[sbilstein]

A large nuclear power plant may use up to 1 billion gallons of water a day and, for this reason, they are often built next to rivers, lakes or oceans to utilise the bodies of water. The water is drawn from these sources and heated to create steam to power the turbine. It then condenses and can be reused in the power generation process. However, it is eventually pumped back into the body of water it originated from, albeit at very high temperatures. This can increase the temperature of the natural water source by up to 30 degrees, posing risks to the aqua life.

from this article:

https://monarchpartnership.co.uk/nuclear-power-water-consump...

[refurb]

The water turned into steam driving turbines doesn't touch the cooling water drawn from rivers. They are closed systems.

[falcolas]

Technically true. But that doesn't stop heat from being transferred between the systems, nor the heat dispersion to the atmosphere or waterways.