SAN JOSE, Calif. (AP) — U.S. officials are worried that an earthquake could collapse a big dam near Silicon Valley.

They ordered its reservoir to be completely drained by October due to concerns that the dam could send floodwaters into communities.

The Mercury News reports that the Federal Energy Regulatory Commission says the 240-foot earthen Anderson Dam poses too great a risk of collapse and  must be fully drained. Retrofit plans have been in the works for years and the dam's water level has been kept at a maximum of 74% since 2009.

As of Monday, the reservoir was just 29% full.