Editing Middlesex Canal (section)

===Impact===
The opening of the canal diminished the commercial viability of the port of [[Newburyport, Massachusetts]], the outlet of the [[Merrimack River]], since all trade from the Merrimack Valley in New Hampshire now went via the canal to Boston, rather than through the sometimes difficult-to-navigate river.<ref>Muir, Diana, Reflections in Bullough's Pond, University Press of New England, p.112</ref>

The canal also played a prominent role in the eventual growth of Lowell as a major industrial center. Its opening brought on a decline in business at the [[Pawtucket Canal]], a transit canal opened in the 1790s which bypassed the [[Pawtucket Falls (Massachusetts)|Pawtucket Falls]] just downstream from the Middlesex Canal's northern end. [[Proprietors of Locks and Canals|Its owners]] converted the Pawtucket Canal for use as a power provider, leading to the growth of the mill businesses on its banks beginning in the 1820s. The Middlesex Canal was used for the transport of raw materials, finished goods, and personnel to and from Lowell.

The canal's use of the Concord River had significant long-term environmental consequences. The raising of the dam height at North Billerica was believed to cause flooding of seasonal hay meadows upstream and prompted numerous lawsuits against the canal proprietors. These were all ultimately unsuccessful, due in part to the uncertainty of the science, and also in part to the political power of the proprietors. As the canal was in decline in its later years, the state legislature finally ordered the dam height to be lowered, but then repealed the order before it was executed.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 [[wetland]]s.

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.<ref>Clarke, p. 10</ref>