A tugboat sank into the Gowanus Canal amid a multi-million dollar federal cleanup of the polluted waterway.

Workers with the city’s Department of Transportation spotted the vessel, named the Barbara Ann, taking on water Sunday afternoon near Union Street during a rainstorm and alerted the U.S. Coast Guard, according to Petty Officer Cory Mendenhall. Investigators with the Coast Guard arrived later that day to discover the boat was almost entirely submerged with only a small section of the vessel poking out from the water, said Mendenhall. Officials with the U.S. Environmental Protection Agency (EPA) said Monday that the ship sank because of a failed water pump.

“During the storm while the boat was moored and not in use, the bilge pump on the boat failed and the weight of the accumulated rain water caused [the] boat to lean to one side,” EPA spokesperson Tayler Covington told Curbed.

Conway Marine Construction was hired to “dewater” the vessel and pull it from the depths of the canal. The tugboat was contracted by GZA, an environmental contractor for National Grid that is in the midst of Superfund related work. On Monday, workers used a pump to flush out water from the vessel, and divers attached flotation devices to the boat and “floated it out,” said Covington. Pardon Me For Asking first noted the sinking tug.

GZA subcontracted the tugboat on behalf of National Grid to work on a barrier wall near the former Fulton Manufactured Gas Plant (MGP), National Grid spokesperson Karen Young confirmed. Workers did not observe a “sheen” on the surface of the canal that would signal fuel is leaking from the vessel, but deployed an inflatable yellow boom around the area to capture any contaminants as a safety measure.

“As a precaution, spill prevention and environmental control measures were implemented in the area,” said Young.

The work is part of the canal’s federal Superfund cleanup—an enormous effort to rehabilitate the heavily polluted, 1.8-mile long waterway by dredging toxic muck known as black mayonnaise from the bottom of the channel. The U.S. Environmental Protection Agency (EPA) is spearheading the cleanup.

National Grid’s wall, which will be erected in front of the existing bulkheads on the eastern bank of the canal, is being constructed out of 880 feet of steel sheet piling, according to the EPA. The barrier will ultimately extend from the canal’s head end to the Union Street Bridge. Once completed, it will serve as both a barrier to prevent liquid tar from seeping back into the canal from the former MGP, and as a structural support for forthcoming dredging. National Grid’s contractor began constructing the wall in August.

Residents who spotted the wreckage Sunday also stepped in to alert local authorities and groused about the irony of a boat conducting work related to the cleanup sinking into the canal and potentially polluting it further.

“Protocols should change to prevent this sort of incident as the Canal cleanup effort intensifies,” said Brad Vogel, the captain of the Gowanus Dredgers Canoe Club. “The Gowanus is already polluted enough as it is.”