Water expands when it freezes, which is why ice floats and why pipes burst in a hard winter.

What it means

Almost every substance contracts as it solidifies, packing its molecules closer. Water does the opposite below four degrees Celsius, because hydrogen bonds force the molecules into an open crystal with gaps in it. The consequence is that lakes freeze from the top down and life survives underneath, rather than freezing solid from the bottom up and killing everything in them.

The claim comes from U.S. Geological Survey, and the page it comes from was read on 2026-08-27 to confirm it still says this.

This is not the kind of claim that goes out of date, which is why it was set as a puzzle rather than a fact with a shelf life.

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This fact is a cryptogram here: 73 letters over 20 different ones, graded hard.

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