The accident occurred at about 3:30 p.m. in the Longbo Reservoir in Shanxian County, said Zhang Zongzhi, a local government official.
Zhang said five people came to the reservoir for pleasure and four of them (two men and two women) took a boat when no guards were there.
Rescuers had recovered three bodies. All the victims were aged 27. A man, 22, was missing.
Rescue efforts are still under way. Investigation into the cause has begun.
