The Tennessee Valley authority has reduced the output of three of its nuclear power plants for the second summer in a row, thanks to unusually warm temperatures in the rivers into which they would normally discharge water.

Of note: There's no physical reason why the plants can't use the warm water. Laws say that power plants can't heat the rivers into which they discharge above 86.9 degrees F because it's bad for fish. But even without the plant’s help, climate change already caused the Tennessee River to bust right through that threshold. (This means that whatever fish are still living can probably handle it.)

One way around this problem is installing plants that recirculate their cooling water. Rather than taking water continuously from a river or lake, it's possible to run a supply of cooling water through a cooling tower and use it again, a practice common to plants that aren't adjacent to abundant supplies of water. Record heatwave or no, this is probably the wave of the future, given the end of cheap water.

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