The independent Board of Consultants agreed with the California Department of Water Resources that the vegetative green spot that appears across the face of the earthen Oroville dam is caused by temporarily trapped rainwater. The report finds the spot poses no threat to public safety.
The area was first noticed during construction in 1966, before the reservoir was filled. But after the Oroville dam spillway failed in February, some feared the spot suggested the dam was also at risk.
The Board's report finds that seepage measurements at the base of the 770 foot dam have remained consistently low. The California Department of Water Resources says the vegetation dries out during the summer months, which it would not do if it had a constant source of seepage.