ocean noun One of the huge bodies of salt water covering most of Earth's surface. The ship sailed across the Atlantic Ocean for nearly two weeks. + tide noun The regular rise and fall of the sea's surface caused mainly by the moon's gravitational pull. We collected shells at low tide when the beach was widest. + wave noun A moving ridge of water on the surface of the sea or another body of water. Large waves crashed loudly against the rocks during the storm. + current adjective Belonging to or happening in the present time. The current mayor has held office for three years now. + coral noun A hard, often colorful substance formed by the skeletons of small marine animals, building reefs in warm seas. Divers marveled at the vivid coral covering the shallow reef near the shore. + reef noun A ridge of rock, coral, or sand lying just below or at the surface of the sea. Divers explored the coral reef, marveling at its bright fish and intricate formations. + shore noun The land along the edge of a sea, lake, or other large body of water. We walked along the shore collecting seashells as the tide went out. + coastline noun The outline or shape of a coast, especially as seen on a map or from the air. The country's jagged coastline is dotted with small fishing villages. + dune noun A hill or ridge of sand formed by the wind, common in deserts and along some coastlines. The hikers climbed the tall dune to watch the sunset over the desert. + tide pool noun A shallow pool of seawater left among rocks along the shore when the tide goes out. The children found a starfish and tiny crabs in the tide pool. + lagoon noun A shallow body of water separated from the sea by a sandbar, reef, or barrier island. Tourists snorkeled in the calm, clear waters of the coral lagoon. + estuary noun A coastal area where a river's freshwater meets and mixes with the sea's saltwater. Migrating birds gather in the estuary each autumn to feed before flying south. + plankton noun Tiny organisms that drift in oceans, lakes, or rivers and form the base of aquatic food chains. Whales filter huge amounts of plankton from seawater as their main food source. + kelp noun A large brown seaweed that grows in dense underwater forests along cool, rocky coastlines. Sea otters wrap themselves in kelp to keep from drifting while they sleep. + seaweed noun A plant or algae that grows in the sea, often found washed up on beaches or used in cooking. Strands of seaweed covered the rocks after the tide went out. + submarine noun A watercraft capable of operating underwater, used for military, scientific, or exploration purposes. The submarine descended slowly to study creatures living near the ocean floor. + marine adjective Relating to the sea, especially its animals, plants, or ecosystems. The aquarium specializes in marine life collected from tropical coral reefs. + aquatic adjective Relating to or living, growing, or taking place in water rather than on land. Otters and beavers are aquatic mammals that spend much of their lives in rivers and lakes. + horizon noun The line where the earth's surface appears to meet the sky, as seen from a distance. We watched the sun sink slowly below the horizon over the calm ocean. + surf verb To ride on the crest or face of a wave, typically while standing on a board. They spent the morning learning to surf at the local beach. + undertow noun A strong underwater current moving away from shore, beneath waves flowing in the opposite direction. Lifeguards closed the beach after several swimmers were caught in a dangerous undertow. + saltwater adjective Consisting of or living in water that contains a high concentration of salt, such as the sea. Saltwater fish like tuna cannot survive long in a freshwater aquarium. + shell noun A hard outer covering that protects an animal, egg, seed, or nut. The crab retreated into its shell the moment it sensed danger. + driftwood noun Wood that has been carried onto a shore or riverbank by water after breaking off or floating loose. They collected pieces of driftwood along the beach to build a small fire. + sandbar noun A ridge of sand built up by currents just below or near the surface of water. The boat ran aground on a sandbar hidden just beneath the river's surface. + breaker noun A large wave that crests and foams as it approaches the shore. Surfers waited beyond the breakers for the right wave to ride in. + lighthouse noun A tower with a powerful light at the top, built to guide or warn ships near dangerous coastlines. The old lighthouse still guides fishing boats safely into the harbor at night. + snorkel noun A tube that lets a swimmer breathe air while keeping the face submerged near the water's surface. She fitted her mask and snorkel before swimming out to see the coral reef. + buoy noun A floating marker anchored in water to guide ships or warn of hazards. The sailors steered carefully between two red buoys marking the channel. + habitat noun The place and conditions in which an organism normally lives. The hedgerow provides habitat for nesting birds. +