A delta is usually formed when a river empties its water into an ocean, a lake or any other body of water. Some of the river's sediments are deposited at its mouth, forming a delta.
A delta is a wetland, which means an area of land that is saturated or covered by water. There are three kinds of delta, fan-shaped or arcuate, cuspate and bird's foot. The fan-shaped delta is formed when a river splits numerous times at its mouth, forming a fan effect. An example is the Niger Delta. An arcuate delta is tooth-shaped and the pointed version is the cuspate type, for example, the Tiber Delta. An example of the bird's foot type is the Mississippi Delta, which has a few, broadly spaced tributaries that seem bird-like.
According to National Geographic, deltas support diverse ecological systems with freshwater in the upper delta and salt water in the lower two plains. Pollution is absorbed and filtered from excess water runoff caused by upriver storms and floods as it flows towards the delta. Plants such as lilies and hibiscus, as well as wort, a herbal medicinal plant used to treat muscle strains, swelling and depression, lavishly grow in a delta environment.
Shallow, shifting delta waters support a wide array of indigenous creatures, including bass and catfish, shellfish, snow geese and other migratory birds, as well as a variety of bugs, including grasshoppers and robber flies.
According to the Encyclopedia Britannica, river deltas vary "in size, structure, composition and origin" in accordance with influencing factors such as weather conditions, geography and the rhythm of the tides.