What is the usual shape of a river delta?

The usual shape of a river delta is triangular. The term “delta” comes from the uppercase Greek letter delta, Δ, because the Nile Delta resembles a triangle where the river spreads toward the sea.

A delta forms when a river slows as it enters a lake, sea, or ocean. The reduced flow causes sediment—such as silt, sand, and clay—to settle near the river mouth. Over time, these deposits build outward and the river divides into smaller channels called distributaries.

Not every delta is a perfect triangle. Waves, tides, currents, and the amount of sediment can produce fan-shaped, arcuate, bird-foot, or cuspate forms. The Mississippi Delta, for example, has long, branching distributaries, while the Nile is a classic arcuate delta.

The answer refers to the familiar textbook appearance, not a strict rule for every delta. A river mouth without substantial sediment deposition may instead form an estuary.