The –NgāStillwater Ngākawau Line (SNL), formerly the Stillwater–Westport Line (SWL) and the Ngakawau Branch, is a secondary main line, part of New Zealand's national rail network. It runs between Stillwater and Ngakawau via Westport on the West Coast of the South Island. It was one of the longest construction projects in New Zealand's history, with its first section, at the south end, opened in , and the beginnings of the Ngākawau Branch, at its Westport end, in 1875. The full line was completed in . The only slower railway projects were Palmerston North to Gisborne, 1872 to 1942, and the Main North Line to Picton, 1872 to 1945.
The main traffic has always been coal. In 2021 opencast mines along the line produced 1,321,541 tonnes of coal, 984,951 tonnes of it from Stockton Mine at Ngākawau. All the other mines in the country produced only 1,234,560 tonnes.
Passenger journeys peaked at around 500 a day in 1946 and ceased in 1967. From 1891 until about 1970 the line had a refreshment room, initially at Totara Flat, then Ikamatua, then Stillwater.
Construction
A railway link from Greymouth east to Brunner was opened in 1876, but work on a link from this point to Westport became delayed for ten years by disputes over the best route to link the West Coast with Nelson and Canterbury. A route for a railway was first proposed by the Nelson Province Engineer, John Blackett, in 1863. As this 1886 map shows, when the extension started, it was intended to be part of a much larger network, which would have linked to Blenheim, as well as Nelson. The distance from Westport to Blenheim, via a summit at Tophouse, was surveyed as and to Nelson , with the longest tunnel being , opposite Lyell. Ultimately, the New Zealand Midland Railway Company (NZMRC) was formed to construct the route, and in 1886, work recommenced. The junction of the route to Westport and the Midland Line to Canterbury was established just east of Brunner in Stillwater, and the NZMRC put most of its energy into the first portion of the SWL from Stillwater to Reefton. This was due to the comparatively easier terrain faced by the route in the valley of the Grey River, and in 1889, the line was opened to Ngahere. On 29 February 1892, the NZMRC opened the line all the way to the south bank of the Inangahua River, directly opposite Reefton, and with the Stillwater–Reefton portion complete in their view, they redirected their energy to the Midland route from Stillwater to Otira.
In the mid-1890s the NZMRC ran out of funds and, after a dispute in the courts, was taken over by the central government. Work on the SWL recommenced in the 20th century, with the Inangahua River bridged, the present-day Reefton station established, and a further section to Cronadun opened in 1908. At the Westport end, construction also commenced, with a 9 km line opened in 1912 from Westport to Te Kuha at the western end of the Lower Buller Gorge. In 1914, the line from Cronadun reached Inangahua Junction, where the NZMRC intended its lines to Westport and Nelson to diverge (in fact, Inangahua remained the probable site for a junction until all work on the Nelson Section ceased in 1931). Work was slowed after the Reform Government took over in 1912. However, the outbreak of World War I brought a halt to construction with only the section through the Buller Gorge to complete. In 1921 the slow progress of the line was being criticised and there was speculation that a route to Nelson might follow the Gowan valley.