When a river is approaching its mouth, the speed of water significantly reduces because the layout of the land is flat, the process of a river slowing as it approaches its mouth is referred to as meandering. As the river meanders, it forms wave-shaped structures referred to as meanders. As the water flows constantly, it erodes the inner banks of the meanders reducing the area of land separating one meander from the next. As the erosion continues, the edges of the cut off from the mean meander. Because the river has formed a new route, deposits sand and silt in the outer meander blocking the previous route through the meander, completely isolating a body of water that was once part of the river. The isolated meander, cut off from the main river is a land-form known as an oxbow lake.