While some fish are bottom feeders and you expect them to hug the pond floor, rarely seen except perhaps at feeding time, other fish like koi and goldfish are expected to be seen frolicking closer to the surface. That’s the whole point of introducing colorful fish with gorgeous tails and markings, right? The simplest reason for these fish to hug the bottom of your pond is temperature extremes. The bottom layers of a pond are neither warmed directly by the sun nor cooled by frigid wind blowing across the surface, so fish will retreat there to find a comfy spot to wait out extreme or seasonal weather. During an exceptional heat wave, it may be worth it to install a few large umbrellas or sails around the perimeter of the pond to provide areas of cool relief. You could add cool water from the tap (appropriately treated, of course) or even float a few gallon size jugs filled with water and frozen to provide a cooling effect at the surface. Just make sure you locate them near the pump so the cooler water gets evenly distributed through the pond. If summer weather is consistently too warm for your fish, consider some more permanent solutions: add floating plants like water lilies to cover 60% of your pond’s surface, plant some overhanging bushes for shade or even trees. Keep in mind, though, that some trees and bushes will drop lots of trash like flowers, leaves and even twigs into your pond and create a whole new problem. In wintertime, fish will also dive deep to stay warm. This may seem counterintuitive, but it’s the water at the surface that is exposed to frigid air and deeper water rarely freezes. During the cold winters, your fishes’ metabolism will naturally slow and they’ll lie somnolent near the bottom. This is a natural process and it’s not a good idea to try to perk them up; they’ll get moving again in the spring.
Other possible reasons for your fish to huddle together at your pond’s bottom are poor health and excessive stress. Overfeeding, poor nutrition, overcrowding, a lack of oxygen and poor water quality can all contribute to the situation. You can start by testing your water and correcting any outlying conditions, then checking the quality of your fish food or reducing the amount you offer. Add some aeration to your pond and make sure your pump is powerful enough to circulate 100% of the pond’s volume every 24 hours at minimum. It’s a good idea to survey your population and compare it to an appropriate fish load - there are online calculators that can help you with that. If you’ve got too many fish in too little space, it may be time to share your bounty with some fellow enthusiasts.
