If you’re talking about steam, the visible part of steam is actually liquid water falling out of gas phase in tiny droplets. Actual gaseous H20 is invisible.
If your pot was at a very high temperature, the water might stay in gas phase long enough to spread into the environment and not oversaturate the air. Therefore, as the pot cools to closer to boiling temperature, you might get more visible steam as more water comes out of the air.
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