Beijing-based Institute of Public and Environmental Affairs, told China Daily that besides checking on industrial polluters along the river, the environmental watchdog should reset wastewater treatment standards in the dam area.

     "Construction of the dam has slowed the velocity of many rivers in the area, which weakens the self-purification capability of water body," Ma said.

     "It is another reason why the Xiangxi River has rampant algae.

     "The amount of pollution emissions the dam area is able to purify naturally should be recalculated. With a big reduction of pollutant emission budget, the pollution credits need to be allocated again," he said.

     Ma also said wastewater treatment plants should strengthen treatment capability of phosphor and nitrogen.

     The Xiangxi and six tributaries of the Yangtze saw algae blooms last year because of excessive amounts of pollutants pumped into them, a report by the Ministry of Environmental Protection said.