About 97,000 gallons of red wine spilled from a winery in Sonoma County, Calif., this week and thousands of gallons made its way into the Russian River, according to a report from the Governor’s Office of Emergency Services.

According to the person who reported the incident to authorities, a Rodney Strong Vineyards’ blending tank door had “popped out for unknown reasons” causing the release of 97,112 gallons of cabernet sauvignon into Reiman Creek on Wednesday. An estimated amount between 46,000 and 96,000 gallons eventually flowed into the Russian River, the report said. The amount of the spill would almost be enough to fill 500,000 standard wine bottles.

About 20% of the spill had been contained, according to the report.

The winery has opened up an internal investigation, Rodney Strong spokesman Chris O’Gorman said Thursday, according to The Press Democrat, which originally reported the story. O’Gorman said that the company has “almost completely” determined that human error did not cause the wine leak.

The amount that spilled out was “enough to fill eight large tanker trucks,” according to the Associated Press.

It is likely the biggest wine spill in county history, Don McEnhill, executive director of nonprofit Russian Riverkeeper, told The Press Democrat.

Local and state officials are investigating to assess the extent of environmental damage, consider any harmful impacts on the river’s ecosystem and evaluate whether the winery is in compliance with water quality rules, according to The Press Democrat.

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Write to Sanya Mansoor at sanya.mansoor@time.com.