The Mangatainoka River is a prominent North Island fishery flowing through the northern Wairarapa and Manawatū-Whanganui regions. It originates on the eastern slopes of the Tararua Range southwest of Eketahuna and travels roughly parallel to State Highway 2 and the Wairarapa Line railway before joining the Tiraumea River near Woodville. The river is celebrated for its excellent brown trout fishing, with approximately 50 kilometers of easily accessible water. Historically lined with dense native forests of matai, rimu, and totara, the surrounding landscape has been converted to agriculture, which has altered the river's flow characteristics. The water is notably pure, a quality that famously led to the establishment of the Tui Brewery on its banks. The river is a freestone stream, and its character changes significantly from its headwaters to its lower reaches.