Back to top


In-Stream Hydro

Mini hydroelectric power station with 12 kilowatts of installed power produces around 33,000 kilowatt-hours of electricity per year in Bruton, Somerset, England.

Hydropower conjures images of massive, landscape-shattering dams, such as the Three Gorges on upper tributaries of the Yangtze River in China. Large hydroelectric dams produce enormous amounts of electricity, but they also swallow up vast swaths of natural and human habitat. They impact water movement and quality, sediment patterns, and fish migration.

Smaller in-stream turbines are different. Placed within a free-flowing river or stream, they capture water’s kinetic energy without creating a reservoir and its repercussions. The underwater analogue to wind turbines, their blades rotate as water moves past, generating relatively continuous electricity. No barriers, diversions, or storage are required, only limited structural support. No emissions ensue.

In remote communities from Alaska to Nepal, this technology is expanding electrification and replacing expensive and dirty diesel generators. In urban environments, in-stream turbines can be placed within city water mains (called conduit hydropower).

As in-stream hydro grows, it is important to note that not all “run-of-river” projects actually let the river run. Some have diverted waterways, caused floods, and impeded fish migration. Careful design and installation can ensure clean energy that is also ecologically sound.


Three Gorges…displaced 1.2 million people: Watts, Jonathan. “Three Gorges Dam May Force Relocation of a Further 300,000 People.” The Guardian. January 22, 2010.

native communities in rural Alaska: Mooney, Chris. “Alaska’s Quest to Power Remote Villages—and How It Could Spread Clean Energy Worldwide.” Washington Post. August 14, 2015.

Waterways fed by Himalayan snowmelt: Lee, Amy. “Microhydro Drives Change in Rural Nepal.” New York Times. June 20, 2012

city water mains; Portland, Oregon: Profita, Cassandra. “Portland Now Generating Hydropower In Its Water Pipes.” Oregon Public Broadcasting. January 20, 2015; Slavin, Terry. “From Oregon to Johannesburg, Micro-Hydro Offers Solution to Drought Hit Cities.” The Guardian. September 18, 2015.

[potential of] U.S. hydrokinetic resources: National Research Council. An Evaluation of the U.S. Department of Energy’s Marine and Hydrokinetic Resource Assessments. Washington, D.C.: National Academies Press, 2013.

view all book references


p. 27

Correction: If in-stream hydro grows to supply 3.7 percent of the world’s electricity by 2050, it can reduce 4 gigatons of carbon dioxide emissions and save $568.4 billion in energy costs.

view all errata

Research Inquiry Form

Want more information on Project Drawdown’s research methodology and models? Complete this form to contact the Drawdown Research team.

Which Drawdown solution sector most interests you? * (choose one)
Do you have a copy of Drawdown: The Most Comprehensive Plan Ever Proposed to Reverse Global Warming? *
What would you like to know about Drawdown’s research methodology and models? * Please note that, due to time and resource constraints, we may not be able to provide extensive information or data.
Other questions, comments, or suggestions:
Back to top

Join Us

We would like to stay in touch with you. Please sign up for updates to discover ways you can participate in the work of Drawdown.


Click to expand
Please send me more information about ways that I can participate as: (check all that apply)