Thousands of tons of "black water" are being discharged into Lake Chao in Anhui Province, forming a layer of black sludge along the southern shore of the lake.
The waste water comes from seven sand washing plants located on the south bank of the lake.
Thousands of tons of "black water" are discharged into Lake Chao every day.
The sand washing plants were set up in Sanbing Township at the beginning of this year. They use lake water to wash raw sand and discharge untreated waste water directly back into the lake. The discharge has created a large area of black silt along the shore.
The local environmental protection team said that, although it contains no toxins, the waste water is a threat to the ecology of the lake and nearby residential areas.
Officials from the township government said the sand washing plants had been established by local people without official approval.