Dreaming of relaxing at the pool, lake, or ocean this summer? Have a great time, but be prepared, says David Moershel, MD, a physician at Group Health Veradale Medical Center in Spokane and an avid sailor.

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"Accidents happen when people overestimate their abilities and underestimate the dangers," says Dr. Moershel. "While it's a myth that you have to wait to swim until after eating, there are some actual risks to keep in mind."

Bring a buddy when you swim. Even if you're a strong swimmer, you may need help if you get a cramp. Let someone on land know where you're going and when you'll be back.

Don't rely on lifeguards and swimming aids. A lifeguard isn't a guarantee that you're safe, especially at a crowded pool or beach where the lifeguard-to-swimmer ratio is low. And don't put your trust in inflatable devices such as floaties. They can help kids feel more comfortable as they learn to swim, but they're no substitute for U.S. Coast Guard-approved life vests. Stay close by and watchful when your kids are in the water.

Look before you leap. Be careful about diving and jumping into any unfamiliar body of water. You might not be able to see obstructions in murky water, and the water may seem deeper than it actually is. If the sign says "no diving," there's a reason. Diving injuries can cause spinal cord damage, paralysis, or even death.

Remember that you may have currents, waves, wind, and other factors to contend with in rivers, lakes, and oceans. Read and follow any posted warning signs. Trust your instincts about water and weather conditions. And expect that you may tire more quickly in open water.

Consider the water temperature. Water that is below 70 degrees is a shock to the system, and body temperature drops more quickly in water than on land. Stay close to shore if you're swimming in cold water. Chilly conditions can elevate your blood pressure and heart rate, and bring on hypothermia.

"First-stage symptoms of hypothermia include goose bumps, numb hands, and a feeling of weakness. Shivering is a second-stage symptom," says Dr. Moershel. "If you feel hypothermia coming on, leave the water immediately and warm up. Judgment is increasingly impaired in second-stage hypothermia." Pay special attention to children: they may not speak up about being cold soon enough.

Wear a life vest when boating. "The new CO2 vests inflate with submersion," says Dr. Moershel. "They're more comfortable and less bulky than other types of vests, and are great for people who would normally refuse a life jacket."

Alcohol and water sports are a dangerous cocktail. A high percentage of boating and swimming fatalities — particularly among teenage boys — are related to alcohol use. The combination of sun, wind, noise, vibration, and boat motion can triple the effects of alcohol when you’re on the water.

"Alcohol worsens hypothermia and impairs judgment," says Moershel. "Alcohol and boating, just like alcohol and driving, don’t mix — especially when you’re in cold weather or cold water."