Lake Temagami, Freshwater lake in Nipissing District, Ontario, Canada

Lake Temagami is an irregularly shaped lake in Nipissing District, Ontario, about 80 km north of North Bay. It extends almost 50 km from north to south and about 35 km from east to west, with long north, northeast and southwest arms and approximately 1,259 islands, the largest being Temagami Island. The town of Temagami sits at the end of the northeast arm.

The Hudson's Bay Company operated a fur trading post here during the 1800s as part of regional commerce. This period shaped the economic foundation of the area.

The name comes from an Ojibwa word meaning deep water by the shore. The lake and surrounding forests shape how people spend their time here today.

Cottages and resorts are permitted only on the lake's islands, a restriction dating from the 1901 Temagami Forest Reserve that still applies. The lake stretches almost 50 km north to south and about 35 km east to west, with roughly 1,259 islands, so plan routes by arm. Over 2,000 km of interconnecting canoe routes link the surrounding lakes.

Part of Lake Temagami lies over the Temagami Magnetic Anomaly, an egg-shaped geologic structure stretching from Lake Wanapitei to Bear Island. It resembles the Sudbury Basin, one of the world's richest mining camps. The area also holds pillow lava about 2 billion years old, evidence of ancient submarine volcanoes.