Question
is is a good idea to install a pond under an existing mulberry tree? will koi digestive system or health be endangered if they weere to eat mulberries that fall from the tree?

Answer
Hi Jorge:  Trees and ponds are an issue because of the root system of the tree.  Tree roots seek out water and the potential for the tree to invade the pond is high.  Depending on how large the pond is the leaves and fruit from the tree may fowl the water and make the water toxic thus requiring a lot of pond maintenance.  I am not sure if the Mulberry is toxic to koi... dave