A new report from a UC Berkeley group researching what caused the Lake Oroville spillway to fail in February is concerned that a green spot on the nation’s tallest dam might mean it is leaking. This is not the first time the “green spot” on the southern end of Oroville Dam has been brought up. It has been asked and answered at community meetings, where state Department of Water Resources officials have said it is caused by rain or is a natural spring. Robert Bea and his team at UC Berkeley are far from convinced.