As Lake Mead continues to shrink, human remains have been discovered for the fourth time since May.
National Park Service rangers received a call reporting human skeletal remains on Saturday morning at Swim Beach in the Lake Mead National Recreation Area, according to a National Park Service press release.
The Clark County Medical Examiner was called to determine the cause of death.
Three other bodies have been discovered in the shrinking lake recently. The first body was discovered in early May, and police believe it dates back to the late 1970s to early 1980s and are investigating it as a homicide, according to CNN.
Receding water levels also revealed a sunken World War II era landing craft in July.
A National Park Service spokesperson told CNN a possible explanation for some of the remains is that they could be people who drowned in the lake when the water levels were higher in the 1980s.
Water levels for the lake were at their highest in 1983 at 1225 feet.
Lake Mead water levels are at their lowest since the filling of the reservoir for the first time in 1937, according to NASA, with the lake at 27% capacity on July 18.
The lake’s water levels need to remain above 1000 feet for the Hoover Dam to operate at normal levels and as of July 18, water levels are at 1041 feet.