The failure of the Oroville spillway in February led people to notice a large green spot on Lake Oroville's dam. The spot has been there for years, but the questions remain as to whether it's a sign the dam is leaking.
It’s become known as the “green spot” regardless of the season. It comes and goes, green in the spring, brown in the summer.
Erin Mellon with the California Department of Water Resources said there are actually several green spots on the dam where the type of soil used during construction allows rainwater from above to seep out, which contributes to more grass in those areas.
"In the early days of construction, those green spots still existed. The second most important thing to notice about these green spots is there's a drainage system in place between the dam and the hillside and that drainage system collects any seepage that might be occurring," Mellon said.
The failure of the Oroville spillway in February led people to notice the spot and question what was supplying water to the grass.
A report last month by the Center For Catastrophic Risk Management questions if water is seeping through the dam, but does not offer much in the way of proof that it actually is.
DWR says drains in the dam remove seepage and are monitored.
Mellon says the volume of water that drained from the dam was consistent this year with previous years.
DWR has inspected this part of the dam several times over the years, according to publicly-available reports, and has found no evidence to suggest the dam is leaking.
One report from 1999 includes a recommendation from the Federal Energy Regulatory Commission that DWR monitor the spots.