In reply to ow arm:
Gear: I've never wanted any gear for outdoor swimming, other than my Suunto Core to get a water temperature and to give me a maximum depth when diving under the sea. If you get used to going in just your boxers then you can swim anywhere, anywhen without needing to carry kit.
Technique: I'm a great fan of breast stroke when in rivers - it seems more stable when you get into the choppy water approaching a waterfall (from below!) and it disturbs the wildlife much less, with the later forming half the charm.
Tips: The key for me is to get adapted to cold water - every year I spend a couple of weeks swimming in the sea daily, typical temperature range 14oC to 19oC. I start at 15 mins/day and build up to 25-30. After that most of the rivers and lakes seem warm!
Local yoof (or their parents) often know of excellent spots. On the down side you may find your day interrupted when, pissed as a fart, one of them jumps in from the wrong rocks and lays moaning in the shallows.
Safety: Find a way to objectively gauge your strength, for example timing yourself between points parallel to the shore - so you can calibrate how fast your muscles wear down from the cold vs how you feel.
Beware peaty water - it can make rocks very slippery, and it obscures sight of boulders under the surface.
Respect currents of water in rivers - they can be an awful lot stronger than you think. Often swimming sideways gets you out of them but it's better not to find out the hard way.
Don't swim where there are fishing people, and don't sit under a waterfall a canoe is likely to come over!
