The Normalized Difference Water Index (NDWI) is a calculation used in remote sensing to measure the amount of moisture in vegetation and surface water bodies. Similar to the normalized difference vegetation index (NDVI), NDWI is based on unique reflection and absorption patterns in the visible and near-infrared spectra of light. This calculation has many applications, such as water resource management, agriculture, ecology and environmental management, and climate change studies. Depending on whether NDWI is being calculated for water moisture in vegetation or water on the Earth’s surface, different satellite bands are used in the calculation. Through different formulas and calculations, NDWI values can be used to map out the presence of water and moisture. An example of using NDWI is the mapping of the extend of flooding in areas susceptible to flooding, like around the Red River in Minnesota and North Dakota. NASA researchers used NDWI to calculate the intensity of the flooding of the Red River from Landsat 8 satellite imagery, providing a visual representation of flooded areas. NDWI is a valuable tool in remote sensing to monitor and manage water resources and environmental changes.