the effect is that people who are in the water too long can die.

because water will probably start to enter and trigger the reaction of laryngospasm. Now this reaction makes the vocal cords tightly close the airways to protect the lungs, but at the same time also makes it harder to scream

Over time the oxygen supply decreases and people under the sea will get hypoxia to make their consciousness disappear. The body enters the relaxation phase so that water can fill the lungs.