A British dad and his family found dead on a mountain trail in California may have been killed by exposure to poisonous algae, say investigators.
Police were stumped after the bodies of Snapchat software engineer John Gerrish, his wife Ellen Chung, their one-year-old daughter Miju and their pet dog Oski were found in the Sierra National Forest.
As post-mortem examinations were carried out, the local sheriff said toxic algae blooms are among the hazards being considered by his investigators.
Toxic gases, including carbon monoxide, from abandoned gold mines were also being considered as a possibility, although the family were found three miles from the only known mine in the area north-east of Mariposa.
Mr Gerrish, originally from Lancashire, and his family lived in Mariposa, a small community set in the foothills of the Sierra Nevada mountains.
Sheriff Jeremy Briese told the Sacramento Bee newspaper: "I don’t believe it’s connected to a mine. We don’t know the cause. … We won’t rest until we figure it out.”
He said the only mine he's aware of is three miles away, and teams have been searching the area to make sure they didn't miss any mines or other hazards.
Mr Briese said officers are considering toxic algae blooms as a possible cause of death.
The US Forest Service had posted warnings about the algae near to where the family was found, he added.
The sheriff added: “From what I’ve gathered, these algae blooms are due to the recent drought, but I don’t know too much detail about the toxicity of them.
“I’ve been here for 20 years and I’ve never seen a death-related case like this."
Sierra National Forest had warned about the algae a month ago.
It wrote on Facebook : "The Sierra National Forest (SNF) would like to inform those visitors who like to enjoy this area of the Merced River and SNF, not to swim, wade or allow their pets to enjoy the water.
"This due to the Toxic Algal Mats that have formed and are present.
"While harmful algal blooms (HABs) are caused by algae or cyanobacteria that grow suspended in the water column (planktonic), some algae grow attached to the bottom (benthic zone) of water bodies and can form algal mats.
"Some species can produce toxins, and if present, can pose a risk to humans and pets."
The family were found dead on the Savage-Lundy Trail in Devil’s Gulch on Tuesday. Their bodies were about 1.5 miles from their vehicle.
There was no visible trauma on the bodies or signs of foul play, and emergency responders treated it like a hazmat situation.
Mr Gerrish's father Peter had previously told how his family was in "shock" and "heartbroken" over the deaths as they waited for updates from the authorities in California.
