IJssel

IJssel
Gelderse IJssel
River
Sunset on the IJssel at Deventer
Country	Netherlands
Province	Gelderland, Overijssel
Regions	Liemers, Veluwe, Achterhoek, Salland
Tributaries
- right	Oude IJssel, Berkel, Schipbeek
Cities	Arnhem (suburbs), Doesburg, Zutphen, Deventer, Zwolle (suburbs), Kampen
Source	Nederrijn
- location	Westervoort, Gelderland, Netherlands
Mouth	Ketelmeer (inlet of lake IJsselmeer)
- location	Kampen, Salland, Overijssel, Netherlands
- coordinates	52°34′58″N 5°50′24″E / 52.58278°N 5.84000°E / 52.58278; 5.84000Coordinates: 52°34′58″N 5°50′24″E / 52.58278°N 5.84000°E / 52.58278; 5.84000
Length	125 km (78 mi)
Discharge
- average	340 m3/s (12,007 cu ft/s)
Location of river IJssel in dark blue.

The River IJssel (Dutch pronunciation: [ˈɛi̯səl]), sometimes called Gelderse IJssel ("Gueldern IJssel") to avoid confusion with the Hollandse IJssel, is the branch of the Rhine in the Dutch provinces of Gelderland and Overijssel. The Romans knew the river as Isala. The IJssel flows from Westervoort, east of the city of Arnhem, until it discharges into the IJsselmeer ("Lake IJssel", known prior to the 1932 completion of the Afsluitdijk as the Zuiderzee, a North Sea inlet). The River IJssel is one of the three major distributary branches (along with the rivers Nederrijn and Waal) into which the Rhine divides shortly after crossing the German-Dutch border.

The name includes the digraph ij, which behaves like a single letter in Dutch orthography - this explains why both letters appear capitalized (compare: IJmuiden and IJsselmeer).

The name IJssel (older Isla, Isala, from *Īsalō), is thought to derive from a Proto-Indo-European root *eis- "to move quickly" (cf. Old Norse eisa "to race forward", Latin ira "anger"). In the Middle Ages, the Zuiderzee had not yet formed, and in its place there was an inland lake known as Vlies (Lat. Flevo), and the IJssel flowed through the surrounding lakelands. However, since the formation of the Zuiderzee and obstruction from the Afsluitdijk, the IJssel no longer flows into its estuary, the Vlie, now restricted in meaning and referring only to the strait separating the islands of Vlieland (itself named after the Vlie strait) and Terschelling. It is hypothesised that the now-poldered tidal inlets near Medemblik and the IJ (near Amsterdam) once were branches of river IJssel.