The waterfall and rapids below it drop a total of 32 feet in a little under a mile,[1][2] and was an important fishing ground for the Pennacook Indians in pre-colonial times.
In the 1820s, the falls, the canal, and the hydropower they provided led to the choosing of this site as America's first planned factory town, Lowell.
To maximize the head the canals provided, increase volume, and regulate flow, a dam was begun at the top of the falls in the 1820s and was enlarged into the 1840s.
The final structure, which exists in the same form today, is a stone dam topped with five foot wooden flash-boards, capable during much of the year of channeling the entire Merrimack into the canal system.
When heavy flow tops the dam, the waterfall created, which is a fraction of the total loss in elevation of 32 feet, is referred to as the Pawtucket Falls.