If the heron is smart enough to sit on my neighbor's roof to scope out the place, fly down and under strings that have been strung out to the trees, be aware of dogs and humans but still get the fish, why would a piece of stationary plastic in the water scare the heron? Are alligators a natural threat in your state or vicinity? Then I could see it but I don't understand how a heron would know to fear one in Michigan.