A plume of brown substance was flowing into the Baltimore harbor near the U.S.S. Constellation in June 2018, prompting the city to investigate. (Jerry Jackson/Baltimore Sun video)

A plume of brown sediment leaked from a storm drain into Baltimore’s Inner Harbor on Thursday afternoon, discoloring the water in what one environmental group called a “major pollution event.”

The sediment appeared to come from a drainage improvement project at the Howard Street Tunnel, which carries freight trains below the city to the port of Baltimore, according to the Maryland Department of the Environment.


It flowed into the Harbor from the northwest corner, near Harborplace and the U.S.S. Constellation.

“We directed that the discharge of sediment into the storm drain system that eventually leads to the Inner Harbor be stopped,” environment department spokesman Jay Apperson said.

CSX Transportation, the railroad that owns the tunnel, said in a statement Thursday night that the source of the discharge is not confirmed and it’s working to repair the Camden Street stormwater line.

“CSX is working closely with local and state officials as we assess the situation and ensure the protection of the environment. We will continue to work closely with the City and MDE as this project moves forward.”

The city Fire Department, Department of Public Works and Office of Emergency Management were also monitoring the situation, officials said.

Blue Water Baltimore, an environmental advocacy group, said its Baltimore Harbor Waterkeeper team was looking into the “major pollution event.”

“Indications point to our storm drain system,” the group tweeted.

A preliminary investigation showed that the leak wasn’t a hazard to people walking along the Inner Harbor pavilion, officials said.