Mangapu River
The New Zealand Ministry for Culture and Heritage gives a translation of "double stream" for Mangapū.
SH3 crosses the river on a 111 m (364 ft) bridge near Ōtorohanga built in 1966 and near Hangatiki on a 41 m (135 ft) concrete bridge built in 1977. The railway follows the east bank for about 6 km (3.7 mi), crossing only small tributaries, though it did suffer from flooding, for example in 1905.
The river at Ōtorohanga is classed as being in the worst 25% of similar sites as regards all measured pollutants, though some attempts are being made at restoration.
Pehitawa Kahikatea Forest Reserve
The reserve 18.5 ha (46 acres) of kahikatea forest on the east bank of the river, was purchased by the Native Forests Restoration Trust in 2001. Kahikatea forest once covered 41,000 ha (100,000 acres) in the Waipa Ecological District, now reduced to 158 ha (390 acres), of which 52 ha (130 acres) are in the Mangapu valley, though over 70 ha (170 acres) has been felled since 1975. A major drainage scheme was carried out just upstream from the reserve in the 1930s, including emptying of a lake. The forest floods in winter and flood protection would be uneconomic. Some kahikatea in the reserve are about 120 years old. The reserve also has swamp maire, mataī, tītoki and pukatea. Te Araroa long-distance walkway passes through the reserve and crosses the river on a suspension bridge.