The Charles River was given this name in honor of Charles I of England, the reigning monarch, by John Smith in the 1600s. Subsequent European settlers harnessed the river for industrialization, and by 1640 entrepreneurs on the Neponset River had diverted its water to power their mills.
Waltham was the site of the first factory in America, built by Francis Cabot Lowell in 1814, and by the 19th century, the Charles River was one of the most industrialized areas in the United States. Its hydropower soon fueled many mills and factories. By the century's end, 20 dams had been built across the river, mostly to generate power for industry. An 1875 government report listed 43 mills along the 9.5-mile (15 km) tidal estuary from Watertown Dam to Boston Harbor.
In portions of its length, the Charles drops slowly in elevation and has relatively little current. Despite this, early settlers in Dedham, Massachusetts, found a way to use the Charles to power mills. In 1639, the town dug a canal from the Charles to a nearby brook that drained to the Neponset River. By this action, a portion of the Charles's flow was diverted, providing enough current for several mills. The new canal and the brook together are now called Mother Brook. The canal is regarded as the first industrial canal in North America. Today it remains in use for flood control.