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More human remains have been found at Lake Mead near Las Vegas, the fourth such discovery since May, authorities announced Saturday.
The National Park Service (NPS) was alerted about the skeletal remains at Swim Beach in Lake Mead National Recreation Area at about 11 a.m. on Aug. 6.
“Park rangers responded and set a perimeter to recover the remains with the support from Las Vegas Metropolitan Police Department’s dive team,” the NPS said in a news release.
The Clark County Medical Examiner will determine the person’s cause of death.
The investigation is ongoing, the release states.
The remains are the fourth found in Lake Mead since May.
On May 1, boaters found a barrel on an embankment in Hemenway Harbor containing the body of a homicide victim.
“The cause of death was gunshot wound,” Clark County Coroner Melanie Rouse tells PEOPLE.
Las Vegas Metropolitan Police Department detectives believe the victim was killed some time in the mid-1970s to early ’80s, based on the clothing and footwear the victim was found with.
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“The victim’s clothes and shoes were sold at Kmart in the mid-to-late 1970s,” Metro Police Homicide Lt. Ray Spencer told local news outlet KLAS.
Rouse says the FBI is assisting “in processing of specimens for DNA.”
“Our office is mandated to attempt to make identification,” says Rouse. “That identification process does often require us to utilize other subject matter experts including individuals such as anthropologists, forensic odontologists or forensic dentists, and other specialists, including outside agencies for the purpose of extracting and compiling DNA when possible.”
A second set of remains was found at Lake Mead on May 7. In that incident, NPS rangers were called to Callville Bay in Lake Mead National Recreation Area around 2 p.m. on May 9 after two paddle boarders found the remains.
“These remains have been determined to be male,” says Rouse. “And we have an estimated range from 28 to 38 years of age.”
The cause of death has been ruled undetermined, she says.
The third set of remains was found at Boulder Beach around 4:30 p.m. on July 25 and have not been identified.
“Cause and manner of death in this particular case is still pending further studies,” says Rouse.
“It is not uncommon to have deaths that do come to us from recreational areas,” she says. “So that is pretty common that we will respond to a recreation area throughout the year.”
Climate change and drought have caused the lake’s water levels to drop to their lowest levels in recorded history, according to the Associated Press.