The Lewis River is a river in the Canterbury region of New Zealand. The valley of this river forms the southeastern approach to Lewis Pass; the river is thus adjacent to State Highway 7. The Lewis River is a tributary of the Boyle River. The Nina River flows into the Lewis River a few kilometres upstream from the confluence with the Boyle River. [1] Land Information New Zealand lists the name of the river as "not official", i.e. the name is not confirmed by the New Zealand Geographic Board. [2] It was named for the surveyor Henry Lewis, who discovered [a] the pass in 1860 alongside his colleague Christopher Maling. Later in 1860, the river was named by Julius von Haast during his own expedition; von Haast became the brother-in-law of Lewis' daughter in 1866. [3]