McMahon’s Mill and Big Slackwater

Chesapeake & Ohio Canal National Historical Park 

McMahon’s Mill and Big Slackwater

Red wooden mill with metal wheel
McMahon's Mill and Big Slackwater provides peace and quiet for towpath travelers

NPS Photo

Closures: Between January 9th and 16th 2017, there will be towpath closures between McMahon's Mill (88.1) and Lock 42 (89.3) for geotechnical testing. Visitors should expect intermittent closures and delays between these dates during the hours of 7AM-4PM on weekdays. 

The peacefulness and serenity of the Big Slackwater and McMahon’s Mill area are unmatchable along the Chesapeake & Ohio Canal National Historical Park. Stretching from milepost 84.4 to 88.1, these areas of the towpath provide majestic views of the calm water of the Potomac River. Although the C&O Canal boats traveled within the canal prism, Big Slackwater was one of the few areas along the towpath that boats exited into the Potomac River. Anchored by the Dam No. 4 stop gate (milepost 84.6) and a guard lock (milepost 85.8), boats were able to exit and enter the canal’s prism for a short trip in the Potomac River. Following a journey through Big Slackwater, you will notice the red wooden structure of McMahon’s Mill (milepost 88.1). Also known as Charles Mill, Cedar Grove Mill, Shaffer's Old Flouring Mills, and Avis Mill, The mill's steel wheel helps provide a sneak peek into what industries once operated along the C&O Canal.