(EN) U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National MapArchiviato il 29 marzo 2012 in Internet Archive., accessed May 26, 2011
(EN) U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National MapArchiviato il 29 marzo 2012 in Internet Archive., accessed May 26, 2011