Osimiri Potoma ahụ na -asọfe kilomita 383 site na Fairfax Nkume, West Virginia ruo Point Lookout, Maryland. Ọ na-emetụta ihe karịrị nde mmadụ 6 bi n'ime mmiri mmiri Potomac, ala 14,670-square kilomita ebe mmiri na-asọba n'ọnụ ọnụ osimiri ahụ. Ihe ngosi a na-egosi ebe osimiri ahụ na ebe mmiri mmiri ya na-agafe n'ọtụtụ ógbè ndị dị na mpaghara ala ndị dị na Appalachian Plateau, Ridge & Valleys, Blue Ridge, Piedmont, na Plain Coastal.
Isi ihe ndị ọzọ na-agbakwunye ndị isi niile na-agbanye ụba na-eme ka mmiri dị na 12,878.8 na-eme Potomac Osimiri 21 kasị ukwuu na United States. Ndị isi nke Osimiri Potoma bụ North Branch, Savage River, South Branch, Cacapon, Shenandoah, Antietam Creek, Osimiri Monocacy, na Osimiri Anacostia. Potoma na-abanye n'ime ala Chesapeake Bay .