Whether you don't own a strobe, or if you simply don't feel like carrying your strobes along with you on some dives, you can still get good underwater photos to record your journey and evoke memories of what you experienced while enjoying a particular dive site. Let's grab our compact underwater cameras, and take some surprisingly good photos, no strobe required.
Using Internal Flash Properly
Your internal flash will do no good when photographing subjects that are more than about 12 inches away from your camera. To make the most of it for close ups, put your camera in macro mode and use forced flash. Adjust your settings to block out natural light if possible; if you only have auto mode, see if your camera is capable of defaulting to F2.8, 1/60th. If your camera is adjustable, go to F8, 1/60th, ISO 100 in all but the shallowest, most sunny conditions.
If you only have auto mode, then your photos will turn out best when you're in dark places. Shady areas, deeper spots, and night dives are your best bets for getting good photos with the camera and flash you have.
Taking Advantage of Natural Light
To take advantage of natural light, you need to be in shallow water, usually at 20 feet or less, although at some clear, sunny dive sites, you'll be able to make good use of ambient light at depths to about 30 feet. Unless you're going for a sunburst or silhouette, then keep the sun behind you as you shoot.
Use custom white balance and a red filter if possible, and ensure your camera's speed is 1/60th or faster when you shoot. After you're done with your dive, go home and play with the levels tool in Photoshop or another photo editor to enhance colors and contrast.
Avoiding Poor Color
Whether you use a flash or a strobe, the light in the photos you take is going to be coming from two sources: your flash, or the sun. The sun's light isn't the best, and any time your camera is letting in too much ambient light, your colors will be poor.
Remember that you've got to get close to your subjects to get good color. If you're further than 12 inches away, the result is a condition known as "light falloff" in which more light reaches the center of the image than reaches the edges. If you're experiencing light falloff, you need to get closer. Your colors will automatically look brighter when you do.
Avoiding Blurry Photos
There are two main reasons why underwater photos blur, besides poor buoyancy control or movement on the part of the photographer or subject. First, it could be that you're having a problem with focus as the result of being in macro mode when you shouldn't be, or out of macro mode when you should be. Double check your settings to avoid this.
The second reason for blurry underwater photos is that your shutter speed is too slow. To solve this problem, you can increase the ISO. When you're zoomed all the way out, you'll need at least 1/30th for still objects, 1/60th for slow-moving fish and other critters, and 1/125th for faster fish and other divers moving at a normal pace.
While you might feel satisfied with the photos you're taking without strobes, you might at some point feel like you're ready to purchase an external strobe or two to increase your success with underwater photography. Once you can get good macro shots using the internal flash, and so long as your camera supports aperture priority or manual mode, a strobe will make a huge difference. Practice with what you have for now, and get better equipment when you feel like you're ready.