legislature finally ordered the dam height to be lowered, but then repealed the order before it was executed. Analysis done in the 20th century suggests that the dam, which still stands (although no longer at its greatest height), probably had a flooding effect on hay meadows as far as 25 miles up the watershed. Many of these meadows had to be abandoned, and some now form portions of the Great Meadows National Wildlife Refuge; they are classified as wetlands. The canal featured a number of innovations and was referred to as an example for later engineering projects. The use of hydraulic cement to mortar the locks is the first known use of the material in North America. The route was surveyed using a Wye level (an early version of a dumpy level), again the first recorded use in America. At North Billerica, where the canal met the Concord River at the millpond, a floating towpath was devised to handle the needs of crossing traffic patterns. Today Though significant portions of the Middlesex Canal are still visible, urban and suburban sprawl is quickly overcoming many of the remains. The Middlesex Canal Association, founded in 1962, has erected markers along portions of the canal's path. Prominent portions of the canal that are still visible include water-filled portions in Wilmington, Billerica, and near the Baldwin House in Woburn. Dry walkable sections can be found in Winchester, most notably a section at the Mystic Lakes where an aqueduct was situated, and Wilmington, where aqueduct remnants are also visible in the town park off Route 38. Most of the canal south of Winchester has been overbuilt by roads and residential construction, although traces may still be discerned in a few places. In 1967 the canal was designated a Historic Civil Engineering Landmark (one of the first such designations made) by the American Society of Civil Engineers. The surviving elements of the canal are the subject of a 1972 listing on the National Register of Historic Places, while the entire route, including parts that have been overbuilt, is the subject of a second listing in 2009. The Middlesex Canal Association maintains a museum in North Billerica, MA at the Faulkner Mills. Directions and additional information are available on the Middlesex Canal Association website. Gallery Notes References Sources Further reading Other online archives of The New England Magazine. This is how the Middlesex Canal Corporation was dissolved.