image sourcePolice handoutimage captionThe family were found dead in a popular hiking area of the Sierra National Forest
A family of three who were found dead on a hiking trail in California may have been killed by poison algae, investigators say.
The bodies of British man John Gerrish and his wife, Ellen Chung, and one-year-old daughter Miju were found in the Sierra National Forest on Tuesday.
Nearby waterways are being tested for toxic algae blooms, officials said.
Post-mortem examinations have been carried out in an effort to establish the cause of death.
The family's dog, Oski, was also found dead at the scene in the Devil's Gulch area of the forest, which is a popular hiking destination.
"We don't know the cause… we won't rest until we figure it out," Mariposa County Sheriff Jeremy Briese told the Fresno Bee newspaper.
"There's no obvious indicators of how it occurred… you have two healthy adults, you have a healthy child and what appeared to be a healthy canine all within a general same area, deceased," he said.
Investigators suspected the deaths may have been linked to escaping gas from abandoned gold mines, but Mr Briese appeared to rule out that possibility on Thursday.
"I don't believe it's connected to a mine," he said. "It's frustrating and we're not going to rest… it's devastating to everyone."
"From what I've gathered, these algae blooms are due to the recent drought," Mr Briese said. "But I don't know too much detail about the toxicity of them."
Algae blooms can produce "extremely dangerous toxins that can sicken or kill people and animals", according to the US Environmental Protection Agency.
Last month, the US Forest Service posted warnings about the potentially toxic algae in the Sierra National Forest on Facebook.
"[The park] would like to inform those visitors who like to enjoy this area… not to swim, wade or allow their pets to enjoy the water," one post read.