Predator control, specifically of herons, is an important part of keeping your koi fish healthy and safe. Herons are very large, migratory birds that live across most of the United States; Florida has especially high populations of these birds. Full-grown herons will eat your koi, while the smaller herons will stab them for practice even if they can’t yet eat them.
There are several different methods to control herons around your koi pond. Motion-activated decoys that look like crows and squirt water when they detect motion are a good method. This will startle the heron and cause it to fly away. You can also use motion-activated spotlights to startle the herons. Netting your pond will keep them out altogether.
There are also some pond predator control methods out there that don’t work. Some people will put fake snakes around the koi pond or in the trees; usually the heron figures out the snakes are not real and then they approach the pond.
Plastic heron decoys are also not very effective. You would place these by your koi pond to deter the herons from entering another bird’s territory, but often the real heron will simply fish from the other side of your koi pond. Flight lines are also ineffective because the herons will simply wade in over them.
In summary, motion-activated decoys and spotlights, and netting are the most effective ways to keep herons from eating or harming your koi fish. Netting is the best.