In angling books, Leptophlebia mayfly nymphs have a reputation as poor swimmers. In reality, they're very adept swimmers, much moreso than most other mayfly nymphs categorized as "crawlers."
Water boatmen are excellent swimmers, and you can see here how they use their oars to push themselves through the water, a motion easily imitated by the fly fisher.
Damselfly nymphs are among the most effective invertebrate predators in freshwater. You have to see one in motion to get a feel for their slow, deliberate style of stalking.
Dragonfly nymphs propel themselves through the water with a miniature jet engine, taking water in below their mouths and shooting it out their back ends. You can see the ripples from the jet out this one's back in this video.