I copied this from the following link. I have lived in Florida and been around water most of my life and I did not know this information. Even years ago when I took advanced Life Saving, I did not learn this. It is a little long but very important to know. I encourage you to go to the link and read the entire article but I have pasted the most important information below.
Drowning Doesn't Look Like Drowning
Dr. Pia, in an article in the Coast Guard’s On Scene Magazine, described the instinctive drowning response like this:
1. Except in rare circumstances, drowning people are physiologically unable to call out for help. The respiratory system was designed for breathing. Speech is the secondary or overlaid function. Breathing must be fulfilled, before speech occurs.
2. Drowning people’s mouths alternately sink below and reappear above the surface of the water. The mouths of drowning people are not above the surface of the water long enough for them to exhale, inhale, and call out for help. When the drowning people’s mouths are above the surface, they exhale and inhale quickly as their mouths start to sink below the surface of the water.
3. Drowning people cannot wave for help. Nature instinctively forces them to extend their arms laterally and press down on the water’s surface. Pressing down on the surface of the water, permits drowning people to leverage their bodies so they can lift their mouths out of the water to breathe.
4. Throughout the Instinctive Drowning Response, drowning people cannot voluntarily control their arm movements. Physiologically, drowning people who are struggling on the surface of the water cannot stop drowning and perform voluntary movements such as waving for help, moving toward a rescuer, or reaching out for a piece of rescue equipment.
5. From beginning to end of the Instinctive Drowning Response people’s bodies remain upright in the water, with no evidence of a supporting kick. Unless rescued by a trained lifeguard, these drowning people can only struggle on the surface of the water from 20 to 60 seconds before submersion occurs.
(Source: On Scene Magazine: Fall 2006 (page 14))
This doesn’t mean that a person that is yelling for help and thrashing isn’t in real trouble – they are experiencing aquatic distress. Not always present before the instinctive drowning response, aquatic distress doesn’t last long – but unlike true drowning, these victims can still assist in their own rescue. They can grab lifelines, throw rings, etc.
Look for these other signs of drowning when persons are in the water:
• Head low in the water, mouth at water level
• Head tilted back with mouth open
• Eyes glassy and empty, unable to focus
• Eyes closed
• Hair over forehead or eyes
• Not using legs – Vertical
• Hyperventilating or gasping
• Trying to swim in a particular direction but not making headway
• Trying to roll over on the back
• Appear to be climbing an invisible ladder.
So if a crew member falls overboard and everything looks OK – don’t be too sure. Sometimes the most common indication that someone is drowning is that they don’t look like they’re drowning. They may just look like they are treading water and looking up at the deck. One way to be sure? Ask them, “Are you alright?” If they can answer at all – they probably are. If they return a blank stare, you may have less than 30 seconds to get to them. And parents – children playing in the water make noise. When they get quiet, you get to them and find out why.