The Orneau (French pronunciation: [ɔʁno]; Walloon: Ôrnô) is a river in Belgium. It is a tributary of the Sambre and therefore sub-tributary of the Meuse.

The Orneau flows from north to south, through the province of Namur, and after a journey of about 25 kilometres (16 mi), it flows into the Sambre at Jemeppe-sur-Sambre.

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