 The watershed itself encompasses a few parks and trails originating in Reston and reaching all the way to the Potomac River, at the end of the Difficult Run trail in Great Falls.Additionally, Difficult Run offers access to Great Falls National Park from certain areas of the trail, adding to the options for recreational activity.Using community planning, a secluded 12-mile (19 km) hiking and biking trail was built along Difficult Run from Reston to Great Falls Park.