The Amur carp is a hardy fish, and koi retain that durability. Koi are coldwater fish, but benefit from being kept in the range, and do not react well to long, cold, winter temperatures; their immune systems are very weak below 10 °C. Koi ponds usually have a metre or more of depth in areas of the world that become warm during the summer, whereas in areas that have harsher winters, ponds generally have a minimum of . Specific pond construction has been evolved by koi keepers intent on raising show-quality koi.