Nidelva (Aust-Agder)

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This article is about the river in the Arendal drainage system in southern Norway. For Nidelva which runs through Trondheim see Nidelva.

Nidelva in Aust-Agder is the main river in the Arendal drainage system. It is formed by the confluence of two rivers, Nisserelva and Fyreselv. The river flows into Skagerak at Arendal. The total length of the system is 210 km, the watershed covers 4000 km². Sixteen hydro-electric power stations are built along the river, making this one of Norway's most controlled drainage systems.

Salmon can be found 22 km up the river, where the Evenstad power station is located. At Rygene the average waterflow is 110 m³/s, the highest recorded was in the autumn of 1987, with 1200 m³/s.