The Swimming Pool and Spa Program recommends avoiding prolonged underwater breath-holding. People who hold their breath while swimming or practicing breath-holding underwater in pools are at risk of “passing out” due to lack of oxygen. This phenomenon is commonly referred to as Shallow Water Blackout (SWB).
SWB is a medical term for a faint brought on by a lack of oxygen and carbon dioxide while swimming. SWB does not only occur in shallow water, it can happen in any depth of water.