River mouth in the context of Density

A drainage basin is an area of land in which all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean. A basin is separated from adjacent basins by a perimeter, the drainage divide, made up of a succession of elevated features, such as ridges and hills. A basin may consist of smaller basins that merge at river confluences, forming a hierarchical pattern.

Other terms for a drainage basin are catchment area, catchment basin, drainage area, river basin, water catchment, water basin, and impluvium. In North America, they are commonly called a watershed, though in other English-speaking places, "watershed" is used only in its original sense, that of the drainage divide line.

A river delta is a landform, archetypically triangular, created by the deposition of the sediments that are carried by the waters of a river, where the river merges with a body of slow-moving water or with a body of stagnant water. The creation of a river delta occurs at the river mouth, where the river merges into an ocean, a sea, or an estuary, into a lake, a reservoir, or (more rarely) into another river that cannot carry away the sediment supplied by the feeding river. Etymologically, the term river delta derives from the triangular shape (Δ) of the uppercase Greek letter delta. In hydrology, the dimensions of a river delta are determined by the balance between the watershed processes that supply sediment and the watershed processes that redistribute, sequester, and export the supplied sediment into the receiving basin.

River deltas are important in human civilization, as they are major agricultural production centers and population centers. They can provide coastline defence and can impact drinking water supply. They are also ecologically important, with different species' assemblages depending on their landscape position. On geologic timescales, they are also important carbon sinks.

A freshwater marsh is a non-forested marsh wetland that contains shallow fresh water, and is continuously or frequently flooded. Freshwater marshes primarily consist of sedges, grasses, and emergent plants. Freshwater marshes are usually found near the mouths of rivers, along lakes, or are present in low lying areas with low drainage like abandoned oxbow lakes. Unlike its counterpart the salt marsh, which is regularly flushed with sea water, freshwater marshes receive the majority of their water from surface water.

A liman is a wide estuary formed as a lagoon at the mouth of one or more rivers where flow is constrained by a sediment bar created by sea or river current. The hydrological term comes from the Russian language and is used in various national and regional languages for estuary lagoons all around the Black Sea and Sea of Azov coasts.

A liman is classified as either maritime or fluvial: "maritime" if its sediment bar was formed by sea current; "fluvial" if the bar is created by obstructed flow in a saturated river.

The Shatt al-Arab (Arabic: شط العرب, lit. 'River of the Arabs') is a river about 200 kilometres (120 mi) in length that is formed at the confluence of the Euphrates and Tigris rivers in the town of al-Qurnah in the Basra Governorate of southern Iraq. The southern end of the river constitutes the Iran–Iraq border down to its mouth, where it discharges into the Persian Gulf. The Shatt al-Arab varies in width from about 232 metres (761 ft) at Basra to 800 metres (2,600 ft) at its mouth. It is thought that the waterway formed relatively recently in geological time, with the Tigris and Euphrates originally emptying into the Persian Gulf via a channel further to the west. Kuwait's Bubiyan Island is part of the Shatt al-Arab delta.

The Karun, a tributary which joins the waterway from the Iranian side, deposits large amounts of silt into the river; this necessitates continuous dredging to keep it navigable.

The Ohio River (Seneca: Ohi:yo') is a 981-mile-long (1,579 km) river in the United States. It is located at the boundary of the Midwestern and Southern United States, flowing in a southwesterly direction from Pittsburgh, Pennsylvania, to its mouth on the Mississippi River in Cairo, Illinois. It is the third largest river by discharge volume in the United States and the largest tributary by volume of the Mississippi River. It is also the sixth oldest river on the North American continent. The river flows through or along the border of six states, and its drainage basin includes parts of 14 states. Through its largest tributary, the Tennessee River, the basin includes several states of the southeastern United States. It is the source of drinking water for five million people.

The river became a primary transportation route for pioneers during the westward expansion of the early U.S. The lower Ohio River just below Louisville was obstructed by rapids known as the Falls of the Ohio where the elevation falls 26 feet (7.9 m) in 2 miles (3.2 km) restricting larger commercial navigation, although in the 18th and early 19th century its three deepest channels could be traversed by a wide variety of craft then in use. In 1830, the Louisville and Portland Canal (now the McAlpine Locks and Dam) bypassed the rapids, allowing even larger commercial and modern navigation from the Forks of the Ohio at Pittsburgh to the Port of New Orleans at the mouth of the Mississippi on the Gulf of Mexico. Since the "canalization" of the river in 1929, the Ohio has not been a natural free-flowing river; today, it is divided into 21 discrete pools or reservoirs by 20 locks and dams for navigation and power generation.

Khabarovsk Krai (Russian: Хабаровский край, romanized: Khabarovskiy kray, IPA: [xɐˈbarəfskʲɪj kraj]) is a federal subject (a krai) of Russia. It is located in the Russian Far East and is administratively part of the Far Eastern Federal District. The administrative centre of the krai is the city of Khabarovsk, which is home to roughly half of the krai's population and the largest city in the Russian Far East (just ahead of Vladivostok). Khabarovsk Krai is the third-largest federal subject by area, and had a population of 1,343,869 as of 2010.

