What is created when sediment accumulates in an area of still water?

When sediment accumulates in an area of still water, a delta is formed. Deltas typically occur at river mouths where the river water slows down and loses energy upon entering a larger body of water, such as an ocean or a lake. As the water's velocity decreases, it cannot carry as much sediment, leading to the deposition of sediment in a fan-shaped accumulation. This process allows for the formation of various landforms, typically characterized by rich soil and diverse ecosystems.

The formation of a delta is specifically associated with the interaction of flowing water that meets still water, and the unique conditions of sediment deposition create this specific landform. Other choices represent different sedimentary processes. For instance, a bar forms in a river as sediment is deposited along the stream, while a deposit refers more generally to any accumulation of sediment, and an alluvial fan is created when sediment is deposited as water exits a canyon or steep slope onto flatter terrain, usually not directly involving still water.