The Mallows Bay-Potomac River National Marine Sanctuary consists of an area of approximately 18 square miles of waters of the state of Maryland and the submerged lands thereunder, over, around, and under the underwater cultural resources in the Potomac River. The precise boundary coordinates are listed in appendix A to this subpart. The western boundary of the sanctuary approximates the border between the Commonwealth of Virginia and the State of Maryland along the western side of the Potomac River and begins at Point 1 north of the mouth of Aquia Creek in Stafford County, Virginia, near Brent Point. From this point the boundary continues to the north approximating the border between Virginia and Maryland cutting across the mouths of streams and creeks passing through the points in numerical order until it reaches Point 40 north of Tank Creek. From this point the sanctuary boundary continues east across the Potomac River in a straight line towards Point 41 until it intersects the Maryland shoreline just north of Sandy Point in Charles County, Maryland. From this intersection the sanctuary boundary then follows the Maryland shoreline south around Mallows Bay, Blue Banks, and Wades Bay cutting across the mouths of creeks and streams along the eastern shoreline of the Potomac River until it intersects the line formed between Point 42 and Point 43 just south of Smith Point. Finally, from this intersection the sanctuary boundary crosses the Potomac River to the west in a straight line until it reaches Point 43 north of the mouth of Aquia Creek in Stafford County, Virginia, near Brent Point.