Lake Mapourika is in Westland in the South Island. It is ten km north of Franz Josef Glacier and only takes ten minutes by car. It is the largest of the several Westland post-Ice Age glacial lakes immediately accessible from State Highway 6. Lake Moeraki and Lake Paringa are to the south, and Waihapo and Ianthe are to the north.
There is no major river inflow, with the lake fed by numerous streams and runoff from the surrounding forested hills. The lake is especially dark due to the tannins washed into it from the forest. The main outflow is the Ōkārito River which runs to the Ōkārito Lagoon, a large lagoon on the edge of the coast north of the hamlet of Ōkārito. It is also quite sheltered and often generates superb reflections.
There is a campsite on the lake's northeast side, and it is a great spot for kayaking.
Thanks to Georgia (@the_cornishpixie) and Jan Rozen for the photos.