National Wetland Inventory Maps. Important Disclaimer: National Wetland Inventory maps are produced by the U.S. Fish and Wildlife Service from interpretation of aerial photographs. They provide approximate information on the types, extent, and locations of wetland resources and are used for a variety of purposes. The accuracy of the NWI wetland information, especially wetland sizes and locations, can be a factor of the time of year when photographs were taken, the density of tree canopies, and other obstacles to photo-interpretation. They therefore should not be used as the sole source of information when accurate wetland information is critical. NWI maps do not substitute for site specific field investigations and wetland boundary delineations required by the Department pursuant to the Natural Resources Protection Act (38 M.R.S.A. §§480-A et seq.) and the Maine Wetland Protection Rules (Chapter 310). Go here for national wetland inventory maps (off-site).