In the United States, a River mile is a measure of distance in miles

Miles

Miles is the plural of mile.Miles may also refer to:- People :*Miles Brothers, American cinema pioneers* Miles ** Miles Browning, World War II admiral** Miles Davis, jazz trumpet player** Miles Austin, Dallas Cowboys wide receiver...

 along a river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 from its mouth

River delta

A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river...

. River mile numbers begin at zero and increase further upstream. The corresponding metric unit using kilometers

Kilometre

The kilometre is a unit of length in the metric system, equal to one thousand metres and is therefore exactly equal to the distance travelled by light in free space in of a second...

 is the River kilometer. They are analogous to vehicle roadway mile markers, except that river miles are rarely marked on the physical river; instead they are marked on navigation charts, topographic maps, and the like. Riverfront properties are sometimes partially legally described by their river mile.

The river mile is not the same as the length of the river, rather it is a means of locating any feature along the river relative to its distance from the mouth, when measured along the course (or navigable channel) of the river.

River mile zero may not be exactly at the mouth. For example, the Willamette River

Willamette River

The Willamette River is a major tributary of the Columbia River, accounting for 12 to 15 percent of the Columbia's flow. The Willamette's main stem is long, lying entirely in northwestern Oregon in the United States...

 (which discharges into the Columbia River

Columbia River

The Columbia River is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia, Canada, flows northwest and then south into the U.S. state of Washington, then turns west to form most of the border between Washington and the state...

) has its river mile zero at the edge of the navigable channel in the Columbia, some 900 feet (274.3 m) beyond the mouth. Also, the river mile zero for the Lower

Lower Mississippi River

The Lower Mississippi River is the portion of the Mississippi River downstream of Cairo, Illinois. From the confluence of the Ohio River and Upper Mississippi River at Cairo, the Lower flows just under 1600 kilometers to the Gulf of Mexico...

 Mississippi River

Mississippi River

The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...

 is located at Head of Passes

Head of Passes

Head of Passes is where the main stem of the Mississippi River branches off into three distinct directions at its mouth in the Gulf of Mexico: Southwest Pass , Pass A Loutre and South Pass...

, where the main stem of the Mississippi splits into three major branches before flowing into the Gulf of Mexico

Gulf of Mexico

The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...

. Mileages are indicated as AHP (Above Head of Passes) or BHP (Below Head of Passes).

Uses

River miles are used in a variety of ways. The Commonwealth of Pennsylvania

Pennsylvania

The Commonwealth of Pennsylvania is a U.S. state that is located in the Northeastern and Mid-Atlantic regions of the United States. The state borders Delaware and Maryland to the south, West Virginia to the southwest, Ohio to the west, New York and Ontario, Canada, to the north, and New Jersey to...

, in its 2001 Pennsylvania Gazetteer of Streams, lists every named stream and every unnamed stream in a named geographic feature in the state, and gives the drainage basin

Drainage basin

A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...

 area, mouth coordinates, and river mile, specifically the distance from the mouth of the tributary to the mouth of its parent stream. Some islands are named for their river mile distance, for example the Allegheny River

Allegheny River

The Allegheny River is a principal tributary of the Ohio River; it is located in the Eastern United States. The Allegheny River joins with the Monongahela River to form the Ohio River at the "Point" of Point State Park in Downtown Pittsburgh, Pennsylvania...

 in Pennsylvania has Six Mile Island, Nine Mile Island, Twelve Mile Island, and Fourteen Mile Island. (The last two islands form Allegheny Islands State Park

Allegheny Islands State Park

Allegheny Islands State Park is a Pennsylvania state park in Harmar Township, Allegheny County, Pennsylvania in the United States. The undeveloped park is composed of three alluvial islands located in the middle of the Allegheny River northeast of Pittsburgh. The islands are just north of the...

, although Fourteen Mile Island was split into two parts by a dam). The Susquehanna River

Susquehanna River

The Susquehanna River is a river located in the northeastern United States. At long, it is the longest river on the American east coast that drains into the Atlantic Ocean, and with its watershed it is the 16th largest river in the United States, and the longest river in the continental United...

's Three Mile Island

Three Mile Island Nuclear Generating Station

Three Mile Island Nuclear Generating Station is a civilian nuclear power plant located on Three Mile Island in the Susquehanna River, south of Harrisburg, Pennsylvania. It has two separate units, known as TMI-1 and TMI-2...

's nuclear generating station famously melted down

Three Mile Island accident

The Three Mile Island accident was a core meltdown in Unit 2 of the Three Mile Island Nuclear Generating Station in Dauphin County, Pennsylvania near Harrisburg, United States in 1979....

 in 1979.

The state of Ohio uses the "River Mile System of Ohio", which is "a method to reference locations on streams and rivers of Ohio." This work began by hand measurements on paper maps between 1972 and 1975 and has since been converted to a computer-based electronic version, which now covers the state in 787 river mile maps. Locations of facilities such as wastewater treatment plants

Sewage treatment

Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and household sewage, both runoff and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants...

 and water quality measurement sites are referenced via river miles. Ohio uses one of two systems. The simplest is just the name of the river and the location in river miles. In cases where there is ambiguity, for example when more than one stream has the same name, it uses a series of river mile strings referring to the distance to the ocean along either the Ohio River

Ohio River

The Ohio River is the largest tributary, by volume, of the Mississippi River. At the confluence, the Ohio is even bigger than the Mississippi and, thus, is hydrologically the main stream of the whole river system, including the Allegheny River further upstream...

 (and Mississippi River

Mississippi River

The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...

) or through Lake Erie

Lake Erie

Lake Erie is the fourth largest lake of the five Great Lakes in North America, and the tenth largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and therefore also has the shortest average water residence time. It is bounded on the north by the...

 (and the Saint Lawrence Seaway

Saint Lawrence Seaway

The Saint Lawrence Seaway , , is the common name for a system of locks, canals and channels that permits ocean-going vessels to travel from the Atlantic Ocean to the North American Great Lakes, as far as Lake Superior. Legally it extends from Montreal to Lake Erie, including the Welland Canal...

).

The U.S. Army Corps of Engineers uses river miles for its navigation maps.