The International Great Lakes Datum (IGLD) is a geodetic reference system used to measure elevations and water levels in the Great Lakes region of North America. It provides a consistent framework for mapping and surveying, ensuring that measurements are comparable across different locations and times. The current version, IGLD 1985, was established to improve accuracy in water level monitoring and management. IGLD is crucial for various applications, including navigation, environmental studies, and infrastructure development. It helps agencies and researchers understand changes in water levels, which can be influenced by factors such as climate change and human activities.