Lake Pukaki in the context of Lake Ōhau

Rock flour, or glacial flour, consists of fine-grained, silt-sized particles of rock, generated by mechanical grinding of bedrock by glacial erosion or by artificial grinding to a similar size. Because the material is very small, it becomes suspended in meltwater making the water appear cloudy, which is sometimes known as glacial milk.

When the sediments enter a river, they turn it grey, light brown, iridescent blue-green, or milky white. If the river flows into a glacial lake, the lake may appear turquoise in colour as a result. When appearing as any shade of blue, the colour is most commonly caused by the Tyndall Effect, with the particular hue determined by suspended particle size. When flows of the flour are extensive, a distinct layer of a different colour flows into the lake and begins to dissipate and settle as the flow extends from the increase in water flow from the glacier during snow melts and heavy rain periods. Examples of this phenomenon may be seen at Lake Pukaki and Lake Tekapo in New Zealand, Lake Louise, Moraine Lake, Emerald Lake, and Peyto Lake in Canada, Gjende lake in Norway, and several lakes (among others, Nordenskjöld and Pehoé) in Chile's Torres del Paine National Park, and many lakes in the Cascade Range of Washington State (including Diablo Lake, Gorge Lake, and Blanca Lake).

The Waitaki River is a large braided river in the South Island of New Zealand. It drains the Mackenzie Basin and runs 209 kilometres (130 mi) south-east to enter the Pacific Ocean between Timaru and Oamaru on the east coast. It starts at the confluence of the Ōhau and Tekapo rivers, now at the head of the artificial Lake Benmore, these rivers being fed by three large glacial lakes, Pukaki, Tekapo, and Ōhau, at the base of the Southern Alps. The Waitaki flows through Lake Benmore, Lake Aviemore and Lake Waitaki, these lakes being contained by the hydroelectric dams of Benmore Dam, Aviemore Dam and Waitaki Dam. The Waitaki has several tributaries, notably the Ahuriri River and the Hakataramea River. It passes Kurow and Glenavy before entering the Pacific Ocean. The river lends its name to the Waitaki District on the south side of the river.

The river's flow is normally low in winter, with flows increasing in spring when the snow cloaking the Southern Alps begins to melt, with flows throughout the summer being rainfall dependent and then declining in the autumn as the colder weather begins to freeze the smaller streams that feed the catchment. The median flow of the Waitaki River at Kurow is 356 cubic metres per second (12,600 cu ft/s).

Lake Tekapo (Māori: Takapō) is the second-largest of three roughly parallel lakes running north–south along the northern edge of the Mackenzie Basin in the South Island of New Zealand (the others are Lake Pukaki and Lake Ōhau). It covers an area of 83 km (32 sq mi) and is at an altitude of 710 m (2,330 ft) above sea level.

Lake Tekapo (often known simply as Tekapo (Māori: Takapō) to avoid confusion with the lake itself) is a small township located at the southern end of the lake of the same name in the inland South Island of New Zealand. It had 558 residents according to the 2018 census, being one of five settlements in the sparsely populated Mackenzie Basin.

State Highway 8 runs directly through the township – 227 kilometres (141 mi) from Christchurch and 256 kilometres (159 mi) from Queenstown. Daily shuttle services link Lake Tekapo to Christchurch and Queenstown. The lake is a popular tourist destination, and several resort hotels are located at the township. Lake Tekapo Airport is located 5 kilometres (3.1 mi) west of the town where local tourism operator Air Safaris is based. Twizel lies 60 km (39 minutes drive) south of Lake Tekapo via Lake Pukaki and Burkes Pass lies 21 km (15 minutes drive) west along State Highway 8.