TORONTO - Canada's aviation authority has denied any responsibility for a string of incidents in which human faeces fell from the sky in western Canada.

According to The Guardian, the phenomenon was first reported in May by a Susan Allan from the city of Kelowna, British Columbia, who described how a deluge of "lumpy poo" fell on her and her son through the open sunroof of her car as she waited at a traffic light.

Since then, local newspapers have reported at least 10 other incidents in which victims described a foul-smelling substance which fell from the sky.

Transport Canada, the country's aviation authority, has received 18 reports of people and vehicles being drenched in the mysterious substance - but said that airplanes were not involved in any of them.

Ms Allan said that the agency told her that while there were three planes in the area at the time, "no aircraft overflew the intersection noted during the time frame in question", adding that "there were no malfunctions that would have caused the lavatory waste systems to leak" from any of the airlines, The Guardian reported.

Environmental scientists have suggested the splattering was the result of a "poopsicle" - the phenomenon that occurs when a leaking airplane lavatory ices over and then slowly melts as the plane descends.

The faecal matter falling from the sky did not contain blue colouration, a key an indication it came from a plane, Transport Canada told The Guardian, adding that it considered the matter closed.

However, Ms Allan is convinced that a plane was the source. "When we looked up there was an airplane flying over us," she said.

Environmental experts say a simple DNA test would solve the mystery.

Environmental scientist Robert Young said that the smell and the fact that the matter caused conjunctivitis strongly suggests it was faeces. While unlikely, it is also possible the faeces could have been caused by a large bird or series of birds, he said.

"It's just a matter of identifying the perpetrator," he said, adding that: "I don't think this will be one of the great mysteries of the universe."