Washington City Canal Outfall

The water is still flowing underneath Constitution Avenue in a 200-year-old buried canal that was later incorporated into the modern sewer system.

Originally known as the Washington City Canal, this manmade channel cut across the heart of the city and once had barges floating down the same route that is today swarmed with tourist buses and bicycle rickshaws. 

The Washington City Canal was dreamed up by city planner Pierre L’Enfant, who hoped that it would facilitate the District’s development as an industrial center. The canal opened for business in 1815 but the development never really materialized, and it eventually turned into a festering sewer. One can only imagine the combined smell of human waste and decaying garbage, baking in the stagnant water under an August sun. 

Then there was the issue of the drownings. Not as many people knew how to swim back in the day, and there was a real risk of falling into the filthy canal at night in the era before street lighting. In 1859 the Washington Evening Star dubbed it The Man Trap, “because of the number of persons who have walked into it and drowned.”

In the early 1870s, the much-maligned Washington City Canal was bricked over at ground level and repurposed as a stormwater sewer, with the newly created B Street (as Constitution Ave was then known) passing over top. However, that didn’t quite put a hard stop to the septic issues. The Washington Evening Star noted alarmingly in 1878 that three or four times a year the sewer would back up during heavy rains, “with very foul water [flooding] into the cellars on the avenue.”

City engineers eventually worked out the myriad plumbing issues, and these days the old canal is a fully functional bit of civil infrastructure, none the younger for its 202 years. The D.C. coastline was altered dramatically by turn-of-the-century landfilling, and the canal’s old outlet into the Potomac is now located at 17th and Constitution (right underneath the modern Potomac Park flood levee). The underground sewer connection was extended to the river just north of the Watergate Complex, ending at a tunnel opening that is officially known as CSO Outfall #021.