Hydroelectric power means using [?] water. Nowadays this turns a turbine which runs a [?] to make electricity. This can be done with a water wheel and a fast-flowing stream, but a modern [?] power station has a huge [?] which creates a deep [?], which stores lots of [?] potential energy in the water so it flows fast through the turbines.

The [?] dam on the Colorada river in the USA provides [?] for the city of Las Vegas.

Hydroelectric power is [?], needs no [?] and produces no [?]. However, the dams are [?] to build and you need to [?] a large area to create the lake, with environmental consequences.