Potomac River is formed 21 miles below Cumberland, MD, and flows southeasterly about 285 miles and enters Chesapeake Bay, about 80 miles from Atlantic Ocean. Washington, DC is 108 miles upstream of mouth, and head of tidewater is at mile 117.
Plane of reference is mean low water.
The following documents are available detailing this current activitiy. 1.3MB File Format Adobe Acrobat.pdf.