Answer: Water hyacinths are considered annual plants (they come from the tropics), however some have managed to survive over winter in natural bodies of water and have become an invasive weeds. You can try to keep yours alive indoors in an aquarium with lights, or even in a bucket of water set in a south-facing window. If you leave it in the pond it will freeze for sure, but sometimes even black, slimy, dead-looking water hyacinths spring back to life when the weather warms.
Hope this provides at least some guidance!
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