Lake cover strongly affects the reflectance of the land surface over large areas of Alaska, and was useful for identifying extensive wetlands. Lake cover was based on the number of AVHRR water pixels in each mapped polygon, divided by the number of pixels in the polygon. Since the imagery has a pixel size of 1 km^2, lake cover is underestimated for areas with many small lakes. Pixels within 2 km of the coastline were excluded to avoid ocean water. The percent cover data were grouped into six categories: 25%.