We tend to think of "fruit" in two ways in natural language. One is as food that grows on trees and vines, sweet and delicious, and able to be eaten without harming the plant in any way. Another is as the things we produce, what our work yields for the betterment of the world. These are obviously connected: we are like trees, producing things that "feed" the world in some way, just as the tree produces fruit that feeds us. It makes sense, then, that the idea of fruit in the Bible is bound closely to the idea of goodness. Fruits that are eaten represent the desire for good and the energy to do what is good; fruit that is produced is the actual good that we go into the world and do.

In Exodus 15:8, this signifies falsities gathered together. Waters normally signify truths, but in this case, where they were blocking the escape of the Children of Israel from slavery and signify the opposite: falsities.

(References: Arcana Coelestia 8286)