On Kauai, legends recall that the menehune were a small, brown people who kept to the thickly forested areas of the islands. (The human population tended to keep to the shorelines, fearing evil spirits in the woods.) Like the faeries, the menehune were believed to be magical folk, capable of constructing great works in a single night. Superstition also holds that anything the menehune start must be finished that same night. If one sees them at work, or disturbs them, they will stop immediately and vanish, never to complete that project. (Such a superstition must have made menehune marriage very interesting. It may have been just a superstition, however, since at one time the meneuhune population was thought to be around 500,000.)
As a result, while the menehune of Kauai are often blamed for life's small misfortunes, they are also considered responsible for several island mysteries. These places are feats of construction that cannot be attributed to the Islands' early residents. On the island of Kauai, one such place is the Alekoko Fishpond, a large pond purportedly built over 1,000 years ago as a gift for a princess. Another is the Menehune Ditch, an aqueduct of closely fitted stones. Two of the island's numerous heiaus (temples) are also believed to be menehune work.
"Kauai's Menehune." http://www.europa.com/edge/mene.html
Doughty, Andrew, and Friedman, Harriet. The Ultimate Kauai Guidebook : Kauai Revealed (Ultimate Kauai Guidebook, 4th Ed).
Lihue: Wizard Publications, 2001. pp 13, 57.