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LAS VEGAS (AP) — A week after a decades-old body was found in receding Lake Mead, authorities in Las Vegas are trying to identify a second set of newly discovered human remains.

Two sisters from the Las Vegas suburb of Henderson were paddle boarding on the drought-stricken Colorado River reservoir when they spotted bones Saturday in the Callville Bay area of the lake.

Lindsey Melvin told KLAS-TV that they thought at first it was a bighorn sheep, but saw what appeared to be a human jaw and called park rangers. The National Park Service confirmed in a statement that the bones found were human.

Investigators are not treating the case as a homicide, Las Vegas police said. The remains are currently with the Clark County Coroner’s Office.

The discovery came after a body in a barrel was found May 1 along newly exposed shoreline of the lake formed by Hoover Dam between Nevada and Arizona.

In that case, police said the body was a man who had been shot, probably between the mid-1970s and the early 1980s because he was wearing shoes manufactured during that period.

Drought has dropped the Lake Mead water level so much that Las Vegas’ uppermost water intake became visible two weeks ago.