HIGH levels of toxic algae were found close to where a Brit software engineer mysteriously died alongside his wife, baby and dog on a hiking trail in California.
A murder investigation was initially launched last month after Jonathan Gerrish, 45, his wife Ellen Chung, 31, and their one-year-old daughter Muji, were found by search teams in a remote area of the Sierra National Forest known as Devil's Gulch.
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However cops later ruled out homicide despite being unable to give an explanation or a possible cause of death.
Now authorities have confirmed the presence of toxic algae in the Merced River a few miles from where the bodies were found, the New York Post reports.
Elizabeth Meyer-Shields of the Bureau of Land Management said: "These algal blooms can produce toxins that can make people and pets extremely sick.
"We will continue to monitor for the algae’s presence and look forward to when the public can safely recreate in the Merced River."
Campgrounds and recreation areas along the river, between the towns of Briceburg and Bagby, were shut after water samples revealed the algae.
Forest officials also closed access to trails in the area citing "unknown hazards."
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Local reports claim investigators are looking at whether the family may have drunk water from the river.
But the cause of death remains a mystery after cops ruled out any weapons being used or dangerous gases from a mine.
Sheriff Jeremy Briese said: "We know the family and friends of John and Ellen are desperate for answers.
"Our team of detectives is working round the clock.
"Cases like this require us to be methodical and thorough while also reaching out to every resource we can find to help us bring those answers to them as quickly as we can."
Gerrish, 45, was a software engineer who worked for Google before moving to Snapchat.
He was originally from Lancaster, England, while his wife was from Orange, California.
The couple are said to have lived in San Francisco before moving to Mariposa.
The family was found dead in mysterious circumstances on August 17 after being reported missing by a relative.
Authorities located the bodies two miles from their car near the Sierra National forest gate, in an area with no phone reception.
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