After centuries of disputes, negotiations, arbitration, and court cases, it is clear that Maryland owns the Potomac River to the low-water mark on the Virginia side... but that boundary still creates confusion.
In 1986, a man was convicted in Loudoun County of murdering his ex-wife. In 1988, that conviction was overturned by the Virginia Court of Appeals because the body had been found floating in the Potomac River at least six feet away from the shoreline. Under homicide law, prosecution occurs where the body is found unless the actual location of the crime is unknown, so the body was in Maryland and officials from that state had to pursue the murder case.1
Further downstream, Virginia and Maryland have continued to debate Maryland's control over the bottom of the Potomac River. The 1958 Maryland-Virginia Compact replaced the Compact of 1785 in hopes of resolving disputed claims to oyster beds and fishery resources, but lawsuits continue to cite colonial-era documents as well as the 1958 agreement.
In 1997, Maryland claimed that the Fairfax County Water Authority needed a Maryland state permit in order to extend a water pipe to the middle of the Potomac River. Fairfax wanted to minimize the sediment in the water that it will treat at its Corbalis Water Treatment plant, near the Loudoun County line, by extracting raw water from the middle of the river.
The old Fairfax County intake pipe on the southern shoreline was receiving water with too much sediment, partly due to muddy runoff from housing developments in Loudoun County. Fairfax wanted to suck cleaner water from the middle of the river. The water in the middle of the Potomac River is cleaner, in large part because C&O Canal National Historical Park on the Maryland side provides a buffer of natural vegetation and there is less mud flowing into the Potomac on the north bank.
That 1997 proposal created yet one more Virginia v. Maryland lawsuit in front of the US Supreme Court. Maryland opposed the plans of the Fairfax County Water Authority (now Fairfax Water), and tried to force the Virginia county to get a Maryland state permit before constructing the intake pipe on the bed of the Maryland river. Part of the "back story" is that Maryland wanted Virginia to reduce the impacts of shoreline development that pollute the Potomac River. Simply avoiding those impacts by extending the intake pipe addressed the symptom without dealing with the cause.
In 2003, the US Supreme Court ruled that Fairfax County has the right to place the intake pipe on Maryland's river bed without having to obtain a permit from Maryland. Though Maryland owns the whole river due to the wording in the 1634 charter, various bi-state negotiations and court decisions (including the 1877 Black-Jenkins Award) have made it possible for Virginia to use the Potomac River.
In 2011, landowners in Maryland claimed control over the riverbank downstream of Harpers Ferry, on the Virginia side of the river at Potomac Wayside. Maryland sold rights to the bottom of the river until 1862, and the parcel in dispute has been private property since 1833.13
Potomac Shores, Inc. asserted that their 1833 deed described property boundaries that extended to the median high-water mark (the average of the water level throughout the entire year) on the southern bank of the Potomac River. Based on that claim, canoeists and rafters who floated downstream past Harpers Ferry 175 years later were trespassing on private property in Maryland when getting back on dry land at Potomac Wayside. The company also claimed the rocks above water in the middle of the Potomac River were private property as well.
The commercial outfitters had obtained permits from the National Park Service to use Potomac Wayside, and paid fees to the Federal agency. Potomac Shores claimed its deed documented a strip of land between the low-water mark and the median high-water mark was privately owned, and sought to force commercial outfitters to pay fees to Potomac Shores as well.2
In a tactical legal decision, Potomac Shores filed suit against the commercial outfitters in a Maryland court. The company did not pursue a suit against the National Park Service to quiet title for the land; the Federal agency had far more resources for defending their claim. The outfitters did not compromise in order to minimize their legal expenses (estimated at $10,000). Judge Long of the Washington County Circuit Court of Maryland ruled in 2013 that the 1877 Black-Jenkins arbitration decision had settled the issue:3
When the Potomac River shifts, the low water line shifts. The Virginia-Maryland border follows that shifting boundary, upstream of Tidewater where the Matthews-Nelson Survey of 1927 fixed the boundary.