The City of Summerside, P.E.I., is still trying to figure out how hundreds of litres of oil got into its wastewater treatment plant.

Sam Arsenault, the city's wastewater supervisor, said a worker noticed oil in the water at the plant last Tuesday.

The cleanup began immediately.

Arsenault said there were several concerns. The plant is not designed to process oil, so it could have ended up in the harbour. There was also the possibility of damage to the plant.

"One of the stages … makes use of micro-organisms," Arsenault said.

"If the oil was to poison a significant number of those it may harm your ability to treat wastewater for some time, possibly one or two months."

Arsenault had to scour companies in the surrounding area for cleanup kits after using up all the ones they had on hand. About 500 litres of oil was removed.

The workers were able to prevent damage to the plant, but the cleanup cost about $15,000.

There were no oil spills reported in Summerside last week, so the source of the oil is not known. They were able to locate that the source was between Greenwood Drive and Granville Street.

Arsenault said the oil most closely resembled used engine oil. Used engine oil can be recycled for free at many locations in the province, he said.

Arsenault urged anyone with information about this or any other oil spill to call the province's oil spill hotline, 1-866-368-5044 during regular working hours or 1-800-565-1633 after hours. A quick response can make cleanup efforts easier and more effective, he said.