There are lots of fish in large pond. One koi grew from 2 inches to over 1.2 feet, and a second to slightly under 1 foot, just in one season. They are very aggressive - eat waterplants and possibly small fish as well. Three levels of winter protection has been installed for them to live through winter. First, there is a 750 gallon per hour pump to circulate water from large pump, to the purifall system, small pond, and another waterfall. Effective flow rate is slightly less, because it lifts water up about 1 feet for waterfalls. For the system, there is about 1 feet long of 2 inches pipe above the group. The pipe has been well insulted and covered with pond-liner to provent from freezing. Tye pump sits about 3.5 feet below water surface and is expected to pump warm water to small ponds. The purifall water system is covered with pondliner as well and small pond is completely encircled inside a large green house (4 feet by 8 feet in width and length, and 10 feet in arch length). There are lots of waterplants in the small ponds and expected to live through the winter inside the greenhouse. A secondary greenhouse is on the opposite end of the large pond, where some waterplants still grow. Underneath a wooden bridge, a de-ice pump has been installed. It again pumps water from the bottom of the pond to the surface at a floating device. It will maintain at least a small airation hole of about 5 inches in diameter when the rest of pond surface is frozen. It has been claimed that the airation hole remains open even at -5 degree F! Multiple layers of protection ensure the security of the winterization systems. Three days after the green houses were setup and after first frost night, a beautiful butterfly was apparently season-confused and lost in the flower gardens. She should be in Florida by then!