Riuwaka is the name given to the spring, that resurges from the Greenlink cave system, by the Maori canoe captain Hui Te Rangiora. He arrived in Tasman Bay after travelling from Rarotonga via Antarctica (he missed NZ and realised his mistake when he started seeing ice bergs). He walked up the river and found the spring. The riu is the bilge of a waka (canoe) or basin, where water would gather, and if you look into the water you can see what Hui Te Rangiora saw, the rock is the same shape as the prow of a waka. In this instance riu is a reference to the pools just downstream of the resurgence. TheProw.org.nz
More recently pakeha settlers called the spring Riwaka, but that turned out to be a spelling mistake. The first two sumps of the Riuwaka Resurgence cave were dived in 1963 by five scuba divers.
In 1974 Nelson cavers discovered the entrance to Greenlink cave on top of Takaka Hill. A dye trace confirmed that Greenlink was a tributary of the Riuwaka Resurgence and the dream of finding a route from one to the other was born. The following year, Middle Earth cave was discovered, but is was not until 1993 that a connection was found to Greenlink. This highlighted the poor quality of the surveys, as it was difficult to reconcile the maps with what was actually found under the ground. A notion to resurvey the caves took hold, but so big was the task (about 4.1km), it was not until 2005 that this started in earnest, led by Lindsay Main and John Atkinson. Another lull, and then Michael Brewer and Bruce Mutton took up the mantle. It never seemed to finish, and by 2010 there was 11km of survey, 2013, 27km and 2017, almost 34km.
As at 2018 there are a number of other caves that have been connected or nearly connected; Swiss Maid, Perseverance, Dwarfs Door, Black Sabbath, Kiwi Burger, Winter Cave, Snail Cavern, and not least, Riuwaka Resurgence Cave, a mere 1100m away. It goes on...