Boundary Channel is a sheltered tidal channel that parallels the west bank of the Potomac River in the Washington, D.C. area, forming Columbia Island. It offers a pocket of quiet, no-wake paddling in the heart of Pentagon City, providing a calmer alternative to the main river. The channel runs from near the Pentagon north to the southern end of Theodore Roosevelt Island, where it reconnects with the Potomac. A key consideration for paddlers is the tidal nature of the Potomac River system. The channel is shallow, and paddlers must ensure the tide is high or they risk running aground. Planning a trip to paddle with the tide is advisable, and the channel can be used to bypass rougher conditions on the open river, especially later in the day when winds often build.

The primary public access point is Gravelly Point Park, located on the east side of the George Washington Parkway immediately north of Ronald Reagan National Airport. This site offers four concrete boat ramps with adjacent floating docks, adjacent paved and unpaved parking at no fee, restrooms, and picnic tables. An alternative launch is Columbia Island Marina, though this is a private facility. From Gravelly Point, paddlers typically head east onto the Potomac and then north to find the southern entrance to the channel. The final mile back to the park from the channel's northern exit requires negotiating the open Potomac. Motorboat traffic is generally light on weekdays but increases on weekends, particularly around and below Key Bridge, creating wake. The area is urban, with constant sounds of capital traffic and overhead flights, but the channel itself becomes more natural-looking as you paddle north. Notable sights include a striking, close-up view of the Pentagon at the channel's western turn, with manicured gardens and a large flag, and the War College building along its banks. Water quality can be an issue after heavy rain, as raw sewage may be present in the river system. Paddlers should also be mindful of vehicle security at access points, avoiding leaving valuables in cars.