Lake Mackintosh is a 17.5-kilometre-long (10.9 mi) reservoir with a surface area of 3,100-hectare (7,700-acre) that forms part of the Pieman power development running north–south past Mount Farrell, adjacent to the town of Tullah in Tasmania.

The lake's deepest point is roughly 60 metres (200 ft) deep at the base of the main dam.

It is one of the larger sized water impoundments of the Pieman power scheme.

The Murchison Highway borders the lake to the west.

The Cradle Mountain-Lake St Clair National Park as a component part of the Tasmanian Wilderness World Heritage Area, has its western boundary lying to the east of the lake shores.