The lake is known for its clarity and chilly temperature. Because of its depth, the surface of the lake freezes later than other lakes in the Northeast Kingdom.
Watershed
Willoughby Lake is part of the Saint-François River watershed, its waters eventually reaching the St. Lawrence River in Canada. Willoughby River is the outlet from the lake and runs north through Brownington to feed into the Barton River. The Barton River is tributary to Lake Memphremagog and thence to the Magog River, then the Saint-François River, then the St. Lawrence River, and ultimately to the Gulf of St. Lawrence. Prior to the floods of 1927, the river had three dams. All were destroyed by the flood. An iron bridge that ran from Evansville to Brownington Center was destroyed and rebuilt. A dam where the Whetstone Dam had formerly stood, was rebuilt to run a sawmill, which was still in operation in 2008. The "state Fish and Game Department" bought the dam rights to allow rainbow trout to swim upriver.
Geology
Lake Willoughby is a southeast trending basin. Willoughby is a glacial lake over deep in places, the deepest lake entirely contained in the state and second to only Lake Champlain whose deepest point reaches. Lake Willoughby resembles a Norwegian fjord. The rock between Mount Pisgah on the east and Mount Hor on the west was eroded by a valley ice lobe. This ice flow cut across the Willoughby granodiorite and adjacent metamorphic rocks. The ice flow may have exploited highly fractured bedrock along the margin of the Willoughby pluton or joint surfaces within the pluton. Other mountains in territory of Westmore, Vermont are on:
East bank: Mount Hedgehog , Mount Goodwin , Mount Bald , Mount Heystack and Mount McSherry ;
West bank: Mount Wheeler in Caledonia County, Mount Valley , Mount May Pond ;
Tiny steam boats operated on the lake for tourists from 1884 to the early 1900s when steam was replaced by the gasoline engine. In 1915, Robert Frost mentioned the lake in a poem, "A Servant to Servants, "I see it's a fair, pretty sheet of water, Our Willoughby! How did you hear of it? I expect, though, everyone's heard of it. In a book about ferns? Listen to that!"
Toponymy
The toponym "lake Willoughby" was officially recognized on September 1, 1992, by GNIS of United States.
Local customs and culture
Devil's Rock, located on the Mount Pisgah side of the lake at a less than halfway point from the lake's southern beach, is a popular diving spot for daring locals and vacationers. It takes its name from a painted image of a devil on the front of the rock facing out toward the lake. It is also called Devil's Rock because when reflected in still water, the image of a skull lying on its side can be seen. Along the eastern shore, there are a series of natural waterslides that flow into Lake Willoughby. In the winter, these turn into an ice wall which is used by ice climbers.
Economy
Lake facilities offer swimming, hiking, and ice fishing. There is a nude beach on the lake's southern shore. Surrounding the Willoughby Lake, there are some campgrounds and cottage rental services for tourists. The Route 5A runs along the lake's eastern edge.