A water nymph’s fins never stop growing. Their uses are multiple : they allow for the extraction of dioxygen from water, they can vibrate for underwater communication, and not unlike a cat’s whiskers allow nymphs to test the width of a passage before entering it completely. Their glow is directly related to the salt levels in the water ; the saltier the water, the brighter they glow. Because of this, water nymphs don’t often dwell in the seas and oceans, and prefer small lakes, ponds, and sometimes marshes. A nymph’s fins may glow in a variety of colors : green and blue are the most common, but mauve, yellow and pure white can also be found, especially in populations from northern Europe, Russia and central Asia.