Toxic algae blooms in the Sierra National Forest, California, are being analyzed by state officials and considered by investigators as the possible cause of the mysterious death of an entire family last week while hiking a trail in northeastern Mariposa County.

Authorities in the U.S. state of California reported the death of a couple, their one-year-old daughter, and a pet dog on a pedestrian trail in the Sierra National Forest near Hite’s Cove. The leading hypothesis indicates that they may have died after becoming contaminated with a toxic algae species, NBC News reported.

Following an intense search, after an entire family was reported missing, they were found lifeless last week on a trail in the Sierra National Forest.

This news comes days after tests confirmed that cyanobacteria, also known as blue-green algae or harmful algal blooms, were found on the shoreline of the Trinity River east of Willow Creek. 

Cyanobacteria can be present in any freshwater bloom and are identified as green, blue, white, or brown foam or blotches floating on the water’s surface. 

Warm temperatures and excess nutrients in the water can cause this type of algae to develop faster than normal and produce certain natural toxins that are potentially dangerous. The trade journal Active reported that small animals and children are more likely to be affected due to their smaller body size and tendency to stay in the water for longer periods of time. 

Search crews initially located the family’s vehicle near a gate in the Sierra National Forest and then found the bodies of three deceased people, identified as John Gerrish, his wife, Ellen Chung, their 1-year-old daughter, Muji, and their dog near an area known as Devil’s Gulch on the Southfork of the Merced River, the Mariposa County Sheriff’s Office reported. The search began after a report from a family friend the night before the grisly find.

Investigators were shocked after confirming the mysterious death without any obvious injuries or traces of any violence, which forced them to lean towards the theory of some kind of death by intoxication. 

“This is a unique and very unusual situation,” said Kristie Mitchell, the sheriff’s office spokeswoman. “There were no signs of trauma, no obvious cause of death. There was no suicide note.”

Mariposa County Sheriff Jeremy Briese said that at the moment, the leading theory being considered by investigators as a possible cause of death is a toxic algae bloom on the banks of the river, but added, “We’re not sure.” 

The U.S. Forest Service issued a series of warnings about the possible existence of toxic algae at the trailhead where the family was found.

They even posted a message on their Facebook account in mid-July, reporting a ‘high concentration of potentially toxic algae blooms.’

“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 or allow their pets to enjoy the water. This is due to the development of toxic algae that has formed and is present,” the statement said.

The bodies were transported to the coroner’s office in Mariposa for autopsies and toxicology tests.

The autopsies and toxicology tests are expected to reveal more information confirming whether the toxins found in the algae could be dangerous enough to kill a person so quickly. 

Briese said the family’s dog, Oski, will also undergo an autopsy through a partnership with Tulare County and UC Davis.

Twelve dog deaths have been documented since 2001 as a result of toxicity from this type of algae. If confirmed, the recent events would be the first time human deaths have been determined to have been caused by it, raising alarms because it could mean that the toxicity of the algae has increased for some unknown reason.