Q. Last spring we built a fish pond outside. It is about 3 feet wide, 9 feet long and 3 feet deep. The pond structure is pressure-treated wood lined with Styrofoam, then lined with plastic and finally lined with a pool liner. Roughly 1 foot of the depth is in the ground and the rest is above. We are wondering if we could leave the fish out all winter and, if we can, should the water level be lowered?
A. I have been receiving an increasingly large number of letters from folks in northern climates who have, or intend to install, outdoor ponds. Several letters have come from Alaska! Northern winters strain pondkeeping talents to the limit.
Here in New England, my in-ground ponds freeze solid at least a foot deep — sometimes more — every winter. All above-ground structures in this region filled with water freeze almost solid. I would venture that the conditions in Ontario are even more severe.
It is likely that your pond will freeze to within 6 inches of the bottom. In severely cold winters it would probably freeze to a solid block. Lowering the water level will only guarantee the latter result.
While it is possible that a few hardy pond comets might survive a number of winters outdoors, most pond fish will not. Certainly not koi or fancy goldfish. Although there are many stories of someone in Greenland who has kept his or her fish outdoors for 30 years and never lost one, that is not the common experience.
Moreover, even if the fish manage to survive they will be in terrible shape. Such conditions during periods of severe and extended cold — coupled with low oxygen levels — are just too stressing over the long run. All it takes is one colder-than-usual winter and all the fish will be dead.
You will either have to heat the pond to keep two 1-foot-square areas ice free, or bring the fish indoors. I recommend the latter.