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The headwaters of a river or stream is the farthest place in that river or stream from its estuary or downstream
confluence In geography, a confluence (also: ''conflux'') occurs where two or more flowing bodies of water join to form a single channel. A confluence can occur in several configurations: at the point where a tributary joins a larger river (main stem); o ...
with another river, as measured along the course of the river. It is also known as a river's source.


Definition

The United States Geological Survey (USGS) states that a river's "length may be considered to be the distance from the mouth to the most distant headwater source (irrespective of stream name), or from the mouth to the headwaters of the stream commonly known as the source stream". As an example of the second definition above, the USGS at times considers the Missouri River as a tributary of the Mississippi River. But it also follows the first definition above (along with virtually all other geographic authorities and publications) in using the combined Missouri—lower Mississippi length figure in lists of lengths of rivers around the world. Most rivers have numerous tributaries and change names often; it is customary to regard the longest tributary or stem as the source, regardless of what name that watercourse may carry on local maps and in local usage. This most commonly identified definition of a river source specifically uses the most distant point (along watercourses from the river mouth) in the drainage basin from which water runs year-around ( perennially), or, alternatively, as the furthest point from which water could possibly flow ephemerally. The latter definition includes sometimes-dry channels and removes any possible definitions that would have the river source "move around" from month to month depending on precipitation or ground water levels. This definition, from geographer Andrew Johnston of the Smithsonian Institution, is also used by the National Geographic Society when pinpointing the source of rivers such as the
Amazon Amazon most often refers to: * Amazons, a tribe of female warriors in Greek mythology * Amazon rainforest, a rainforest covering most of the Amazon basin * Amazon River, in South America * Amazon (company), an American multinational technology co ...
or
Nile The Nile, , Bohairic , lg, Kiira , Nobiin: Áman Dawū is a major north-flowing river in northeastern Africa. It flows into the Mediterranean Sea. The Nile is the longest river in Africa and has historically been considered the longest ri ...
. A definition given by the state of Montana agrees, stating that a river source is never a
confluence In geography, a confluence (also: ''conflux'') occurs where two or more flowing bodies of water join to form a single channel. A confluence can occur in several configurations: at the point where a tributary joins a larger river (main stem); o ...
but is "in a location that is the farthest, along water miles, from where that river ends." Under this definition, neither a lake (excepting lakes with no inflows) nor a confluence of tributaries can be a true river source, though both often provide the starting point for the portion of a river carrying a single name. For example, National Geographic and virtually every other geographic authority and atlas define the source of the Nile River not as Lake Victoria's outlet where the name "Nile" first appears, which would reduce the Nile's length by over (dropping it to fourth or fifth on the list of world's rivers), but instead use the source of the largest river flowing ''into'' the lake, the
Kagera River The Kagera River, also known as Akagera River, or Alexandra Nile, is an East African river, forming part of the upper headwaters of the Nile and carrying water from its most distant source.Stanley, H.M., 1899, Through the Dark Continent, London: G ...
. Likewise, the source of the Amazon River has been determined this way, even though the river changes names numerous times along its course. However, the source of the Thames in England is traditionally reckoned according to the named river Thames rather than its longer tributary, the Churn — although not without contention. When not listing river lengths, however, alternative definitions may be used. The Missouri River's source is named by some USGS and other federal and state agency sources, following
Lewis Lewis may refer to: Names * Lewis (given name), including a list of people with the given name * Lewis (surname), including a list of people with the surname Music * Lewis (musician), Canadian singer * " Lewis (Mistreated)", a song by Radiohe ...
and Clark's naming convention, as the confluence of the
Madison Madison may refer to: People * Madison (name), a given name and a surname * James Madison (1751–1836), fourth president of the United States Place names * Madison, Wisconsin, the state capital of Wisconsin and the largest city known by this ...
and Jefferson Rivers, rather than the source of its longest tributary (the Jefferson). This contradicts the most common definition, which is, according to a
US Army Corps of Engineers , colors = , anniversaries = 16 June (Organization Day) , battles = , battles_label = Wars , website = , commander1 = ...
official on a USGS site, that " eographersgenerally follow the longest tributary to identify the source of rivers and streams." In the case of the Missouri River, this would have the source be well upstream from Lewis and Clark's confluence, "following the Jefferson River to the
Beaverhead River The Beaverhead River is an approximately tributary of the Jefferson River in southwest Montana (east of the Continental Divide). It drains an area of roughly . The river's original headwaters, formed by the confluence of the Red Rock River and H ...
to Red Rock River, then Red Rock Creek to
Hell Roaring Creek Hell Roaring Creek is a fast-running creek in southern Montana. The creek flows from Brower's Spring, which is considered the ultimate source of the Missouri River.Demetriades , Anthony (July/August 2005"The True Utmost Reaches of the Missouri" ...
."


