is HPP. When determining the amount of water to be used in hydroelectric power plants, the amount of water required for the ecosystem that should be discharged to nature should be calculated. The amount of water needed for the ecosystem to maintain its current structure without change is defined as the environmental flow. In this study, the environmental impact and environmental flow of the Korkuteli Stream HPP Project located within the borders of the Korkuteli District of Antalya Province have been determined. Wetted perimeter, flow duration index (Q25, Q50, Q75, and Q95), and base flow methods have been used to determine the environmental flow of the Korkuteli Stream. In calculating environmental flow 44 years of discharges of the Salamur Strait flow observation station (FOS) on Korkuteli Stream have been used. As a result, the optimal environmental flow was calculated at 17% using the wetted perimeter method.