Massive glaciers retreated, leaving a carved-out landscape behind. Chesapeake Bay was formed at the end of the last ice age. The Chesapeake Bay, on the East Coast of the United States, is a coastal plain estuary. Coastal plain estuaries (1) are created when sea levels rise and fill in an existing river valley. Types of Estuaries There are four different kinds of estuaries, each created a different way: 1) coastal plain estuaries 2) tectonic estuaries 3) bar-built estuaries and 4) fjord estuaries. Geographical features such as reefs, islands, mud, and sand act as barriers from ocean waves and wind. Most estuaries, however, are protected from the ocean's full force. During a storm season, storm surges and other ocean waves may flood the estuary with saltwater. The estuary shrinks, and becomes much more saline. During the dry season, the outflow from rivers may slow to a trickle. During the rainy season, rivers may flood the estuary with freshwater. These features also rise and fall with the seasons. In estuaries, water level and salinity rise and fall with the tides. Heated by the sun, anti-estuarine currents are much warmer than estuarine currents. Anti-estuarine currents are strongest near the surface of the water. When less-dense freshwater from a river flows into the estuary, it has an anti-estuarine current. Saltwater is heavier than freshwater, so estuarine currents sink and move near the bottom of the estuary. High tides can create estuarine currents. When dense, salty seawater flows into an estuary, it has an estuarine current. Tides create the largest flow of saltwater, while river mouths create the largest flow of freshwater. Water continually circulates into and out of an estuary. An estuary may also be called a bay, lagoon, sound, or slough. Brackish water is somewhat salty, but not as salty as the ocean. In estuaries, the salty ocean mixes with a freshwater river, resulting in brackish water. An estuary is an area where a freshwater river or stream meets the ocean.
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