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More human remains have been found in Lake Mead, just one week after the body of a suspected murder victim was found in the rapidly shrinking reservoir.

The latest remains were reported to park rangers on Saturday. On 1 May, a body was found in a barrel stuck in the mud of the lake's receding shoreline.

The largest US reservoir, Lake Mead supplies drinking water to 20 million people from Las Vegas to Los Angeles.

Police warn that more bodies will probably be found as the lake recedes.

Lake Mead levels have been declining since 2000 - droughts have been getting worse in recent years, with scientists saying climate change is exacerbating the situation.

Investigators say the body found last week by boaters belonged to a person who was fatally shot in the 1970s or 80s.

Las Vegas homicide detective Lt Ray Spencer told local media the timing was determined due to the victim's clothes and shoes, which were sold at Kmart stores at the time.

Further research is being conducted to study the corroded metal of the barrel for more evidence.

"It's going to be a very difficult case," Lt Spencer told CBS News in Las Vegas after the first discovery. "I would say there is a very good chance as the water level drops that we are going to find additional human remains."

And this weekend, that prediction proved accurate.

The National Park Service, which patrols Lake Mead, said the latest discovery of "human skeletal remains" was reported by witnesses on Saturday afternoon.

"The investigation is ongoing. No further information is available at this time," park officials said in a press release.

Saturday's discovery was made by two sisters who were paddleboarding, they told local media, adding they thought it was a large rock before finding bones.

"At first I thought it was a bighorn sheep and then we started digging around a little bit and as we discovered the jaw, we realised it was human remains," Lindsey Melvin told CBS.

"For the longest time I was in disbelief. Like I did not think that we actually found human remains," her sister Lynette Melvin added.

Las Vegas police said on Monday that no foul play is suspected in the second death at this point, but they "will investigate if it is determined to be a homicide or a suspicious death".

Lake Mead, which is on the Nevada-Arizona state border, was created by the Hoover Dam in the 1930s.

The grisly discoveries come as the lake once again sinks to its lowest level since it was first filled.

Last month, water levels at Lake Mead dipped low enough to expose a water intake valve that began supplying water to customers in the region in 1971.

In February, researchers concluded that the drought in the US southwest is the worst it has been in at least a millennium.

Not all droughts are due to climate change, but excess heat in the atmosphere is drawing more moisture out of the earth and making droughts worse.

The world has already warmed by about 1.2C since the industrial era began and temperatures will keep rising unless governments around the world make steep cuts to emissions.