>What do plants that live in water do during winter months?
As mentioned before, many survive under the ice (if there is any.)
Many others will spend the winter as seeds and sprout in the spring. That is,
they are annuals--growing, flowering, and setting seed all in one year. The
parent plant may die, but its offspring will return.
Still others will die back to the ground and come up from a crown, roots,
rhizome, bulb, etc. in the spring. (Being frozen doesn't bother some
plant parts.) These are perennials.
Hope this helps.
Texas A&M University