A heart was reportedly discovered at a water treatment plant in Detroit where officials have found at least three other organs within the last two weeks.

Sources told FOX 2 Detroit that a total of four kidneys and one heart were found at the Water Resource Recovery Facility as the mystery surrounding the organs deepens.

The news station reported the heart was discovered on December 23, just days after a possible human organ was spotted floating at the wastewater plant.

Two organs – believed to be kidneys – were found at the plant in two separate incidents earlier this month.

“There is an investigation into it right now,” Detroit Police Capt. Darin Szilagy told FOX 2 last week. “The results are still not back from the medical examiner for the origin of the recovered organs in the past week, so it’s an ongoing investigation.”

The Wayne County Medical Examiner’s Office is working to determine if the organs are human or animal.

A spokeswoman for the Great Lakes Water Authority, which manages the wastewater treatment plant, said the suspected organs did not affect the process because they were found in the filtering process pre-treatment.

Fox News' Katherine Lam contributed to this report.