河心滩是由河床中部的沉积物构成，形成于河流从狭窄段流入开阔段的部位。在河床突然变宽处，河水流速降低，水流向两侧发生散流，侵蚀两岸。置身其中，感“天在清溪底，滩石拥水流，款步携影行，宛若入仙源”。

The river island is formed by the sediments in the middle of the riverbed where the river flows from a narrow reach to a wide reach. As the riverbed suddenly becomes wider, the flow speed drops and the water flows sideways and erodes the banks.