People salvage flaky substance in the river in Mudanjiang, the third largest city of northeast China's Heilongjiang province, February 22, 2006.

An unknown substance found near a water inlet supplying Mudanjiang has triggered panic among local residents, but officials said the water is safe to drink.

A distillery emitting a great deal of distillers' grains into Hailanghe River might have caused the unidentified flocs at a water supply source in Mudanjiang, Xinhua reported.