by Jake Maxwell Watts / Quartz

Last week was not a good time to be a fish in Yunnan. Just a few days apart, the southern Chinese province suffered two mass die-offs—around 100 tons of fish on a Nanpan River reservoir and a massive 1,200 tons on the Sinan River.

The causes are elusive, but it’s the fourth time that fish have died on the Nanpan in as many years. A previous incident in October 2009 raised suspicions that a chemical plant upriver may have been responsible. Pointing fingers seems like a natural response, given previous cases—just last week eight people were arrested, including legal representatives of a mining company, for deliberately dumping chemicals in another local river. And it’s not just Yunnan. A policeman who saved a 14-year-old girl from a Wenzhou city river on Friday also ended up in hospital from exposure to pollution.

China’s rivers are under assault on multiple fronts. In attempt to supply a power hungry country and reduce dependence on coal, Beijing is pursuing a relentless program of hydropower projects, many of which are in Yunnan province. Damming, combined with heavy demand for water from farmers, has caused the disappearance of over half of China’s 50,000 rivers in the last 20 years.

The level of anger among Chinese people is palpable, as recent protests have shown. One last year even ended in a riot. Beijing has doled out fines to misbehaving countries and promised to do more by holding party officials responsible, but another batch of dead fish will do nothing to help its image, whatever the cause.