A teenager who was found dead in Orrell Water Park following a brutal attack died from wounds to the neck.
Ellen Higginbottom, 18, was reported missing by her family at 7.20pm on Friday, when she failed to return from college.
They said this was extremely out of character for her.
Ellen's friends said she had last been near the reservoirs in Wigan.
Greater Manchester Police (GMP) searched the area and discovered a body at around 2.30am on Saturday.
A post-mortem examination gave the teenager's cause of death as multiple wounds to the neck.
Detective Superintendent Howard Millington, from GMP's Major Incident Team, said: "This is an absolute tragedy; my thoughts are with Ellen's family and friends. What they must be going through is unimaginable.
"We are also working with Wigan Council and Winstanley College, where Ellen was a pupil, to ensure support is in place for anyone affected by this shocking incident.
"The post-mortem has now taken place and we have a clearer picture of what may have happened to Ellen, but we are still piecing together her exact movements in the lead-up to her death."
GMP said it is leaving no stone unturned in the investigation and asked for the public to get in touch if they had seen anyone acting suspiciously in the area on Friday or in the days before.
Mr Millington said: "Attacks of this severity are thankfully incredibly rare, but that in itself makes this all the more shocking.
"Our officers will be patrolling the streets in the area whilst we continue our investigation. Anyone with any concerns should come and speak to our officers. "