The New England Water Resource Region is one of 21 major geographic areas, or regions, in the first level of classification used by the United States Geological Survey to divide and sub-divide the United States into successively smaller hydrologic units. These geographic areas contain either the drainage area of a major river, or the combined drainage areas of a series of rivers. The New England region, which is listed with a 2-digit HUC code of 01, has an approximate size of 73,753 square miles, and consists of 11 sub-regions, which are listed with the 4-digit HUC codes of 0101 through 0111.