The Potomac River at Violette's Lock is a favorite spot of local paddlers seeking beginner whitewater adventure. Outfitters lead groups of whitewater boats here, but with a little skill it's runnable in most any canoe or kayak. At typical summer water levels (2.5 - 4 ft on the Little Falls gauge) the rapids are challenging enough to sharpen your maneuvering skills but shallow and relatively safe enough for novices to learn.
When you put in at the river bank adjacent to the canal lock, paddle across the Potomac initially staying in the slackwater above the rocky area known as Seneca Breaks. You can then either run down the middle of the river if the water level is good (about 3+ feet), or you can enter the chute on the Virginia side. (Since you will be paddling back upriver in the C&O Canal, I would suggest doing 2 circuits so you can experience both).
The mid-river option through the Seneca Breaks has endless lines so you can zigzag your way through the rocks and over the ledges. The Virginia chute is the remnants of the old "Patowmack" canal that is now a river channel, and offers fun rapids and waves with a swift current. Below the drop marked with a "13" sign, you can eddy out to the left then play in the wave, practice your roll, or watch other paddlers coming by.
In either case, there are plenty of places to stop and swim or fish, and remember to pack a lunch so you can stop on one of the islands and enjoy the scenery. Watch out for strainers in the chute, which tend to alter the course of the routes from one visit to the next. As you come to a gap in the islands and can see the main river channel, turn a sharp left and ferry your way back over to the Maryland side. Portage at the marked tree over into the C&O Canal, and paddle back up to Violette's Lock where you started. The total circuit is about 4 miles and you can easily do 2 circuits in 2-3 hours.
2 portajohns at the parking lot.
from I-495 take exit 39A onto River Rd. travel northwest for 11.5 miles, then turn left on Violette's Lock Rd.
The parking lot at Violette's Lock is a small dirt/gravel lot with room for maybe 20 cars. On the weekends, get there at 8 am or earlier before it fills up. As you jockey for a spot stay out of the little ditch on the right, we saw a truck get stuck there. Carry your boat over the wooden bridge crossing the C&O Canal, then down the path to the right to put in on the Potomac.
Down river, where the water smooths out again ferry across to river left; there is a dirt path leading over the bike path to the C&O Canal. Look for a high spot on the tree line. The large trees facing the river are marked with yellow blazes, but they're hard to see until you get close.
National Park Service: http://www.nps.gov/CHOH
AWW Description: http://www.americanwhitewater.org/content/River/detail/id/739/