Rivers can carry all sizes of particles that they deposit in characteristic ways. A. Particles tend to be largest upstream and smallest downstream, probably because water flowing downstream erodes fine sediment from the larger particles. B. A wide variety of deposits, including bars, alluvial fans, and deltas, are formed as a result of an increase in the speed of the downstream current. C. Bars commonly shift from being point bars on a river bank to being mid-channel bars. D. Deposits of sediment are found where flow velocity decreases, and when there is excessive sediment a stream may become braided, dividing into several channels. E. Rivers that flow through arid and semiarid mountainous regions tend to form alluvial fans at bends in the river. F. Deltas, which are formed where streams enter lakes or the ocean, are naturally unstable landforms that can extend over a large area.