Investigators say the body was found around 5:15 Sunday night near the Delta-Mendota canal, near Bass Street.
Officers say it was discovered in some brush in the area known as Mendota Pool Park.
Homicide detectives were called in to assist in the investigation after sheriff's deputies determined the person did not die of natural causes.
Authorities said Sunday night's conditions were making it difficult to collect evidence.
Detectives say they will resume their investigation after daylight on Monday morning.