This is the time of year that a lot of poison is laid out to control geese, and other animals. The problem is people use anything from antifreeze to poisoned grain feed, or rodent poison. People do not like geese pooping all over their property, with a secondary poisoning, which can happen the poison can be seen in the feces in different colors depending on what was used. Birds of prey are sometimes victims after consuming poisoned animals, and even with round the clock care they usually die, feces color normally gives an indication of what was used after they are found sick. People use avitrol to sicken geese and make them leave. Not sure but maybe they pooped some poison into your pond, if your fish died suddenly.
