The new trail opened in 2012 runs beside this section of the Slackwater. The original trail was destroyed by flooding.

The Big Slackwater is an area of the Potomac River upstream from Dam 4 where the water has collected due to the presence of the dam. There is no canal in this section. The boats used to be pulled along the shore. The towpath (today's trail) runs along the river. The canal restarts at Dam 4 and slightly upstream of this section of the river.