River boundaries are typically defined by the "thread of the channel" (the river's
thalweg, usually in the approximate middle of the river's channel), under a rule that the United States inherited from England, where it applies to boundaries between counties. In the United States, there are at least six exceptions, however, where the boundary is one bank of the river rather than the thread of the channel: • The boundary between
New Hampshire and
Vermont is the west bank of the
Connecticut River. This was established as the eastern boundary of
New York by a grant of
King Charles II in 1664. It was disregarded by Governor
Benning Wentworth of New Hampshire, who treated the
New Hampshire Grants west of the river as a
de facto part of New Hampshire during the years 1649–1764, but
King George III put an end to that in 1764. In August 1781, the
Continental Congress decided it would recognize the
then largely unrecognized state of Vermont, which had been organized in defiance of New York, on condition that Vermont would agree to certain boundaries. In 1782, the legislature of Vermont agreed, but nonetheless Vermont was not
admitted to the Union until 1791. In 1933, citing the 1782 legislation, the
United States Supreme Court denied
the petition from the state of Vermont to make the boundary the thread of the channel. • The boundaries between
Kentucky and
West Virginia and the three states to their north –
Ohio,
Indiana, and
Illinois – is based on the historical northern bank of the
Ohio River. In 1763, Britain defeated France in the
Seven Years' War, whose North American theater was called the
French and Indian War. At that time, Canada, which had been a French colony, became a British colony, and Parliament made the north bank of the Ohio the southern boundary of Canada. The river was thus included in the district of Kentucky, which was then a part of Virginia. In January 1980, the U.S. Supreme Court ruled in
Ohio v. Kentucky that the state line is the low-water mark of the Ohio River's north shore as of Kentucky's admission to the Union in 1792. Because both damming and natural changes have rendered the 1792 shore virtually undetectable in many places, the exact boundary was decided in the 1990s in settlements among the states. • The boundary between
Delaware and
New Jersey north of 39° 30' north latitude is the east bank of the
Delaware River. • The boundary between Delaware and New Jersey south of a certain point is the east bank of the Delaware River, rather than the thread of the channel. • The boundary between
Maryland and
Virginia is the south bank of the
Potomac River. This also applies both to the border between Maryland and West Virginia (from
Harper's Ferry to the source of the Potomac near the
Fairfax Stone) since the latter was at one point part of Virginia, and to the border between Virginia and
Washington, D.C., since the capital was established from a section of Maryland property. • The boundary between
Alabama and
Georgia, south of
West Point, Georgia, is the west bank of the
Chattahoochee River at the mean water mark. This was established in an 1860 Supreme Court ruling,
Alabama v. Georgia. • The course of the
Charles River was used to indirectly define the border between Massachusetts and Rhode Island. The
Merrimack River defines part of the border between Massachusetts and New Hampshire, which runs parallel to the river, three miles north of it (see
Northern boundary of Massachusetts.) == List of river borders ==