Wash load is the portion of sediment that is carried by a fluid flow, usually in a river, such that it always remains close to the free surface (near the top of the flow in a river). It is in near-permanent suspension and is transported without deposition, essentially passing straight through the stream. It consists of the finest particles and can be defined by having a Rouse number of <0.8, meaning that the turbulent mixing velocity is far greater than the settling velocity.