Being dominated by the Siberian High winter cold, the continental climates of the krai see extreme freezing for an area adjacent to the sea near the mid-latitudes, but also warm summers in the interior. The southern region lies mostly in the basin of the lower Amur River, with the mouth of the river located at Nikolaevsk-on-Amur draining into the Strait of Tartary, which separates Khabarovsk Krai from the island of Sakhalin. The north occupies a vast mountainous area along the coastline of the Sea of Okhotsk, a marginal sea of the Pacific Ocean. Khabarovsk Krai is bordered by Magadan Oblast to the north; Amur Oblast, Jewish Autonomous Oblast, and the Sakha Republic to the west; Primorsky Krai to the south; and Sakhalin Oblast to the east.

The head of navigation is the farthest point above the mouth of a river that can be navigated by ships. Determining the head of navigation can be subjective on many streams, as the point may vary greatly with the size or the draft of the ship being contemplated for navigation and the seasonal water level. On others, it is quite objective, being caused by a waterfall, a low bridge that is not a drawbridge, or a dam without navigation locks. Several rivers in a region may have their heads of navigation along a line called the fall line.

Longer rivers such as the River Thames may have several heads of navigation depending on the size of the vessel. In the case of the Thames, that includes London Bridge, which historically served as the head of navigation for tall ships; Osney Bridge in Oxford, which has the lowest headroom of any bridge on the Thames that generally restricts navigation to smaller vessels such as narrowboats and cabin cruisers, and the long reach above St John's Lock, the first lock downstream of the river’s source, on the outskirts of Lechlade, where the river can become treacherously narrow and shallow for anything but small motorboats and human-powered vessels.

The Liaodong or Liaotung Peninsula (simplified Chinese: 辽东半岛; traditional Chinese: 遼東半島; pinyin: Liáodōng Bàndǎo) is a peninsula in southern Liaoning province in Northeast China, and makes up the southwestern coastal half of the Liaodong region. It is located between the mouths of the Daliao River (the historical lower section of the Liao River) in the west and the Yalu River in the east, and encompasses the territories of the whole sub-provincial city of Dalian and parts of prefectural cities of Yingkou, Anshan and Dandong.

The word "Liaodong" literally means "Liao region's east", referring initially to the Warring States period Yan commandery of Liaodong, which encompassed an area from modern Liaoning-Jilin border in the north to the Chongchon River on the Korean Peninsula in the south, and from just east of the Qian Mountains to a now-disappeared large wetland between the western banks of middle Liao River and the base of Yiwulü Mountain, historically known as the "Liao Mire" (遼澤, Liáo zé) roughly in between the modern Xinmin, Liaozhong, Tai'an, Panshan and Beizhen). The modern usage of "Liaodong", however, simply refers to the half of Liaoning province to the left/east bank of the Liao/Daliao River.

The South Branch Potomac River has its headwaters in northwestern Highland County, Virginia, near Hightown along the eastern edge of the Allegheny Front. After a river distance of 139 miles (224 km), the mouth lies east of Green Spring, Hampshire County, West Virginia, where it meets the North Branch Potomac River to form the Potomac.

The Timok (Serbian and Bulgarian: Тимок, Romanian: Timoc), sometimes also known as Great Timok (Serbian: Велики Тимок / Veliki Timok, Romanian: Timocul Mare), is a river in eastern Serbia, a right tributary of the Danube. For the last 15 km of its run it forms a border between eastern Serbia and western Bulgaria.

It is a branchy system of many shorter rivers, many of them having the same name (Timok), only clarified with adjectives. From the farthest source in the system, that of the Svrljiški Timok, until its confluence (as Veliki Timok), the Timok is 202 km long. The area of the river basin is 4,626 km (1,786 sq mi). Its average discharge at the mouth is 31 m/s (1,100 cu ft/s). The Timok Valley is known for the most important Vlach population in Eastern Serbia.

The Maeotian Swamp or Maeotian Marshes (Ancient Greek: ἡ Μαιῶτις λίμνη, hē Maiōtis límnē, literally Maeotian Lake; Latin: Palus Maeotis) was a name applied in antiquity variously to the swamps at the mouth of the Tanais River in Scythia (the modern Don in southern Russia) and to the entire Sea of Azov which it forms there. The sea was also known as the Maeotian Lake (Ancient Greek: ἡ Μαιῶτις λίμνη, hē Maiōtis límnē; Latin: Lacus Maeotis) among other names. The people who lived around the sea were known as the Maeotians, although it remains unclear which was named for which. The Kerch Strait joins the Sea of Azov and the Black Sea.

The Ixomates were a tribe of the Maeotes. To the south of the Maeotes, east of the Crimea were the Sindes, their lands known as Scythia Sindica.

A mouth bar is an element of a deltaic system, which refers to the typically mid-channel deposition of the sediment transported by the river channel at the river mouth.