North Canal Historic District
The Great Stone Dam was constructed across the Merrimack River at a place called Bodwell's Falls, where there is a five-foot drop. The dam was built to raise the height of the drop to . It is made of granite blocks laid on a bed of hydraulic cement. At its base it is thick, shrinking to at its top. It has three sections: the central span is , a south wing directs flow to the South Canal, and a wing directs water into the North Canal. It has a gatehouse, from which 24 gates in its sluiceway were controlled before the controls were electrified. Nearby on the island are also the surviving gatekeeper's house, an 1845 Greek Revival wood-frame structure, and a c. 1860s barn. The North Canal runs parallel to the Merrimack River, and is long. It ranges in width from at its upper end to where its wasteway joins the Spicket River. The canal is trapezoidal in its cross-section, with walls lined by granite, and a bottom made of granite rubble that has been sealed with clay. It is capable of delivering 4,000 cubic feet of water per second; water power is still used in some of the mills lining its banks. The canal used to have operable locks for navigation; the upper ones were removed and the lower ones were filled in. The Pacific Mills complex is an extensive array of buildings in the western (upper) and central parts of the district. The oldest standing building, a storehouse, dates to 1860, and there are remnants of an earlier 1852 structure. One of the more impressive structures is the Weave Shed built in 1890; it is a two-story brick building long. Its main cotton complex comprises five buildings on the north side of the canal. In the central part of the district the Pacific Mills include buildings in which both cotton and worsted wool products were manufactured. The Atlantic Mill Company buildings stand next to those of the Pacific Mills in the upper portion of the island. Only two notable buildings survive, the c. 1906 spinning mill, and a boarding house (one of two such buildings to survive in the district) that dates to 1847 and is the only surviving remnant of what was once a much more extensive housing district. The central portion of the district includes mill buildings from a number of manufacturers, including the Bay State Woolens Company (whose c. 1847 brick boarding house is now the visitor center of Lawrence Heritage State Park), the Washington Mills, and buildings of the American Woolen Company and the Pemberton Mill. Other notable buildings here include the Essex Company Offices and Yard (separately listed on the National Register). The lower portion of the district is predominantly occupied by the mill complexes of the Everett Mills and the Kuhnhardt Woolen Mills.
Canal and Great Stone Dam
In 1845 they company acquired land from then towns of Methuen and Andover and began construction on the North Canal and the Great Stone Dam.