The teen found a woman's body, and when he approached another man in the area, he confirmed it was a body and called 911.
Officers who responded to the scene said the body showed signs of trauma, so they called homicide detectives to conduct an investigation.
HPD said the investigation was challenging because the woman was located away from a road. Detectives had to hike through rough terrain as they worked to find out what happened.
"This is a flood control reservoir. It's dry," Lt. Larry Crowson said. "So right now, people use it to hike, ride their bikes, a lot of recreation out there. But it is very isolated."
In a Thursday afternoon update, HPD said it was trying to get an ATV to the scene to help expedite the investigation.
Detectives said it was too early to identify any suspects or determine a cause of death, but they did say the investigation's circumstances were suspicious.