These lovely ladies are the sparkly NYMPHS of running waters, babbling brooks, silvery streams and rippling rivers.
Being water spirits (HYDRIADS) of individual streams, they tend to be loyal to their locality, and often seem to end up marrying or otherwise dallying with the local king or hero. They are also on hand to rescue maidens in distress; some of them used to be maidens in distress themselves.
They take a very dim view of water pollution. Do not pee in the stream or chuck your garbage in the river. Take your trash home or face the consequences.