| Oude IJssel | |
| Name Other: | Issel |
| Subdivision Type1: | Countries |
| Subdivision Name1: | Netherlands and Germany |
| Length: | 81.7km (50.8miles) |
| Discharge1 Location: | Doesburg |
| Discharge1 Avg: | NaNm3/s |
| Source1 Location: | near Raesfeld, Westphalia, Germany |
| Source1 Coordinates: | 51.7946°N 6.8305°W |
| Source1 Elevation: | NaNm (-2,147,483,648feet) |
| Mouth Location: | near Doesburg, in the IJssel, Gelderland, Netherlands |
| Mouth Coordinates: | 52.0128°N 6.128°W |
| Mouth Elevation: | NaNm (-2,147,483,648feet) |
| Basin Size: | NaNkm2 |
| Tributaries Right: | Bocholter Aa → Aa Strang, Schlinge (river) → |
| Custom Label: | Progression |
The Oude IJssel (Dutch, in Dutch; Flemish pronounced as /ˌʌudə ˈʔɛisəl/, literally old IJssel) or Issel (German, pronounced as /de/) is a river in Germany and the Netherlands approximately long. It is a right tributary of the river IJssel. Oude IJssel is Dutch for "Old IJssel"; the Oude IJssel was the upper course of the IJssel until the connection with the Rhine was dug, possibly in the Roman era.
This connection made the Rhine the largest contributor to the flow of the IJssel, although only a relatively small amount of the total flow of the Rhine made its way into the system. Various tributaries can sometimes add water to the total flow of the river, for example the Berkel and the Schipbeek. The IJssel river is the only branch of the Rhine delta that consumes tributary rivers instead of giving birth to distributary rivers. The latter only happens at the last part of the river, where the small IJssel Delta is created.
The Oude IJssel begins near Borken in North Rhine-Westphalia, Germany. It flows southwest until it nearly reaches the Rhine near Wesel, then it turns northwest. After Isselburg it crosses the border with the Netherlands and enters the province of Gelderland. It flows through Doetinchem and joins the IJssel in Doesburg.