Stormwaters receded on Monday behind the nation's tallest dam, in Northern California, as engineers raced to drain the rain-swollen reservoir and shore up a crumbling overflow channel before new storms sweep the region later this week.
Authorities said they had averted the immediate danger of a catastrophic failure - one capable of unleashing a wall of water three stories tall on towns below.
But evacuation orders for some 188,000 residents remained in effect indefinitely, Butte County Sheriff Kory Honea said at a midday news conference. The risk to those living in the Feather River valley below the Lake Oroville Dam, 65 miles (105 km) north of Sacramento, was still being reviewed, he said.
Residents below the dam were abruptly ordered from their homes on Sunday when an emergency spillway that acts as an automatic overflow channel appeared on the brink of collapse from severe erosion during what is on track to be Northern California's wettest winter on record after years of drought.The situation grew less dire later on Sunday as water levels dropped,leaving the weakened unpaved emergency spillway largely intact. By Monday, the level of the lake fell enough so that water was no longer pouring over the hill.
Erosion caused by the hole in the side of the main spillway appeared to have abated by Monday, and it was back to more or less normal operations, officials said.