U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National Map. [2019-03-09]. (原始内容存档于2012-04-05)., accessed May 3, 2011
webcitation.org
U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National Map. [2019-03-09]. (原始内容存档于2012-04-05)., accessed May 3, 2011