They inspire awe with their aesthetics, engineering and sheer scale, but many dams – from China's Three Gorges to Brazil and Paraguay's Itaipu – are also playing crucial roles when it comes to global power generation.
The International Energy Agency (IEA) has described hydropower as being "the largest single renewable electricity source today."
But how does it work and why should you care?
Ebbs and flows
Put simply, the movement of water is crucial to hydropower.
As the U.S. Energy Information Administration (EIA) notes, both the change in elevation from one area to another and volume of water flow are crucial in determining "the amount of available energy in moving water."
As such, a big, fast moving and powerful body of water has the potential to produce a significant amount of energy.
Variety
A river may be fast flowing and possess bundles of energy, but technology is needed to harness it.
There are several types of hydropower systems, as noted by the International Hydropower Association: run-of-river hydropower, storage hydropower, pumped-storage hydropower and offshore hydropower.
As the EIA explains, a run-of-river system uses the force of the river's current to put pressure on a turbine, while in a storage system, water is held back by a dam and then "released as needed to generate electricity."
Impact
There are drawbacks when it comes to hydropower. Hydropower facilities can impact local communities – who sometimes have to be relocated – the migration of fish and also, as the IHA notes, "significantly alter downstream flows."
The impact of hydropower on carbon emissions has been significant, however.
According to the World Bank, hydropower helps to cut "annual global emissions by some 2.8 billion tons of CO2 equivalent every year."
