York City fire officials don't know the origin of an oily substance that occasionally drips from a drainpipe into the Codorus Creek -- or even what the substance is, Fire Chief David Michaels said.

But it happened again Tuesday morning.

"There's a storm drain right by the Susquehanna Commerce Center," next to the Philadelphia Street bridge over the creek, Michaels said. "And there are times, like when it starts raining, when an oily substance comes out of there."

The chief said the substance is most likely being dumped into the drain and sits there until rain washes it down the pipe.

A commerce-center employee watches the drainpipe and calls for help when he sees the material dripping into the Codorus, Michaels said.

Crews were called there about 9:45 a.m. Tuesday and used absorbent booms to collect the substance from the creek water, he said, adding only a small amount leaked into the Codorus.

Anyone with information about who might be dumping an oil-type product into storm drains is asked to call York City's Department of Fire/Rescue Services at (717) 854-3921.