In a mountain village in southwest China’s Sichuan province, authorities have demolished seven small dam projects this year along a river to clear illegal developments in a new nature reserve. The demolition is part of a nationwide program to close hundreds of tiny and often ramshackle dams and turbines and bring order to China’s massive hydropower sector after years of unconstrained construction.

The dams sat on an unnamed tributary of the fierce and flood-prone Dadu river, which feeds into the Yangtze, Asia’s largest and longest river, where the government says the “irregular development” of thousands of small hydropower projects has wrecked the ecology.

But green groups say the campaign will not necessarily save the environment because it will not affect big state hydropower stations, which they say have caused the most damage, according to Reuters.

On the Zhougong river, another tributary, seventy-year-old farmer Zhang, who declined to give his full name, reckons big dams have devastated the ecology. Zhang described himself as a “hydropower migrant” after his land was inundated by state dam builders 10 years ago.

He said changes in the Zhougong’s flow and temperature had devastated the local fish population, with one species favored by the Sichuan-born former leader Deng Xiaoping now wiped out.

“The fish here now taste terrible, and are fit only for dogs,” he said, pointing to three silver carp he had caught after they were swept down river by flood waters from an upstream reservoir.

China triggered an aggressive damming program 20 years ago as it looked for ways to develop industry and bring electricity to poor rural regions not connected to the power grid.

Investors rushed in and environmentalists likened the frenzy to the construction of backyard steel smelters during the ill-fated 1958 “Great Leap Forward”, a program that aimed to industrialize China’s agrarian society but caused widespread famine as farmers made metal instead of food.

Now, the government wants to reverse course and the environmentally conscious leadership must decide how much of China’s 100 gigawatts of small-scale capacity needs to close, while at the same time protecting expensive state investments.

“Hydropower was a good thing at the time, but as is often the case in China, it turns into a swarm and we basically lose control,” said Chen Guojie, a hydropower expert with the China Academy of Sciences in Chengdu, central China.

Sichuan underlines the case. Total hydropower reached more than 75 GW in 2017, greater than the total in most Asian countries. It was also more than double the capacity of the province’s power grid, meaning lots of wasted power.

China’s official hydropower capacity was about 340 GW at the end of June and around a third of that is considered small hydropower, projects of less than 50 MW. China’s overall power capacity, including coal and nuclear plants, is 1,740 GW.