Garibaldi Lake lies in a deep subalpine basin, with its surface at nearly 1,500 m (4,900 ft) above sea level and a depth exceeding 250 m (800 ft). It is almost entirely surrounded by mountains except at its northwestern tip, with volcanoes along the north, west, and south sides and non-volcanic peaks along the northeast and eastern shores. Lava flows from the volcanoes of Mount Price and Clinker Peak to the south blocked the ancestral valley, damming the waters of the lake behind the lava formation known as The Barrier. This lava dam is over 300 m (1,000 ft) in thickness and about 2 km (1.2 mi) wide where it impounds the lake. A series of lava outcrops along the northwestern shore of the lake form the numerous tiny Battleship Islands, several of which have been connected to the shore by simple man-made stone causeways.