Lake Ianthe / (Matahi) is a Lake located on the West Coast of New Zealand's South Island. A number of small streams flow into the lake and it empties into the Wanganui River. It is close to the coast and near the rural settlements of Pukekura and Hari Hari and State Highway 6 runs along the eastern shore of the lake on its route between Ross and the Franz Josef Glacier. The lake is popular for boating, swimming, and trout fishing. In the early 20th century, a privately run bush tramway was established from the end of the New Zealand's Railways Departments Ross Branch Railways to logging interests in the Lake Ianthe area. This bush tramway was closed in 1959 when the sawmilling operation that owned the line shut down.