Want to Learn More? Estuaries Defined Freshwater Estuaries Estuary Classification Estuaries are Unique and Important Places

• Coastal Plain – Millions of years ago, as ancient glaciers melted, some coastal streams and rivers became covered with water as sea levels rose. The Chesapeake Bay in Maryland and Narragansett Bay in Rhode Island are examples of coastal plain estuaries that were once river valleys.
• Bar-built – Sandbars or barrier islands built up by ocean currents and waves in coastal areas created a protected area fed by small streams or rivers. The barrier islands off the Atlantic coastline of North Carolina and Massachusetts enclose bar-built estuaries.
• Delta system – Deltas are formed at the mouths of large rivers from sediment and silt depositing instead of being washed away by currents and waves. When the river flow is restricted by the delta, an estuary may form. The estuaries at the mouth of the Nile River in Egypt and the Mississippi River in Louisiana are examples of delta systems.
• Tectonic – Tectonic estauaries were created when a major crack or a large land sink in the Earth, often caused by earthquakes, produced a basin below sea level that fills with water. These types of estuaries usually occurr along fault lines. San Francisco Bay in California is an example of an estuary created by tectonics.
• Fjords – Advancing glaciers ground out long, narrow valleys with steep sides. Then when glaciers melted, seawater flooded in. Glacier Bay in Alaska is an example of a fjord.

Learn how estuaries can be classified according to their water circulation.