If a wood nymph is near a tree, or a water nymph is near a fountain, they won’t wander very far from it. Specifically, their AI would tell them to consider any space more than X distance from a fountain to be invalid.

They also don’t teleport away from fountains, unless they’re scared or carrying stolen items. When they do teleport, their destination is biased towards any trees or fountains that are on the level, respectively.