News report (https://news.agu.org/press-release/small-dams-on-chinese-river-harm-environment-more-than-expected-study-finds/) writes:
A fresh look at the environmental impacts of dams on an ecologically diverse and partially protected river in China found that small dams can pose a greater threat to ecosystems and natural landscapes than large dams. Although large dams are generally considered more harmful than their smaller counterparts, the research team’s surveys of habitat loss and damage at several dam sites on the Nu River and its tributaries in Yunnan Province revealed that, watt-for-watt, the environmental harm from small dams was often greater—sometimes by several orders of magnitude—than from large dams.
One particularly detrimental impact of the small dams observed in this study is that they often divert the flow of the river to hydropower stations, leaving several kilometers of river bed dewatered, Kibler explained.
Small dams in China “often lack sufficient enforcement of environmental regulations” because they are “left to the jurisdiction of the province,” said Guy Ziv, lead scientist for the Natural Capital Project, an organization which develops tools to assess and quantify natural resources, and a researcher for the Woods Institute for the Environment at Stanford University. This study, he added, is “an important contribution to the field of natural resource management.”
The lack of regulation paired with a dearth of communication between small dam projects in China allows for the impacts to multiply and accumulate through several dam sites, the study authors write.
Cumulative biophysical impact of small and large hydropower development in Nu River, China
 Support for low-carbon energy and opposition to new large dams encourages global development of small hydropower facilities. This support is manifested in national and international energy and development policies designed to incentivize growth in the small hydropower sector while curtailing large dam construction. However, the preference of small to large dams assumes, without justification, that small hydropower dams entail fewer and less severe environmental and social externalities than large hydropower dams. With the objective to evaluate the validity of this assumption, we investigate cumulative biophysical effects of small (<50 MW) and large hydropower dams in China’s Nu River basin, and compare effects normalized per megawatt of power produced. Results reveal that biophysical impacts of small hydropower may exceed those of large hydropower, particularly with regard to habitat and hydrologic change. These results indicate that more comprehensive standards for impact assessment and governance of small hydropower projects may be necessary to encourage low-impact energy development.
Now, there is a news from 2016 that China is planning to shelve idea of building dams on last wild river left in country i.e. Nu river.
China May Shelve Plans to Build Dams on Its Last Wild River