NASHUA - Firefighters were again alerted to the presence of an oil sheen in the Nashua River this past weekend, and city officials are saying it is related to a previous oil leak in February.

Justin Kates of the Office of Emergency Management said it is suspected that the source of both reported oil leaks are from someone probably illegally dumping oil down a drain of a nearby parking lot.

"They probably didn't know it was illegal, or that it would lead to the river," Kates said of the possible culprits.

Unlike the first spill in February, which required petroleum absorbent booms and a concerted cleanup by city and state officials, Kates said the recent leak located just west of the Main Street Bridge in Notre Dame Park off Water Street was minimal in nature, small enough that officials felt they could just let it disperse in the river.

"It was not enough to cause significant damage to the environment, and no response was possible because the amount was so small," Kates said.

Kates added that the state Department of Environmental Services said that after the first significant rainstorm or snow event the city could expect to see a small amount of oil that had latched onto the walls of the offending pipe flushed out into the river.

True to the DES's warning, a small oil sheen was seen on the river after the snow began to melt this past weekend, and the fire department and wastewater department were called in. Once on the scene, both determined nothing could be done, Kates said.

Police are not investigating despite the suspected cause of the leak being illegal in nature, Kates said.

"It is likely something accidental in nature. Maybe they didn't know the law, but maybe it was intentional. Maybe they didn't want to dispose (of the oil) in proper way. Fifty years ago no one would have thought this was illegal, but now we take better care of the environment and it is illegal to dump that kind of stuff," Kates said.

Deputy Fire Chief Michael O'Brien previously said city officials were very concerned about the potential environmental damage being done by the first leak.

"Any time a contaminant gets into the water it is a concern," O'Brien said previously.