It’s the fourth time since May that debris has been uncovered as drought in the West forces shoreline to recede into the shrinking Colorado River reservoir behind Hoover Dam. National Park Service officials said rangers were called to the reservoir between Nevada and Arizona around 11 a.m. Saturday after skeletal remains were discovered at Swim Beach. Rangers and a Las Vegas Metropolitan Police Department dive team went to recover the remains. Park Service officials said the Clark County Medical Examiner’s Office will try to determine when and how the person died as investigators review missing person records. On May 1, a barrel containing human remains was found near Hemenway Harbor. Police believe the remains were of a man who died of a gunshot wound and the body was likely dumped in the mid-1970s to early 1980s. Less than a week later, authorities say human skeletal remains were found in Calville Bay. Most recently, some human remains were found in the Boulder Beach area on July 25. Police speculate that more remains may be discovered as the water level in Lake Mead continues to recede. The discoveries have sparked speculation about unsolved missing persons and murder cases dating back decades – all the way back to organized crime and the early days of Las Vegas, which is just a 30-minute drive from the lake. The lake level has dropped more than 170 feet (52 meters) since the reservoir was filled in 1983. The drop in lake levels comes while the vast majority of peer-reviewed science says the world is warming, largely due to rising levels of carbon dioxide and other greenhouse gases in the atmosphere. Scientists say the US West, including the Colorado River Basin, has become warmer and drier over the past 30 years.