The National Map. National Hydrography Dataset high-resolution flowline data. U.S. Geological Survey. [May 4, 2011]. (原始内容存档于2012-03-29).|url-status=和|dead-url=只需其一 (帮助)
The National Map. National Hydrography Dataset high-resolution flowline data. U.S. Geological Survey. [May 4, 2011]. (原始内容存档于2012-03-29).|url-status=和|dead-url=只需其一 (帮助)