"It is estimated that approximately 800 million tons of wastewater are discharged into the lake each year."
(See photos of life along China's dangerously toxic Yellow River.)
During the same period, "declines of aquatic animal populations and of species diversity in [the] lake have been observed," he added.
The study was published in a recent edition of the journal Environmental Toxicology and Chemistry.
Urgent Measures
In a companion study published in Fresenius Environmental Bulletin, Wang and colleagues discovered hazardous amounts of mercury, a highly toxic and persistent pollutant, in porpoise organ samples.
Porpoise calves were discovered to have the highest levels of mercury poisoning, which could account for the dwindling porpoise population, he said.
These discoveries provide additional evidence that contaminants need to be reduced throughout the porpoises' habitat to avert its extinction, said Swiss geochemist Mueller.
Li Lifeng, director of WWF China's freshwater program, agreed.
"Urgent measures need to be undertaken to save this porpoise.
"Pollution control is one of the most important, but this will take time and huge efforts by the government and companies," he said.
WWF China has helped maintain a natural preserve for the Yangtze porpoise along an oxbow of the river at Tian-e-Zhou.
But the survival of the species will depend on reversing contamination of the water and limiting harm caused by shipping and "large infrastructure projects including dams, sluices, roads, bridges, and harbors," Li said.
The Institute of Hydrobiology, meanwhile, has scored small successes with its captive-breeding program, with a third calf expected to be born at its dolphinarium this summer.
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