Silt In the Unified Soil Classification System (USCS) and the AASHTO Soil Classification system, the sand–silt distinction is made at the 0.075 mm particle size (i.e., material passing the #200 sieve). Silts and clays are distinguished mechanically by their plasticity. Silt is easily transported in water or other liquid and is fine enough to be carried long distances by air in the form of dust. Thick deposits of silty material resulting from deposition by aeolian processes are often called loess. Silt and clay contribute to turbidity in water. Silt is transported by streams or by water currents in the ocean. When
Silt out which is also likely to disturb silt where it makes contact, and the underwater work may also disturb silt. For these reasons surface supplied divers must often operate in very poor visibility. Remotely operated underwater vehicles and submersibles manoeuver by using thrusters, and the water blast from thrusters has a similar effect to the wash from fins. Silt outs are dangerous situations for scuba divers, particularly in enclosed spaces or when there is no direct access to the surface (an overhead environment). Training courses in overhead environment diving, such as wreck or cave diving teaches various methods to cope with