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. In Romania, its length is 100 km (62 mi) and its basin size is 1,392 km (537 sq mi).

Hydronymy

The Hungarian name of the river means "brook". The Romanian name derives from that.

Tributaries

The following rivers are tributaries to the river Ier:

• Left: Checheț, Santău, Sărvăzel, Pir
• Right: Cubic, Sânmiclăuș, Pârâul Morii, Zimoiaș, Rât, Salcia, Ierul Îngust