Water behind 'quake lake' nears top of dam

BEIJING, China (CNN) - Authorities in southwestern China watched nervously Wednesday as rising water behind an earthquake-created dam neared a spillway designed to relieve pressure on it.

The threat of aftershocks from the May 12 quake and more rain, meanwhile, put the area in "extreme danger," said Liu Ning, chief engineer of the Ministry of Water Resources.

Heavy rainfall and severe aftershocks could compromise the integrity of the dam and send water cascading out. In the event of particularly heavy rain and a major aftershock, the chances of a catastrophic failure would stand at 93 percent, Liu estimated.

Authorities have evacuated about 200,000 people who are considered to be at risk if water overflows the dam. Engineers built the spillway to drain water from the lake in a controlled way once it tops the lowest levels of debris blocking the river.