It depends on the dock and the water. A floating dock in a cold climate will probably not last very long if it's left in the water during winter. The ice will damage the dock and it will eventually sink. In a warmer climate, a floating dock may be fine if it's left in the water during winter, but it's best to check with your local marina or boatyard to make sure.

A floating dock should be fine in the water during winter as long as it is properly sealed and caulked. The main concern would be with the lock system, which could potentially freeze and break. If you live in an area where the temperature regularly drops below freezing, you may need to have someone check on the dock periodically during winter to make sure everything is okay.