A beach is the sandy, pebbly, or rocky shore of a body of water. Beach types vary widely, especially depending on where they are. When most of us think of a beach, we picture sandy ocean beaches with waves crashing, wind blowing, and seagulls flying overhead. But beaches in the United States are also found in urban areas, on estuaries and lagoons, and on lakes and rivers.

Beaches provide many recreational opportunities for millions of people. Boating, fishing, swimming, walking, beachcombing, bird-watching, and sunbathing are among the common activities beachgoers enjoy. Beaches also provide some protection to residents living near the ocean by acting as a buffer against the high winds and waves of powerful storms or rough seas.

A beach is also a sensitive environment that supports a variety of plants and animals.

Beaches are inhabited by a variety of invertebrates and insects. In the surf zone, bivalve mollusk, crustaceans, and tube-building worms adapt to their environment of tide cycles and buffeting waves by burrowing to protect themselves from wave impact, temperature fluctuations, desiccation, and predation. The smooth shells of clams and other bivalve burrowers reduce friction when they tunnel through the fine sandy beaches of their preferred habitat. At low tide, water retained between the sand particles is filled with millions of microscopic diatoms and zooplankton upon which the buried bivalves feed, using long siphons that reach to the sand surface. Fine screens within the siphons filter out sand particles by allow the passage of water and suspended organic material that provide an abundant food supply for the filter- feeding bivalves. Razor clams, surf clams and coquina clams are common burrowers along California beaches. Pismo clams occupy a special niche in the surf zone of Central California beaches, well-adapted to the crashing surf by nature of their large, heavy shells, which act as anchors. these giant clams are dependent upon the high-oxygen content of the roiling surf to survive.

Inland from the surf zone, sand craves scavenge in the sun-dried kelp and bury in the sand, using their antennae to rake food particles to their mouths. Kelp flies, wrack flies, rove beetles, tiger beetles, and dune beetles ream the beach foreshore. The dry upper beach is inhabited by air-breathing pill buys and beach hoppers. Numerous beetle species inhabit the dunes, some burrowing in the sand during the day to escape predators and the heat.

The natural process of beach building and erosion has been altered by extensive development of the California coast. Prior to development, natural loss of sand from beaches, largely to dunes and submarine canyons, and natural sand supply, mostly from rivers and streams, were in rough balance. The damming of rivers alone has reduced half of the natural sand supply to beaches from Santa Barbara to Mexico. The natural balance of beach sand supply and loss has been altered by the construction of offshore breakwaters, groins, and jetties, which may divert sand from one location to another and change beach slope. In a few locations large-scale beach nourishment projects have created wide beaches that may last several decades or more before eroding away.