What if rivers made electricity everywhere?

Rivers rush and splash. Moving water is strong!

People use it to make electricity. What if every river everywhere made electricity?

Stand by a river and you can feel its power: water rushing over rocks, pushing sticks along, roaring down waterfalls. People learned long ago to put that push to work.

Today, moving water makes electricity in many places. So why not everywhere? Could every river light up homes? To find out, we'll look at how dams make electricity, what they mean for fish, and how tiny water wheels can work on small streams.

Hydropower converts the energy of moving water into electricity. The U.S. Energy Information Administration (EIA) explains that the volume of the flow and the change in elevation, called the head, determine how much energy is available.

This thought experiment pictures hydropower on every river. It follows three threads: large dams and how they work, the effects of dams on fish and rivers, and small diversion and micro-hydro systems. It describes engineering trade-offs, not what anyone should build.

Some big rivers have dams with machines inside. The water spins the machines to make electricity.

Long ago, people used water wheels to grind grain.

In 2025, hydropower made about 5.6% of the electricity from large U.S. power plants, according to the EIA. Most U.S. hydropower comes from big dams on major rivers. About half of the country's hydropower capacity is in just three states: Washington, California and Oregon. Washington's Grand Coulee Dam is the biggest U.S. hydropower plant.

People have used moving water for a very long time. Thousands of years ago, paddle wheels on rivers turned to grind grain. The first U.S. hydroelectric plant to sell electricity opened in Appleton, Wisconsin, on September 30, 1882.

EIA data for 2025 put hydroelectricity at about 5.6% of total U.S. utility-scale generation and 23.1% of utility-scale renewable generation, from about 79,892 MW of conventional capacity, roughly half of it in Washington, California and Oregon. Washington's Grand Coulee Dam is the largest U.S. hydropower facility.

The history is long: paddle wheels ground grain thousands of years ago; the first industrial use of hydropower for electricity in the United States lit 16 brush-arc lamps at a Grand Rapids, Michigan, chair factory in 1880; and the first plant to sell electricity opened on the Fox River near Appleton, Wisconsin, on September 30, 1882.

Now pretend every river makes electricity.

But some rivers are slow and flat. They don't have much push. And fish need to swim up and down rivers too!

Not every river would make much electricity. The EIA explains that it depends on how much water flows and how far it falls. A steep mountain river could make lots; a slow river across flat land could make little.

And there's more to think about. Rivers are homes and highways for fish. A dam on every river would mean many more fish needing a way past. So a world of river power everywhere might work better with careful choices: big plants where water falls far, small systems on streams, and ways for fish to get by. These are ideas, not plans.

Available power scales with flow and head, so river sites differ enormously: high-head mountain sites can be productive, while low-gradient rivers offer little. 'Everywhere' would therefore yield very uneven returns.

There is also existing infrastructure to consider. DOE notes that fewer than 3% of more than 90,000 U.S. dams produce power, and EIA reports a 2012 DOE estimate of 12,000 MW of potential capacity at non-powered dams. Whether more hydropower would come from new dams, existing ones or small diversions, and how environmental effects would be weighed, are questions this lab leaves open.

Water flows down a big pipe. It spins a wheel called a turbine.

The turbine spins a generator, and the generator makes electricity!

At many hydropower plants, a dam holds back water in a lake called a reservoir. Water flows from the reservoir down through a pipe called a penstock, pushes against the blades of a turbine and spins it. The turbine turns a generator, which makes electricity.

Other plants don't need a big reservoir. A run-of-the-river plant uses the river's own current, sometimes with a low wall, called a weir, to steer water into the turbines. Either way, the more water and the farther it falls, the more electricity.

EIA describes the chain: water flows through a penstock, pushes against and turns turbine blades, and the turbine powers a generator. Conventional facilities include run-of-the-river systems, where the current applies pressure to a turbine, sometimes with a weir to divert flow, and storage systems, where reservoirs behind dams release water as needed.

DOE classifies plants as impoundment, diversion (run-of-river) or pumped storage, and by size: large above 30 MW, small from 100 kW to 10 MW, and micro up to 100 kW. Pumped storage, EIA notes, generally uses more electricity to pump water uphill than it later produces, so it stores energy rather than adding it.

Some dams have fish ladders. They are like stairs of water, so fish can swim up past the dam!

One dam even has fish elevators!

Many fish, such as salmon and shad, swim up rivers from the sea to lay their eggs, and a dam can block their way. The EIA describes fixes: fish ladders and elevators that help fish move around or over dams. The Safe Harbor Dam on Pennsylvania's Susquehanna River has elevators that lift migrating shad to the top.

Dams can also change a river's temperature, flow and mud. That's one reason small systems interest people. The Department of Energy says micro hydropower plants, up to 100 kilowatts, can make enough electricity for a single home, farm, ranch or village.

EIA notes that dams and reservoirs can obstruct fish migration and change natural water temperature, chemistry, flow and silt loads, affecting river ecology; reservoirs may cover natural areas, farmland or archeological sites, and may require relocating people. Turbines also injure some fish that pass through; DOE-sponsored research has aimed at turbines with fish losses below 2%, compared with 5% to 10% for the best existing turbines.

Mitigations include fish ladders and fish elevators, such as those lifting shad at the Safe Harbor Dam. DOE also notes that most U.S. dams serve purposes such as recreation, farm ponds, flood control, water supply and irrigation, and that small and micro plants can serve a single home, farm, ranch or village.