For the third time this summer, a search operation is underway downstream of Great Falls after another swimmer disappeared in the Potomac River. Swift water rescue crews from Montgomery and Fairfax counties returned to the river Wednesday to search for the missing man before pausing operations for the evening. The victim's disappearance marks the third tragedy in the exact same stretch of the Potomac River in recent weeks. "The C&O Canal, the Potomac River, it’s a beautiful area. "The one big, big no is you don’t go swimming in the lower part of the Potomac River.