Water is a crucial component of ecosystems and a critical resource that cannot be replaced for social progress or human life. It supports temperature variation, the cycling of carbon, and other ecological processes. In this study, Agulu Lake, an inland water body located in Anambra, south-east Nigeria, was mapped, classified, and delineated with remote sensing and GIS tools with the aim of analyzing the spatial-temporal changes that occur in the lake’s surface water from 2000 to 2022. To achieve this goal, remotely sensed data from the United States Geological Survey (USGS) portal, including Landsat 7 TM (2000), ETM+ (2011), and Landsat 8 OLI (2022), were used to create various classification maps, including land and water surface classes. The Google Earth image was also used to show the general overview of Agulu Lake and its environs. The ArcGIS 10.5 software and maximum likelihood classifier were used to classify the images. The findings demonstrate that over the study period, the land surface class has grown whereas the water surface class (Agulu Lake) has shrunk. The research demonstrates that GIS and remote sensing are useful methods for tracking, mapping, and defining lakes and other open water bodies. The study is recommended as a starting point for monitoring developments that influence the lake’s water quality.