A valve linked to the Nacimiento Water Project pipeline contributed to a mudslide on a roadway between Lake Nacimiento and Paso Robles on Sunday.
The valve, which allows air to escape from the pipe while it's being filled with water, inadvertently stayed open and allowed water to escape, Nacimiento Project Manager John Hollenbeck said.
Officials haven't determined how much water was lost or when the flow began, Hollenbeck added.
A motorist notified the CHP of the incident on County Route G14, which becomes Nacimiento Lake Road, around 4:50 p.m. Sunday. Hollenbeck said he was notified at 5 p.m.
The site was cleaned and the valve shut off by 9 p.m. No permanent damages or injuries were sustained.