Lake Arrowhead Reservoir, Mountain reservoir in San Bernardino Mountains, California.

Lake Arrowhead Reservoir is an artificial lake on Little Bear Creek in the San Bernardino Mountains, covering about 780 acres (320 ha) with a capacity of 48,000 acre-feet. Its branching arms reach into forested slopes, and a straight dam edge with a small white structure stands at the water's edge. Docks and clusters of buildings touch the left arm, and wooded islands and peninsulas sit near the center.

Construction of the dam began in 1904, but disputes over water rights delayed its completion until 1922 when the Arrowhead Lake Company finished the project. This development transformed how the region managed and distributed water to growing communities.

The lake was long called Little Bear Lake, after the creek that feeds it, before the Arrowhead Lake Company renamed it in the 1920s. The surrounding town took the lake's name and was laid out with Norman-style architecture. Access is reserved for residents holding lake rights, administered by the Arrowhead Lake Association.

Access to the water is limited to Lake Arrowhead residents holding lake rights, so most visitors see it from the surrounding roads and trails. The North Shore Trail follows Little Bear Creek along the northern shore and ends at Hook Creek; the North Shore Public Campground and the Mountains Community Hospital parking area sit on that side. From the south, California State Route 18 connects the lake with Running Springs; from the north, State Route 173 leads toward Hesperia.

The lake was first dammed in the 1890s as Little Bear Lake, before the 1904 start of the larger project; that earlier reservoir formed the base of today's Lake Arrowhead. The canyon around it holds sugar and Jeffrey pines, oaks, mountain maple and incense cedar, and is known for wild turkeys.