A contractor was using a hose and vacuum truck Friday to collect paper fibers that were contained in an accidental discharge of 15,600 gallons of cooling water at the Catalyst Mill in Rumford.

The leak of “thermal seal water” went into the Androscoggin River on Thurdsay afternoon. State environmental officials said the leak involved “essentially hot water with paper fiber.”

Maine Department of Environmental Protection officials were at the spill site Friday to assess the situation and offer help if needed, the agency said. The DEP said an independent contractor was using high-pressure water to gather the fibers in piles and then vacuuming them up with the truck.

The DEP said the discharge was considered a non-emergency and no chemicals were in the spilled water. However, the discharge violated the mill’s permit with the DEP.

The department said officials will visit the site again next week to monitor the progress of the cleanup.