The federal Bureau of Land Management closed 28 miles of the Merced River Friday after test results revealed high levels of toxic algae just downstream from where a family was found dead from mysterious causes last month.

The bodies of John Gerrish, 45; his wife Ellen Chung, 31; their 1-year-old daughter, Muji, and the family dog were found dead on the morning of August 17 near Hite’s Cove in the Sierra National Forest, as CrimeOnline previously reported. With no visible signs of trauma, authorities have been so far stumped about what killed the family.

Earlier in the week, park officials closed the trail where the family was found as well as several additional recreation areas and trailheads, citing “unknown hazards found in and near the Savage Lundy Trail,” and said they expected to keep them closed for at least a month.

Then, on Friday, tests on the river’s water found the algae bloom, which forms in shallow, warm waters, ABC7 reported.

“These algal blooms can produce toxins that can make people and pets extremely sick,” Elizabeth Meyer-Shields, a BLM field manager, said in a statement. “We will continue to monitor for the algae’s presence and look forward to when the public can safely recreate in the Merced River.”

BLM closed campgrounds and recreation areas between the towns of Briceburg and Bagby.’

Investigators are still awaiting toxicology reports and have not determined the family’s cause of death, although they have ruled out acute trauma and some chemical hazards that they initially thought may have been involved.

The river closures will remain in effect until September 17.

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