Water Resources Regions United States A designated natural Drainage Basin or Hydrologic Area that contains either the drainage area of a major river or the combined drainage areas of two or more rivers. Of the 21 designated water-resources regions, delineated by the Water Resources Council in 1970, 18 are in the conterminous United States, and one each are in Alaska, Hawaii, and Puerto Rico. The following represents a listing of U.S. water- resources regions and the states primarily and partly included: 1 Region 01 New England Region (Maine, New Hampshire, Massachusetts, Connecticut, Rhode Island, and part of Vermont) 2 Region 02 Mid-Atlantic Region (New York, Pennsylvania, New Jersey, Maryland, Washington D.C., Virginia, and parts of Vermont and West Virginia) 3 Region 03 South Atlantic–Gulf Region (North Carolina, South Carolina, Georgia, Alabama, Florida, and parts of Virginia and Mississippi) 4 Region 04 Great Lakes Region (Michigan, and parts of Wisconsin, Indiana, Ohio, and New York) 5 Region 05 Ohio Region (Indiana, Ohio, West Virginia, Kentucky, and parts of Illinois, Tennessee, Virginia, Pennsylvania, and New York) 6 Region 06 Tennessee Region (Tennessee and parts of Alabama, Georgia, Virginia, and North Carolina) 7 Region 07 Upper Mississippi Region (Minnesota, Wisconsin, Iowa, Illinois, and parts of Missouri and Indiana) 8 Region 08 Lower Mississippi Region (parts of Arkansas, Mississippi, Louisiana, Tennessee, Kentucky, and Missouri) 9 Region 09 Souris–Red–Rainy Region (parts of North Dakota and Minnesota) 10 Region 10 Missouri Region (Montana, Wyoming, North Dakota, South Dakota, Nebraska, and parts of Colorado, Kansas, Missouri, Iowa, and Minnesota) 11 Region 11 Arkansas–White–Red Region (Oklahoma and parts of Colorado, New Mexico, Kansas, Texas, Missouri, Arkansas, and Louisiana) 12 Region 12 Texas–Gulf Region (Texas and parts of New Mexico and Louisiana) 13 Region 13 Rio Grand Region (New Mexico and parts of Texas and Colorado) 14 Region 14 Upper Colorado Region (parts of Utah, Colorado, Wyoming, Arizona, and New Mexico) 15 Region 15 Lower Colorado Region (Arizona and parts of California, Nevada, Utah, and New Mexico) 16 Region 16 Great Basin Region (Nevada and parts of Utah, California, Oregon, Idaho, and Wyoming) 17 Region 17 Pacific Northwest Region (Washington, Oregon, Idaho, and parts of Montana, Wyoming, Nevada, and Utah) 18 Region 18 California Region (California and parts of Oregon and Nevada) 19 Region 19 Alaska Region (Alaska) 20 Region 20 Hawaii Region (Hawaii) 21 Region 21 Caribbean Region (Puerto Rico) Also see Hydrologic Unit Maps USGS and Hydrologic Units (Classification Codes) USGS.