United States Geological Survey (USGS) - http://water.usgs.gov/GIS/huc.html
Secretaría de Medio Ambiente y Recursos Naturales (SEMARNAT - México) - http://infoteca.semarnat.gob.mx/website/geointegra/Cmviewer/viewer.htm
Geogratis - National Resources Canada http://geogratis.cgdi.gc.ca/geogratis/en/option/select.do?id=27730
Ricardo A. Lopez M.S. - Geo-spatial Technologies & Webmaster (TCWP) John Jacob, Ph.D. - Team Leader (TCWP)
Texas Coastal Watershed Program (TCWP) - http://www.urban-nature.org/ Tx Cooperative Extension/Tx Sea Grant - Texas A&M University Stsystem
