River and stream lengths are measured in miles, and lakes, reservoirs, and wetlands are measured in acres.
The river and stream mileage is typically generated from the linework of the National Hydrography Dataset (NHD) that was developed by the United States Geological Survey (USGS). While the NHD is fairly accurate, there are some localized issues that may impact stream segment length.
Lake, reservoir, and wetland acreages are gathered from multiple sources, including newly developed (as of April 2021) polygons generated from the NHD. These values are approximations, since aerial photo quality, rainfall amounts, and differing definitions on the appropriate "boundary" of lakes can result in significant variation in the estimated size of these waterbodies.
Due to the inexact nature of these values, caution should be exercised in their use.