Umlambo wasePotomac uhamba malunga neekhilomitha ezili-383 ukusuka eFallfax Stone, eNtshona Virginia ukuya kwiPot Lookout, eMaldin. Ichaphazela abantu abangaphezu kwezigidi ezi-6 abahlala ngaphakathi kwe-Potomac, i-14,670-square-miles-mile endaweni yomhlaba apho amanzi aphuma emlonyeni womlambo. Le mephu ibonisa indawo yomlambo kunye nommandla wasemanzini ojikelezayo kwiindawo ezininzi zeendawo ezibandakanya iiplateau ze-Appalachian, i-Ridge & Valleys, i-Blue Ridge, i-Piedmont kunye ne-Coastal Plain.
I-stem ehamba phambili kunye nazo zonke iindleko ezinkulu eziqhelekileyo eziyi-12,878.8 iikhilomitha ezenza uMlambo wasePomomac ube ngowama-21 ngobukhulu eMelika. Izixhobo eziphambili zoMlambo wasePotomac yiSebe laseNyakatho, uMlambo waseSavage, isebe laseMzantsi, iCacapon, iShenandoah, i-Antietam Creek, uMlambo weMonocacy, kunye noMlambo wase-Anacostia. I-Potomac ingena kwiChesapeake Bay emzantsi.