The Lake Oroville water level is beginning to drop, but officials say the emergency is clearly not over. A relentless runoff from the Sierra Nevada has brought about the evacuation of thousands of residents in the area amid warnings of a catastrophic failure of the dam after its main spillway began to collapse.

The Oroville Dam is a earthfill embankment dam of 770 feet and is the tallest dam in the US. The dam impounds the second larges man-made lake in the State of California. Located in the Sierra Nevada foothills, the dam is capable of storing 3.5 million acre feet of water.