Water scarcity in Egypt requires better management of water resources. The most important parameters needed for lake water management are the lake surface area and volume at any specific time. This study focused on developing an innovative technique that enables the accurate calculation of the lake surface area at any specific time using satellite images. Neal-real time and long-term water body monitoring is essential for the effective management and conservation of Lake Nasser as one of the most important water resources in Egypt, which is enormously benefited from the advent of remotely sensed images. However, an efficient as well as robust method to perform water detection from these images remains challenging due to the various noise sources from heterogeneous backgrounds. A robust methodology is designed in this study to extract free surface water from multi-temporal and multispectral images acquired by Landsat-8 Operational Land Imager (OLI) and sentinel-2 satellites. To achieve the objectives of the study many Water Index image-processing techniques used to delineate the water body boundary. The study shows that the Modified Normalized Difference Water Index (MNDWI) is most useful technique more than the Normalized Difference Water Index (NDWI), to delineate water surface from other land features.