The Mariout Lake is one of the most severely impacted water bodies in the Nile Delta. Multidates satellite images have been used in this study to detect the trends of environmental changes in Mariout Lake, particularly for the main two lake ecosystems; water, and aquatic vegetation during the past four decades from 1972 to 2016. A combination of LandSat-1(MSS), LandSat-5 (TM), LandSat-7 (ETM+), SPOT-1, SPOT-4, SPOT-5, RapidEye, and Sentinel-2 Satellite data was used to analyze temporal changes in the Lake ecosystem. Different image processing techniques were undertaken that performed with the ERDAS Imagine (2013) and ARCGIS (10.2.2) software such as; atmospheric correction, geometric correction, on-screen digitizing to delineate the lake boundary, the Normalized Difference Water Index (NDWI) to quantify the change in the water body area of the Lake, and change detection to ascertain the changes in water and aquatic vegetation features during last four decades interval. The results of analysis indicated that Lake lost 11.19 km² of its overall size; NDWI indicated that change in aquatic vegetation for all basins increased by 27.68 km², and the changes in water for all basins decreased by 38.67 km². The change detection results showed changed area that converted into aquatic vegetation, unchanged area that still water, and lost area that no longer exists. These results that due to different anthropogenic activities such as drying and reclaiming some areas that have dangerous impacts on its quality and a subsequent deterioration in its ecological parameters.