A water plant in Shanghai has been told to improve its discharge system after turning a downtown river a "weird" bright blue color.

Changqiao Water Plant in Shanghai's Xuhui District has been releasing colored waste water into a river near Chunshen Harbor, linking the Dingpu and Huangpu rivers.

Changqiao Water Plant in Shanghai's Xuhui District has been releasing colored waste water into a river near Chunshen Harbor, linking the Dingpu and Huangpu rivers. [Photo/Xinmin.cn]

While the water is not toxic, the plant has been instructed to renovate its system, said the Xuhui Water Authority yesterday.

A water authority official said the blue color was caused by chlorine.

The water has been a sky blue color since Monday and looks very polluted, a nearby resident, surnamed Hu, said.

Other discharges from the plant turn the river yellow and black, added Hu.

"The color looks weird and we're wondering whether the water quality from the plant will be affected," Hu said.

Changqiao Water Plant on Shangzhong Road supplies water to the downtown area, getting its supplies from the Qiangcaosha Reservoir on the Yangtze River.

"The water authority has told the plant to overhaul its discharge system and there are plans to dredge the river near Chunshen Harbor," said the Xuhui Water Authority official.

Renovations should improve the appearance of the waste water, while dredging means outflow can disperse in a larger volume of water.

Despite the lurid colors, official said the waste water meets standards.