U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. «The National Map». Arkivert fra originalen 5. april 2012., accessed March 18, 2011
U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. «The National Map». Arkivert fra originalen 5. april 2012., accessed March 18, 2011