The lake is irregularly shaped with long north, northeast and southwest arms, shorter northwest and south arms and several smaller bays. The town of Temagami is located at the end of the northeast arm of the lake. It extends almost 50 km from north to south and about 35 km from east to west. There are approximately 1,259 islands, the largest of which is Temagami Island. The lake's outflow is the Temagami River which in turn flows into the Sturgeon River. A number of peninsulas are associated with the lake, such as the McLean, Cynthia and Joan peninsulas, as well as Sand Point, which separates the Northwest Arm from the rest of the lake.