Sadly, swimmers die about monthly in the near-shore waters of Hawaii, almost all in situations that are totally avoidable. This is not the sort of fact that is up front in slick travel brochures and magazine articles. Every beach can be unsafe for swimming on a given day.
Okay, good news: Follow a few rules and the aquamarine waters of paradise pose no threat to you or your family.
1. Big waves mean dangerous conditions. All that incoming white water needs to go back out, and it does so in swift channels called rip currents. Rip currents often run paralell to the shoreline, and then escape in blue channels through openings in the reef, or through flat, riffling between breakers. You can see rip currents from the shore, mostly easily from an elevated viewing spot. When waves are high, conditions are dangerous. The mantra is: If in doubt, don't go out.
2. Not all wave action means treacherous rip currents. Throw a stick in the water to see where it floats. When you are in the water, check to see which way you are drifting. Swim against the current during the first part of the swim, so you will swim with it coming back.
3. If caught in a rip current, stay calm. This can be difficult, but many swimmers exhaust themselves and drown while trying to combat an overpowering current. Rip currents are near-shore events that release you immediately once beyond the wave action.
4. Wear a mask and fins to maximize visibilty and swimming power.
5. Swim at beaches with lifeguards (called watermen in Hawaii; they are among the world's best).
Watch the surf for many minutes before deciding how close is safe. Rogue waves come infrequently, but they do arrive. When walking the shore, keep an eye on the waves. You can outrun waves easily—if you see them. Being swept away at the shore is the most common way people drown in Hawaii.
All Trailblazer guides come with all sorts of outdoor-adventure safety tips, as well as the particular safety concerns about a given trail or beach. They are available on Amazon.com and barnesandnoble.com.