• Batteries: Many digicams require proprietary lithium-ion batteries. They are compact and have excellent storage capacity-twice that of NiCd's- but with the LCD screen on and some in-camera editing, a few hours is all you'll get before the battery runs down. This is fine for day trips, and possibly overnights, but for extended paddles you'll want a few spares (at about $50 apiece). Recharge from an AC outlet takes 1 to 2 hours. Some digicams take AA batteries.

Digicams eat power too quickly for regular use of alkaline AAs, so it's best to use rechargeables. NIMH (Nickel-Metal Halide) have 40% more capacity than NiCad's (Nickel-Cadmium) and can be recharged without being fully discharged. And you'll be charging a lot. A NIMH charger and a dozen batteries will handle weekend-long excursions. For expeditions, solar chargers available commercially for NIMH batteries would tip the scales toward AA's.

• Image storage format: JPEG, a compressed format designed for photographic images, is the most common. Compressed images take less storage space, but at the expense of image quality. If you want top-quality images, digicams with TIFF compression will retain the highest image quality.

• Memory: The removable memory cards differ: Canon uses CompactFlash; Olympus uses SmartMedia; Sony has a proprietary Memory Stick. You can process your images with your computer and printer or take your memory card to a digital mini-lab or kiosk to make low-cost prints.

• Variable ISO: The light sensitivity of the CCD is listed in equivalencies of ISO ratings for film and can be changed to suit the image. You'll have the flexibility to capture action in low light at ISO 400, and, moments later, a tripod-mounted, color-saturated sunset at ISO 50.

• USB (Universal Serial Bus) port: Most new digicams come with a cable to connect to the computer USB port for downloading images. If your computer was manufactured in 1998 or later, it almost surely has USB.

• Video port: Some cameras have a video port so you can view the pictures on your TV or transfer images to a video tape.

• Web publication: If you want images for e-mail or Web use, any low-end digicam will surpass your need. E-mail and Web images are best kept small. A 480x640 pixel, low-quality JPEG is usually as big as you'll need and will download quickly.

• Print publication: Most magazines, including Sea Kayaker, print photographs at 300 dpi (dots per inch). This means the top-quality 2048x1536 image from the 3.2 Megapixel Canon S30 (reviewed below) will print no larger than 5" x 7", or half a page. Newspapers print at 150 dpi, so a 3.2 pixel image will work for 10" x 14". For home printing, 200 dpi generally makes very satisfactory prints.

• White balance: Many digicams allow you to adjust color balance, a great feature when indoors. For kayakers, it's a plus in the pool, or while snorkeling, or while ashore in shade.

• Waterproof case: Finally, the reason to consider on-the-water digital in the first place: the availability of compact waterproof housings that allow camera operation by way of external buttons. This years cases are rated for submersion to 100 feet or more, and made from ABS plastic that should take some abuse. The cases aren't pocket-sized, as the cameras are, but the extra bulk makes the camera easier to handle. The extension of the case around the zoom lens is likely to partly block the viewfinder. In addition, some of the camera functions may not be accessible via the buttons.