Mile 85.8 - Past the Big Slackwater parking lot and boat launch is the
guard lock for Dam 4. It was here that boats would leave the canal and be pulled
along the river using the bank as the towpath. So the canal stops here and
doesn't reappear until lock 41 at mile 88.9. It was the dam itself that caused
the slack water.
An artsy shot of the lock.
On the other side of the guard lock the canal ends at this inlet gate. Water
from the river would enter this gate to fill the canal and was controlled by the
sluice gates you can (barely) see here. You could see them better if the gate
hadn't been cemented in.
Water from the Potomac enters here and flows to the inlet gate. The slab on the
top is the bridge over the towpath and the dangling logs a sort of "filter".