The Waitangiroto Nature Reserve is a protected area of 1,534 ha (3,790 acres) near Whataroa, in the West Coast of New Zealand. The reserve consists of lowland kahikatea swamp forest either side of the Waitangiroto River. It is notable as the site of the only breeding colony of kōtuku or white heron (Ardea alba modesta) in New Zealand, comprising 100–120 birds. Royal spoonbills and little shags also breed alongside the kōtuku. The breeding colony is a visitor attraction during the breeding season, but access to the entire nature reserve is by permit only. Visitors can view the birds from a hide across the Waitangiroto River. Tours of the reserve operate from a base in Whataroa.

Although the kōtuku nesting colony is commonly known as the "Ōkārito colony", Ōkārito is some distance to the south, over a glacial moraine in a different drainage basin. White herons can be commonly seen feeding in Ōkārito Lagoon, a possible cause of the confusion.

The kōtuku colony was known to local Māori, and in 1860 they unsuccessfully petitioned the authorities to create a native reserve which included it.

On 30 December 1865 surveyor Gerhard Mueller took a waka and paddled up the "Waitangi-Roto" River, in search of a lake he was told was fifteen or twenty miles inland. A few miles up the river, he came across the "cranery", and described the white herons there in a letter to his wife Bannie:

Of these birds (near 4 ft. high) imagine seeing around you from 50 to 60, sitting on high pines and lower trees, in a circle of about 150 yards, their pure white feathers shining in the sun. It was a glorious sight—I gave up pulling, and watched the tribe for a long time. They were not at all shy—kept up a continual 'plappering' amongst themselves, and seemed to be astonished at me more than afraid ... I am glad now I had no gun with me—it would have been a pity to disturb this peaceful community.

This was the first sighting of the kōtuku colony by Europeans. Six years after Mueller's account Thomas Potts visited and counted 25 nests. In 1876 Augustus Hamilton found only six nests remaining, and because "certain miscreants destroyed a quantity of nearly-hatched eggs", tearing down saplings to procure them, the birds had abandoned the colony; Hamilton hoped the birds would "find a more secure place for their new home".

A short documentary film about the kōtuku breeding colony was produced by the New Zealand National Film Unit in 1954. The film was shown as a preview to Queen Elizabeth II in Christchurch during her five week long visit to New Zealand, after the Queen was honoured with a Māori greeting "Welcome, O stranger from beyond the horizon, the rare white heron of a single flight".

The reserve includes kahikatea forest, bog, lake, lagoon, and other coastal habitats. Mueller remarked on the dense bush either side of the river, with "beautiful Kowhai trees abounding and almost all shrubs in flower…". At the colony, kōtuku and little shags / kawaupaka (Microcarbo melanoleucos) nest in the crowns of tree ferns (Dicksonia squarrosa), kōwhai (Sophora microphylla), kāmahi (Pterophylla racemosa), and māhoe (Melicytus ramiflorus). Royal spoonbills / kōtuku ngutupapa (Platalea regia) nest higher up in emergent kahikatea (Dacrycarpus dacrydioides) trees. The Waitangiroto River which flows through the reserve is slow, peat-stained, and swamp-fringed, typical of coastal West Coast waterways.