River island in the context of Tributary

An island or isle is a piece of land, distinct from a continent, completely surrounded by water. There are continental islands, which were formed by being split from a continent by plate tectonics, and oceanic islands, which have never been part of a continent. Oceanic islands can be formed from volcanic activity, grow into atolls from coral reefs, and form from sediment along shorelines, creating barrier islands. River islands can also form from sediment and debris in rivers. Artificial islands are those made by humans, including small rocky outcroppings built out of lagoons and large-scale land reclamation projects used for development.

Islands are host to diverse plant and animal life. Oceanic islands have the sea as a natural barrier to the introduction of new species, causing the species that do reach the island to evolve in isolation. Continental islands share animal and plant life with the continent they split from. Depending on how long ago the continental island formed, the life on that island may have diverged greatly from the mainland due to natural selection.

The Tiber Island (Italian: Isola Tiberina, Latin: Insula Tiberina) is the only river island in the part of the Tiber which runs through Rome. Tiber Island is located in the southern bend of the Tiber.

The island is boat-shaped, approximately 270 metres (890 feet) long and 67 metres (220 feet) wide, and has been connected with bridges to both sides of the river since antiquity. Being a seat of the ancient temple of Asclepius and later a hospital, the island is associated with medicine and healing. The Fatebenefratelli Hospital founded in the 16th century, and the basilica church of San Bartolomeo all'Isola dating from the 10th century, are located on the island.

In geography, a confluence (also conflux) occurs where two or more watercourses 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); or where two streams meet to become the source of a river of a new name (such as the confluence of the Monongahela and Allegheny rivers, forming the Ohio River); or where two separated channels of a river (forming a river island) rejoin downstream from their point of separation.

River bifurcation (from Latin: furca, fork) occurs when a river (a bifurcating river) flowing in a single channel separates into two or more separate streams (called distributaries) which then continue downstream. Some rivers form complex networks of distributaries, typically in their deltas. If the streams eventually merge again or empty into the same body of water, then the bifurcation forms a river island.

River bifurcation may be temporary or semi-permanent, depending on the strength of the material that is dividing the two distributaries. For example, a mid-stream island of soil or silt in a delta is most likely temporary, due to low material strength. A location where a river divides around a rock fin, e.g. a volcanically formed dike, or a mountain, may be more lasting as a result of higher material strength and resistance to weathering and erosion. A bifurcation may also be man-made, for example when two streams are separated by a long bridge pier.

A point bar is a depositional feature made of alluvium that accumulates on the inside bend of streams and rivers below the slip-off slope. Point bars are found in abundance in mature or meandering streams. They are crescent-shaped and located on the inside of a stream bend, being very similar to, though often smaller than, towheads, or river islands.

Point bars are composed of sediment that is well sorted and typically reflects the overall capacity of the stream. They also have a very gentle slope and an elevation very close to water level. Since they are low-lying, they are often overtaken by floods and can accumulate driftwood and other debris during times of high water levels. Due to their near flat topography and the fact that the water speed is slow in the shallows of the point bar they are popular rest stops for boaters and rafters. However, camping on a point bar can be dangerous as a flash flood that raises the stream level by as little as a few inches (centimetres) can overwhelm a campsite in moments.

Pheasant Island (French: Île des Faisans/Île de la Conférence, Spanish: Isla de los Faisanes, Basque: Konpantzia, Faisaien Uhartea Konferentziako Uhartea, Faisaien Irla) is an uninhabited river island located in the Bidasoa river, located between France and Spain, whose administration alternates between the two nations every six months.

Ostrów Island (Polish pronunciation: [ɔstruf]) is a river island, located in the delta of the Vistula river, within the city limits of Gdańsk in northern Poland. Administratively, it is located within the district of Młyniska.

The northern border of the island is formed by the waters of Port Channel (Gdańsk), while the southern border is a rather moribund branch of the Vistula called Martwa Wisła, literally meaning dead Vistula.

Hisingen (Swedish pronunciation: [ˈhîːsɪŋɛn]) is the fifth-largest island of Sweden (after Gotland, Öland, Södertörn and Orust), with an area of 199 km (77 sq mi). It is a river island, formed by the split of the Göta Älv at Bohus, and is defined to the east and south by the main arm of that river, to the north by the smaller arm (known as the Nordre Älv), and to the west by the Kattegat. The southern part of Hisingen is extensively urbanised, representing the northern suburbs of the city of Gothenburg. The island is divided between the historical provinces of Västergötland and Bohuslän, but lies entirely within the modern county of Västra Götaland.

According to the 2023 census, the island of Hisingen in Sweden has a population of 176,047, making it the second most populous island in Sweden, after Södertörn but before Gotland.

An ait (/eɪt/, like eight) or eyot (/aɪ(ə)t, eɪt/) is a small island. The term is especially used to refer to river islands found on the River Thames and its tributaries in England.

Aits are typically formed by the deposit of sediment in the water, which accumulates. An ait is characteristically long and narrow, and may become a permanent island should it become secured and protected by growing vegetation. However, aits may also be eroded: the resulting sediment is deposited further downstream and could result in another ait. A channel with numerous aits is called a braided channel.

The Si Phan Don (Lao: ສີ່ພັນດອນ; meaning '4,000 islands') is a riverine archipelago in the Mekong River, Champasak Province in southern Laos. Si Phan Don is part of Khong District, including the islands and part of the mainland in the east. Si Phan Don is dotted with numerous islands, half of which are submerged when the Mekong River is in flood. The principal islands of Si Phan Don are Don Khong (the largest), Don Som (the second largest), Don Det and Don Khon. Si Phan Don borders Cambodia and historical and cultural ties link the people on both side of the border. Pakse is the closest of the bigger cities in Laos to the area.

Key features of the Si Phan Don archipelago include:

Majuli (also spelled Majoli) is the largest river island in Assam, a state in Northeast India. It is bordered by the Brahmaputra River to the south and east, the Subansiri River to the west, and an anabranch of the Brahmaputra to the north.

The island is inhabited by members of the Mising, Deori, and Sonowal Kachari tribes, and serves as a hub of Assamese neo-Vaishnavite culture. It is accessible by ferry or boat from Jorhat, which is located approximately 250 kilometers northeast of Guwahati.

An anabranch is a section of a river or stream that diverts from the main channel or stem of the watercourse and rejoins the main stem downstream. Local anabranches can be the result of small islands in the watercourse. In larger anabranches, the flow can diverge for a distance of several, or even hundreds, of kilometers before rejoining the main channel.