An estuary is a body of fresh and salt water that flows through rivers and streams out into the ocean. There are four types of estuaries: coastal plain, tectonic, bar-built, and fjord. Estuaries are important to our marine life because they protect fish, crustacean, shellfish and marine plants. Estuaries are typically found on the coast like a river or a bay, where the water leads to the ocean. Some examples of estuaries are the Chesapeake Bay, Hudson River and Delaware River. Human impact plays a very important role to the estuaries because humans don’t realize what they have been doing to the estuaries. 
Types of estuaries
The first type of estuary is a coastal plain estuary. Coastal plain estuaries occur when sea level rises. A good example of one is the Chesapeake Bay. The second type of estuary is a tectonic estuary. Tectonic estuaries occur where tectonic plates shift. San Francisco Bay is a tectonic estuary. A third type is a bar-built estuary. Bar-built estuaries are where a lagoon or a bay is protected from the ocean by a barrier like a sandbar. The Outer Banks in North Carolina is a bar-built estuary. The last type of an estuary is fjord estuary. Fjord estuaries are created by glaciers. In Alaska, Puget Sound is a fjord estuary. 
Estuaries are important because they are a protected environment where there is plenty of food and a location for fish and shellfish to reproduce, commonly called the nurseries of the sea. Another reason why estuaries are so important is because they provide high level of nutrients as water flows through them.
Threats and human impact
There have been threats to marine life in estuaries and a lot of them have been coming from humans. Dumping any toxic waste into the water is polluting the water, and is becoming harmful to the marine life in the estuaries. Since estuaries provide plenty of food the marine life can feed in there, but since there is pollution in the estuaries, the fish are dying by eating this food that has been polluted. Another problem with pollution is that it leads out to our oceans, therefore it is polluting not only the estuaries, but it is also polluting the oceans. Road building can also be harmful to estuaries because it can runoff into the water carrying sediments.
Other closely related articles in this wiki include:
- Estuary - by Encyclopedia of Earth
- Estuary - by Encyclopedic entry by National Geographic Education
- Estuaries - by NOAA Ocean Service Education
- Estuaries - by EPA
- NOAA report highlights climate change threats to nation’s estuaries - by NOAA News (August 7, 2013)