Koi ponds that keep fish safe from herons is a common challenge for Koi lovers.
There are many options available to deter these persistent birds visiting Koi ponds. I tried them all. The netting that is used to cover ponds is not only unsightly but difficult to place. It tends to sag below the water level.
One inventive person claimed a rubber mat pelted with short nails would work. I tried this method. Spikes of nails protruding through the mat would surely keep them away. I placed the mat in the bottom of the Koi pond.
I stood watch as the heron not only landed on them, but walked back and forth over them.
The next experiment was to place “scarecrows” around the perimeter. These are similar to the sprinklers you find on playgrounds that shoot water when triggered by a motion sensor and oscillate in a circle. This is very effective when turned on, however, during the day it was constantly being triggered by any movement such as the wind blowing a flower. Each time I wanted to walk on the pathway it had to be turned off to prevent drowning myself. Bottom line, it was just too inconvenient although I did turn it on at night and early morning.
I read many positive reviews on Amazon about the effectiveness of floating alligator heads. Although we have no alligators in the northwest, it must be instinctive to herons to fear them. So I ordered one and to my surprise I saw no herons that year at all. Apparently it wasn’t meant to be permanent as they eventually came back. This experiment failed and the heron grabbed a fish right from under the alligator’s nose.
The most effective method to prevent the demise of my Koi was to build an additional Koi pond in which the heron could not land. I dug it 5 feet deep with steep sides. It included a ledge that could hold containers for plants but was covered with pots to prevent a landing place. The sides slope to the depth so there is no where for herons to gain any foothold. This has worked. For several years the heron continue to fish in my shallow pond, but the Koi have remained safe and have grown to nearly 15 inches long. The comets in the shallow pond are very prolific and have become feeder fish. I guess heron have to eat to.