A gaping hole continues to grow in the spillway of America’s tallest dam – causing massive erosion and threatening major overflow On Tuesday, a huge hole formed in the spillway of California’s Oroville Dam Officials say the hole will continue to grow until it hits bedrock Right now, the spillway isn’t releasing enough water to keep up with the lake’s intake So there’s a threat that the lake will overflow at some point on Saturday, engaging an emergency spillway that hasn’t been used since the dam was opened in 1968 If that happens, officials won’t be able to control the water flow, and it can cause even more erosion as water sweeps through vegetation on its way down to the river below.