I hope it occurs to you that youre asking for quite a bit: a camera that can withstand cold, get knocked around, and then take a swim. And actually, no SLRs are up to the task; their interchangeable lens mounts are a natural leak point, so theyd need some sort of waterproof case (more on that in a moment).
On the point-and-shoot front, probably your best bet is the Olympus 770SW ($325; olympus.com), which Olympus bills as the toughest camera made." And it might be. It has a steel case thats crush-proof, is designed to take a 5-foot fall, can go as deep underwater as 33 feet, and operates well down to 14 degrees. Not bad! Plus its a decent little camera, with 7 megapixels of resolution and a 3x optical zoom lens. No viewfinder, but you do have a large LCD screen for composing photographs. I personally think LCD screens are terrible devices for composing photos, but I realize I may be in the minority.
Also, the freeze-proof" claim for the 770SW is a bit of a canard. Digital cameras have almost no moving parts, so are far less prone to cold-weather problems than film cameras, which have a film transport mechanism, mechanical shutter, and other bits that could go wrong. The real issue always is the battery, and whether or not its warm, because cold temps suck battery life. So in cold weather (sub-freezing) its always prudent to keep a camera warm by keeping it in a pocket or under a jacket. And carry a spare battery in your pocket or someplace warm so you can swap it out if the electrons get frostbite and refuse to move.
Given that NO digital SLR sports the same degree of water-proofness, then ANY would work. Im a Canon loyalist so will tout the Canon 30d ($1,000 for body; canon.com). Tamron (tamron.com) recently loaned me an amazing zoom lens that fits Canon: an 18-250mm f3.5-6.3 (and macro) lens. $475 street price. Thats an amazing zoom range, and optical performance is good to excellent. Like all zoom lenses, its not especially well-suited for low-light photography, but from a focal-length perspective it certainly covers 99 percent of the photos one might want to take. For underwater use, an Aquapac AQUA 450 soft case ($125; aquapac.net) should suffice for light snorkeling and diving down to 10-15 feet.
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