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22-595: It rises in two branches, the West Branch and East Branch, both of which have their headwaters in Hancock County , each about 38 miles (61 km) long and which join in Belmond . The Iowa then proceeds roughly in a southeast direction, passing through the city of Iowa Falls , through a scenic valley to Steamboat Rock , then through the cities of Eldora , Marshalltown , Tama , and Marengo , and through

44-413: A river flows into a larger body of water , such as another river, a lake / reservoir , a bay / gulf , a sea , or an ocean . At the river mouth, sediments are often deposited due to the slowing of the current, reducing the carrying capacity of the water. The water from a river can enter the receiving body in a variety of different ways. The motion of a river is influenced by the relative density of

66-578: A deficit at the river's mouth. As river mouths are the site of large-scale sediment deposition and allow for easy travel and ports, many towns and cities are founded there. Many places in the United Kingdom take their names from their positions at the mouths of rivers, such as Plymouth (i.e. mouth of the Plym River ), Sidmouth (i.e. mouth of the Sid River ), and Great Yarmouth (i.e. mouth of

88-411: A more substantial and consistent flow that becomes a first-order tributary of that river. The tributary with the longest course downstream of the headwaters is regarded as the main stem . 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

110-600: A prehistoric Native American of middle age or older in the Iowa River in Marshall County. Headwaters The headwater of a river or stream is the point on each of its tributaries upstream from its mouth / estuary into a lake / sea or its confluence with another river. Each headwater is considered one of the river's sources , as it is the place where surface runoffs from rainwater , meltwater and/or spring water begin accumulating into

132-403: A variety of landforms , such as deltas , sand bars , spits , and tie channels. Landforms at the river mouth drastically alter the geomorphology and ecosystem. Along coasts, sand bars and similar landforms act as barriers, sheltering sensitive ecosystems that are enriched by nutrients deposited from the river. However, the damming of rivers can starve the river of sand and nutrients, creating

154-777: Is joined in Washington County by the English River , and then in Louisa County it is joined by the Cedar River to flow into the Mississippi. The Iowa River is noted for recreational and commercial fishing. Game fish include largemouth and smallmouth bass , walleye , northern pike , channel and flathead catfish , crappie and other panfish . The Coralville Reservoir is commercially fished for carp and buffalo fish . Pine Lake State Park

176-639: Is located on the Iowa River at Eldora . The Iowa can flood, notably in the June 2008 Midwest floods , and the Great Flood of 1993 . The Cedar and its tributaries, including the Shell Rock River , can contribute to flooding events. It tore down the historical swinging bridge in Charles City, Iowa. On the afternoon of August 8, 2022, Marshall County Conservation staff discovered a jawbone from

198-515: Is named by some USGS and other federal and state agency sources, following Lewis and Clark 's naming convention, as the confluence of the Madison 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 official on a USGS site, that "[geographers] generally follow

220-784: The Amana Colonies in Iowa County . In Johnson County , it becomes impounded by the Coralville Dam in the Coralville Reservoir , which turns southward to the spillway. The river runs generally south and passes through Iowa City and the University of Iowa campus. A lowhead dam at Burlington Street in Iowa City is the last dam before the river's confluence with the Mississippi. South of Iowa City, it

242-467: The Mississippi River and Missouri River sources are officially defined as follows: 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 word "source", when applied to lakes rather than rivers or streams, refers to the lake's inflow . River mouth A river mouth is where

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264-467: 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 ice . Headwater areas are

286-585: 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

308-540: 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

330-607: 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 to Red Rock River , then Red Rock Creek to Hell Roaring Creek ." Sometimes the source of the most remote tributary may be in an area that is more marsh -like, in which

352-406: The receiving water, as is typically the case when fresh river water flows into the sea, the river water will float along the surface of the receiving water as an overflow. Alongside these advective transports, inflowing water will also diffuse . At the mouth of a river, the change in flow conditions can cause the river to drop any sediment it is carrying. This sediment deposition can generate

374-461: The river compared to the receiving water, the rotation of the Earth, and any ambient motion in the receiving water, such as tides or seiches . If the river water has a higher density than the surface of the receiving water, the river water will plunge below the surface. The river water will then either form an underflow or an interflow within the lake. However, if the river water is lighter than

396-462: The source of rivers such as the Amazon or Nile . A definition given by the state of Montana agrees, stating that a river source is never a confluence 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

418-802: The source of the largest river flowing into the lake, the Kagera River . 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

440-525: 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 900 km (560 mi) (dropping it to fourth or fifth on the list of world's rivers), but instead use

462-664: The upstream areas of a watershed , 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 is at the Continental Divide separating the Atlantic Ocean and Pacific Ocean watersheds of North America . A river is considered a linear geographic feature, with only one mouth and one source. For an example,

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484-473: 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

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