The captain jumped from the deck, fully dressed, and sprinted through the water. He was a former lifeguard, and he knew what to do: He headed straight for a couple swimming between their anchored sportfish and the beach.

“I think he thinks you’re drowning,” the husband told his wife. They had been splashing each other, and she had screamed, but now they were just standing on a sandbar.

“We’re fine. What is he doing?” she asked, annoyed.

“We’re fine!” the husband yelled, waving the captain off.

But he kept swimming. Hard.

“Move!” the captain barked as he sprinted between the couple. Directly behind them, not 10 feet away, their 9-year-old daughter was drowning.

How did this captain know—from 50 feet away—what the father couldn’t recognize from just 10 feet?

The captain was trained to understand that drowning is not the violent, splashing call for help that most people expect. Only after the girl was safely above the surface in the arms of the captain, bursting into tears and screaming, “Daddy!” did the father understand what was going on. Prior to that moment, she hadn’t made a sound.

As a former U.S. Coast Guard rescue swimmer, I wasn’t surprised at all by this story. Drowning is almost always a deceptively quiet event. The waving, splashing and yelling that TV and movies depict is rarely what happens in real life.

If you spend time on or near the water, then you and your crew should know how to determine when a person is in distress. Honing this skill is critical, particularly in light of data from the Centers for Disease Control and Prevention that show more children ages 1-4 die from drowning than any other cause of death. Among kids ages 5-14, drowning is the second-leading cause of unintentional injury death, after motor-vehicle crashes. Every year in the United States, there’s an average of 11 drowning deaths per day. And for every child younger than 18 who dies from drowning, another seven children end up in emergency rooms needing treatment for nonfatal drowning incidents.

Francesco A. Pia, a former lifeguard, is the person who coined the term “instinctive drowning response.” This is what people do to avoid actual or perceived suffocation in the water. When someone is drowning, there is very little splashing. There is also no waving, yelling or calling for help.

As Pia explains, what happens instead is that—except in rare circumstances—drowning people are physiologically unable to call out for help. The respiratory system is designed for breathing. Speech is a secondary function. Breathing must be fulfilled before speech can occur.

The mouths of drowning people sink below, and then reappear above, the water’s surface; they are not above the surface long enough for the victims to exhale, inhale and call for help. When the mouths are above the surface, they exhale and inhale quickly before sinking below the surface again.

Similarly, drowning people cannot wave for help. Instinct forces them to extend their arms laterally and press down on the water’s surface, so they can lift their mouths out of the water to breathe. In this state, the people also cannot move toward a rescuer or reach out for a piece of rescue equipment.

From beginning to end of the instinctive drowning response, drowning people remain upright in the water, with no evidence of a supporting kick. Without being rescued, these people can only struggle on the surface of the water from 20 to 60 seconds before submersion occurs.

This doesn’t mean that a person who is yelling for help and thrashing isn’t in real trouble—he or she is experiencing aquatic distress. It doesn’t last long, but these people can assist in their own rescue by grabbing lifelines, reaching for throw rings and the like.

You can look for these specific visual cues to tell the difference between someone in aquatic distress and a drowning person:

  • Head tilted back with mouth open;
  • Head low in the water, with mouth at water level;
  • Eyes glassy and empty, unable to focus;
  • Eyes closed;
  • Hair over forehead or eyes;
  • Not using legs;
  • Hyperventilating or gasping;
  • Trying to swim in a particular direction but not making headway;
  • Trying to roll over onto the back;
  • Appears to be climbing an invisible ladder.

Most important is to always be aware. If a crewmember falls overboard and everything looks OK, don’t assume that things are fine. Even if they seem to be treading water and staring up at the deck, ask if they are OK. If they can answer, they probably are OK. If they return a blank stare, then you may have less than 30 seconds to get to them.

And parents, make a mental note that children playing in the water make noise. When they get quiet, you need to get to them and make sure they’re not drowning.