The giant Salmonflies of the Western mountains are legendary for their proclivity to elicit consistent dry-fly action and ferocious strikes.
The clumsy-looking mayfly nymphs of the genus Baetisca are surprisingly good swimmers.
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.
These nymphs may be the best swimmers of all North American mayflies.
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.
This little Ephemera nymph swam around for a while and tried to burrow into the sand in my photography tank.
This is one of the earliest videos I made, and I was experimenting with a tank and background that didn't work very well.