The dam was being used to contain mining waste and heavy rain caused the overloaded barrier to break.
An investigation after the incident showed the dumping reservoir was built in violation of regulations and had almost no safety inspections.
The disaster underscored two major public safety concerns in China - the failure to enforce protective measures in the country's notoriously deadly mines, and the unsound state of many of its bridges, dams and other ageing infrastructure.
The country's mining industry is among the most dangerous in the world.
Despite efforts in Beijing to improve regulations, safety measures are often ignored by local officials in their pursuit of higher profits.