Getting help from nature

Besides strict environmental protection of the Shanxi reservoir area to guarantee safe drinking water in Wenzhou, Zhejiang province, local authorities are also observing the behavior of its fish to evaluate water quality.

Teng Yunan, an engineer with Zhaoshandu reservoir, 35 kilometers downstream from the Shanxi reservoir, will check the condition of the red koi in a test pond, monitor data on water quality and decide whether the water is clean enough to be supplied to Wenzhou residents.

"Koi requires high water quality to survive. A little contamination will kill them or cause them to act abnormally," Teng said. The fish in the pond have been in good condition since they were moved there in 2012, he said.