During the summer months, visitors can experience one of the great marvels of American engineering: the Northern Canal. Finished in 1847, the Northern Canal runs along the Merrimack River separated by a 36 foot high granite wall later named the "Great River Wall."
Update- June 18, 2017: Current flow rates are too high to open the walkway. Flow rates continue to drop and are now around 6000-8000 cfs. We are hopeful that the flow rates will be down below 3500 and allow opening of the walkway in the next week or two.
The Northern Canal Walkway (which includes the Great River Wall) provides breathtaking views of the Merrimack River, the canal and the surrounding areas. However, access to the Northern Canal Walkway is only available when the flow rate in the Merrimack River is under 3500 cubic feet per second.
To find out if the Northern Canal Walkway is open, please visit the USGS flowrates page and check the "most recent instantaneous value" towards the bottom of the page. If this value is below 3500 the walkway will be open. (see screenshot of the page below)