FOLSOM (CBS/AP) — Search crews are scouring a lake east of Sacramento for four men who are presumed dead after their speedboat capsized.

California parks department spokeswoman Vicky Waters said divers and boat crews returned to Folsom Lake on Sunday morning to resume looking for the men, who have not been seen since their boat overturned on Saturday afternoon.

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Waters says the search is considered a recovery operation instead of a rescue at this point.

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The speed boat has been recovered and investigators are trying to determine why the 35- to 40-foot vessel capsized. Waters says the accident happened in a part of the 18,000-acre, man-made lake dotted with small islands and where the water’s depth is much more shallow.

The men’s families have been notified, but their names have not been released.

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