Lake Fergus is a lake in the South Island of New Zealand, located at 44°50′42″S 168°6′40″E / 44.84500°S 168.11111°ECoordinates: 44°50′42″S 168°6′40″E / 44.84500°S 168.11111°E.
A small lake between Lake Te Anau and Milford Sound, it lies adjacent to the New Zealand State Highway 94 (the Milford Sound Road). The lake is within the boundary of the Fiordland National Park, and is surrounded by native bush. The west branch of the Eglinton River flows through the lake, and it drains into Lake Gunn located south of it.
The first Europeans to explore the valley were David McKellar and George Gunn in 1861, two from Southland. William H. Homer (after whom the Homer Tunnel is named) and George Barber explored the area in search for a route from Lake Wakatipu to Milford Sound in 1889, setting off from Glenorchy and travelling via the Greenstone Valley. They saw the lake on 4 January, named it after Thomas Fergus, the Member of Parliament for the Wakatipu electorate at the time, and left the following inscription in a log: