The Opawa River is in the Marlborough region of the South Island of New Zealand. It begins in the Wairau valley where floodways are joined. It makes its way down the valley and flows through and looping around the eastern suburbs of Blenheim where it is crossed by the Opawa River Bridge. It joins the Taylor River in Blenheim (keeping the Opawa name) and flows into Cook Strait at Cloudy Bay, just southeast of the mouth of the Wairau River.
There are two possible sources for the river's name. It might have been named after the chief Pawa or Paoa. Rangitāne iwi say that the name is a mutilation of Opaoa, which literally means smoky river. With Blenheim built on swampy land, the river was often brown (or 'smoky') as a consequence.[1]