Generally, though, tourists can count on staying drier than whitewater paddlers. So whitewater folks often like to wear a "spray top," a garment with neoprene seals at the neck, wrists, and waist so that you stay dry almost no matter what. A good example of this is Immersion Research's Session 2.5 jacket ($140-$170; www.immersionresearch.com), which uses a waterproof-breathable fabric to keep you from cooking in the thing.
Tourists in warm climates can usually get by with light synthetic clothing, and have to worry more about sunburn than anything else. Cold-weather paddlers, however, may have to anticipate what might happen if they're in the water for an extended period of time, or get caught in rough, chilly weather. Serious cold-water tourists often wear a full drysuit, such as Kokatat's Gore-Tex Dura Drysuit ($830; www.kokatat.com). It's shockingly expensive, but provides the best protection possible in extreme, cold conditions (of course, you also need to don insulation under it).
So one outfit doesn't suit all conditions. Sometimes shorts and a light shirt are fine. Sometimes you can put on stuff you'd wear backpacking and be fine (plus a personal flotation device, of course). Other times you have to dress as if you were scuba diving. It's all a matter of where you're going, what the water/weather conditions are apt to be, and whether you're just offshore or heading out to sea.
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