Staff at the Bonnybrook wastewater treatment plant in Calgary found a fetus on Saturday afternoon. ((Kyoshi Maguire/CBC))

Calgary police are asking a mother to come forward in case she needs medical attention, after a fetus was found at the Bonnybrook wastewater treatment plant.

Staff at the southeast facility found the fetus on Saturday afternoon in a container that separates organic and inorganic waste emptied from a sewer line that services the northern part of the city, police said Tuesday.

Workers called police, who took the fetus to the medical examiner's office. The fetus was 18 weeks into development and was a Caucasian male, duty Insp. Luch Berti said in a news release.

Berti said it appears the fetus entered the plant from the sewer line system from the area north of Glenmore Trail between 6 a.m. and 2 p.m. Saturday.

Police are asking for the public's help in the investigation.

"Most importantly, this may alert the concerned individual to seek medical assistance, as they should make all efforts to attend at a medical facility to check on their personal and medical welfare," Berti said.

While police said they were concerned about how the fetus was disposed of, they're also trying to determine if this was a spontaneous medical condition, a hidden pregnancy or a premeditated act upon an individual.

"The last of these three situations cannot be overlooked or end without police involvement and determination if a criminal act was committed," said Berti.

The fetus is being held until the mother can be identified and arrangements made for the remains, said police.