A silt out or silt-out is a situation when underwater visibility is rapidly reduced to functional zero by disturbing fine particulate deposits on the bottom or other solid surfaces.
The most common cause in scuba diving is when a divers' fins are used too forcefully or in the wrong direction; disturbing silt, particularly in caves, wrecks or in still fresh water environments.
Another common cause when wreck diving is from exhaled bubbles from open circuit scuba disturbing overhead surfaces and making loose rust particles sink down from above.
Scuba training for silted out situations includes exercises in following and finding (lost) lines, or searching for missing team members with a blackout mask.
[4] Likewise, all core diving skills, including equipment function, controlled ascent, air-sharing and other emergency protocols must be practiced until they can be performed without visual reference.