Much of Marlborough is semi-arid, however a number of rivers flow through the region, in valleys, many resulting from the numerous fault lines that run through the region. The largest river is the Wairau, with the Awatere and Pelorus Rivers also being significant. Each of these major rivers also have a number of smaller tributaries.
Two tributaries of the Wairau, the Branch and the Waihopai Rivers have modest hydroelectric schemes owned by Trustpower which contribute to electricity supply in the region.
While much smaller than the three largest rivers, the Taylor River and Ōpaoa rivers are especially significant to Blenheim.
Under the old provincial boundaries, Marlborough extended south to the Conway River, and the Clarence River fell within the region. Under current local government administrative boundaries, these rivers now fall within the Kaikōura District, however they remain relevant to Marlborough from a historical perspective.