Tagish Lake is a lake in the Yukon Territory and northern British Columbia, Canada. The lake is more than 100 km (60 miles) long and about 2 km wide.

It has two arms, the Taku Arm in the east which is very long and mostly in British Columbia and Windy Arm in the west, mostly in the Yukon. The Klondike Highway runs along Windy Arm south of Carcross. Lake Bennett flows into Tagish Lake, so the northern portion of Tagish Lake was part of the route to the Klondike used by gold-seekers during the Klondike Gold Rush.

On January 18, 2000, a carbonaceous chondrite meteorite fell on the frozen surface of the Taku Arm. A number of fragments were recovered and are being studied by NASA.

Tagish means fish trap in the old Tagish language, an Athabascan language.

Tagish is also home to the Southern Lakes with trophy fishing.