Rainbow Lake, Reservoir in Piscataquis County, Maine, US

Rainbow Lake is an artificial reservoir in Rainbow Township, Piscataquis County, Maine, covering about 1,600 acres with an irregular shoreline featuring numerous coves and inlets. The lake reaches depths of up to 130 feet (40 meters) and maintains good water quality while supporting coldwater fish species in its clean waters.

Rainbow Lake lies in Rainbow township in the North Maine Woods and is the source of Rainbow Stream, which discharges over a dam at the lake's west end and runs 4 miles (6.4 km) south to Nahmakanta Lake. From there the water passes through Nahmakanta Stream and the Pemadumcook Chain of Lakes to the Penobscot River. The Appalachian Trail follows Rainbow Stream and the lake's south shore.

The Appalachian Trail follows Rainbow Stream and the south shore of the lake. The old logging road to the dam at the west end has deteriorated, with boggy stretches no longer passable by four-wheel-drive vehicles, so plan on reaching the water on foot or by paddling in.

Rainbow Lake has a small catchment basin and receives low nutrient input, which produces unusually clear water. It holds a native population of brook trout, and large granite boulders surround the lake. The Appalachian Trail follows Rainbow Stream and the lake's south shore.