When a meander gets cut off from the main stream, an oxbow lake is formed.
A meander, in general, is a bend in a watercourse or river. A meander is formed when the moving water in a stream erodes the outer banks and widens its valley. A stream of any volume may assume a meandering course, alternately eroding sediments from the outside of a bend and depositing them on the inside. The result is a snaking pattern as the stream meanders back and forth across its down-valley.
When water flows along a a curve, the water of the outer curve will flow faster and the water near the inner curve flows slower. Hence there is more chance for erosion at the outer banks and disposition near the inner banks as the slow flowing water is unable to carry away silt / sand and tiny sand particle along.
