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OROVILLE — Flows from one of California’s biggest supplies of drinking water were suspended Tuesday after a massive hole opened in the Oroville Dam spillway amid heavy rains.

In a statement, the state agency said there was “no anticipated threat to the dam or the public.”

Roughly 20 percent of Lake Oroville remains empty, and there is sufficient storage to capture projected inflows from rain showers expected through the rest of the week, according to the agency.

The reservoir has a capacity of 3.5 million acre-feet and currently holds 2.8 million acre-feet. At 700 feet, the dam is among the tallest in the United States and a major source of drinking water in California.

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Employees noticed an “unusual flow pattern and erosion on the spillway,” which was carrying 55,000 cubic feet per second of water to the Feather River, on Tuesday morning and gradually reduced flows until they were completely halted around midday.

Photos show what appear to be boulder-size chunks of concrete in the spillway’s bottom.

The Department of Water Resources expected to resume releases from the gated spillway “at a rate deemed safe” later Tuesday after a thorough inspection was performed.

The Associated Press contributed to this report.