Lake Otamangakau is located approximately 11 km (6.8 mi) southwest of Lake Taupō. The man-made reservoir has a size of around 1.8 km2 (0.69 sq mi)[3] and extends over its northern arm in a 45-degree left curve over a length of around 3.1 km2 (1.2 sq mi) and over its eastern arm to the southern tip over a length of around 2.8 km (1.7 mi). Its widest point is in the middle part of the lake and extends over a length of around 900 m in a north-west-south-east direction.[2][4] The deepest part of the lake is 12 m.[5]
The reservoir is connected to two other reservoirs via two canals, one via the southwestern Otamangakau Canal, which connects Lake Te Whaiau, which in turn carries its waters to Lake Otamangakau, and the other via the Wairehu, which emanates from the eastern arm of the lake Canal with Lake Rotoaira, which is located southeast of Lake Otamangakau. The waters of Lake Otamangakau flow over the Wairehu Canal to Lake Rotoaira, which is 564 m, 47 m lower than Lake Otamangakau.[2] It is surrounded by extensive wetlands to the east and south.[2]
Lake Otamangakau, which is located at an altitude of 611 m, is fed by a few smaller streams from the surrounding area and the lake experiences its regular outflow via a small stream that flows into the Whanganui River around 1.7 km (1.1 mi) further.[2][4]
