U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National MapArkiverad 29 mars 2012 hämtat från the Wayback Machine., accessed August 15, 2011
web.archive.org
U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National MapArkiverad 29 mars 2012 hämtat från the Wayback Machine., accessed August 15, 2011