Characteristics

Sometimes the source of the most remote tributary may be in an area that is more marsh-like, in which the "uppermost" or most remote section of the marsh would be the true source. For example, the source of the River Tees is marshland. The furthest stream is also often called the head stream. Headwaters are often small streams with cool waters because of shade and recently melted ice or snow. They may also be glacial headwaters, waters formed by the melting of
glacial A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betwe ...
ice Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaq ...
. Headwater areas are the upstream areas of a
watershed Watershed is a hydrological term, which has been adopted in other fields in a more or less figurative sense. It may refer to: Hydrology * Drainage divide, the line that separates neighbouring drainage basins * Drainage basin, called a "watershe ...
, as opposed to the outflow or discharge of a watershed. The river source is often but not always on or quite near the edge of the watershed, or watershed divide. For example, the source of the
Colorado River The Colorado River ( es, Río Colorado) is one of the principal rivers (along with the Rio Grande) in the Southwestern United States and northern Mexico. The river drains an expansive, arid watershed that encompasses parts of seven U.S. sta ...
is at the
Continental Divide A continental divide is a drainage divide on a continent such that the drainage basin on one side of the divide feeds into one ocean or sea, and the basin on the other side either feeds into a different ocean or sea, or else is endorheic, not c ...
separating the
Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth#Surface, Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Afr ...
and Pacific Ocean watersheds of North America.


Example

A ''river'' is considered a ''linear'' geographic feature, with only one mouth and one source. For an example, note how the Mississippi River and Missouri River sources are officially defined: * *, Length: , Source: *, Length: , Source:


Related usages

The verb "rise" can be used to express the general region of a river's source, and is often qualified with an adverbial expression of place. For example: *''The River Thames rises in Gloucestershire.'' *''The White Nile rises in the Great Lakes region of central Africa.'' The word "source", when applied to lakes rather than rivers or streams, refers to the lake's
inflow Inflow may refer to: * Inflow (hydrology), the water entering a body of water * Inflow (meteorology), the influx of warmth and moisture from air into storm systems * Capital inflows, in macroeconomics and international finance * Infiltration/Infl ...
.


See also

*
Source of the Amazon River The main source of the largest river in the world has been a subject of exploring and speculations for centuries and continues to cause arguments even today. Determining the origin of the Amazon River has evoked broad debates among scholars, explo ...
*
Source of the Nile The Nile, , Bohairic , lg, Kiira , Nobiin: Áman Dawū is a major north-flowing river in northeastern Africa. It flows into the Mediterranean Sea. The Nile is the longest river in Africa and has historically been considered the longest rive ...
* Spring (hydrology) * Strahler number *
Water well A well is an excavation or structure created in the ground by digging, driving, or drilling to access liquid resources, usually water. The oldest and most common kind of well is a water well, to access groundwater in underground aquifers. Th ...


References

DeBarry, Paul A. (2004). Watersheds: Processes, Assessment and Management. John Wiley & Sons. {{Rivers, streams and springs Water streams Fluvial landforms Freshwater ecology River morphology