The Koau and Matau Rivers, also called the Koau and Matau Branches, are the two

distributaries A distributary, or a distributary channel, is a stream that branches off and flows away from a main stream channel. Distributaries are a common feature of river deltas. The phenomenon is known as river bifurcation. The opposite of a distributary ...

of New Zealand's

Clutha River The Clutha River (, officially gazetted as Clutha River / ) is the second longest river in New Zealand and the longest in the South Island. It flows south-southeast through Central and South Otago from Lake Wānaka in the Southern Alps to the P ...

. The two distributaries split immediately to the southeast of the town of Balclutha, at which point the more northerly branch becomes the Matau and the more southerly becomes the Koau. The two branches both flow generally southeast to reach the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

, surrounding the island of

Inch Clutha Inch Clutha is a large, flat island sitting in the delta between the Matau (northern) and Koau (southern) branches of the Clutha River, downstream from the town of Balclutha in the South Island of New Zealand. Approximately long and wide, th ...

. A small silty channel connects the two rivers close to their mouths, creating a smaller unnamed island to the south of Inch Clutha. The two rivers are named from a Māori myth; the two branches were a husband and wife named Koau and Matau respectively. The point where the two waters flow into one another was known as Wai-hakirara, literally singing waters, because of the happiness of their meeting. The name Matau is likely a corruption of the name Mata-au, meaning eddying currents, which is the

Māori language Māori (), or ('the Māori language'), also known as ('the language'), is an Eastern Polynesian language spoken by the Māori people, the indigenous population of mainland New Zealand. Closely related to Cook Islands Māori, Tuamotuan, and ...

name for the Clutha River overall. The name Koau possibly relates to the pied shag ''

Phalacrocorax varius The Australian pied cormorant (''Phalacrocorax varius''), also known as the pied cormorant, pied shag, or great pied cormorant, is a medium-sized member of the cormorant family. It is found around the coasts of Australasia. In New Zealand, it ...

'', for which a Māori name is ''koau''. Both branches of the Clutha are prone to flooding, and have

meander A meander is one of a series of regular sinuous curves in the channel of a river or other watercourse. It is produced as a watercourse erodes the sediments of an outer, concave bank ( cut bank) and deposits sediments on an inner, convex bank ...

ing courses. Both have also formed numerous

oxbow lake An oxbow lake is a U-shaped lake or pool that forms when a wide meander of a river is cut off, creating a free-standing body of water. In South Texas, oxbows left by the Rio Grande are called '' resacas''. In Australia, oxbow lakes are call ...

s. The Matau is considerably more wandering, hence its greater length of . The town of Kaitangata lies on the eastern (mainland) bank of the Matau. Whereas the path of the Matau is predominantly southeast throughout its course, the Koau turns initially westward, flowing past the southern edge of Balclutha. After its path turns to the southeast, in which direction it flows for the remainder of its length. The settlements of Finegand and Otanomomo lie close to its western (mainland) shore. Dowling, P. (ed.) (2004). ’’Reed New Zealand atlas’’. Auckland: Reed Publishing. Map 113. There are several small islands in the Koau, the largest of which is Shaws Island, a long islet surrounded by a stream which is slowly becoming an oxbow.

References

{{coord, 46, 14, 40, S, 169, 45, 20, E, display=title Clutha River Distributaries Rivers of Otago Rivers of New Zealand