A beach is a strip of land that extends along the shoreline of an ocean, lake, river or even a large pond. It is usually made of loose granular material such as sand, gravel, pebbles and cobbles, but can also be formed by the deposition of marine sediments from the seafloor.
Sand and other sediments are constantly being carried ashore by waves and currents. As they do so, they build up the beach. The size and shape of a beach depends on the strength of the waves, the amount of sediment available and the type of wave.
Beaches are a vital habitat for a variety of marine organisms. In addition to fish and invertebrates, such as crabs and shrimp, many birds nest on ocean beaches, and sea turtles lay their eggs there as well. Plants, such as sea grasses, are also common on a beach.
In the United States, there are more than 7,000 miles of coastline, and approximately one third is covered by sandy beaches. These natural and man-made features are popular destinations for recreational activities, such as swimming, boating, surfing and fishing. They also play important economic roles, often supporting local tourism industries.
A beach is formed by the swash zone, which contains the subaerial beach (berm and beach face) and is dominated by swash processes; the energetic surf zone, with its breaking waves and surf zone currents; and the trough or dune zone that extends down to the water line from the crest of the beach. The trough may be narrow or broad, and it is sometimes lined with dunes that rise above the water line.
There are a number of ways that beaches can be polluted. For example, waves can carry debris, such as broken glass and plastic bottles, from nearby towns or cities. Also, rivers and drainage pipes can carry waste from urban areas to the beach. This waste, which includes raw sewage and industrial chemicals, can wash up on the shore and be ingested by people.
Some beaches are contaminated with disease-causing bacteria, such as E. coli and salmonella. This is particularly the case in coastal waters where erosion and runoff from urban and agricultural sources can contribute to poor water quality. In some cases, beaches are closed to public access after strong storms and high levels of contamination are detected. The best way to reduce the risk of illness is to avoid eating seafood from beaches that have not been treated with chlorine or chlorinated water. In addition, it is best to swim only after heavy rainfall when water quality has improved. Finally, it is important to know when to go and when not to swim at a beach to avoid dangerous conditions such as rip currents and choppy water.