|Counties||Satu Mare County, Bihor County, Hajdú-Bihar County|
|Villages||Andrid, Săcueni, Diosig, Pocsaj|
|Progression||Barcău→ Crișul Repede→ Körös→ Tisza→ Danube→ Black Sea|
The Ier or Eriu (Hungarian: Ér) is a right tributary of the river Barcău (Berettyó) in Romania and Hungary. It discharges into the Barcău in Pocsaj. The Andrid Dam is constructed on this river. The Ier flows through the villages Mihăieni, Eriu-Sâncrai, Ghirolt, Rădulești, Hotoan, Sudurău, Dindești, Andrid, Sălacea, Cherechiu, Săcueni, Diosig in Romania, and Pocsaj in Hungary.
The Hungarian name of the river means "brook". The Romanian name derives from that.
The following rivers are tributaries to the river Ier:
- Left: Checheț, Santău, Sărvăzel, Pir
- Right: Cubic, Sânmiclăuș, Pârâul Morii, Zimoiaș, Rât, Salcia, Ierul Îngust
- Trasee turistice - județul Bihor 
- Trasee turistice - județul Satu Mare 
- Memoriu privind planul de apărare împotriva inundațiilor Satu Mare 
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