Herons are large, fish eating birds that can eat or kill many fish in a pond's stock. Herons will not only eat the fish in a pond, but they may also injure the fish, cause severe stress to the fish, and spread diseases throughout different bodies of water that they visit for hunting. It is illegal to harm these birds because they are a protected species. There are, however, a few preventive measures that a pond owner can take to keep the pond fish safe, without harming the birds.
Scare away a heron by installing a small fence around the pond. If a heron tries to walk up to the pond, it will be blocked by the fence and will fly away before it will step over the fence.
Substitute a fence with low-visibility fishing line. Set the fishing line fence up around the pond so that when the heron walks into it, the bird will be so startled that it will fly away, assuming it walks up to the pond.
Install a heron scarecrow to frighten a heron landing in the shallow end of a pond. A sprinkler scarecrow is motion activated, throwing water and making noise when an animal is detected.
Move the sprinkler scarecrow around the pond area periodically. Herons may become accustom to being sprayed by the water and may no longer fear it, but moving the scarecrow will continue to startle the bird.
Place imitation heron statues around the pond in addition to the scarecrow and fence. Herons are territorial by nature, so if a hungry heron spots another heron in the pond, it may be persuaded to fish elsewhere (see reference 2).
Provide hiding places for the prized pond fish to escape from fishing herons. Create cover with cut pipes or terra cotta flowerpots, and provide surface plants, such as lily pads or floating plants, for the fish hide from predators.
Installing a predator net over the pond is a definite way to prevent herons from removing fish, but may clash with the aesthetic of the water garden. These nets need to be placed over the pond so that fish will not become entangled and must be high enough to keep the heron from attempting to snatch the fish which would result in fish injury.